Wind Erosion in Khartoum State
By:
Adel Mahgoub Farah
B.Sc. Soil and Water Science (1985)
A thesis submitted for the fulfillment for the degree of
Doctorate of Philosophy (Ph.D.)
In
Soil and Environment Science (Desertification)
Department of Soil Science
University of Khartoum
June 2003
١
Declaration
I declare that this work is my own work and
it has not been submitted to any other
university for any kind of degree.
Adel Mahgoub Farah
٢
Dedication
To the one who has given me life, strength
and wisdom to do this work.
٣
Acknowledgement
My deep thanks to my supervisor Professor
Mukhtar
Ahmed
Mustafa
for
his
continuous, keen and wise guidance
throughout the study period. Thanks are
due to Director General of A.R.C.T.
Thanks are due to Omdom Farm Director.
Thanks are due to Director of Alshaab
Scheme. Thanks are due to Director of
Desertification Research Institute. Special
thanks are due to Awad Ismail. Special
thanks are due to the Staff of Soil and
Water Research Centre.
٤
Abstract
The study is about wind erosion in Khartoum State, Khartoum is one of areas
affected by land degradation, and the main process of land degradation in
Khartoum State is wind erosion.
The main objective of the study is: generation of broad-base quantitative actual
and potential data on wind erosion in Khartoum State.
Four locations were selected: South, West, East and North Khartoum State,
with three sites in each location: bare, sheltered, and cultivated fields, West
Khartoum a Qoz field is selected instead of cultivated field.
Vertical and horizontal wind traps were used with different heights and
distances.
The study showed the potential wind erosion of cultivated field in order of
North Khartoum > South Khartoum > East Khartoum.
The study showed inverse relationship between the height and the intensity of
wind erosion, intensity of wind erosion decreases in order of 0 cm > 5 cm > 20
cm > 50 cm heights, intensity of wind erosion increases in order of May > April
> March > February > January > December > November.
Intensity of wind erosion in order of bare field > sheltered field > cultivated
field.
Data of the soil surface layer 0 – 30 cm properties analyzed for 1975 and 2002
showed the coarse, fine sand and silt were increased from 22, 13, and 20% to
24, 18, and 26% respectively, while the clay decreased from 45% to 32% for
the bare field in South Khartoum.
The study showed inverse, and linear relationship between distance and
intensity of wind erosion according to the location and the site.
The study showed the soil erodability of Khartoum State in order of North
Khartoum > South Khartoum > East Khartoum.
The study showed wind erosivity in Khartoum State in order of February >
April > January > March > November > December.
٥
‫ﻣﻠﺨﺺ اﻟﺪراﺳﺔ‬
‫اﻟﺪراﺳﺔ ﻋﻦ اﻟﺘﻌﺮﻳﺔ اﻟﺮﻳﺤﻴﺔ ﺑﻮﻻﻳﺔ اﻟﺨﺮﻃﻮم‬
‫ﻭﻻﻳﺔ ﺍﳋﺮﻃﻮﻡ ﺇﺣﺪﻯ ﺍﻟﻮﻻﻳﺎﺕ ﺍﳌﺘﺄﺛﺮﺓ ﺑﺘﺪﻫﻮﺭ ﺍﻷﺭﺍﺿﻲ ﻭﺍﻟﺘﻌﺮﻳﺔ ﺍﻟﺮﳛﻴﺔ ﻭﺍﺣﺪﺓ ﻣﻦ ﺃﻫﻢ ﻋﻤﻠﻴﺎﺕ‬
‫ﺗﺪﻫﻮﺭ ﺍﻷﺭﺍﺿﻲ ﺑﺎﻟﻮﻻﻳﺔ‪.‬‬
‫ﻣﻦ ﺃﻫﻢ ﺃﻫﺪﺍﻑ ﺍﻟﺪﺭﺍﺳﺔ ﺗﻮﻓﲑ ﻗﺎﻋﺪﺓ ﻣﻌﻠﻮﻣﺎﺕ ﻋﻦ ﺷﺪﺓ ﺍﻟﺘﻌﺮﻳﺔ ﺍﻟﺮﳛﻴﺔ ﺍﳊﻘﻴﻘﻴﺔ ﻭﺍﶈﺘﻤﻠﺔ ﻟﻮﻻﻳﺔ‬
‫ﺍﳋﺮﻃﻮﻡ‪.‬‬
‫ﰎ ﺇﺧﺘﻴﺎﺭ ﺃﺭﺑﻌﺔ ﻣﻮﺍﻗﻊ‪ :‬ﺟﻨﻮﺏ‪ ،‬ﻏﺮﺏ‪ ،‬ﴰﺎﻝ ﻭﺷﺮﻕ ﻭﻻﻳﺔ ﺍﳋﺮﻃﻮﻡ ﻭ ﰎ ﺇﺧﺘﻴﺎﺭ ﺛﻼﺛﺔ ﺣﻘﻮﻝ‬
‫ﻟﻜﻞ ﻣﻮﻗﻊ‪ ،‬ﺣﻘﻞ ﻋﺎﺭﻱ‪ ،‬ﺣﻘﻞ ﳏﻤﻲ ﻭ ﺣﻘﻞ ﻣﺰﺭﻭﻉ ﻭ ﰲ ﻏﺮﺏ ﻭﻻﻳﺔ ﺍﳋﺮﻃﻮﻡ ﰎ ﺇﺳﺘﺒﺪﺍﻝ‬
‫ﺍﳊﻘﻞ ﺍﳌﺰﺭﻭﻉ ﲝﻘﻞ ﻛﺜﺒﺎﻥ ﺭﻣﻠﻴﺔ‪.‬‬
‫ﰎ ﺇﺳﺘﺨﺪﺍﻡ ﻣﺼﺎﺋﺪ ﺭﻳﺎﺡ ﺭﺃﺳﻴﺔ ﻭﺃﻓﻘﻴﺔ ﺑﺈﺭﺗﻔﺎﻋﺎﺕ ﻭﻣﺴﺎﻓﺎﺕ ﳐﺘﻠﻔﺔ‪.‬‬
‫ﺃﻭﺿﺤﺖ ﺍﻟﺪﺭﺍﺳﺔ ﺃﻥ ﺍﻟﺘﻌﺮﻳﺔ ﺍﶈﺘﻤﻠﺔ ﻟﻠﺤﻘﻮﻝ ﺍﳌﺰﺭﻭﻋﺔ ﻛﻤﺎ ﻳﻠﻲ‪:‬‬
‫ﴰﺎﻝ ﺍﳋﺮﻃﻮﻡ < ﺟﻨﻮﺏ ﺍﳋﺮﻃﻮﻡ < ﺷﺮﻕ ﺍﳋﺮﻃﻮﻡ‬
‫ﺃﻭﺿﺤﺖ ﺍﻟﺪﺭﺍﺳﺔ ﺃﻥ ﻫﻨﺎﻙ ﻋﻼﻗﺎﺕ ﻋﻜﺴﻴﺔ ﺑﲔ ﺍﻹﺭﺗﻔﺎﻉ ﻭﺷﺪﺓ ﺍﻟﺘﻌﺮﻳﺔ ﺍﻟﺮﳛﻴﺔ‪.‬‬
‫ﺻﻔﺮ ﺳﻢ < ‪ ٥‬ﺳﻢ< ‪ ٢٠‬ﺳﻢ < ‪ ٥٠‬ﺳﻢ‬
‫ﺷﺪﺓ ﺍﻟﺘﻌﺮﻳﺔ ﺍﻟﺮﳛﻴﺔ ﺗﺘﻨﺎﻗﺺ ﻛﻤﺎ ﻳﻠﻲ‪:‬‬
‫ﻣﺎﻳﻮ < ﺇﺑﺮﻳﻞ < ﻣﺎﺭﺱ < ﻓﱪﺍﻳﺮ < ﻳﻨﺎﻳﺮ < ﺩﻳﺴﻤﱪ < ﻧﻮﻓﻤﱪ‬
‫ﺷﺪﺓ ﺍﻟﺘﻌﺮﻳﺔ ﺍﻟﺮﳛﻴﺔ ﺗﺘﻨﺎﻗﺺ ﻛﻤﺎ ﻳﻠﻲ‪:‬‬
‫ﺣﻘﻞ ﻋﺎﺭﻱ < ﺣﻘﻞ ﳏﻤﻲ < ﺣﻘﻞ ﻣﺰﺭﻭﻉ‬
‫ﻧﺘﺎﺋﺞ ﲢﺎﻟﻴﻞ ﺍﻟﻄﺒﻘﺔ ﺍﻟﺴﻄﺤﻴﺔ ﺻﻔﺮ – ‪ ٣٠‬ﺳﻢ ﻟﻠﺘﺮﺑﺔ ‪ ١٩٧٥‬ﻭ ‪٢٠٠٢‬ﻡ‪.‬‬
‫ﺃﻭﺿﺤﺖ ﺍﻟﺪﺭﺍﺳﺔ ﺃﻥ ﻧﺴﺒﺔ ﺍﻟﺮﻣﻞ ﺍﳋﺸﻦ ﻭﺍﻟﻨﺎﻋﻢ ﻭﺍﻟﺴﻠﺖ ﺇﺯﺩﺍﺩﺕ ﻣﻦ ‪ %٢٠ ،١٣ ،٢٢‬ﺍﱄ ‪،٢٤‬‬
‫‪ %٢٦ ،١٨‬ﻋﻠﻲ ﺍﻟﺘﻮﺍﱄ ﺑﻴﻨﻤﺎ ﺇﳔﻔﻀﺖ ﻧﺴﺒﺔ ﺍﻟﻄﲔ ﻣﻦ ‪ %٤٥‬ﺍﱄ ‪ %٣٢‬ﰲ ﺣﻘﻞ ﻋﺎﺭﻱ ﲜﻨﻮﺏ‬
‫ﻭﻻﻳﺔ ﺍﳋﺮﻃﻮﻡ‪.‬‬
‫ﺃﻭﺿﺤﺖ ﺍﻟﺪﺭﺍﺳﺔ ﻋﻼﻗﺎﺕ ﻋﻜﺴﻴﺔ ﻭ ﻃﺮﺩﻳﺔ ﺑﲔ ﺷﺪﺓ ﺍﻟﺘﻌﺮﻳﺔ ﻭﺍﳌﺴﺎﻓﺔ ﺣﺴﺐ ﺍﳌﻮﻗﻊ ﻭﺍﳊﻘﻞ‪.‬‬
‫ﺃﻭﺿﺤﺖ ﺍﻟﺪﺭﺍﺳﺔ ﺃﻥ ﻗﺎﺑﻠﻴﺔ ﺍﻟﺘﺮﺑﺔ ﻟﻠﺘﻌﺮﻳﺔ ﰲ ﻭﻻﻳﺔ ﺍﳋﺮﻃﻮﻡ ﻛﻤﺎ ﻳﻠﻲ‪:‬‬
‫ﴰﺎﻝ ﺍﳋﺮﻃﻮﻡ < ﺟﻨﻮﺏ ﺍﳋﺮﻃﻮﻡ < ﺷﺮﻕ ﺍﳋﺮﻃﻮﻡ‬
‫ﺃﻭﺿﺤﺖ ﺍﻟﺪﺭﺍﺳﺔ ﺃﻥ ﺳﺮﻋﺔ ﺍﻟﺮﻳﺎﺡ ﺍﻟﱵ ﺗﺴﺎﻋﺪ ﻋﻠﻲ ﺍﻟﺘﻌﺮﻳﺔ ﻛﻤﺎ ﻳﻠﻲ‪:‬‬
‫ﻓﱪﺍﻳﺮ < ﺇﺑﺮﻳﻞ < ﻳﻨﺎﻳﺮ > ﻣﺎﺭﺱ < ﻧﻮﻓﻤﱪ < ﺩﻳﺴﻤﱪ‬
‫‪٦‬‬
Table of Contents
Subject
CHAPTER ONE: Introduction
CHAPTER TWO: Literature Review
2.1: Basic wind erosion mechanisms
2.2: Development of wind erosion studies
2.3: The nature of particle movement
2.4.: The nature of surface deposits and eroded forms
2.5. The factors influencing the location and rates of wind erosion
2.5.1: Erodibility factors
2.5.2: Erosivity factors
2.6: A wind erosion equation
2.6.2: Equivalent wind erosion variables
2.6.3: Relationships between variables
2.7: White Nile dunes
2.7.1: Dune form and distribution
CHAPTER THREE: Materials and Methods
3: Experimental site materials and methods
3.1: Experimental Sites
3.2: Estimation of Potential Wind Erosion Using Woodruff and
Siddways (1965) Model
3.2.1: The field surfaces used for the study
3.2.2: Method for estimating potential wind erosion
3.2.3: Relationships between the variables and computation of E
3.3: Sand traps
3.3.1 Vertical traps
3.3.2 Horizontal trap
3.4. Experimental design
3.5: Measurement and calculation of wind erosion intensity
3.6: Soils of different sites
Chapter Four: Results and Discussion
4.1. Estimation of potential wind erosion
4.2. Measurement of the intensities of wind erosion along field
surfaces at different periods
4.2.1. South Khartoum
4.2.2. West Khartoum
4.2.3. East Khartoum
4.2.4. North Khartoum
4.3. Sand blown analysis of intersects from Soba East to Wad elzaki
west
4.4. Comparison among different sites
4.5 Measurement of soil erodibility in Khartoum State
4.6 Wind erosivity
Chapter Five: Conclusion and References
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5.1 Conclusion
5.2 References
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List of Tables:
Tables
Table: (2.1) A new Assessment of the World Status of Desertification:
Table (3.1) Soil erodibility for soils with different percentages of
nonerodibile fractions as determined by standard dry sieving
Table (3.2) Some meteorological long term average data for Khartoum
State (source: Sudan Meteorological Authority)
Table (3.3) Soil analysis data, South Khartoum
Table (3.4) Soil analysis data, West El Khartoum
Table (3.5) Soil analysis data, East Khartoum
Table (3.6) Soil analysis data, North Khartoum (Al shaab Scheme)
Table (3.7) Soil analysis data, North El Khartoum (Alahamda)
Table (4.1a) Potential wind erosion of cultivated field surface estimated
with the use of wind erosion model by Woodruff and Siddways
(1965)
Table (4.1b) Potential wind erosion of cultivated field surface estimated
with the use of wind erosion model by Skidmore and Siddways
(1968)
Table (4.2) Intensity of wind erosion measured along a bare field in South
Khartoum with Vertical traps at different heights at different
periods (2000-2001)
Table (4.3) Intensity of wind erosion measured along a sheltered field in
South Khartoum with Vertical traps at different heights at different
periods (2000-2001)
Table (4.4) Intensity of wind erosion measured along a cultivated field in
South Khartoum with Vertical traps at different heights at different
periods (2000-2001)
Table (4.5) Intensity of wind erosion measured along a bare field in South
Khartoum with Vertical traps at different heights at different
periods (2001-2002)
Table (4.6) Intensity of wind erosion measured along a sheltered field in
South Khartoum with Vertical traps at different heights at different
periods (2001-2002)
Table (4.7) Intensity of wind erosion measured along cultivated field in
South Khartoum with Vertical traps at different heights at different
periods (2001-2002)
Table (4.8) Comparison between soil properties 1975 and 2002 for a bare
field in South Khartoum
Table (4.9) Comparison between soil properties 1975 and 2002 for
sheltered field in South Khartoum
Table (4.10) Comparison between soil properties 1975 and 2002 for
cultivated field in South Khartoum
Table 4.11: Intensity of wind erosion measured by Goz at different
distances at different Periods in West Khartoum with vertical traps
Table (4.12) Intensity of wind erosion measured along a fenced field at
different distances at different Periods in West Khartoum with
vertical traps
Table (4.13) Intensity of wind erosion measured along a bare land (Wadi)
at different distances at different periods in West Khartoum with
vertical traps
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Tables
Table (4.14) Intensity of wind erosion measured by Goz at different
distances at different Periods in West Khartoum with horizontal
traps
Table (4.15) Intensity of wind erosion measured along a fenced field at
different distances at different Periods in West Khartoum with
horizontal traps
Table (4.16) Intensity of wind erosion measured a bare field (Wadi) at
different distances at different Periods in West Khartoum with
horizontal traps
Table (4.17) Intensity of wind erosion measured along a bare field at
different distances at different Periods in East Khartoum with
vertical traps
Table (4.18) Intensity of wind erosion measured along a sheltered field at
different distances at different Periods in East Khartoum with
vertical traps
Table (4.19) Intensity of wind erosion measured a cultivated field at
different distances at different Periods in East Khartoum with
vertical traps
Table (4.20) Intensity of wind erosion measured a bare field at different
distances at different Periods in East Khartoum with Horizontal
traps
Table (4.21) Intensity of wind erosion measured a sheltered field at
different distances at different Periods in East Khartoum with
Horizontal traps
Table (4.22) Intensity of wind erosion measured a cultivated field at
different distances at different Periods in East Khartoum with
Horizontal traps
Table (4.23) Intensity of wind erosion measured a long sheltered field at
different distances at different Periods in North Khartoum with
vertical traps
Table (4.24) Intensity of wind erosion measured a long cultivated field at
different distances at different Periods in North Khartoum with
vertical traps
Table (4.25) Intensity of wind erosion measured a long a bare field at
different distances at different Periods in North Khartoum with
vertical traps
Table (4.26) Intensity of wind erosion measured a long a sheltered field at
different distances at different Periods in North Khartoum with
Horizontal traps
Table (4.27) Intensity of wind erosion measured a long a cultivated field at
different distances at different Periods in North Khartoum with
Horizontal traps
Table (4.28) Intensity of wind erosion measured a long a bare field at
different distances at different Periods in North Khartoum with
Horizontal traps
Table (4.29) Sand blown analysis of intersect west to east
Table (4.30) Soil erodibility of South, North and East Khartoum State:
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List of Figures
Figures
Fig. 3.1. Chart to determine V from R' or R' from V of standing and flat
anchored small grain stubble with any row width up to 10 inches,
including stover
Fig. 3.2. Chart to determine soil loss E1 = I'K'C'L' from soil loss E2= I'K'
and E3= I'K'C' and from unsheltered distance L' across the field.
Fig. 3.3. Chart to determine soil loss E = I'K'C'L'V' from soil loss E1=
I'K'C'L' and from the vegetative cover factor, V. The chart can be
used in reverse to determine V needed to reduce soil loss to any
degree
Fig. 4.1: Intensity of wind erosion measured a long a bare field in South
Khartoum with Vertical traps at different heights at different
periods (2000-2001)
Fig. 4.2: Intensity of wind erosion measured along a sheltered field in
South Khartoum with Vertical traps at different heights at different
periods (2000-2001)
Fig. 4.3: Intensity of wind erosion measured along a cultivated field in
South Khartoum with vertical traps at different heights at different
periods (2000-2001)
Fig. 4.4:Intensity of wind erosion measured along a bare field in South
Khartoum with vertical traps at different heights at different periods
(2001-2002)
Fig. 4.5:Intensity of wind erosion measured along asheltered field in South
Khartoum with vertical traps at different heights at different periods
(2001-2002)
Fig. 4.6:Intensity of wind erosion measured along cultivated field in South
Khartoum with vertical traps at different heights at different periods
(2001-2002)
Fig. 4.7:Intensity of wind erosion measured by Goz at different distances at
different periods in West Khartoum with vertical traps (2001-2002)
Fig. 4.8:Intensity of wind erosion measured along a fenced field at different
distances at different periods in West Khartoum with vertical traps
(2001-2002)
Fig. 4.9:Intensity of wind erosion measured along a bare land (Wadi) at
different distances at different periods in West Khartoum with
vertical traps (2001-2002)
Fig. 4.10:Intensity of wind erosion Measured by Goz at different distances
at different periods in West Khartoum with horizontal traps (20012002)
Fig. 4.11:Intensity of wind erosion measured along fenced field at different
distances at different periods in West Khartoum with horizontal
traps (2001-2002)
Fig. 4.12:Intensity ofwind erosion measured along a bare field (Wadi) at
different distances at different periods in West Khartoum with
horizontal traps (2001-2002)
Fig. 4.13:Intensity of wind erosion measured along a bare field at different
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Figures
distances at different periods in Khartoum with vertical traps
(2001-2002)
Fig. 4.14:Intensity of wind erosion measured along a sheltered field at
different distances at different periods in East Khartoum with
vertical traps (2001-2002)
Fig. 4.15:Intensity of wind erosion measured along a cultivated field at
different distances at different periods in East Khartoum with
vertical traps (2001-2002)
Fig. 4.16:Intensity of wind erosion measured along abare field at different
distances at different periods in East Khartoum with vertical traps
(2001-2002)
Fig. 4.17:Intensity of wind erosion measured along a sheltered field at
different distances at different periods in East Khartoum with
horizontal traps (2001-2002)
Fig. 4.18:Intensity of wind erosion measured along a cultivated field at
different distances at different periods in East Khartoum with
horizontal traps (2001-2002)
Fig. 4.19:Intensity of wind erosion measured along sheltered field at
different distances at different periods in North Khartoum Scheme
with vertical traps (2001-2002)
Fig. 4.20:Intensity of wind erosion measured along cultivated field at
different distances at different periods in North Khartoum with
vertical traps (2001-2002)
Fig. 4.21:Intensity of wind erosion measured along a bare field at different
distances at different periods in North Khartoum with vertical traps
(2001-2002)
Fig. 4.22:Intensity of wind erosion measured along a sheltered field at
different distances at different periods in North Khartoum with
horizontal traps (2001-2002)
Fig. 4.23:Intensity of wind erosion measured along cultivated field at
different distances at different periods in North Khartoum with
horizontal traps (2001-2002)
Fig. 4.24. Intensity of wind erosion measured a long a bare field at
different distances at different periods in North Khartoum with
horisontal traps intensity of wind erosion (2001-2002)
Fig. 4.25 Comparison of intensity of wind erosion among bare,
sheltered and cultivated fields in South Khartoum season 20002001
Fig. 4.26 Comparison of intensity of wind erosion measured among abare,
sheltered and cultivated fields in South Khartoum with vertical
traps (2001-2002)
Fig. 4.27 Comparison of intensity of wind erosion among GOZ,
sheltered and abare fields in West Khartoum
Fig. 4.28 Comparison of intensity of wind erosion among bare, sheltered
and cultivated fields in East Khartoum vertical traps
Fig. 4.29 Comparison of intensity of wind erosion among bare,
sheltered and cultivated fields in East Khartoum Horizontal traps
Fig. 4.30 Comparison of intensity of wind erosion among bare,
sheltered and cultivated fields in North Khartoum vertical traps
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Figures
Fig. 4.31 Comparison of intensity of wind erosion among bare,
sheltered and cultivated fields in North Khartoum Horizontal traps
Fig. 4.32. Comparison of intensity of wind erosion among GOZ,
bare and sheltered fields in West Khartoum Horizontal traps
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List of Plates
Plate
Plate (1) Wind erosion in South Khartoum (Soba)
Plate (2) Wind erosion in West Khartoum (Rawakeeb)
Plate (3) Wind erosion in East Khartoum (Siliet)
١٤
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CHAPTER ONE
Introduction
Desertification is land degradation in arid, semi-arid dry – sub –
humid areas resulting from various factors including climatic variation
and human activities (UNCED, 1992).
Soil erosion is the detachment and transportation of soil Particles
by wind or water. Erosion has been based on the physical principle that
soil movement occurs in response to forces generated by the flow of wind
or water.
Soil erosion is a natural phenomenon, it has occurred over the
millennia as part of geological processes and climate change. However,
erosion is more severe now, and it is accelerated by adverse human
activities. Globally, moderate to severe soil degradation affects almost
2000 million hectares of arable land grazing land.
Of primary interest is the erosion of the fertile top agricultural soil
by blowing (Wind erosion) or by surface run off (Water erosion). The
erosion of the topsoil directly associated with the loss of plant nutrients
and consequent reduction of crop yield. Erosion may also cause the
creation of washes and gullies, which make the land unsuitable for crop
production. Erosion is one of the most wide spread forms of land
degradation and this it is of concern. The fact that erosion generally
occurs rather slowly and may not create immediate problems is one of the
١٥
reasons for it is not being considered for emergency measures. The loss of
productivity in various soils with the degradation of physical and
chemical properties of the soil occurs with erosion.
Wind erosion is one of the geomorphologic processes that affect
our everyday lives, and in semiarid regions, it influences future
civilization. Soil is essential to sustain humankind, but soil can be
rendered infertile by the complete removal of topsoil or selected removal
of soil fines by wind. The particles removed may be deposited downwind
to become a part of the new landscape or maybe transported to oceans
where the nutrient-rich dust enhances aquatic life (Morales, 1977).
Wind erosion is the process by which loose surface material is
picked up and transported by wind, and the surface material is abraded by
windborne particles. The spatial redistribution and resorting of particles
by wind erosion may have profound effects on the affected soils, their
related micro topography, and any agricultural activity associated with
them. The process operates in a variety of natural environments that lack
a protective cover of vegetation. Its human consequences are undoubtedly
most serious in those agricultural areas that experience low, variable and
unpredictable rainfall, high temperatures and rates of evaporation and
high wind velocity as is the case in semiarid areas, as well as some of the
more humid regions that experience periodic droughts.
١٦
Wind erosion can occur when soil aggregates, capable of being
moved by wind, are present on the soil surface, the wind velocity is
sufficient to detach soil aggregates, and the soil surface is not protected
with nonerodible material. As the wind velocity exceeds the threshold
velocity required to initiate soil movement, individual soil aggregates,
become aerodynamically unstable, injected into the wind stream, and are
transported down wind. The distance traveled by the airborne particles
depends on the velocity of the wind and the shape and density of the soil
particles.
Factors influencing wind erosion are depletion of vegetative cover,
high temperature resulting in dry soil surface, low rainfall, wind intensity
and soil texture. Soils arranged in the following increasing order to
erodibility by wind: clay, loam, silt loam, loam, silt clay, loamy sand, and
sandy clay loam with the latter are the most susceptible. In addition to the
loss of nutrients, which results from wind erosion there is another
problem of wind erosion and that is the abrasiveness of rapidly moving
dust particles near the surface of the soil.
There is a definite pattern in the vertical size distribution of
airborne soils. Content of sand usually decreases with height and the
amount of fine particles increases correspondingly. The ratio of sand
fractions with the sum of silt and clay fractions gradually decreases and
nearly evens out at the height of 0.8 – 1 meter. The largest number of soil
١٧
particles usually in the o.1 to 0.5 mm diameter range is transported at a
height of approximately one meter from the soil surface under the direct
pressure of turbulent air current. Particle sizes greater than o.5mm in
diameter tend to move by rolling and fine particles less than 0.1 mm in
diameter are suspended in a very thin layer of air near the ground. Most of
the mass of wind-transported soil is concentrated in the 0-30 cm layer
above the soil surface.
Soil erosion by wind can be a problem wherever: The soil is loose,
dry, and finely divided, the soil surface is smooth and vegetative cover is
absent or sparse, the field is large, and the wind is sufficiently strong.
Wind erosion is serious in many parts of the world. General areas most
susceptible to wind erosion on agricultural land include much of North
Africa, and the near East, part of southern and eastern Asia, Australia, and
southern South America, and the semi-arid and arid portions of North
America. (FAO, 1960). In addition, such agricultural areas as the Siberian
plain and others in the USSR are potential susceptible to wind erosion
Worldwide, Wind erosion has been recognized for centuries. Scientists
recognized the need to determine the extent of the problem. Woodruff and
(Siddoway, 1965) developed a wind erosion equation to estimate potential
average annual erosion. We now have equipment to measure wind erosion
in the field (Fryrear, 1986).
١٨
No comprehensive survey of the extent of erosion in Africa.
Scattered reports build up and image that crop land in Madagascar are
losing 25-50 tons of topsoil a year from every hectare. In Zimbabwe half
communal lands were severely eroded (Horrison, 1990). Not less than 130
million hectare of Africa total cultivated areas were affected by erosion.
About 35% of the world surface is affected by some degree of erosion
(Bacco, 1992).
First serious degradation in Sudan was reported by (Cook, 1944) in
the Red Sea area. (Dregne, 1991) estimated that nearly 70 million
hectares of Sudan land are very severely degraded. More than 45 million
hectares are severely degraded, and about 30 million hectares of Sudan
land are moderately degraded, more than 64 million hectares are slightly
degraded. Remarkably, strong correlation exists between human
population densities and area of degraded soils in different aridity zones.
The most degraded soils zones were the arid and semi-arid zones. Over
grazing is a widely spread cause of soil degradation in Sudan, this affects
about 30 million hectares. Second cause is the clearance of forests and
woodland cover for firewood and charcoal, this affect about 22 million
hectares. Cropping without appropriate nutrients, inputs have degraded
about 12 million hectares (Ayoub, 1989). The causes of deterioration can
be divided in percentages as follows; 47.5% by over grazing, 22.5%
improper agricultural practices, 19% deforestation and 11% over
١٩
exploitation of vegetation for domestic use (Ayoub, 1998). The areas are
affected by wind erosion are Dar fur, Kordufan, Northern, River Nile,
Kassala, Red Sea, White Nile, El Gezira and Khartoum State. Khartoum
state is affected severely by wind erosion, plates 1, 2, 3, and 4 to show the
wind erosion severity in Khartoum State.
Wind erosion damages in several ways. It physically removes from
the field the most fertile portion of the soil, and thereby lowers its
productivity. Some eroded soil enters the atmospheric dust load, which
obscures visibility, pollutes the air, causes traffic hazards, and fouls
machinery and animal and human health. Blowing soil also covers road
fills, ditches and irrigation canals, reduces survival and growth of plants,
and increases their susceptibility to diseases and the transmission of
diseases to other plants. Agricultural land in Khartoum state is limited,
and the population density is high.
Khartoum state is one of which are seriously affected by
desertification. Wind erosion is the predominant desertification process.
The present study was undertaken to achieve the following objectives
Generate of broad- base quantitative actual and potential data .a
on wind erosion in Khartoum State.
Test of the application of the international wind erosion .b
equation to apply the local environment conditions.
Investigate of the influence of wind erosion in land use. .c
٢٠
Study the influence of wind erosion on soil properties. .d
Identify of a methodology for the assessment of soil wind .e
erosion under Sudan condition.
Collect of data that may help in conservation planning of .f
wind erosion in Khartoum State.
٢١
٢٢
CHAPTER TWO
Literature Review
2.1: Basic wind erosion mechanisms:
Wind erosion can occur when soil aggregates capable of being
removed by wind, are present in the surface soil, the wind velocity is
sufficient to detach soil aggregates and the soils surface is not protected
with non-erodible material.
Some of the removed aggregates are too large or heavy to become
airborne, but may roll along the soil surface in a transport mode of
aggregates 500 to 1000 U m in diameter and comprises 5 to 25 % of the
total material removed or eroded.
٢٣
Aggregated small enough to be injected into the wind stream, but
which gravity pulls back to the soil surface, are in transportation mode
called saltation. Upon striking the soil surface, the salting aggregates
additional aggregates, salting aggregates are usually 100 to 500 U m in
diameter, and comprise 50 to 75% of the total eroded material. If the
aggregates are very light or small, they may actually be transported great
distances in a mode called suspension.
Aggregates usually 2 to 100 Um in diameter and comprise 40% of
the total eroded material (Chepil and Widdruff, 1963).
World wide, wind erosion has been recognized for centuries.
Actual measurements of wind erosion are scarce, but dust loads have been
estimated. Junge (1977) estimated the annual dust load from Sahara to be
60 million to 200 million tons. Hagen and Woodruff (1975) estimated the
annual dust load from the Great Plains region to be 37 million to 551
million tons. Since less than 1% of the total wind eroded material is
transported in the earth’s atmosphere (Gillette, 1977), the quantity of
material moving from one location to another at the soil’s surface is very
large. The “dust bowl” days of the mid 1930 focused attention on the
potential magnitude of wind erosion in the United States and the farreaching impact of uncontrolled wind erosion. The Soil Conservation
Service annually reports the quantity of land damaged by wind erosion
٢٤
each year varies greatly, depending on past rainfall and cropping
conditions. Similar data were not available for other countries.
In the USSR, the number of dust storms each year has been
reported for various locations. The greatest number was observed in
Central Karakum at Cheshme in 1948 (Sapozhnikova, 1970). Dust storms
in USSR usually last less than 3 hours, but in May 1950, in Nebit-Dog, a
dust storm lasted 73 hours, and at Aidin in November 1951 a storm lasted
more than 70 hours.
Soil losses in Bikaner, India, in 1978 over a 75 day period, was 615
tons per hectare, and at Chandan, India, 325 tons per hectare (Gupta et al,
1981). Problems are severe during crop establishment or when grazing
removes the pasture residues.
Additional problems arise when salt-
affected soils are subjected to wind erosion and the eroded soil
accumulates on less saline areas, thus deteriorating the deposit location
(Malscolm, 1983).
The major potential wind eroded areas worldwide correspond to the
distribution of arid soils (Table 2.1).
٢٥
Table: 2.1: A new Assessment of the World Status of Desertification: World Dry Lands in millions of hectares
Africa
Asia
Australia
Europe
North
South
America
America
World
%
Hyper-arid
672
277
0
0
3
26
978
16
Arid
504
626
303
11
82
45
1571
26
Semi-arid
514
693
309
105
419
265
2305
37
Dry sub-humid
269
353
51
148
232
207
1296
21
Total
1959
1949
663
300
736
543
6150
100
32
32
11
5
12
8
100
13.1
13.0
4.4
2.0
4.9
3.6
41.0
66
46
75
32
34
31
41
% world total
% total global land
area
% continent area
(UNEP/GRID, 1991)
٢٦
2.2: Development of wind erosion studies:
In
the
late
nineteenth
and
early
twentieth
centuries,
geomorphological studies of wind were mainly concerned with its relative
importance as an erosive agent, and especially with the competence and
the capacity of the wind to transport fine material and debris.
Numerous other studies of potential relevance to the study of wind
erosion, considered sand movement in deserts and coastal areas mainly in
the context of describing and understanding dune morphology (Cornish,
1897; King, 1916; Kadar, 1934), while some experimental studies were
designed to reveal the precise mechanisms of sand movement (Olsson and
Seffer, 1908).
The studies by R.A Bagnold in the 1930’s, published in his
outstanding treatise on The Physics of Blown Sand and (Desert Dunes,
1941) marked a fundamental advance in the understanding of the winderosion system. Bagnold viewed the problem of wind/sand relationships
as one aerodynamics amenable to direct measurement. Working from a
theoretical basis, he tested his ideas by laboratory experiments in the
controlled conditions of a wind tunnel and by field observations and
measurements in the Libyan Desert Many of Bagnold’s ideas and results
provided the basis for subsequent research on the wind erosion problems.
In particular, the work of W.S. Chepil, A. S. Zingg, N. B.
Woodruff, and others, carried out largely under the auspices of the Wind
٢٧
Erosion Research Station at Kansas State University in the after math of
the "Dust Bowl”, built on Bagnolad’s foundations in the context of winderosion control of cultivated lands. This research attempted to identify
and quantity the factors influencing the location and rates of soil erosion
by wind, and to develop predictors of erosive conditions and soil loss
based on a climatic index (Chepil and Woodruff, 1963). It led to the
formulation in the 1960’s of a wind erosion equation that predicted
potential soil loss from individual fields and facilitated the control of
wind erosion, that wind erosion could be reduced to tolerable level,
(Woodruff and Siddoway, 1965).
This research continues today, concentrating on the tasks of
refining the prediction equation improving control techniques, and
determining ‘tolerable levels’ for different crops.
The later have advanced to a degree that further development in
some areas have been constrained by our inability to collect reliable field
data to test critical modeling assumptions and to verify or refute their
implications for aeolian transport mechanics (Anderson et al, 1991;
Butter Field, 1993).
2.3: The nature of particle movement:
(Chepil, 1961) measured the ratio of lift (caused by negative
pressure at the top of the grain), to drag at various points on a shere, from
the bed of a wind tunnel up to several centimeters above it. At the
٢٨
moment of entrainment the ratio was 0.75, but it decreased rapidly as the
particle grained height, until at several grain diameters above the bed, lift
became negligible, whereas drag increased in the faster airflow. Having
reached its maximum height the particle descends.
According to
(Bagnold, 1941) the angle at which particles strike the surface is
remarkably constant, between 10º and 16º from the horizontal,
irrespective of the height reached. He suggested that this constancy was
due to the balance achieved between the force of gravity acting
downwards and the maximum forward velocity (both of which increase
with height). (Chepil’s, 1961) observations of angle of descent suggested
a slightly lower range, from 6º to 12º.
When the particle hits the ground its momentums can be dispersed
in several ways. Firstly, the particle may rebound into the air flow,
usually with an initial vertical or near vertical component of motion and
possibly a transverse deviation from the main downstream direction of air
movement (Zing, 1953).
This is the bouncing motion called saltation by (Bagnold, 1941),
who followed (Gilbert’s, 1914) use of the term for similar motion in
water, secondly, the impact of a particle on to a surface of loose material
may be sufficient to cause other particles to be thrown into motion which,
without this assistance, may not have been pulled by the air flow alone.
Entrainment by impact can proceed at shear velocities lower than the
٢٩
threshold velocities required to initiate movement, and (Bagnold, 1941)
called the relevant threshold the ‘impact threshold’.
A third way in which momentum may be dispersed is by causing
surface disruption such that aggregates maybe broken (abraded), and
particles struck from behind may be pushed forward by what Bagnold
called ‘surface creep’.
In this way particles with diameters up to six times those of the
impacting grains may be moved. Particles may also be moved in
suspension. This can occur when the terminal velocity of all (determined
by grain size, shape, and density) is less than the mean upward eddy
currents in the air flow (Bagnold, 1941). Particles move in this way are
usually less than 0.1 mm in diameter (Udden, 1894).
The proportion of material carried by the mechanisms of saltation,
surface creep and suspension varies according mainly to wind velocity
and the size distribution of particles. (Chepil, 1945) found the proportion
varied as follows:
From 50 to 75% in saltation, from 3 to 40% in suspension, and from 5 to
25% in surface creep; (Bagnold, 1941) estimated surface creep at from 20
to 25% of total movement; and (Horikawa and Shen, 1960) reported a
similar figure of 20%.
All agree that saltation is quantitatively the most important process,
indeed most creep and suspension would not occur without it.
٣٠
(Olsson-Seffer, 1908) investigated sorting in the 8 cm zone above a
beach sand surface and found that mean particle size in transport
decreased with height.
(Williams, 1964) also studied sorting above a wind-tunnel sand bed
and be also found that, depending on initial surface grinding, the range of
particle size transported decreased with height and the average height at
which grains of particular size were trapped increased with increased
sphericity (a factor also affecting rate of transport).
(Bagnold, 1941) noted that at a given point in time, sand flow
increases downwind until the sand flow is saturated. No further removal
can take place further downwind as time progresses. And removal
continue from the upwind area, the remaining surface debris coarsens and
forms a protective pavement, and the area of removal migrates downwind
leaving behind an increasingly wide zone of quiescent, stabilized surface.
From this account it will be clear that, in monitoring debris
movement in wind it is important to draw a distinction between the
passage of material across a surface which maybe suffering no net loss,
and the actual loss of material reflected in the depletion of a body of
surface sediment.
(Chepil, 1957) referred to the downwind increase in the quantity of
material transported as ‘avalanching’, and he attributed it to several
٣١
causes (1959a). Firstly, there is a progressive increase in the number of
grain impacts which results in the entrainment of material by the impact
mechanism.
Secondly, because of the higher frequency of impact,
abrasion increases and thus increases the supply of erodible material in
addition, the erodible material removed upwind supplements the erodible
material downwind making the soil generally more susceptible to erosion.
Thirdly, particles dislodged from projections are trapped in depression so
that surface roughness is gradually reduced, which leads to an increase in
shear velocity and hence in rate of transport. This process is usually
called ‘detrusion’.
As erosion progresses, the process of sorting due to differential
rates of particle movement becomes more pronounced.
Over
the
whole
area
erosion
and
deposition
occur
contemporaneously, but the net result at a particle site will be determined
by the relations between the forces of erosion and deposition.
Where there are no non-erodible grains and wind velocity exceeds
the thresholds of movement, no protective layer will be formed and
erosion will continue until some other factor causes it to cease (Bagnold,
1941). When soil texture is uniform, non-selective removal may occur in
which all particles are present, the progress of wind erosion may be
seriously restricted, for the amount of material removed is limited by their
height, number, and distribution. As erosion proceeds, the height and
٣٢
number per unit area of non-erodible particles increases until the nonerodible particles completely shelter erodible material from the
‘windstable’ surface.
The final stage can be defined by the ‘critical
surface barrier ratio’.
2.4.: The nature of surface deposits and eroded forms:
Deposition of some or all of the material in transport will place if
one or more of the flowing occurs:
Atmospheric flow slakes, reducing or ending its capacity to
.١
transport;
Local wind velocity is reduced by obstructions such as hedges,
.٢
crops and non-erodible soil material;
The surface becomes stabilized by the onset of rains or
.٣
irrigation;
Surfaces compaction may be reduced so that more of the energy
of saltating grains is dissipated on the bed rather than in maintaining of
forward movement (Bagnold, 1941).
Sedimentation, due to a reduction in wind velocity and involving
material carried in all three modes of transport; accretion, caused by a
reduction in the rate of transport and consisting of creep and saltation
٣٣
.٤
loads; and encroachment, caused by a local increase in slope so that
surface creep is restarted while saltation continues unhindered.
Chepil and Woodruff (1963) considered that the effects of sorting
on soil produced four grades of surface material, arranged in order of
increasing erodibility:
.١
Residual soil materials comprising non-erodible colds and rock
fragments;
.٢
Lag sands, aggregates, and soil aggregates comprising semierodible particles moved as surface creep and widely scattered a cross the
surface;
Sand and clay dunes, together with ripples and possibly sand
.٣
sheets, composed of erodible material moved primarily by saltation; and
Loess, material moved in suspension and often deposited a
considerable distance from its source.
2.5. The factors influencing the location and rates of wind erosion:
The rate of which wind erosion occurs depends on the erodibility
and the erosivity of the wind.
2.5.1.: Erodibility factors:
The erodibility of individual grains is dependent upon their
diameter, density, and shape. Most soils, however, consist largely of
clods comprising individual particles held together by various forces. It is
٣٤
.٤
the state and stability (against abrasion) of these structural units which
largely determines the erodibility of soil in a field (Chepil and Woodruff,
1963). If a soil is well-structured, the number of soil particles small
enough to be moved may be very low and abrasion may be minimal both
to a limited supply of abrasives and to the mechanical strength of the
structural units. On the other hand, soils with weak structures and ample
initial supplies of erodible material maybe rapidly abraded. The state and
stability of the structural units are principally determined by water, soil
texture, organic cements, and disaggregating processes.
(a): Water
Water in the soil tends to bind soil grains together. In the case of
sands, water is easily removed by surface drying and the cohesive bond is
easily broken, as commonly occurs on sandbanks and sandy beaches that
dry out between tides and ‘blow’. Where finer materials predominate, as
on mudflats, moisture retention properties are much better: water
molecules are adsorbed on to grain surfaces by electrostatic forces (Hillel,
1971) and held there despite the high suctions caused by drying: and at
the contact between grains the adsorbed wedge (Hillel, 1971). In a soil
that is wetted and then dried, the moisture retention of the fine grains will
tend to bind the mass together, and the increased pressure between grains
at depth will enhance the strength of the banding.
٣٥
(Chepil, 1956) found that the erodibility of a soil decreased as the
square of the soil moisture increased, up to 15 atmosphere percentage (the
amount held at the suction equivalent to 15 atmosphere pressure and
approximately equal to the permanent wilting point) where no erosion
occurred.
(Belly, 1964) similarly showed that threshold shear velocity
increases rapidly as moisture content increases, until at a moisture content
of (two) 2 or 3% by weight the threshold shear velocity is very high
indeed.
The other main effect of water in the context of wind erosion is the
formation of surface crusts by raindrop impact Chepil and (Woodruff,
1963). The crusts are normally formed of silt and clay, coarser particles
being left lying loosely on the surface.
The loose particles are easily dried, and may be moved by the wind
soon after rainfall has ceased before any significant drying of the surface.
(b): Texture:
(Chepil, 1955) found that in general the higher proportion of silt
and clay in a soil the greater is the production of clods and the lower is
soil erodibility. Silt forms more colds, but they are softer and more easily
broken than those formed by clay.
(c): Cements associated with organic decomposition:
٣٦
A variety of cements are produced from the breakdown of organic
material by micro-organisms. (Chepil, 1955) investigated the effects on
soil erodibility of increasing organic matter. He found that additions to
the soil of between 1 and 6% organic matter during the initial stages of
decomposition (less than one year), led to enhance clod production and
decreased erodibility; but that over a period of four years there was a
decline in clod production and an increase in erodibility.
It was concluded that continuous addition of organic matter is
necessary to improve cohesion, and that material left on the surface
breaks down at a slower rate and is more useful than material mixed in by
plaughing.
2.5.2: Erosivity factors:
The principal factor affecting erosivity is the force of the wind on
the ground surface. The factors affecting this force can be grouped into
two main categories: those related to the nature of atmosphere flow itself
and those related to the main constraint on that flow,which is surface
roughness.
(a): Atmospheric flow factors:
Wind tunnel tests and field measurements have shown that the rate
of soil movement is proportional to the cube of wind velocity. Applying
this relationship to annual mean velocity for Dodge City, Kansas, Zingg
(1935b) calculated the ratio (v/u)3
٣٧
V: mean wind velocity for a given year
U: is a mean velocity for all the years recorded.
(Skidmore and Woodruff, 1968), found that only mean wind speeds
greater than 5.4m/s were considered to be erosive.
(b): Roughness elements:
Although the relative importance of the different factors that
contribute to general surface roughness, and surfaces roughness itself are
often difficult to determine in the field, it is convenient for the purposes of
description to distinguish five major groups of roughness elements:
(i): Vegetation:
The most important properties of vegetation cover in the context of
surface roughness are its height and density, since these determine the
extent to which air flow contacts the group surface, and influences the
height of the mean aerodynamic surface.
The values of height and density will vary with vegetation type and
for a given type, according to the time of year.
Time of year is
particularly important for annually sown crops, and the length of time
taken for each crop to grow to a sufficient size to provide adequate
protection against erosion is a fundamental factor. (Chepil and Woodruff,
1963) suggested that grasses and legumes are the most efficient in
establishing a dense cover. Crop residues are also important in protecting
the surfaces.
٣٨
(ii): Clods and non-erodible fractions:
Erosion continues until a sufficient number of non-erodible
elements are uncovered at the surface. At this stage the non-erodible
elements provide direct cover and shelter the remaining erodible grains on
the surface. This condition may alter with a change in the wind direction.
The point at which this cover is just sufficient to prevent movement from
continuing or starting is called "the critical surface barrier ratio"
(originally called the critical surface roughness constant) by (Chepil,
1950a). The ratio is defined as the distance between the non-erodible
barriers divided by the height of the barriers, (Chepil and Woodruff,
1963), and was found to vary depending upon the wind shear velocity at
the time and the threshold shear velocity of the erodible fractions.
Therefore, the higher the shear velocity and the lower the threshold, the
lower is the critical surface barrier ratio.
The use of this concept can be extended to include other roughness
elements such as ridges and strip crops.
(iii): Ridges:
Ridges produced by tillage have their greatest effect in reducing
erosion by sheltering and trapping when the wind blows at right angles to
them, and a decreasing effect as the wind moves parallel to them. Ridges
consisting of only erodible elements are of little value because they are
easily flattened.
٣٩
Similarly, tall ridges expose the topmost grains to
stronger winds, so that in same circumstances ridges may increase rather
than decrease the amount of erosion.
(iv): Field shelterbelts:
Considerable attention has been paid to the various implications of
shelterbelt construction by such authors as Jensen (1954), Caborn (1957),
and Skidmore and Hagen (1970). Here, remarks will be restricted to the
effects of shelterbelts on air flow. Usually the term shelterbelt is taken to
mean a row (or several rows) of trees, and/or hedge. The principles
concerning air flow over shelterbelts may be applied to fences, Hessian
screens, walls, and rows of tall crops grown between more delicate ones.
(v): Local changes in topography:
In field changes in the micro-topography are likely to lead to a
complex pattern of erosion, and the presence of knolls and hollows is
likely to affect the variables influencing erodibility.
2.6: A wind erosion equation:
The wind erosion equation was developed by the late Dr. W. S.
(Chepil, 1957). It is the result of nearly 30 years of research to determine
the primary variables or factors that influence erosion of soil by wind.
The first wind erosion equation was a simple exponential
expressing the amount of soil loss in a wind tunnel as a function of soil
٤٠
cloddiness percent, amount of surface residue, and degree of surface
roughness. The equation has been modified continually as new research
data became available and now is a complex equation indicating the
relation between potential soil loss from a field and some individual
primary field and climatic variables.
The equation is designed to serve the twofold purpose of determining
(i)
if a particular field is adequately protected from wind
erosion, and
the different field conditions of cloddiness, roughness,
vegetative cover, sheltering from wind barriers, or width and orientation
of field required to reduce potential soil loss to a tolerable amount under
different climates.
2.6.1.1: Primary wind erosion variables:
The wind erodibility of land surfaces is governed by primary
variables, a brief description of each fallow.
2.6.1.2: Soil roughness, Kr:
Kr is a measure of soil surface roughness other than that caused by
clods or vegetation; it is the natural or artificial roughness of the soil
surface in the form of ridges or small undulation.
2.6.1.3: Velocity of erosive wind, V:
The rate of soil movement varies directly as the cube of the wind
velocity. Where average annual soil loss is desired, the mean annual wind
٤١
(ii)
velocity corrected to a standard height of 30 ft, is used. Atmospheric
wind velocities are normally distributed; thus the higher the mean annual
velocity the greater the probability of receiving high winds.
2.6.1.4: Soil surface moisture, M:
The rate of soil movement varies approximately inversely as the
square of effective surface soil moisture since detailed surface soil
moisture is not generally available for different geographic locations, the
wind erosion equation M is assumed to be proportion to the climatic
factor.
2.6.1.5: Distance a cross field, Dr:
Dr is the total distance across a given field measured along the
prevailing wind erosion direction on an unprotected eroding field, the rate
of soil flow is zero on the windward edge and increases with distances to
leeward until, if the field is large enough, the flow reaches a maximum
that a wind of a particular velocity can sustain. The distance required for
soil flow to reach this maximum on a given soil is the same for any
erosive winds. It varies only and inversely with erodibility of a field
surface.
2.6.1.6: Sheltered distance, Dn:
Dn is the distance along the prevailing wind erosion direction that is
sheltered by a barrier if any, adjoining the field.
2.6.1.7: Quantity of vegetative cover, R:
٤٢
Surface residue amounts are determined by sampling, cleaning,
drying and weighing in accordance with Agricultural Research Service
Standardized Procedure.
All quantities of vegetative residue, R,
connected with the wind erosion equation are based on washed, ovendry
residue multiplied by 1.2 to make them comparable to the usual field
measurements where samples are dry cleaned and air-dried.
2.6.1.8: Kind of vegetative cover, S:
S is a factor denoting the total cross-sectional area of the vegetative
material. The finer the material and the greater its surface area, the more
it reduces the wind velocity and the more it reduces wind erosion.
2.6.1.9: Orientation or vegetative cover variable, Ku:
Ku is in effect the vegetative surface roughness variable. The more
erect the vegetative matter, the higher it stands above the ground, the
more it slows the wind velocity near the ground and the lower is the rate
of soil erosion. Ku includes the influence of distribution and location of
vegetation such as width and direction of rows, uniformity or distribution,
and whether the vegetation is in a furrow or on a ridge.
2.6.2: Equivalent wind erosion variables:
Because of the nature of the relationship between soil erodibility
and some of the primary variably, it has been found convenient to
٤٣
disregard some variables, group some, and convert others to equivalents
as follows:
Soil erodibility, I
Soil and knoll erodibility, I
Knoll erodibility, Is
Disregard, crust transient Surface crust stability, Fu
Soil ridge roughness factor, K Soil ridge roughness, K1
Wind velocity, V
Local wind erosion climatic factor,
Surface Soil moisture, M
Distance across field, Dr
Field length, L
Sheltered distance, Dn
Quantity of vegetative cover R
Equivalent
quantity
of S vegetative
Kind of vegetative
cover,
Orientation of vegetative cover, K
2.6.3: Relationships between variables:
The general functional relationship between the dependent variable,
E, the potential average annual soil loss in tons per acre per annum, and
the equivalent variables may be expressed as:
E: f ( I, C, K, L, V)
Mathematical relationships have been established between individual
variables, it will be discussed on chapter three (materials and methods).
٤٤
2.7: White Nile dunes:
Fixed dunes border the White Nile bank between Hashaba and
South Khartoum, and occupy 400000 acres. They extend for over 15 km
between Latitudes 14º 15# N and 15º 15# N, and near El Geteina dunes
extend up to 20 km from the river. The catena is complicated by broken
profiles due to active differential erosion and by the presence of fossil
lake marls.
2.7.1: Dune form and distribution:
Between Wadez Zaki and El Geteina there is a continuous belt of
alternating dune ridges and swales.
The dune occur as broad
‘whalebacks’ or as well-defined longitudinal ridges, from 5 m to 15 m
high and up to 15 km long. The dune forefronts are sometimes scalloped
by gullies, and blow-outs occur sporadically. North Jebel Aulia, the
dunes become smaller and fewer, diminishing with increasing distances
from the river to low ridges 1-2 m high, up to 5 m wide, and up to 1 km
long. South-eastwards from El Geteina isolated dunes may be followed
through the clay plains N of El Azazi towards Sennar on the Blue Nile.
These minor sandy areas vary in form from sinuous, elongated ridges to
low circular sandy mounds. Most of the dunes lie at elevations between
٤٥
380 m and 390 m (relative to the old Khartoum datum, which is 3 m
lower than the new Alexandria datum).
The dominant dune-fixing grass is Panicum turgidum which occurs
in association with a low, open turgidum which occurs in association with
a low, open woodland of Capparis deciduas, Acacia seyal, and Acacia
tortilis.
East of El Geteina and around Wad ez Zaki, Prosopis spacidus and
Leptadenia pyrotechnica are strongly localized, in close association with
Calotropis procera, a bush often considered a sign of soil deterioration
(Fisher, 1944).
The swale floors are sparsely covered with Schoeneldia gracilis,
Aristida funiculate, A. mutabilis, and A. adscenscionis. Settlement is
confined to the wooded dunes, and the treeless seasonally flooded swales
are avaided.
The sand dunes form narrow winding ridges and broad flat-topped
sand sheets with a dominant E-W or SE-NW trend, except in the N,
between Khartoum and Jebel Aulia, where they run parallel to two
alluvial terraces bordering the White Nile and in the S. at Wad ez Zaki
and at Hashaba, where they mark the position of a former White Nile
strand-line.
Some of the higher dunes pursue a sinuous course
reminiscent of braided and meandering channels, but the bulk of the
dunes have been re-sorted by wind action to such a degree that they do
٤٦
not coincide in detail with their original orientation. Erosion is active
along the margins of the dune complex, where numerous low, remnant
sandy hummocks with a conspicuous cover of Panicum turgidum,
Fognonia cretica, Cassia italica, and Cassia senna are Scattered on the
cracking-clay plains.
In the Central Gezira, the dunes may occupy linear depressions
within the clay plain, and gypsum and muscovite occur often in the soil
profile.
٤٧
CHAPTER THREE
Materials and Methods
3: Experimental site materials and methods:
3.1: Experimental Sites
The study was conducted in:
Four locations around Khartoum town:South Khartoum: Soba scheme 22km south Khartoum. Three
.١
sites were selected
A: Bare field.
B: Field sheltered with kitir Acacia millifera.
C: Field cultivated with Barseem Trifolium
alexandrcium.
North Khartoum: El Shaab Scheme and Alahamda, 22 km north
.٢
El Khartoum. Three site were selected
A: Bare field.
B: Field sheltered with kitir Acacia millifera.
C: Field cultivated with Barseem Trifolium.
West Khartoum El Rawakeeb Scheme 35 km West El
Khartoum. Three sites were selected
A: Bare field (wadi)
B: Field fenced with wall 2 m height.
٤٨
.٣
C: GOZ field.
.٤
East Khartoum South Seilet Scheme and Omdom Scheme 35
km east El Khartoum. Three sites were selected
A: Bare field.
B: Field sheltered with kitir Acacia millifera.
C: Field cultivated with Barseem Trifolium.
3.2: Estimation of Potential Wind Erosion Using Woodruff and
Siddways (1965) Model:
3.2.1: The field surfaces used for the study:
Various field surfaces were selected from each of the three sites
named for this study. A bare field; sheltered field, and cultivated field
were selected in south; North, and East Khartoum sites.
In West
Khartoum a bare, sheltered fields and Goz were selected.
3.2.2: Method for estimating potential wind erosion:
The potential wind erosion is defined as the annual soil loss
expressed in tons per acre per annum was estimated with the use of
Woodruff and Siddways (1965) equation:
E=f (I′, K′, C′, L′, V′)
Where:
E: potential soil loss in tons per acre per annum
I′: Soil erodibility index (tons/acre/annum).
٤٩
K′: Soil ridge roughness factor
C′: local wind erosion climatic factor
L′: Distance across field
V′: equivalent quantity of vegetative cover
(a) Estimation of soil erodibility:
Soil erodibility index was estimated with a procedure described by
Chepil (1943). A spade was pushed under the surface layer 3 cm .., thick
when the lands were prepared for cultivation. The soil samples were airdried and the percentages of soil aggregates greater than 0.84 mm in
diameter were determinate a sieve of the same size. The soil erodibility
index (1) was estimated for each field for the percentage of the soil
aggregates greater than 0.84 mm in diameter using table 3.1.
(b) Local wind erosion climatic factor:
Estimation of the local wind erosion climatic factor (C) was based
on metorological data of Khartoum metorological station from which data
of climatological normals was collected for 40 years, including rainfall,
temperature, and wind relocity. Using Table 3.2 the method used to
٥٠
compute the climatic factor was described by Woodruff and Siddways
(1965).
C′=34.483 [(V3)/ (P-E) 2]
Where:
V: mean annual wind velocity for the locality in question at 10 feet
height.
P-E= 115 ∑ [(P/T-10) 10/9]
where P is the mean precipitation for the month (inch) and T is the mean
temperature for the month (i) and a minimum value of 18.4 was adopted
for T=10 (Morgan, 1986).
(c) The soil ridge roughness factor (K′):
This was estimated by the roughness factor R (Morgan, 1986)
where:
R= [(H) 2 /(I)]
Where:
H= height of ridge (mm)
I= distance between ridges
K′= L; R <2.27
K′= 1.125 – 0.153 In R
2.27≤R<89
(d) Distance
across field (Df):
According to Woodruff and Siddways (1965) the total distance
across a given field is measured along the prevailing wind erosion
٥١
direction According to Chepil (1959) Df was computed from width of
field and prevailing wind erosion direction for the different fields
Df= distance across field along the prevailing wind erosion
direction.
W= Width of the field strip.
A= angle of deviation of the prevailing wind erosion direction from
right angel
to the field strip.
(e) Sheltered distance: (Db):
The sheltered distance along the prevailing erosion direction was
determined by multiplying the height of the barrier by 10.
K′= Df- Db
(f) Estimation of the vegetation cover equivalent (V):
Amounts of vegetation residue covering fields surfaces under study
was determined by sampling with the use of one meter square quadrate.
The collected amounts were cleaned, oven-dried, and then their oven dry
weights were recorded. The quantity of vegetation cover (R′) for each
field surface was computed by multiplying the oven-dry by 1.1. This
method was described by Woodruff and Siddways (1956). Then V the
computed for each field from graph prepared for the computation of V
from R at different conditions (Fig. 3.1).
٥٢
3.2.3: Relationships between the variables and computation of E
The functional relationships between potential average annual wind
erosion E expressed in tons per acre per annum and the equivalent
variables is expressed as:
E= f(I′, C′, K′, L′, V)
Woodruff and Siddways (1965) introduced a 5 steps procedure for the
solution of this equation,
Step (1) Determination of erodibility:
E1= I′ that occurred from a field, with a known percentage of dry
aggregate greater than 0.84 mm in diameter.
Step (2) Accounts for the effects of roughness K′, and find the erodibility
E2.
E2= I¯K′
Step (3) Accounts for the effect of C′
E3= I′¯K′¯C′
Step (4) It accounts for the effect of L′
E4= I′¯K′¯C′,f(L′)
Because L′, I′, K′, C′ and I′, K′ are all introduced, a graphical solution
was used, Fig. 3.2 was interrelated by Woodruff and Siddways (1965) to
obtain
E4= I′, K′, C′, f(L′)
٥٣
Step (5) Accounts for the effect of vegetation cover V,
E5= I′¯K′¯C′, f (L′)¯ f (V)
E4, V and E are introduced; a graphical solution was also used. Figure 3.3
was introduced by Woodruff and Siddways (1965) from which the
amount of erosion (E) was found for each field surface.
٥٤
3.3: Sand traps:
3.3.1 Vertical traps:
Tow types of vertical traps were used for the study
(a) Leatherman Trap:
(1) Vertical sand traps were constructed as described by Leatherman
(1978):
The trap consisted of a section of PVC tube with two slits cut in one end.
The trap was buried in the soil so that the base of the slit was flushed
with the surface. One slit saved as a collection orifice, the other was
covered with a screen. The buried portion of the tube was the collection
chamber which was provided with a PVC insert, inside which and
particles were collected. The dimensions of the collecting orifice were
2.5¯30 cm2 (Fig 3.4).
(b) Horikawa and Shen Trap:
Horikawa and Shen (1960), the trap sampled at four heights 0, 5, 20, and
50 cm. Each sampler consisted of a plastic bottle, mounted on a wind
vane which rotated a bout a central iron pole.
One slit saved as a
collection orifice, the other was covered with a screen to provide a
minimum flow through of wind. The dimensions of the collecting orifice
were 1¯ 2 cm2.
3.3.2 Horizontal trap:
٥٥
Traps consisted of sections of PVC tubes, edible oil cans with
various diameters and hights were used as horizontal traps for moving
sand collection. These traps were closed at the lower portions, which was
buried in the soil and left open at the upper part.
Horizontal traps used got the following diameter:
Trap
Internal diameter
(i) Large edible oil can
17.0 cm
(ii) Small edible oil can
08.5 cm
(iii) Large PVC tube
10.0 cm
(iv) Small PVC tube
04.5 cm
3.4. Experimental design:
The experimental design used for this study was split – plot design.
With the distances from the wind ward edging the main plots and periods
of time as the sub-plots for the PVC traps. With the height of the plastic
bottle being the main plots and periods of time as the sub-plots for the
iron pole traps.
3.5: Measurement and calculation of wind erosion intensity:
The collected soil material by the vertical and horizontal sand traps
was weighed and divided by the area through which sand particles entered
the trap and the obtained weight per unit area was converted to soil loss in
ton per hectare per day as follows
٥٦
= Weight of soil per trap (g)2100 ¯100 ¯10000
Area of trap orifice (cm ) ¯ number of
days¯1000¯1000
Ton hectare -1 day-1 = Wt of soil per trap (g) ¯100
Area (cm2) ¯ number of days
٥٧
Table 3.1. Soil erodibility for soils with different percentages of nonerodibile fractions as determined by standard
dry sieving*
Percentage of dry soil
fractions > 0.84 mm
Units
Tens
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
0.0
1
2
3
--134
98
74
56
38
21
12
02
310
131
95
72
54
36
20
11
---
250
128
92
71
52
33
19
10
---
220
125
90
69
51
31
18
08
---
4
5
Tons/acre
195
180
121
117
88
83
67
65
50
48
29
27
17
16
07
06
-----
6
7
8
9
170
113
83
63
47
25
16
04
---
160
109
81
62
45
24
15
03
---
150
106
79
60
43
23
14
03
---
140
102
76
58
41
22
13
02
---
Table 3.2: Some meteorological long term average data for Khartoum State (source: Sudan Meteorological
Authority)
STATION: KHARTOUM
R.H.
RAIN FALL (MM)
CLOUD AMOUNT
(OKTAS)
ELEM
TOTAL
MMS
MONTH
Jan.
Feb.
Mar.
٥٨
MEANS
27
22
17
00
06
12
18
0.7
2.1
2.0
1.7
0.9
2.1
2.0
1.8
0.9
2.3
2.2
1.8
NO. OF DAYS
EVP
PICH
(MM)
MAXIMUM
IN ONE DAY
TOTAL DATE
0.6 30-83
WIND
15.0
PRV.
DIR.
N
MEAN
SPEED
M.P.H.
9
0
0.1
0
1.0
0
10.0
0
0
0
0
0
TR
SEV
17.7
N
10
0
0.1
0.1
0
1.6
2-82
21.1
N
10
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
16
19
28
43
49
40
28
27
30
29
0.6
1.7
2.0
1.2
0.4
0.1
0.8
0
11.8
27-67
23.2
N
9
1.6
2.5
2.4
1.8
4.0
0.9
0.8
0.1
20.3
11-66
21.5
N
8
2.1
3.2
3.3
2.4
5.4
1.2
0.9
0.2
27.5
3-83
20.9
SW
9
3.9
4.9
4.7
4.4
46.3
4.8
3.8
1.4
61.5
8-61
16.3
SW
9
4.2
5.1
4.7
4.7
75.2
4.8
4.0
1.7
200.3
1-88
13.8
SW
9
3.7
4.5
4.4
4.2
25.4
3.2
2.2
0.4
45.2
3-62
15.5
SW
8
1.8
2.5
2.9
2.4
4.8
1.2
0.8
0.1
25.9
2-73
18.0
N
7
0.4
1.5
1.6
1.0
0.7
0
0
0
22.2
1-76
18.0
SW
9
0.6
2.0
1.7
1.2
0
0
0
0
0
-
14.8
SW
9
1.8
2.9
2.8
2.4
162.4 16.3 12.7
3.9
200.5
4-8-88
18.0
-
-
ALL TIMES ARE G.M.T (SUDAN TIME + 2 HOURS)
Note:
= SEVERALS SEV.
= TRACE TR
Table: (3.3) Soil analysis data, South Khartoum
Depth
Cm
0-30
٥٩
CaCO3
%
11.0
Cs
24
Particle size distribution
Fs
Silt
20
10
Sat %
Clay
35
47
30-60
60-100
17.0
15.2
19
15
13
13
11
13
40
44
66
79
Exchangeable Bases Ct mol/Kg
Na
K
7.3
19.0
19.8
1.1
0.7
0.8
pH
Paste
8.4
8.2
8.2
Na
18.0
129.8
140.2
٦٠
Ca
pH
1:5
9.8
9.3
9.5
Mg
CEC
Ct
mol/Kg
33
36
39
E.C
Ds/m
1.8
15.4
17.3
%
O.C
N
C/N
Ratio
0.374
0.359
0.346
0.036
0.031
0.030
10
12
12
Available
P
mg/kg
3.0
2.8
2.6
SAR
ESP
22
53
51
17
40
41
Soluble Cation and onions meq/L (Saturation /Extract)
K
Ca
Mg
Cl
SO4
MCO3
1.8
0.5
6.0
0.0
17.0
4.6
41.8
0.0
17.7
5.4
64.4
0.0
CO3
2.3
1.0
1.1
Table: (3:4) Soil analysis data, West Khartoum
Depth
Cm
0-15
15-35
35-60
60-115
CaCO3
%
0.0
0.0
0.0
0.0
Cs
56
43
40
40
Particle size distribution
Fs
Silt
22
10
24
19
25
19
10
29
Sat %
Clay
12
14
16
21
Exchangeable Bases Ct mol/Kg
Na
K
Ca
0.29
0.62
0.91
0.89
0.35
0.30
0.20
0.25
pH
Paste
7.4
7.2
7.3
7.3
Na
2.7
4.1
2.2
2.2
٦١
Mg
pH
1:5
8.0
7.7
7.9
7.9
K
CEC
Ct
mol/Kg
8
13
17
18
E.C
Ds/m
0.70
0.94
0. 43
0.44
%
O.C
N
C/N
Ratio
0.156
0.178
0.156
0.240
8
8
8
8
3.4
3.4
2.8
2.6
29
37
43
49
Available
P
mg/kg
SAR
ESP
2
3
2
2
4
5
5
5
Soluble Cation and onions meq/L (Saturation /Extract)
Ca
Mg
SO4
Cl
CO3
3.0
1.0
2.6
0.0
3.5
1.0
4.2
0.0
1.5
0.5
1.7
0.0
2.0
0.5
1.5
0.0
MCO3
3.20
3.75
2.10
2.15
Table: (3. 5) Soil analysis data, East Khartoum
Depth
Cm
0-20
20-50
50-80
80-120
120-140
140-195
CaCO3
%
3.2
4.6
3.6
3.0
6.6
18.4
Particle size distribution
Cs
Fs
Silt
17
21
22
18
18
23
13
16
31
15
18
31
17
30
24
21
47
16
Exchangeable Bases Ct
mol/Kg
Na
K
Ca Mg
2.98
3.44
16.08
13.29
11.34
6.13
pH
Paste
7.9
8.0
8.0
7.8
7.9
8.1
٦٢
0.65
0.34
0.53
0.28
0.23
0.11
pH
1:5
8.8
9.0
9.1
8.7
8.9
9.0
CEC
Ct
mol/Kg
37
42
38
42
30
15
%
Sat %
Clay
40
41
40
36
29
16
O.C
N
C/N
Ratio
0.187
0.156
0.140
0.156
0.140
0.047
0.050
0.050
0.025
0.045
0.030
0.025
4
3
6
3
5
2
E.C
Ds/m
0.61
0.71
2.05
14.50
18.00
6.20
57
60
63
69
69
49
Available
P
mg/kg
3.0
3.8
1.0
1.0
2.2
2.2
SAR
ESP
8
9
11
22
25
21
8
8
16
32
38
41
Na
7.8
9. 0
12.6
34.0
66.0
40.0
٦٣
Soluble Cations and onions meq/L (Saturation /Extract)
K
Ca
Mg
Cl
SO4
MCO3
1.5
0.0
1.8
1.6
1.5
0.5
1.6
2.5
2.5
0.0
4.6
1.4
26.5
4.5
33.8
1.1
12.6
2.0
44.2
1.4
5.0
2.0
35.6
1.3
CO3
0.0
0.0
0.0
0.0
0.0
0.0
Table: (3.6) Soil analysis data, North Khartoum (Al shaab Scheme)
Depth
Cm
0-25
25-80
80-100
100-130
130-145
145-155
155-195
CaCO3
%
1
1
2
1.5
0.5
1
1
Particle size distribution
Cs
Fs
Silt
2
10
36
3
14
32
2
8
49
3
7
50
50
41
7
7
77
9
11
78
6
Exchangeable Bases Ct
mol/Kg
Na
K
Ca
Mg
0.68
2.05
1.97
3.43
0.24
0.46
0.32
1.0
0.6
0.4
0.1
0.3
0.5
0.5
pH
Paste
7.7
7.7
8.0
7.9
8.6
8.3
8.5
Na
2.16
٦٤
pH
1:5
8.5
8.2
8.9
8.8
9.0
8.9
8.9
CEC
Ct
mol/Kg
45
43
32
43
3
7
5
%
O.C
N
1.02
0.577
0.515
0.640
0.000
0.000
0.000
0.025
0.071
0.033
0.04
E.C
Ds/m
0.3
0.48
0.34
0.47
0.30
0.45
0.45
Sat %
Clay
51
50
39
38
2
6
4
C/N
Ratio
66
71
66
72
73
39
32
Available
P
mg/kg
SAR
ESP
1.8
4.0
4.6
5.3
2.6
4.5
3.6
1.5
4.5
5.0
5.7
8.0
6.6
6.4
Soluble Cation and onions meq/L (Saturation /Extract)
K
Ca
Mg
Cl
SO4
MCO3
1.84
0.86
2.6
3.20
CO3
1.0
3.60
3.60
3.70
2.16
3.50
2.52
٦٥
1.25
1.12
0.88
1.12
0.80
0.88
0.32
0.16
0.80
0.24
0.32
0.80
2.6
2.5
2.0
2.2
2.2
2.0
2.90
3.60
3.50
2.15
2.60
2.70
2.2
1.2
1.6
1.6
1.8
1.7
Table: (3.7) Soil analysis data, North El Khartoum (Alahamda)
Depth
Cm
0-15
15-40
40-85
85-185
CaCO3
%
1.5
3.0
4.0
4.0
Cs
37
38
35
36
Particle size distribution
Fs
Silt
14
14
13
10
15
9
22
11
Sat %
Clay
34
36
37
37
Exchangeable Bases Ct mol/Kg
Na
K
1.1
6.4
6.0
4.4
0.7
0.3
0.2
0.3
pH
Paste
7.9
8.3
8.2
7.8
Na
3.9
9.2
73.3
119.0
٦٦
Ca
Mg
pH
1:5
8.8
9.6
9.2
8.3
CEC
Ct
mol/Kg
27
30
29
27
E.C
Ds/m
0.50
0.96
6.14
11.14
%
O.C
N
C/N
Ratio
0.50
0.23
0.16
0.11
0.053
0.016
0.009
0.007
10
13
6
14
SAR
Soluble Cation and onions meq/L (Saturation /Extract)
K
Ca
Mg
Cl
SO4
MCO3
2.4
0.1
1.3
4.0
1.4
0.0
5.9
5.2
5.7
2.1
27.2
3.1
23.9
13.7
31.6
2.5
49
45
74
62
Available
P
mg/kg
ESP
4.1
21.3
27.6
16.2
CO3
0.0
0.0
0.0
0.0
٦٧
Fig. 3.1. Chart to determine V from R' or R' from V of standing and flat
anchored small grain stubble with any row width up to 10 inches,
including stover.
٦٨
٦٩
Fig. 3.2. Chart to determine soil loss E1 = I'K'C'L' from soil loss E2= I'K'
and E3= I'K'C' and from unsheltered distance L' across the field.
٧٠
٧١
Fig. 3.3. Chart to determine soil loss E = I'K'C'L'V' from soil loss E1=
I'K'C'L' and from the vegetative cover factor, V. The chart can be used in
reverse to determine V needed to reduce soil loss to any degree.
٧٢
3.6: soils of the different sites:
(a) South Khartoum (2001-2002):
Bare field surface:
Table 4.5 and Fig. 4.4 show that the spatial distribution pattern of the intensity of
wind erosion values depicts a maximum at zero cm height for all periods, where
the intensity of wind erosion for the four heights increased regularly with periods
from November 2001 to May 2002. Temporal variation in intensity of wind
erosion were indicating the variability of intensity of wind erosion with the height.
Sheltered field surface:
Table 4.6 and Fig. 4.5 show that the intensity of wind erosion values for the first
period 1-30/11/2001 (S1) decreased from 0.28 at zero cm height to 0.05 at 5 cm
height to 0.01 at 20 cm height to 0.0 ton/ha/day at 50 cm height. The values of
intensity of wind erosion for the other six periods were decreased regularly with
the height. The values of intensity of wind erosion were increased for the four
heights regularly from November 2001 to May 2002.
(b) Soils of West Khartoum (Rawakeeb):
Brief description of the soils
Soil Name: Erosional/Nubian sandstone plain
Classification: Typic Haplargids, fine loamy over fragmental, mixed
hyper. Generally deep and well drained. Texture is generally sand
loam. The structure is well developed with an argillic horizon. The
colour is strong (5 y R5/6) moist. It is noncalcarous with low pH.
Table 3.4 shows the values of measurement of some physical and
chemical properties of the soil.
٧٣
(c) Soils of East Khartoum:
Soil Name: Eleilafon sandy clay substratum
Classification: Fine, mont., hyper. Typic to vertic
Deep, brown to dark brown, moderately well drained soils, with
accumulation of CaCo3 and Ca SO4 and mottled deep subsoil,
below 140 cm Coarse texture river deposits form, abrupt layer. The
soil is generally has an alkaline reaction.
Table 3.5 Shows some chemical and physical characteristic of the
soil profile.
(d) Soils of North Khartoum:
Al shaab Scheme:
Deep dark brown (10 Y R3/3) moist, silty clay, slightly cracking soil. Texture
of control section is clayey. Structure of the horizon is week blocky structure
breaking into very coarse and coarse Sbk with few pressure faces, sub soil
is massive. It is noncalcareous, moderately alkaline, root penetration
extends to 10 cm, moderately drained and slowly permeable.
(1) Alahamda Mixdture of Blue Nile alluvium and weathered products, Deep, well
drained, the B horizon has a blocky structure and shows an increase in clay
content, C horizons are massive.
Table .3.6 and 3.7 show some physical and chemical characteristics of Al
shaab Scheme and Alahamda (Tables 4.32, 4.33, respectively).
٧٤
Chapter Four
Results and Discussion
4.1. Estimation of potential wind erosion:
a. Using Woodruff and Siddways model (1965):
i. Soil erodibility:
Total amount of soil equal to 1000 gr
Aggregates greater than 0.84 mm equal to 400 gr
I = 400/1000x100 = 40%
From Table (3.1) soil erodibility = 56 ton/acre/annum
No knoll observed at the windward edge of the field
Knoll erodibility = 1
E1 = 56x1=56 ton/acre/annum
E2 = E1x Ќ
ii. Soil ridge roughness (Ќ)
This is estimated by the roughness factor (R) Morgan (1986)
R= (H2)/I
H= height of ridge
I= distance between ridges
٧٥
K= 1.125 – 0.153 ln R = 0.9109
E2 = E1 x K = 56x0.9109 = 51 ton/acre/annum
iii. Local climatic factor (C):
Local climatic factor = {(1.12/2.9)x100} = 38.6
E3 = E2 x C = 51x0.39 = 19.69 ton/acre/annum
iv. Distance across field (Df):
Df = W/cos A
Df = Distance across field along the prevailing wind erosion
direction
W = width of the field strip
A= angle of deviation of the prevailing wind erosion
direction from right angle of the field strip
L = 60x3.3/0.7071 = 280 ft
E4 = E3 x L
With the use of figure (3.2) to obtain E4 = I x K x C x F(L)
Cut out movable E3 = I, K, C, ordinate so that 19.69 on
movable scale coincide with 65 on ordinate.
Move to the rightly, down along curved line to intersection
of L = 280 ft, then move horizontally left to movable E4
scale and reach E4.
E4 = I, K, C, F(L) = 8.0 ton/acre/annum
v. Vegetative cover:
Determination of f(v) from Figure (3.1)
From the amount of plant residue (R = 1.1 x 103 Pounds
/acre), vegetative cover from Figure (3.1) equivalent 4 x 103
E5 = starting with E4 = 8.0 on abscissa of FigurePounds
(3.3) move
/acre
vertically upward to intersection of V = 4000 then move
longitudinary to left to ordinate E5 = 0.5ton/acre/annum
E5 = 1.25 ton/ha/annum
٧٦
Potential wind erosion of cultivated field in order of North
Khartoum greater then South Khartoum equal to East
Khartoum Table (4.1a).
٧٧
Table (4.1a) Potential wind erosion of cultivated field surface estimated with the use of wind erosion model by
Woodruff and Siddways (1965)
Side and field
Soil and knoll erodibility
surface
Soil ridge
Climatic
Field length
Vegetative
Potential
roughness
factor %
along
cover
wind
prevailing
Pound/acre
erosion
wind
ton/ha/annu
erosion
m
distance
Soil
Knoll
Soil and
erodibilit erodibilit
y
y
knoll
erodibilit
y
1.
South
56
1
56
0.9109
38.6
280
4000
1.25
15.6
1
15.6
0.9109
38.6
280
7000
1.25
54.2
1
54.2
0.9109
38.6
280
4000
1.75
Khartoum
2. East Khartoum
3.
North
Khartoum
٧٨
٧٩
b. Using Skidmore and Siddways model (1968):
i. Soil erodibility = 126
ii. Rich roughness = (H2/I) = 0.336 exp (0.013 H2/I) = 0.568
1 12
∑U
100 i=1
3
 ETPi − Pi 
 × d = 0.95 iii. Climatic factor =

 ETPi 
U = is the mean monthly wind speed
ETPi= is potential evapotranspiration
Pi = is precipitation
d = is a total number of days in the month
iv. Field length:
L = IW/I{cos(Л/2+ -ǿ)+W/sin(Л/2+ -ǿ)}=60 m
I = is large length
W = is small width
= is the wind direction clockwise from north in radians
ǿ = is clockwise angle between field length and north in
radians cover:
v. Vegetative
SG = axb = 1.2Mg/ha
SG = is the flat small grain equivalent, X = is quantity of
residue or grass to be converted
Ψ1 = exp (-0.759 v – 4.74 x 10-2 x v2 + 2.95 x 10-4 x v3) =
0.0057
Ψ2 = (1 + 8.93 x 10-2 x v + 8.51 x 10-3 x v2 – 1.5 x 10-5
x v3)
= 1.70768
E1 = 126
E2 = 126 x 0.568 = 71.568
E3 = 71.568 x 0.9 = 64.41
E4 = (WF0.348 + E30.348 – E20.348)2.87 = 61.47
(WF) = E2 {1.0 -0.122(L/L0)}-0.383 = 69.2
Lo = 1.56 x 106 x E2-1.28
exp(-0.00156 x E2) = 5857 m
E5 = Ψ1 (E4)Ψ2 = 6.46 ton/ha/year
٨٠
Potential wind erosion of cultivated fields in order of North
Khartoum greater than South Khartoum greater than East
Khartoum Table (4.1b).
٨١
Table (4.1b) Potential wind erosion of cultivated field surface estimated with the use of wind erosion model by
Skidmore and Siddways (1968)
Side and field
Soil
Soil ridge
Climatic factor
Field length
Vegetative
Potential wind
surface
erodibility
roughness
%
along
cover
erosion
prevailing wind
Mg/ha
ton/ha/annum
erosion
distance
1.
South
126
0.568
90.33
60
1.2
6.46
35
0.568
90.33
60
1.2
0.763
134
0.568
90.33
60
1.2
7.286
Khartoum
2. East Khartoum
3.
North
Khartoum
٨٢
4.2. Measurement of the intensities of wind erosion along field
surfaces at different periods.
4.2.1. South Khartoum (2000-2001):
(a) Bare field surface:
Data of Table 4:2 and Fig. 4.1 show that the intensity of wind
erosion during the first period 1-30/11/2000 (S1) decreased from 5.21 at
the height of zero cm to 0.1 at height of 5cm to 0.03 at height of 20 cm
and, to 0.0 ton ha-1 day-1 at 50 cm height. This trend was consistent
for the other six sampling periods 1-31/12/2000 (S2), 1-31/1/2001 (S3),
1-28/2/2001 (S4), 1-31/3/2001 (S5), 1-30/4/2001 (S6), and 1-31/5/2001
(S7). At each of the four heights wind erosion decreased in the following
order:
S7> S6> S5 > S4 > S3> S2> S1
The results indicate that the intensity of wind erosion increased from 5.21
in November 2000 at zero cm height to 9.38 Ton/ha/day in May 2001 for
the same height. The other three heights obtain the same result. It is
inverse relationship between wind intensity and height.
Sheltered field surface: (b)
Data of table 4:3 and Fig. (4.2) show that the intensity of wind
erosion during the first period 1-30/11/2000 decreased from 0.22 at the
height of zero cm to 0.03 at 5 cm height to 0.01 at 20 cm height to 0.0
ton/ha/day at 50 cm height. This trend was consistent for the other six
sampling periods.
The results indicate that the intensity of wind erosion increased from
0.22 in November 2000 at zero height to 0.86 ton/ha/day in May 2001 for
the same height, the other three heights indicated that the intensity of
wind erosion increased continuously from November 2000 to May 2001.
Cultivated field surface: (c)
٨٣
Data of table 4.4 and Fig. 4.3 that the intensity of wind erosion
during the first period 1-30/11/2000 (S1) decreased from 0.13 at the zero
height to cm 0.1 at 5 cm height to 0.00 at
20 cm height
and 50 cm
height. The other six sampling periods obtain that the intensity of wind
erosion decreased with the height.
٨٤
Table 4.2: Intensity of wind erosion measured along a bare field in
South Khartoum with Vertical traps at different heights at different
periods (2000-2001)
Height
cm
0
5
20
50
Mean
C.V.
Periods
Ton Hectare-1 day-1
2000
1 - 30/11 1 - 31/12
5.21
0.10
0.03
0.00
1.34
1.94
5.67
0.33
0.05
0.01
1.51
1.83
1 - 31/1
1 - 28/2
2001
1 - 31/3
1 - 30/4
1 - 31/5
6.47
0.43
0.07
0.02
1.75
1.80
7.37
0.57
0.09
0.04
2.02
1.77
8.40
0.70
0.19
0.06
2.36
1.71
9.27
0.75
0.22
0.08
2.58
1.73
9.38
0.82
0.46
0.12
2.70
1.66
Mean C.V.
7.40
0.53
0.17
0.05
Each data point is a mean of three data points
٨٥
0.23
0.49
0.92
0.91
Fig. 4.1: Intensity of wind erosion measured a long a bare field in South Khartoum
with vertical traps at different heights at different periods (2000-2001)
٨
٧
٦
٥
٤
٢
1
٠
١٠
-1 0
٨٦
٢٠
٣٠
٤٠
٥٠
٦٠
Table 4.3: Intensity of wind erosion measured along a sheltered field
in South Khartoum with Vertical traps at different heights at
different periods (2000-2001)
Height
cm
0
5
20
50
Mean
C.V.
Periods
Ton Hectare-1 day-1
2000
1 - 30/11 1 - 31/12
0.22
0.03
0.01
0.00
0.07
1.60
0.33
0.05
0.02
0.00
0.10
1.55
1 - 31/1
1 - 28/2
2001
1 - 31/3
1 - 30/4
1 - 31/5
0.39
0.08
0.03
0.01
0.13
1.39
0.47
0.12
0.05
0.02
0.17
1.26
0.69
0.15
0.09
0.04
0.24
1.24
0.80
0.20
0.12
0.06
0.30
1.16
0.86
0.25
0.17
0.07
0.34
1.05
Mean C.V.
0.54
0.13
0.07
0.03
Each data point is a mean of three replicates
٨٧
0.46
0.64
0.85
1.00
Fig. 4.2: Intensity of wind erosion measured a long a sheltered field in South Khartoum
with vertical traps at different heights at different periods (2000-2001)
٠٫
٠,٥
٠,٤
٠,٣
٠,٢
٠,
١
٠
0
٨٨
١٠
٢٠
٣٠
٤٠
٥٠
٦٠
Table 4.4: Intensity of wind erosion measured along a cultivated field
in South Khartoum with Vertical traps at different heights at
different periods (2000-2001)
Height
cm
0
5
20
50
Mean
C.V.
Periods
Ton Hectare-1 day-1
2000
1 - 30/11 1 - 31/12
0.13
0.01
0.00
0.00
0.04
1.81
0.16
0.03
0.01
0.00
0.05
1.49
1 - 31/1
1 - 28/2
2001
1 - 31/3
1 - 30/4
1 - 31/5
0.19
0.05
0.02
0.00
0.07
1.32
0.22
0.07
0.03
0.01
0.08
1.15
0.27
0.09
0.05
0.01
0.11
1.09
0.30
0.11
0.07
0.02
0.13
0.98
0.39
0.14
0.08
0.04
0.16
0.97
Mean C.V.
0.24
0.07
0.04
0.01
Each data point is a mean of three replicates
٨٩
0.38
0.64
0.82
1.28
: Intensity of wind erosion measured a long a cultivated field in South Khartoum ٣Fig. 4.
with vertical traps at different heights at different periods (2000-2001)
٠٫
٠,٢٥
٠,٢
٠,١٥
٠,١
٠,٠٥
٠
0
٩٠
١٠
٢٠
٣٠
٤٠
٥٠
٦٠
The results indicate that the intensity of wind erosion for each height
increased continuously from November 2000 to May 2001.
The results of South Khartoum indicate that for the three field
surfaces the intensity of wind erosion decreased in the following order:
Bare surface> sheltered surface > cultivated surface.
The results show that the intensity of wind erosion for the three
field surfaces decreased with height that means this major effective
mechanisms is surface creep. The data indicated that there is deposition
of blown material from south west direction during the summer period.
(The factors influence wind intensity are temperature, wind velocity,
rainfall, soil texture, soil erodibility, and land use, which has a major role
in decreasing intensity of wind erosion). The source of the blown material
in South Khartoum is the mobile sand dunes, which are extended from El
Gitaina to Gabal Awleya and extended to the North West part of El
Gezira Scheme.
٩١
Table 4.5: Intensity of wind erosion measured along a bare field in
South
Khartoum with Vertical traps at different heights at different periods
(2001-2002)
Height
cm
0
5
20
50
Mean
C.V.
Periods
Ton Hectare-1 day-1
2001
1 - 30/11 1 - 31/12
4.17
0.09
0.02
0.00
1.07
1.93
4.72
0.10
0.03
0.00
1.21
1.93
1 - 31/1
1 - 28/2
2002
1 - 31/3
1 - 30/4
1 - 31/5
5.31
0.25
0.05
0.01
1.41
1.85
5.85
0.32
0.09
0.03
1.57
1.82
6.72
0.48
0.15
0.05
1.85
1.76
7.12
0.59
0.27
0.09
2.02
1.69
8.56
0.71
0.43
0.11
2.45
1.66
Mean C.V.
6.06
0.36
0.15
0.04
Each data point is a mean of three replicates
٩٢
0.25
0.66
1.02
1.07
٩٣
Table 4.6: Intensity of wind erosion measured along a sheltered field
in South
Khartoum with Vertical traps at different heights
at different periods (2001-2002)
: Intensity of wind erosion measured a long a bare field in South Khartoum ٤Fig. 4.
)٢-200١
with Vertical traps at different heights at different periods (200
٨
٧
٦
٥
٤
٢
1
٠
١٠
-1 0
Height
cm
0
5
20
50
Mean
C.V.
٢٠
٣٠
٤٠
٥٠
٦٠
Periods
Ton Hectare-1 day-1
2001
1 - 30/11 1 - 31/12
0.28
0.05
0.01
0.00
0.09
1.55
0.29
0.06
0.01
0.00
0.09
1.15
1 - 31/1
1 - 28/2
2002
1 - 31/3
1 - 30/4
1 - 31/5
0.35
0.09
0.03
0.01
0.12
1.31
0.41
0.11
0.04
0.02
0.15
1.25
0.63
0.15
0.07
0.04
0.22
1.24
0.83
0.18
0.10
0.07
0.30
1.22
0.93
0.27
0.19
0.09
0.37
1.03
Mean C.V.
0.53
0.13
0.06
0.03
Each data point is a mean of three replicates
٩٤
0.50
0.59
1.00
1.08
: Intensity of wind erosion measured a long a sheltered field in South Khartoum ٥Fig. 4.
with Vertical traps at different heights at different periods (2001-2002)
٠,٧
٠٫٦
٠,٥
٠,٤
٠,٣
٠,٢
0.1
٠
-0.1
١٠
0
٩٥
٢٠
٣٠
٤٠
٥٠
٦٠
Cultivated field surface: (a)
Table 4.7 and Fig. 4.6 show that the values of intensity of wind
erosion decreased with increasing height for the seventh periods, where
the values increase for the four heights regularly for the periods from
November 2001 to May 2002.
The data indicated that the intensity of wind erosion in South
Khartoum for the three field surfaces was affected by the following.
Land use: Cultivation of sorghum or (Barseem) decreased the intensity of
wind erosion significantly; shelter belt decreased the intensity of wind
erosion significantly. The values of intensity of wind erosion decreased
in the following order:
Bare surface> sheltered surface > cultivated surface.
Height: for the three field surfaces the results indicated that the
intensity of wind erosion decreased with the height.
(a)
The maximum
values were obtained at zero cm height, that means the major mechanism
is surface creep.
Period: the intensity of wind erosion for the three field surfaces
(b)
and for the four heights increased regularly from November to May.
Summer is a critical season of intensity of wind erosion.
The source of the depositional material is the mobile sand
dunes which are extended from El Getaina to Jabal Awleya to the North
West part of El Gezira Scheme.
Size of blown materials: (d)
Fine sand is the least resistante to wind erosion. Large soil particles
are resistant to transport because of the greater velocity required to move
them, on the other hand, small particles, (clay particles) are resistant
to detachment because of their cohesiveness.
٩٦
(c)
Shape of blown material: (e)
Regular shape of blown material is resistant to be picked up the
material into wind
stream.
Topography: (f)
Topography has important effect on the wind
erosion.
Moisture of the soil: (g)
The moisture of the soil effect the soil detachment, clay soils
with high moisture content are resistant to soil eroblibility.
٩٧
Table 4.7: Intensity of wind erosion measured along cultivated field
in South Khartoum with Vertical traps at different heights at
different periods (2001-2002)
Height
cm
0
5
20
50
Mean
C.V.
Periods
Ton Hectare-1 day-1
2001
1 - 30/11 1 - 31/12
0.11
0.02
0.00
0.00
0.03
1.62
0.13
0.03
0.01
0.00
0.04
1.40
1 - 31/1
1 - 28/2
2002
1 - 31/3
1 - 30/4
1 - 31/5
0.16
0.07
0.03
0.01
0.07
0.99
0.18
0.08
0.04
0.02
0.08
0.89
0.29
0.10
0.05
0.03
0.12
1.01
0.37
0.13
0.07
0.05
0.16
0.95
0.43
0.16
0.08
0.07
0.19
0.91
Mean C.V.
0.24
0.08
0.04
0.03
Each data point is the arithmetic mean of three replicates
٩٨
0.53
0.60
0.74
1.03
: Intensity of wind erosion measured a long a cultivated field in South Khartoum ٦Fig. 4.
with Vertical traps at different heights at different periods (2001-2002)
٠,٣
٥
٠٫٣
٠,٢
٥
٠,٢
٠,١
٥
٠,١
0.05
٠
-0.1
٠
-0.2
٩٩
١٠
٢٠
٣٠
٤٠
٥٠
٦٠
Wind velocity: (h)
Increasing velocity lead to set heavier particles,
(larger, denser) in motion.
Temperature: (i)
Wind erosion increased gradually from November to
May, (from winter to summer).
Quantity of rain fall: (j)
The amount of rainfall in the rainy season affect
wind erosion, the reason of the deference between
the two seasons is the quantity of the rain fall on
wind erosion gradually from the winter to summer
according to the increase in air temperature which
decrease the soil moisture.
4.2.1.3. Comparison of some soil properties of the surface layer for
the three fields:
(a) Bare field surface:
Table 4.8 shows the data of the soil surface layer 0-30 cm
properties analyzed for 1975 and 2002. The coarse fine sand and silt were
increased from 22, 13, and 20% to 24, 18, and 26%, respectively, while
the clay decreased from 45% to 32%. The means there were deposition of
coarse fine sand and silt, while there was removal of clay, and
accordingly, the cation exchangeable capacity was decreased from 39 to
28 meq/100g. This mean that the fertility and the water holding capacity
were decreased for the surface layer.
(b) Sheltered surface:
١٠٠
Table 4.9 shows the data of soil surface layer (0-30 cm) properties
analyzed for 1975 and 2002. The coarse and fine sand were decreased
from 26 and 16% to 13 and 15%, respectively, while the silt and clay
were increased from 20 and 38 to 31 and 41, respectively. That means the
coarse textural material was decreased and the fine textural material was
increased. According to that, the cation exchangeable capacity and the
water holding capacity were increased, the fertility of the surface layer
was increased.
١٠١
Table (4.8) Comparison between soil properties 1975 and 2002 for a bare field in South Khartoum
Date of
analysis
1975
2002
Date of
analysis
1975
2002
١٠٢
Exchangeable
CaCO
3 Mechanical analysis
O.C
N
C/N
Sat bases meq/100
Depth
%
gm
%
Cm
Cs Fs Silt Clay
Na
K CEC %
% Ratio
0-30
14.3
22 13 20 45
1.00 39
0-30
8.3
24 18 26 32 62 3.9 0.93 28 0.296 0.028 11
Dept
h
Cm
0-30
0-30
pH
Paste
pH
1:5
8.6
8.3
9.6
8.3
E.C
mmhos
/
cm
SA
R
ESP
1.0
9
14
Available P
PPm
4.8
Soluble Cation and onions meq/L (Saturation
/Extract)
HCO3
Na K Ca Mg SO4 Cl CO3
9.4
1.5
0.5
4.5
0.0
3.5
Table (4.9) Comparison between soil properties 1975 and 2002 for sheltered field in South Khartoum
Date of
analysis
Dept
h
Cm
CaC
O3
%
1975
0-30
2002
0-30
Date of
analysis
Dept
h
Cm
Silt
Clay
8.5
26 16 20
38
6.4
13 15 31
41
pH
Past
e
1975
0-30
8.5
2002
0-30
8.1
١٠٣
Mechanical
analysis
Cs
p
H
1:
5
9.
9
8.
Fs
Exchangeable
bases meq/100
Sat
gm
%
Na
K CE
C
55 13.9 0.9 34
0
0
79 10.9 0.9 40
0
4
E.C
mmhos
/
cm
SAR
2
22
38
14
23
27
ESP
O.C
N
C/N
%
%
Rati
o
0.42 0.03
1
7
Available
P
PPm
11
5.0
Soluble Cation and onions meq/L (Saturation
/Extract)
Na
K
CO3
0.2
9.0
0.0
2.8
0.6
8.3
0.0
4.6
Mg
17.0
1.0
103.0
32.5
SO4
MCO3
Cl
Ca
8
١٠٤
(c) Cultivated surface:
Table 4.10 Shows the data of the soil surface layer (0-30 cm)
properties analyzed for 1975 and 2002. The data show that coarse fine
sand and slit were increased from 23 to 15 and 19 to 27, 16 and 24%
That means the soil fertility was decreased. That
respectively.
degradation of the cultivated field was the fact that there was no
cultivation activities during the summer season in the area due to the
irrigation water shortage.
١٠٥
Table (4.10) Comparison between soil properties 1975 and 2002 for cultivated field in South Khartoum
Mechanical
Date of Depth CaCO3
analysis
%
Cm
Cs Fs Silt Clay
analysis
1975
0-30
11.5 23 15 19 43
2002
0-30
5.4
27 16 24 33
Date
of
analysi
s
1975
2002
١٠٦
Dept
h
Cm
pH
Past
e
0-.30
7.8
0-30
7.9
p
H
1:
5
8.
3
8.
8
E.C
mmhos
/
cm
5.2
SAR
Sat
%
48
62
ESP
Exchangeable
O.C
N
C/N Available
bases meq/100
gm
P
Na
K CEC %
% Ratio
PPm
1.80 0.40 34
4.02 0.88 34 0.390 0.036 11
3.0
Soluble Cation and onions meq/L (Saturation
/Extract)
Na
17
12
K
Cl
CO3
HCO3
3.6
1.0
0.0
4.0
2.5
6.5
0.0
4.0
Ca
Mg
18.0
25.4
40.0
8.0
SO4
4.2.2. West Khartoum (Rawakeeb Scheme):
(a) Vertical traps:
(i) GOZ field:
Data of Table 4.11 and Fig. 4.7 show that the intensity of wind
erosion during the first period 16-31/1/02 (S1) decreased from
150.37 at the first trap to 72.22 at 10 m distance for the first trap
and then increased to 227.41 Ton/ha/day at 20 m distance from the
first trap. This trend was consistent for the other eight sampling
periods.
The results indicate spatial variation was highest (C.V=23) at
20 m distance.
The results also indicate that deposition was greater than
removal for the 10 m distance.
(ii) Fenced field surface:
Table 4.12 and Fig. 4.8 show that the intensity of wind erosion
for the eight periods (S2 to S9). The trend was consistent, the
intensity of wind erosion decreased from 10 m distance to 20 m
distance to 30 m distance but (S1) obtained that 10 m distance
increased at 20 m distance and then decreased at 30 m distance.
The results indicate that the intensity of wind erosion
decreased by increasing the distance from the shelter.
(iii) Bare field surface:
Table 4.13 and Fig. 4.9 indicate that the intensity of wind
erosion during the first period 16-31/1/2002 (S1) increased from
83.33 at first trap to 166.67 at 10 m distance and then decreased to
94.44 Ton/ha/day at 20 m distance. This trend was consistent for
the other eight periods.
The results indicate spatial variation was highest (C.V= 26 ) at 10
m distance.
١٠٧
Table 4.11: Intensity of wind erosion measured at Goz at different distances at different Periods in West Khartoum with vertical traps
Distance
M
1631/1/02
First 150.3
trap
7
10 72.22
20
227.4
1
Mean 150.0
0
C.V 0.52
1-15/2/02
83.33
1628/2/02
98.51
55.56
66.67
134.5
7
91.15
159.2
5
108.1
4
0.43
0.44
Periods
Ton Hectare-1 day-1
1-15/3/02
16131/3/02
15/4/02
87.23
102.3
88.8
5
9
48.62
77.41
55.5
6
104.4
163.0
96.1
5
8
1
80.10
114.2
80.1
8
9
0.36
0.39
0.27
16-30/4/02
1-31/5/02
mean
87.5
5
46.7
3
95.3
8
76.5
5
0.34
122.2
2
56.3
95.73
146.6
6
108.3
9
0.43
128.5
0
58.12
C.
V
0.1
4
0.1
8
0.2
3
Each data point is a mean of three replicates
١٠٨
١٠٩
Fig. 4.7: Intensity of wind erosion measured by Goz at different distances at different
periods in West Khartoum with vertical traps (2001-2002)
١٤٠
١٢٠
١٠٠
٨٠
٦٠
٤٠
20
٠
-0.1
0
-0.2
١١١
٥
١٠
١٥
٢٠
٢٥
٣٠
١١٢
Table 4.12: Intensity of wind erosion measured along a fenced field at different distances at different Periods in West
Khartoum with vertical traps
Distance
M
1631/1/02
115/2/02
٣.3٨٨
٨٥.١٠١
10
٣٣.١٨٣
٣٣.٨٣
20
٣٣.١٣٣
Mean
First trap
C.V
1628/2/02
98.51
Periods
Ton Hectare-1 day-1
116115/3/02
31/3/02 15/4/02
16-30/4/02
٣٢.١٠٦
١١.١٥1
8.89٩
٧.٥٣
٤٤.٩٤
٥١.١٠١
٦٢.١٠٣
٤٥.٩٤
٨٩46.
٠٥.٦٦
0٤.٨٧
٠٧.٩١
٨٩.٩٢
٣٤.٨٣
.00٣٥1
٧٤.٨٣
٤٥.٩٣
٦٣.٩٩
٨٧.٠٣1
٣٥0.
٢١0.
٠٦0.
٠٨0.
١١0.
131/5/02
131.85
mean
C.V
100.89
0.24
115.56
91.40
0.24
٥٩.٤٢
٥٩.٩٢
79.42
0.24
.23٩٢
٧٣.٤٧
٣.3١٣1
٠٩0.
١٢0.
١٧0.
Each data point is a mean of three replicates
١١٣
١١٤
: Intensity of wind erosion measured along a fenced field at different distances ٨Fig. 4.
at different periods in West Khartoum with Vertical traps (2001-2002)
١٤٠
١٢٠
١٠٠
٨٠
٦٠
٤٠
20
٠
-0.1
٠
٥
-0.2
١١٥
١٠
١٥
٢٠
٢٥
٣٠
Table 4.13: Intensity of wind erosion measured along a bare land (Wadi) at different distances at different periods in
West Khartoum with vertical traps
Periods
Distance
Among
traps
Ton Hectare-1 day-1
M
First trap
16-31/1/02
1-15/2/02
16-28/2/02
1-15/3/02
16-31/3/02
1-15/4/02
16-30/4/02
1-31/5/02
٣3.3٨
75.92
85.93
5٣91.
100.07
75.56
81.48
78.46 0.25
10
16.67١
94.44
98.96
110.32 ١20.0١
93.73 6٠9.٩
27.31١
105.15
83.33
8.89٣
50
98.35
98.33 0.26
95.24
111.11 95.02 0.12
Mean
98.15
4٨110.
61.38
96.98
0.17
6.66٩
0.13
103.47
C.V.
5.80٨
0.14
3٣78.
79.07
0.14
3١0.
5٠0.
0.49
5١0.
٠2
82.51
mean
C.V
Each data point is a mean of three replicates
١١٦
١١٧
Fig. 4.9: Intensity of wind erosion measured along a bare land (Wadi) at different
distances different periods in West Khartoum with Vertical traps (2001-2002)
١٤٠
١٢٠
١٠٠
٨٠
٦٠
٤٠
20
٠
-0.1
٥
0
-0.2
١١٨
١٠
١٥
٢٠
٢٥
٣٠
(b) Horizontal traps:
(i) GOZ field surface:
Table 4.14 and Fig. (4.10) present intensity of wind erosion values as
measured by horizontal traps.
The horizontal traps yielded higher
intensity wind erosion values than vertical traps. That mean the effective
mechanism of the blown material is surface creep. Expressing spatial
grand mean values for the horizontal traps as percentages of those for the
vertical traps for this surface gave 337,6% for S1, 245,5% for S2, 246.4%
for S3, 247,6% for S4, 238% for S5, 291% for S6, 161.4% for S7, 212.9%
for S8 and 321.4% for S9. The grand mean were 272.1% for the first
trap, 373.6% at 10 m and 235.8% at 20 m.
The spatial distribution pattern of the intensity of wind erosion
values was similar to that obtained by vertical traps. Maximum value
were depicted at 20 m distance.
(ii) Sheltered field surface:
Table 4.15 and Fig. (4.11) present intensity of wind erosion values
by horizontal traps. The horizontal traps yielded higher intensity of wind
erosion than vertical traps on the sheltered field. Expressing spatial grand
mean values for the horizontal traps as percentages of those for the
vertical traps for these surface gave 173.1% for S1, 234.6% for S2,
291.2% for S3, 292.5% for S4, 237.3% for S5, 200.4% for S6, 253.0% for
S7, 154.2% for S8 and 148.8% for S9. The grand mean were 233.9% at
first traps, 193.1% at 10 m and 249.3% at 20 m.
The results indicate that surface creep is a very effective transportation mechanism on this field surface.
(iii) Bare field surface:
١١٩
Table 4.16 and Fig. 4.12 show intensity of wind erosion along this
surface at different periods. The highest value was obtained at 10 m
distance except S7, S8, and S9. Grand mean intensity of wind erosion
values measured with vertical traps were 195.0% for S1, 207.9% for S2,
237.4% for S3, 241.9% for S4, 2456.5% for S5, 281.2% for S6, 146.2%
for S7, 255.2% for S8 and 234.1% for S9. These percentages were
257.2 for first traps, 205.0% for 10 m and 227.6% for 20 m distance.
١٢٠
Table 4.14: Intensity of wind erosion measured at Goz at different distances at different Periods in West Khartoum
with horizontal traps
Periods
Distance
Ton Hectare-1 day-1
M
First trap
10
٠2
Mean
C.V.
16-31/1/02
1-15/2/02
16-28/2/02
1-15/3/02
16-31/3/02
1-15/4/02
16-30/4/02
1-31/5/02
mean
C.V
535.71
242.07
741. 53
216.37
202.55
252.38
261.56
242.67
295.13
271.06
253.13
310.10
295.71
273.73
346.50
235.35
203.71
260.92
124.42
102.91
143. 42
292.05
268.9
307.72
242.36
221.09
273.74
0.25
0.27
0.24
506. 44
0.50
223.77
0.11
266.45
0.10
278.10
0.14
305.31
233.33
0.12
123.58
0.16
289.56
0.07
0١0.
Each data point is a mean of three replicates
١٢١
١٢٢
: Intensity of wind erosion measured by Goz at different distances
diff
i d i W
Kh
ihh i
١٠Fig. 4.
l
(2001 2002)
٣٥٠
٣٠٠
٢٥٠
٢٠٠
١٥٠
100
50
٠
-0.1
٠
-0.2
١٢٣
٥
١٠
١٥
٢٠
٢٥
٣٠
١٢٤
Table 4.15: Intensity of wind erosion measured along a fenced field at different distances at different Periods in West
Khartoum with horizontal traps
Periods
Ton Hectare-1 day-1
Distance
M
First trap
10
٠2
Mean
C.V.
16-31/1/02
1-15/2/02
16-28/2/02
1-15/3/02
16-31/3/02
1-15/4/02
16-30/4/02
1-31/5/02
mean
C.V
187.07
157.02
357.13
214.76
194.32
180.38
295.13
263.20
257.420
317.31
287.92
269.01
286.41
247.31
205.72
213.18
187.91
153.51
133.87
112.52
130. 21
209.15
138
164.82
238.54
204.45
194.44
0.27
0.32
0.27
233.74
0.46
196.49
0.09
271.92
0.07
291.41
0.08
246.48
184.87
0.16
125.53
0.09
170.66
0.21
6١0.
Each data point is a mean of three replicates
١٢٥
١٢٦
1: Intensity of wind erosion measured along fenced field at different distances
diff
i d i W
Kh
ihh i
l
(2001 2002)
٣٥٠
٣٠٠
٢٥٠
٢٠٠
١٥٠
100
50
٠
-0.1
٥
٠
-0.2
١٢٧
١٠
١٥
٢٠
٢٥
١Fig. 4.
٣٠
Table 4.16: Intensity of wind erosion measured a bare field (Wadi) at different distances at different Periods in West
Khartoum with horizontal traps
Periods
Ton Hectare-1 day-1
Distance
M
First trap
10
٠2
Mean
C.V.
16-31/1/02
1-15/2/02
16-28/2/02
1-15/3/02
16-31/3/02
1-15/4/02
16-30/4/02
1-31/5/02
mean
C.V
212.58
246.59
212.58
173.64
185.55
176.18
223.38
235.42
229.67
243.61
256.66
250.49
263.33
281.09
275.10
213.72
232.19
221.24
79.65
89.51
100.00
217.10
226.09
263.71
187.50
201.87
198.46
0.32
0.32
0.29
223.92
0.09
178.46
0.04
229.49
0.03
250.25
0.03
273.17
0.03
222.38
0.04
89.72
0.11
235.63
0.00
Each data point is a mean of three replicates
١٢٨
2: Intensity of wind erosion measured along bare field (Wadi) at different ١Fig. 4.
distances at different periods in West Khartoum with horizontal traps (2001-2002)
٢٠٦
٢٠٤
٢٠٢
٢٠٠
١٩٨
١٩٦
١٩٤
١٩٢
190
188
186
٠
١٢٩
٥
١٠
١٥
٢٠
٢٥
٣٠
The data indicate that there is extremely severe wind erosion in West
Omdurman. The effective transportation mechanism is surface creep.
The traditional irrigation system is not applicable for framing activities.
Activation of farming in North Kordufan and North Darfur, especially in
Wadies is needed to stop sand moving to the study area by using Agro
forestry systems. Utilization of the rainfall during autumns by using
water harvesting method could be favorable.
4.2.3 East Khartoum:
Vertical traps: (a)
(i) Bare field surface:
Table 4.17 and Fig. 4.13 present the data of intensity of wind erosion
for this field. Spatial variation was obtained at 20 m distance. The values
of intensity of wind erosion in the first period 13/1-13/2/2002 (S1)
increased S2 by increasing the distance.
The general pattern of increase in the intensity of wind with time was
in the order: S5 > S3 > S4 = S2 > S1.
(ii) Sheltered field surface:
Table 4.18 and Fig. 4.14 show the value of intensity of wind erosion
in sheltered surface in South Sileit Scheme.
The special distribution pattern of the intensity of wind erosion was
similar to that obtained by vertical traps for bare surface in East
Khartoum.
The values of intensity of wind erosion for sheltered field were
greater than that for bare field because the sheltered field were located in
the eastern part that means the intensity of wind erosion in East Khartoum
increases in the east direction.
The general pattern of increase in the intensity of wind erosion with
time was in the order 5S> S3> S4> S2 = S1.
١٣٠
(iii) Cultivated field surface:
Table 4.19 and Fig. 4.15 show the data of intensity of wind erosion for cultivated
field.
The spatial distribution pattern of the intensity of wind erosion was
similar to that obtained for the bare and sheltered fields.
The general pattern of increase in the intensity of wind erosion with
time was in the order 5S> S3> S4> S2 = S1.
١٣١
distances at different Periods in East Table 4.17: Intensity of wind erosion measured along a bare field at different
Khartoum with vertical traps
Distance
M
Firest trap
10
20
Mean
C.V.
Periods
Ton Hectare day-1
-1
13/1-13-2/02
0.13
0.16
0.24
0.18
0.32
Mean
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.26
0.29
0.35
0.30
0.15
0.27
0.32
0.40
0.33
0.20
0.26
0.30
0.38
0.31
0.20
0.29
0.34
0.43
0.35
0.20
0.24
0.28
0.36
C.V.
0.26
0.25
0.20
Each data point is a mean of three replicates
١٣٢
١٣٣
: Intensity of wind erosion measured a long a bare field at different distances at١٣Fig. 4.
different periods in Khartoum with Vertical traps (2001-2002)
٠,٤
٠,٣
٥
٠٫٣
-0.1
-0.2
٠,٢
٥
٠,٢
٠,١
٥
٠,١
0.05
٠
-0.1
٠
١٣٤
٥
١٠
١٥
٢٠
٢٥
٣٠
Table 4.18: Intensity of wind erosion measured along a sheltered field at different distances at different Periods in
East Khartoum with vertical traps
Distance
M
10
20
30
Mean
C.V.
Periods
Ton Hectare day-1
-1
13/1-13-2/02
0.17
0.28
0.32
0.26
0.30
Mean
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.17
0.30
0.39
0.29
0.39
0.09
0.31
0.42
0.31
0.38
0.37
0.4
0.51
0.43
0.23
0.39
0.42
0.53
0.45
0.17
0.26
0.34
0.43
C.V.
0.43
0.19
0.20
Each data point is a mean of three replicates
١٣٥
١٣٦
4: Intensity of wind erosion measured along a sheltered field at different
١Fig. 4.
distances at different periods in East Khartoum with vertical traps (2001-2002)
٠,٥
٠,٤
٥
٠,٤
٠,٣
٥
٠٫٣
٠,٢
٥
٠,٢
٠,١
٥
0.1
0.05
0
٠
١٣٧
٥
١٠
١٥
٢٠
٢٥
٣٠
Table 4.19: Intensity of wind erosion measured in a cultivated field at different distances at different Periods in East
Khartoum with vertical traps
Distance
M
10
20
30
Mean
C.V.
Periods
Ton Hectare-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.07
0.08
0.10
0.08
0.18
0.07
0.10
0.13
0.10
0.30
0.09
0.13
0.15
0.12
0.25
0.13
0.13
0.19
0.15
0.23
0.15
0.19
0.21
0.18
0.17
0.10
0.13
0.16
C.V.
0.36
0.33
0.29
Each data point is a mean of three replicates
١٣٨
١٣٩
: Intensity of wind erosion measured along a cultivated field at different
١٥Fig. 4.
distances at different periods in East Khartoum with vertical traps (2001-2002)
٠,٢
٠,١
٨
٠,١
٦
٠,١
٤
٠٫١
٠,١
٠,٠
٨
٠,٠
٦
0.04
0.02
0
٠
١٤٠
٥
١٠
١٥
٢٠
٢٥
٣٠
(b) Horizontal traps:
(i) Bare field surface:
Table 4.20 and Fig. 4.16 present the values of intensity of wind
erosion for this field. For the first periods 13/1-13/2/2002 (S1), the values
increased with increasing the distance, other four periods are similar to
first periods.
The general pattern of increase in the intensity of wind erosion with
time was in the order S5> S4> S3> S2 = >S1.
Expressing spatial grand mean values for the horizontal traps as
percentages of those for the vertical traps for this surface gave 355.6% for
S1, 320.0% for S2, 363.6% for S3, 471.0% for S4 and 462.9% for S5.
The results indicate that surface creep is effective transportation
mechanism.
(ii) Sheltered field surface:
Table 4.21 and Fig. (4.17) show the values of intensity of wind
erosion for this field.
First period 14/2/-14/3/2002 (S2) the values
increased by increasing the distance, S3, S4 and S5 obtained similar result
to S2 and S1 the value decrease at 20 m and then increased again at 30 m
distance.
The general pattern of increase in the intensity of wind erosion with
time was in the order S5> S4> S3> S2 >S1.
Expressing spatial grand mean values for the traps for the for this
surface gave 253.8% for S1, 389.7% for S2, 393.5% for S3, 409.3% for
S4 and 413.3% for S5.
The values indicate that surface creep is the most effective
transportation mechanism.
(iii) Cultivated field surface:
١٤١
Table 4.22 and Fig. (4.18) show the values of intensity of wind
erosion for this surface.
The horizontal traps.
Traps yielded higher
intensity of wind erosion values than vertical traps on this cultivated field.
Expressing spatial grand mean values for the horizontal traps as
percentages of those for the vertical traps for this surface gave 175.0% for
S1, 700.0% for S2, 750.0% for S3, 826.7% for S4 and 750.0% for S5.
١٤٢
Table 4.20: Intensity of wind erosion measured on bare field at different distances at different Periods in East
Khartoum with Horizontal traps
Distance
M
10
20
30
Mean
C.V.
Periods
Ton Hectare-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.40
0.60
0.92
0.64
0.41
0.64
0.91
1.32
0.96
0.36
0.69
1.21
1.71
1.20
0.42
0.82
1.56
2.01
1.46
0.41
0.87
1.73
2.25
1.62
0.43
0.68
1.20
1.64
C.V.
0.27
0.38
0.32
Each data point is a mean of three replicates
١٤٣
١٤٤
6: Intensity of wind erosion measured along a bare field at different distances at ١Fig. 4.
different periods in East Khartoum with vertical traps (2001-2002)
٢
١,٨
١,٦
١,٤
١٫٢
١
٠,٨
٠,٦
0.4
0.2
0
٠
١٤٥
٥
١٠
١٥
٢٠
٢٥
٣٠
١٤٦
Table 4.21: Intensity of wind erosion measured on sheltered field at different distances at different Periods in East
Khartoum with Horizontal traps
Distance
M
10
20
30
Mean
C.V.
Periods
Ton Hectare-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.66
0.50
0.81
0.66
0.79
0.68
0.86
1.85
1.13
0.86
0.72
1.03
1.91
1.22
0.99
1.17
1.63
1.48
1.76
0.74
1.26
1.81
2.51
1.86
4.66
0.90
1.17
1.91
C.V.
0.33
0.47
0.36
Each data point is a mean of three replicates
١٤٧
١٤٨
: Intensity of wind erosion measured a long a sheltered field in East Khartoum ١٧Fig. 4.
with Vertical traps at different heights at different periods (2001-2002)
٠,٣
٥
٠٫٣
٠,٢
٥
٠,٢
٠,١
٥
٠,١
0.05
٠
-0.1
٠
-0.2
١٥٠
٥
١٠
١٥
٢٠
٢٥
٣٠
distances at different Periods in
Distance
M
10
20
30
Mean
C.V.
Table 4.22: Intensity of wind erosion measured along cultivated field at different
East Khartoum with Horizontal traps
Periods
Ton Hectare-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.14
0.07
0.22
0.14
0.52
0.50
0.42
1.18
0.70
0.60
0.71
0.59
1.14
0.90
0.49
1.07
0.73
1.92
1.24
0.49
1.13
0.85
2 .06
0.35
0.47
0.71
0.53
0.36
C.V.
0.85
0.57
0.54
Each data point is a mean of three replicates
١٥١
١٥٢
: Intensity of wind erosion measured along a cultivated field at different distances ١٨Fig. 4.
at different periods in East Khartoum with horizontal traps (2001-2002)
٢
٠,٩
٠,٨
٠,٧
٠٫٦
٠,٥
٠,٤
٠,٣
0.2
0.1
0
٠
١٥٤
٥
١٠
١٥
٢٠
٢٥
٣٠
The spatial distribution pattern of the intensity of wind
erosion values were similar to those obtained by vertical traps.
Maximum values were depicted at 20 m distance. Surface creep is
the effective mechanism.
The results indicate that in tensity of wind erosion increases
with increasing the distance in the east direction. Agroforestry
Farming System in Northern State and River Nile State especially
along Attbra River can reduce wind erosion in the Easterns part of
Khartoum State.
4.2.4. North Khartoum:
(a) Vertical traps:
(i) Sheltered field surface:
Table 4.23 and Fig. 4.19 present the values of intensity of wind
erosion for this field. The highest values were obtained at 20 m distance.
The intensity of wind erosion increases with the time in the order S5>
S4> S3> S2> S1.
(ii) Cultivated field surface:
Table 4.24 and Fig. 4.20 present the values of intensity of wind
erosion for this field. The intensity of wind erosion increases with the
time in the order S5> S4> S3> S2> S1.
(iii) Bare field surface:
This site is located at 4 km east El Shaab Scheme (Alahamda).
Table 4.25 and Fig. 4.21 give values of intensity of wind erosion. The
intensity of wind erosion increases with time in the order of S5> S4> S3>
S2> S1.
The highest values were obtained at 20 m distance.
١٥٥
١٥٦
Table 4.23: Intensity of wind erosion measured a long sheltered field at different distances at different Periods in
North Khartoum with vertical traps
Distance
M
10
20
30
Mean
C.V.
Periods
Ton Hectare-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.06
0.09
0.16
0.10
0.50
0.07
0.11
0.18
0.12
0.46
0.09
0.13
0.19
0.14
0.37
0.12
0.17
0.23
0.17
0.32
0.14
0.19
0.26
0.20
0.31
0.10
0.14
0.20
C.V.
0.35
0.30
0.20
Each data point is a mean of three replicates
١٥٧
١٥٨
: Intensity of wind erosion measured along a bare field at different distances١٩Fig. 4.
٢
at different periods in North Khartoum with vertical traps (2001-2002)
٠,٣
٥
٠٫٣
٠,٢
٥
٠,٢
٠,١
٥
٠,١
0.05
0
٠
١٥٩
٥
١٠
١٥
٢٠
٢٥
٣٠
Table 4.24: Intensity of wind erosion measured a long cultivated field at different distances at different Periods in
North Khartoum with vertical traps
Distance
M
10
20
30
Mean
C.V.
Periods
Ton Hectar-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.03
0.04
0.06
0.04
0.35
0.05
0.07
0.09
0.07
0.29
0.07
0.09
0.11
0.09
0.22
0.09
0.11
0.14
0.11
0.22
0.11
0.14
0.17
0.14
0.21
0.07
0.09
0.11
C.V.
0.45
0.42
0.38
Each data point is a mean of three replicates
١٦٠
١٦١
: Intensity of wind erosion measured along a sheltered field at different ٢٠Fig. 4.
٢
distances
at different periods in North Khartoum with vertical traps (2001-2002)
٠,٣
٥
٠٫٣
٠,٢
٥
٠,٢
٠,١
٥
٠,١
0.05
0
٠
١٦٢
٥
١٠
١٥
٢٠
٢٥
٣٠
Table 4.25: Intensity of wind erosion measured a long a bare field at different distances at different Periods in North
Khartoum with vertical traps
Distance
M
Frist trap
10
20
Mean
C.V.
Periods
Ton Hectare-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
1.00
1.25
1.66
1.30
0.26
1.82
2.32
2.96
2.37
0.24
2.13
2.72
3.67
2.84
0.27
2.41
3.12
4.06
3.20
0.26
2.53
3.31
4.22
3.35
0.25
1.98
2.54
3.31
C.V.
0.31
0.32
0.32
Each data point is a mean of three replicates
١٦٤
٢
1: Intensity of wind erosion measured along a cultivated field at different distances ٢Fig. 4.
at different periods in North Khartoum with vertical traps (2001-2002)
٠٫١
٠,١
٠,٠
٨
٠,٠
٦
0.04
0.02
0
٠
١٦٥
٥
١٠
١٥
٢٠
٢٥
٣٠
(b) Horizontal traps:
(i) Sheltered field surface:
Table 4.26 and Fig. 4.22 show the intensity of wind erosion in this
field.
The horizontal traps yielded higher intensity of wind erosion values
than vertical traps on this sheltered field.
The spatial distribution pattern of the intensity of wind erosion
values were similar to those obtained by vertical traps.
Expressing spatial grand mean values for the horizontal traps as
percentages of those for the vertical traps for this surface gave 760.0% for
S1, 675.0% for S2, 692.9% for S3, 682.3% for S4 and 630.0% for S5.
(ii) Sheltered field surface:
Table 4.27 and Fig. 4.23 show the values of intensity of wind
erosion.
The horizontal traps yielded higher intensity of wind
erosion values. The spatial distribution pattern of the intensity of wind
erosion values were similar to that obtained by vertical traps.
Expressing spatial grand mean values for the horizontal traps as
percentages of those for the vertical traps for this surface gave 800.0% for
S1, 671.4% for S2, 666.7% S3, 709.0% for S4 and 592.9% for S5.
(iii) Cultivated field surface:
Table 4.28 and Fig. 4.24 show the values of intensity of wind
erosion. The horizontal traps yielded higher intensity of wind erosion
values compared to vertical traps on this field.
The spatial distribution pattern of the intensity of wind erosion
values were similar to those obtained by vertical traps.
Expressing spatial grand mean values for the horizontal traps as
percentages of those for the vertical traps for this surface gave 109.2% for
S1, 109.7% for S2, 114.8% S3, 106.9% for S4 and 106.6% for S5.
١٦٦
The data indicate that the intensity of wind erosion values increase in
the east direction.
Agroforestry farming system in the Northern and River Nile States
can reduce the intensity of wind erosion on North and North east
Khartoum State.
١٦٧
Table 4.26: Intensity of wind erosion measured a long a sheltered field at different distances at different Periods in
North Khartoum with Horizontal traps
Distance
M
10
20
30
Mean
C.V.
Periods
Ton Hectare-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
0.49
0.73
1.05
0.76
0.37
0.51
0.82
1.10
0.81
0.36
0.63
0.97
1.32
0.97
0.35
0.76
1.07
1.64
1.16
0.39
0.79
1.19
1.81
1.26
0.41
0.64
0.96
1.38
C.V.
0.22
0.19
0.24
Each data point is a mean of three replicates
١٦٨
١٦٩
2: Intensity of wind erosion measured along a bare field at different distances at ٢Fig. 4.
different periods in North Khartoum with horizontal traps (2001-2002)
٤
٣,٥
٣
٢,٥
٢
١,٥
1
0. 5
0
٠
١٧٠
٥
١٠
١٥
٢٠
٢٥
٣٠
Table 4.27: Intensity of wind erosion measured a long a cultivated field at different distances at different Periods in
North Khartoum with Horizontal traps
Distance
M
10
20
30
Mean
C.V.
Periods
Ton Hectare-1 day-1
13/1-13-2/02
0.24
0.28
0.45
0.32
0.34
14/2-14/3/02
0.28
0.41
0.72
0.47
0.48
15/3-15/4/02
0.31
0.57
0.92
0.60
0.51
Mean
16/4-16/5/02
0.51
0.73
1.09
0.78
0.38
C.V.
17/5-17/6/02
0.56
0.79
1.14
0.83
0.35
0.38
0.56
0.86
0.38
0.38
0.33
Each data point is a mean of three replicates
١٧١
١٧٢
3:
Intensity of wind erosion measured along a sheltered field at different ٢Fig. 4.
distances
٢
diff
i d i N h Kh
ihh i
l
(2001 2002)
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
٠
١٧٤
٥
١٠
١٥
٢٠
٢٥
٣٠
Table 4.28: Intensity of wind erosion measured a long a bare field at different distances at different Periods in North
Khartoum with Horizontal traps
Distance
M
First trap
10
20
Mean
C.V.
Periods
Ton Hectare-1 day-1
Mean
13/1-13-2/02
14/2-14/3/02
15/3-15/4/02
16/4-16/5/02
17/5-17/6/02
1.21
1.37
1.67
1.42
0.16
2.07
2.62
3.11
2.60
0.20
2.81
3.09
3.87
3.26
0.17
3.02
3.26
3.98
3.42
0.15
3.20
3.41
4.09
3.57
0.13
2.46
2.75
3.34
C.V.
0.33
0.30
0.30
Each data point is a mean of three replicates
١٧٥
4: Intensity of wind erosion measured along a cultivated field at different distances ٢Fig. 4.
at different periods in North Khartoum with horizontal traps (2001-2002)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
٠
١٧٦
٥
١٠
١٥
٢٠
٢٥
٣٠
4.3. Sand blown analysis of intersects from Soba East to Wad elzaki
west:
Table 4.29 show the data of analysis. According to the data the blown
materials are from one source and that source is (Elsahra Alkubra).
The differs in Soba West and Wad elzaki West is the blow sand is mixed
with the local soil erodible surface.
١٧٧
١٧٨
Table (4.29) Sand blown analysis of the intersect west to east sector
Location
Wad El
Zakie E
Wad El
Zakie W
Soba W.
Soba E.
Location
Wad El Zakie
W
Wad El Zakie
W
Soba W.
Soba E.
١٧٩
Mechanical analysis Sat
CaCO3
%
Cs Fs Silt Clay %
Exchangeable
bases meq/100 gm
Na
K CEC
O.C
N
C/N
0.0
63
32
3.0
2
34
0.10
0.23
3
Available
%
% Ratio
P
PPm
0.031 0.012
3
1.4
0.0
34
57
4.0
5
43
0.20
0.30
3
0.047 0.016
3
1.6
3.8
0.0
20
64
39
22
14
10
27
4
57 2.53 0.68
34 0.100 0.58
24
2
0.125 0.022
0.052 0.014
6
4
1.8
1.2
pH
Paste
pH
1:5
E.C
mmhos/ SAR ESP
cm
7.4
8.0
0.86
2
3
2.8
4.0
1.5
4.6
0.0
7.8
8.5
0.97
5
7
5.8
2.0
1.0
6.3
0.0
7.6
7.5
8.4
8.0
3.4
0.85
9
2
11
5
21.3
2.6
8.0
4.5
3.0
1.0
19.4
4.9
0.0
0.0
Soluble Cation and onions meq/L (Saturation
/Extract)
Na
K
Ca Mg SO4 Cl CO3 MCO3
١٨٠
4.4. Comparison among different sites:
(a) South Khartoum:
The general pattern of increase in the intensity of wind erosion with
the land use in South Khartoum for horizontal and vertical sand traps
were in the order of bare surface > sheltered surface> cultivated surface.
Fig 4.25 and 4.26.
(b) West Khartoum
(i) Vertical traps:
The general pattern of increase in the intensity of wind erosion with
the land use in West Khartoum for vertical traps were in the order of QOZ
> Bare> Sheltered surface. Fig. 4.27.
(ii) Horizontal traps:
The general pattern of increase in the intensity of wind erosion with
the land use in Wet Khartoum for horizontal traps were in the order of
QOZ > Sheltered> bare surface. Fig. 4.28.
Bare surface is a wadi.
(c) East Khartoum:
(i) Vertical traps:
The general pattern of increase in the intensity of wind erosion with
the land use in East Khartoum for vertical traps were in the order of Bare
surface> Sheltered surface> Cultivated surface. Fig. 4.29.
(ii) Horizontal traps:
The general pattern of increase in the intensity of wind erosion with
the land use in East Khartoum for Horizontal traps were in the order of
Sheltered surface > Bare surface> Cultivated surface. Fig. 4.30.
(d) North Khartoum:
(i) Vertical traps:
١٨١
The general pattern of increase in the intensity of wind erosion with
the land use in North Khartoum for vertical traps were in the order of
Bare> Sheltered > Cultivated surface. Fig. 4.31.
(ii) Horizontal traps:
The general pattern of increase in the intensity of wind erosion with
the land use in North Khartoum for horizontal traps were in the order of
Bare> Sheltered > Cultivated surface. Fig. 4.32.
١٨٢
clxxxiv
clxxxv
clxxxvi
clxxxvii
clxxxviii
clxxxix
4.5 Measurement of soil erodibility in Khartoum State:
Table 4.30 shows the soil erodibility of Khartoum State, soil erodibility in order
of North Khartoum greater than South Khartoum greater than East Khartoum.
Table 4.30 Soil erodibility of South, North and East Khartoum State:
Location
Aggregates
Erodibility
Erodibility
greater than 0.84
Woodruff &
Skidmore &
mm
Siddways
Siddways
.١
42
52.4
118
.٢
38
59.6
134
.٣
42
52.4
118
.٤
35
65
146
.٥
40
56
126
.٦
32
70.4
158
.٧
41
54.2
122
.٨
35
56
146
.٩
40
56
126
.١٠
40
56
126
58.7
132
South Khartoum:
Average
North Khartoum:
.١
28
78.8
177
.٢
22
93.2
209
.٣
40
56
126
.٤
46
45.2
101
.٥
40
56
126
.٦
43
50.6
114
.٧
40
56
126
.٨
36
63.2
142
.٩
15
116
260
.١٠
38
59.6
134
67.4
151.5
Average
East Khartoum:
.١
80
2
4
.٢
71
11
22
.٣
63
18.3
41
cxc
Location
Aggregates
Erodibility
Erodibility
greater than 0.84
Woodruff &
Skidmore &
mm
Siddways
Siddways
.٤
65
16.5
37
.٥
60
21
47
.٦
66
15.6
35
.٧
80
2
4
.٨
61
20.1
45
.٩
90
1
90
.١٠
60
21
47
12.9
28.4
Average
cxci
cxcii
cxciii
cxciv
cxcv
cxcvi
Chapter Five
Conclusion and References
5.1 Conclusion
The study obtains the following:
Inverse relationship between intensity of wind erosion and height -١
for the different fields surfaces (bare, sheltered and cultivated), with
vertical and horizontal traps. In South Khartoum.
Linear relationship between intensity of wind erosion and distance -٢
for Qoz and bare fields with vertical and horizontal traps. In West
Khartoum.
Inverse relationship between intensity of wind erosion and distance -٣
for sheltered fields with vertical and horizontal traps. In West
Khartoum.
Linear relationship between intensity of wind erosion and distance -٤
for bare, sheltered and cultivated fields with vertical and horizontal
traps, except the cultivated fields with the horizontal traps obtains
inverse relationship In East Khartoum.
Linear relationship between intensity of wind erosion and distance -٥
for bare, sheltered and cultivated fields with vertical and horizontal
traps.
cxcvii
Surface creep in the main mechanism of transportation obtained by -٦
the data of horizontal traps.
Generally, wind erosion increase from winter to summer. -٧
Khartoum State is suffering from wind erosion from the four -٨
directions.
Intensity of wind erosion is differ in the four directions. -٩
Soil erodibility in Khartoum State in order of North
-١٠
Khartoum > South Khartoum > East Khartoum.
Wind erosivity in Khartoum State in order of February >
-١١
April > January > March > November > December.
cxcviii
5.2 References:
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recent progress in our understanding of aeolian sediment
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degradation in the Sudan. Journal of Arid Environment. 38,
Bagnold, R. A. (1939). The Physics of Blown Sand and397-409.
Desert Dunes,
Methuen, 265.
Bagnold, R. A. (1941). The Physics of Blown Sand and Desert Dunes,
William Morrow, New York, 265 pp.
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Turbulence, Perspectives on Flow and Sediments Transport,
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Chepil, W. S. (1945). Dynamics of wind erosion. The nature of
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of wind
erosion and its control. In A. G. Norman, ed. Advances in
Agronomy, Vol. 15, pp. 211-301 New York: Academic Press.
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Dregne, H., Kassas, M. and Rozanov, B. (1991). A new assessment of
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cc
Agriculture Handbook No. 346. U. S. Department of
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