HYDROLOGY ASSESSMENT REPORT ON A TRIBUTARY OF JUKSKEI RIVER
IN,
THE OBSERVATORY GOLF COURSE, JOHANNESBURG, GAUTENG
PROVINCE
PREPARED BY:
PREPARED FOR:
Thembakele Consulting Engineers (Pty) Ltd
CONTACT PERSON:
LN Ntlokwana
Tel: 076 770 3749
ISRA Consulting
CONTACT PERSON:
Mr .T.I Mabale
PLOT 1
DALMADA
0699
Tel: 012 336 8495
ii
Confidentiality Notice
All information contained in this document and its appendices is privileged and confidential and is
under no circumstances to be made known to any person or institution without the prior written
approval of Thembakele Consulting Engineers (Pty) Ltd and iSRA Consulting (Pty) Ltd
iii
EXECUTIVE SUMMARY
iSRA Consulting (Pty) Ltd has been appointed by Thembakele Consulting Engineers (Pty) Ltd to
undertake a Hydrology Report of the entire catchment 3 and in the Observatory Golf Course ,
Johannesburg.
This report deals with determining flood lines within the tributary of the Observatory Golf Course,
the report also looks at the extent of problems caused by urbanisation in the area. Lastly, the report
will attempt propose how to manage the surface water drainage problems within the catchment in
line with Sustainable Drainage System (SuDs).
In order to manage the storm water runoff within the catchment, this report focuses on:

Managing the Quantity of flow, by quantifying flood waters and sizing a bypass channel in
order to protect the interventions that are in line with SuDs.

Estimating the pond storage size in order to attenuate steady flows for water treatment
purposes

Manage storm water quality by sizing a sedimentation trap, and an artificial wetland

Biodiversity and improving the aesthetics of the tributary is also mentioned in the report
however it should be noted that these will be discussed in great detail by a Biodiversity,
Flora and Fauna specialist and a Landscaper, in other technical reports which are part of this
project.
Some of the catchment characteristics that were considered for the recommended flood peaks are
summarised in Table 1 and 2 below.
CATCHMENT INFORMATION
Table 1: Basic catchment characteristics
Area (km2)
2.3
Longest water Tc (hrs)
course(km)
3.149
Slope (m/m)
0.62
MAP (mm)
0.02964
750
Tc is the time concentration in hours, it is the assumed time it will for a water to move the throughout the longest water course.
Table 2:Recommended flood peaks
Return period (years)
2
5
10
Flood peaks (m3/s)
iv
25
50
12
14
19
24
38
A summary of intervention and findings that stem from this report are as follows:

A pass channel will be designed using 1:25 year return interval flood

The bypass shall be trapezoidal with side slopes of 1 in 2 and base width of 3.5m.

The pond which is design to attenuate base flows before the artificial wetland shall have a
storage volume of 1000m3, before diverting flow in the bypass channel

The outlet pipe of the attenuating pond should be more than 100mm diameter and will take
12 hours to drain the attenuating pond from full supply level.

The sedimentation trap shall be 1.5m height and will need to be cleaned 4 times a year
From an operational perspective a gross litter trap design is recommended, because it is likely to
lower the maintenance cost associated fixing damage caused by storms.
v
Contents
1.
INTRODUCTION AND PROJECT BACKGROUND ............................................................................... 1
1.1
Problem Statement ..................................................................................................................... 1
1.2
Locality ........................................................................................................................................ 1
2.
AIM .................................................................................................................................................. 3
2.1
Objectives .................................................................................................................................... 3
3.
METHODOLOGY .............................................................................................................................. 3
4.
APPLICABLE LEGISLATION ............................................................................................................... 3
4.1
The Constitution of South Africa Act 108 of 1996 ....................................................................... 4
4.2
National Environmental Management Act 107 of 1998 ............................................................. 4
4.3
National Water Act 36 of 1998 ................................................................................................... 4
4.4
Johannesburg Road Agency Policy (Roads and Stormwater Manuel's Code of Procedure
Volume 1) ................................................................................................................................................ 5
5.
LIMITATION AND ASSUMPTION ...................................................................................................... 6
6.
HYDROLOGICAL ASSESSMENT......................................................................................................... 7
6.1
MEAN ANNUAL RAINFALL ........................................................................................................... 7
6.1.1
6.2
FLOOD FREQUENCY ANALYSIS .................................................................................................... 8
6.2.1
7.
Rainfall .................................................................................................................................... 7
Assessment of results ............................................................................................................. 9
DEVELOPMENT MODELLING ........................................................................................................... 9
7.1
Spillway Capacity ...................................................................................................................... 10
7.2
Outlet pipe................................................................................................................................. 11
8.
8.1
9.
SEDIMENTATION CONTROL DESIGN ............................................................................................. 12
Assessment of results ................................................................................................................ 13
LITTER TRAP .................................................................................................................................. 14
10.
CONCLUSION ............................................................................................................................. 15
11.
REFERENCE ................................................................................................................................ 16
12.
APPENDIX A Hydrology .............................................................................................................. 1
vi
13.
APPENDIX B
Detention Pond Volume Estimation - S.I. units .................................................. 2
14.
APPENDIX C
Attenuating Structure Outlet Flow Control Design - S.I. units .......................... 3
15.
APPENDIX D By-Pass Spillway Capacity ...................................................................................... 6
16.
APPENDIX E SEDIMENTATION TRAP......................................................................................... 7
17.
APPENDIX F FLOODLINES ........................................................................................................ 11
18.
APPENDIX G PRE AND POST DEVELOPMENT VELOCITY .......................................................... 13
vii
1. INTRODUCTION AND PROJECT BACKGROUND
A storm-water management system has already been conducted by Thembakele Consulting
Engineers (Pty) Ltd, and an ecological assessment has been conducted by iSRA Consulting (Pty)
Ltd on the Observation suburb which is upstream of Bruma. These studies found the
Observatory Catchment had experienced an increase in flood peaks because of urban
development and the polluted water may flow untreated into the Jukskei river because of
damage to wetlands and lining of stormwater channels. In order to minimise the impact
pollution from high density suburbs of Bellevue Suburb, Yeoville and the Observatory Golf
Course, an attenuation pond with a wetland is required. Thembakele Consulting Engineers (Pty)
Ltd appointed iSRA Consulting (Pty) Ltd, as sub-contractor, in order to conduct the hydraulic and
hydrological assessment of the required attenuation ponds.
This report details the hydraulic and hydrological assessment of the water treatment structures
such as a sedimentation fore-bay, and artificial wetland. In order to protect the artificial
wetland, flow entering the wetland may need to be controlled or diverting by an attenuating
structure. Furthermore a flood line study of tributaries within the Observatory Golf Course is
included in order to assist with position of erosion preventive structures.
1.1 Problem Statement
Urban development's impacts on waterways by generating higher stormwater peak flows,
increased erosion of unlined slopes, and increase pollution caused by a combination of high
density populations. During rainfall stormwater conduits transport pollutants through storm
drains into the Observatory Golf Course, and into the Jukskei River. The water quality of
catchment might be improved by an artificial wetlands or sedimentation traps; this study will
seek to assess the hydraulic and hydrological parameters for the artificial wetland and its
attenuating structure.
1.2 Locality
The study area (tributaries within the Observatory Golf Course) flow through Bruma Lake and
into the Jukskei River. The catchment falls under Crocodile West Marico Water Management
Area within quaternary catchment A21C (Jukskei Catchment), and is within City of Johannesburg
Metropolitan Municipality in Gauteng Province. Figure 1 below shows position of the artificial
wetland and litter trap on the Observatory Golf Course, in Observatory Johannesburg.
1
Figure 1: Locality map showing the study area: including the Attenuation Pond site on the Observatory Golf Course
Observatory
Golf Course
Figure 2: Map depicting the location of the study area, including Bruma Lake and its feeder streams
2
2. AIM

Explore sustainable solutions to treat water quality of the Observatory tributary stream

Determine the capacity of an attenuating structure that is required for water quality
treatment

Determine peak flows and overflows in order to protect treatment structure from failing.
2.1 Objectives

Determine peak flow flows for different return periods

Estimate pond volume

Determine spillway capacity based 1:25 year return interval storm

Determine the size of pond outlet pipes and discharge flow.

Determine the total sedimentation yield of the catchment.

Calculate trap storage volumes and cleaning frequencies of the sedimentation trap.
3. METHODOLOGY
In order for the specific objectives of the report to be met, the following steps were taken.

Literature review

Applicable legislature

Pre and Post development criterion

Determine flood peaks for different return periods

Determine the capacity of attenuating structure

Size the sedimentation fore bay
4. APPLICABLE LEGISLATION
The protection and management of South African watercourses is entrenched in a number of
South African legislation. The following Acts are an indication of the relevant legislation
pertaining to the development, protection, conservation and management of watercourses in
the South Africa. The following list shows abstracts of random sections in the Acts and is by no
means a full legal review:
3
4.1 The Constitution of South Africa Act 108 of 1996
The legal source for environmental law in South Africa is the Constitution of the Republic of
South Africa (108 of 1996). The Constitution fundamentally altered the legal environment in
South Africa and all laws must be interpreted within the context of the Constitution. Under the
Constitution greater emphasis has been given to improving the social environment. The Bill of
Rights is fundamental to the Constitution of the Republic of South Africa, and in Section 24
states that:
Everyone has the right (a) to an environment that is not harmful to their health or well-being;
and (b) to have the environment protected, for the benefit of present and future generations
through reasonable legislative and other measures that (i) prevent pollution and ecological
degradation; (ii) promote conservation; and (iii) secure ecologically sustainable development and
use of natural resources while promoting justifiable economic and social development.
4.2 National Environmental Management Act 107 of 1998
The Act provides for the right to an environment that is not harmful to the health and well-being
of South African citizens; the equitable distribution of natural resources, sustainable
development, environmental protection and the formulation of environmental management
frameworks. In addition there is recognition that development must be socially, environmentally
and economically sustainable and that the disturbance of ecosystems and loss of biological
diversity are avoided, or, where they cannot be altogether avoided, are minimised and remedied
(Government Gazette, 1998).
National Environmental Management Act (107 of 1998) extends legal liability beyond simply the
person directly responsible for environmental degradation. In terms of the Act the landowner,
his representatives and the person responsible for the environmental degradation will be liable
for any costs of remediation if any construction were to take place within the Permanent / Semipermanent and Seasonal aquatic area boundary.
4.3 National Water Act 36 of 1998
According to Section 2 of the National Water Act (36 of 1998), the purpose of the Act is to
ensure that the countries water resources are protected in a sustainable and equitable manner
for the benefit of all South Africans. The purpose of this Act is to ensure that the nation’s water
resources are protected, used, developed, conserved, managed and controlled in ways which
take into account amongst other factors such as:(d) Promoting the efficient, sustainable and beneficial use of water in the public interest;
(g) Protecting aquatic and associated ecosystems and their biological diversity;
4
(h) Reducing and preventing pollution and degradation of water resources; and
(i) Meeting international obligations.
4.4 Johannesburg Road Agency Policy (Roads and Stormwater Manuel's Code of Procedure
Volume 1)
The policy applied to all new developments amounts to the following:

All developments on land exceeding 8 500m² are subject to storm water attenuation on
site.

The preferred means of attenuation is on surface.

Attenuation off site, to compensate for the lack of an on-site facility is acceptable.

The runoff associated with the development is to be attenuated such that the
predevelopment flows for the 1: 5 year as well as the 1:25 – year storm events are not
exceeded. The attenuation structure must be able to withstand the 1:50 - year storm
event.

Discharge from the attenuation facility is subject to approval by the landowner
downstream.

Site Development Plans will only be approved if supported by an acceptable storm water
management strategy.

Clearance for the issue of a Section 82 or Regulation 38 certificate will only be given
once the storm water management strategy is in place.

The proposed management of the attenuation facility is to be stated in the outline
scheme report.
5
5. LIMITATION AND ASSUMPTION
The scope of this report is to conduct a hydrological and hydraulic assessment of proposed solutions
of the Observatory tributary stream tributary stream.
This report is based on the following assumptions and limitations:

The Catchment is assumed to be predominately urban

The purpose of the Sustainable Drainage System developments targets steady flows in order to
manage water quality and quantity of the channel for environmental reasons.

In this project there is no new development on land; the pre and post development flow within
the stream has negligible changes, therefore there may be no need for pre and post
development hydrographs to be produced.

Subsurface water studies that involve groundwater recharge and groundwater quality were not
conducted at the time this study was completed

Although it is recognised that there is a link between treatment of water within the attenuation
pond or wetland and reintroduction of fauna and flora species, it should be noted that the
specific details are dealt with by a flora and fauna specialist in a separate report within this
project.

A 1:25 year return period is recommended for sizing the by-pass channel.

The interventions proposed in this report will benefit the Jukskei River, however this report is
limited to the Observatory Golf Course Tributary and Suburbs contributing storm water to the
tributary.
6
6. HYDROLOGICAL ASSESSMENT
6.1 MEAN ANNUAL RAINFALL
For weather stations where used to attain the average rainfall in order to determine the design
storm events. Design rainfall of 760 mm per annum was found to be comparable with JRA's
(Roads and Stormwater Manuel's Code of Procedure Volume 1) design rainfall of 750mm per
annum.
6.1.1
Rainfall
The South Africa Weather Services have various rainfall stations situated in and around the
catchment of the Observatory Golf Course. Three SAWS rainfall station where chosen on the
basis of reliability, record length and location. Storm rainfall, for different return periods were
calculated, see Table 3-6 for results. The catchment MAP was established as 757.2 mm per
annum which is slightly higher than JRA recommended rainfall of 750 per annum across the
entire City of Johannesburg Catchment .
Table 3: Rain station 0476100
Duration
One Day
0.5TC
Tc
2Tc
MAR=762.9 mm/a
2
5
55
23
31
39
75
31
42
53
Table 4: Rain station 0476101
Duration
One Day
0.5TC
Tc
2Tc
Duration
One Day
0.5TC
20
50
104
43
58
73
125
52
70
88
20
50
102
42
57
71
121
50
68
85
20
50
91
38
105
43
MAR=763.8 mm/a
2
5
52
22
29
37
73
30
41
51
Table 5: Rain station 0476160
Return Period
10
Rainfall
89
37
50
63
Return Period
10
Rainfall
88
36
49
61
MAR=744.9 mm/a
2
5
52
22
70
29
Return Period
10
Rainfall
81
33
7
Tc
2Tc
29
36
39
49
Table 6: Total for the catchment
Duration
Return Period
2
45
57
51
64
58
73
20
50
MAR=757.2 mm/a
5
53
73
10
Rainfall
86
22
30
30
37
99
117
35
41
48
41
48
55
65
51
60
69
82
One Day
0.5TC
Tc
2Tc
6.2 FLOOD FREQUENCY ANALYSIS
Rehabilitation and lining of streams may results in the increased runoff generation from the site,
resulting in an increase in both the total runoff and runoff peaks. The siting and sizing of the
artificial wetland is essential in order to control normal flows and divert floods.
Inputs:

The artificial wetland will have a catchment area of 2.3 km2 ,and the longest water
course in the catchment has a length of 3.15 km. Slope, lengths and heights were
measured from AutoCAD software. The time of concentration (tc) was estimated at 0.62
hrs.

A site visit was conducted on the 11th of April 2016 in order to determine the condition
of the waterways and lining of streams.
No water level gauging structures or results were found throughout the tributary of the Bruma
Lake, let alone the Observatory Suburb. A Statistical analysis could therefore not be done.
Deterministic and empirical methods were used in the flood frequency analysis of the artificial
wetlands attenuation structure. To compare results only the flood peak estimates at tc = 0.62
are shown in table 7 below
the Alternative Rational method and Unit Hydrograph methods were not developed for small
catchments less than 20km2, (Kruger,2006), such as the Observatory catchment and therefore
were not used. The SDF and Rational methods results are shown in Table 7
8
Table 7: Estimated flood peaks
Method
Rational
SDF
Alt rational
Mi & PI
Average
6.2.1
2
5
10
3
19
12
14
33
11
19
Return Period
10
Flood Peaks (m3/s)
19
24
44
16
22
25
50
24
36
55
21
34
38
53
73
30
48
Assessment of results
The results of the SDF method are smaller than the Rational in lower return periods, but results
get closer to the rational method at the higher return periods.
The results of the rational method compared reasonable well with all methods and the average
Peaks. After evaluating all the above information the results of the Rational Method are
recommended.
7. DEVELOPMENT MODELLING
Predevelopment criterion is as follows

There is currently no storage of water within the tributary of the Observatory Golf
Course

Manning's value n = 0.02 (sandy bed natural channel with limited vegetation ) and n =
0.03 banks (with sparse vegetation/bush)

Downstream = normal depth with average slope of 0.014 assuming uniform or normal
flow condition at the downstream boundary (Upstream = critical depth)

The cross section area is irregular

The soil lose is 11 tons/ha.year
Post development criterion is as follows

Manning's value n = 0.033 (natural channel with few cobbles and vegetation ) and n =
0.035 banks (natural banks stabilised with Reno-mattress and allowing vegetation
growth)

Downstream = normal depth with average slope of 0.013 assuming uniform or normal
flow condition at the downstream boundary (Upstream = critical depth)
9

A artificial pond will reduce the quantity of flow downstream by improving Adsorption,
infiltration and biodegradation and also improve evapo-transpiration
It is worth noting that the flow of water entering the storm water channel and exiting the
channel has negligible changes, that is likely because the distance between the inlet and outlet
of the channel is too short to have an effect on the flow.
Outputs for pre-development modelling as follows for

Flow velocity for a 1:25 year return interval is 3.86m/s

Flow for a 1:25 year return interval Q = 24m3/s
Outputs for post-development modelling as follows for

Vegetating the channel will slow the velocity a 1:25 year return interval is 3.07m/s
(Appendix G)

Flow for a 1:25 year return interval Q = 24m3/s

A 1.5m high pond wall with a 100 mm outlet pipe will slow steady flow and allow flow of
0.02m3/s into an artificial pond

7.1 Spillway Capacity
In attenuation pond is constructed in order to slow down normal flow of the stream to improve
treatment within the artificial wetland, see Figure 4 for a generic design of an attenuating pond
. The bypass spillway is necessary in order to divert stormwater away from the artificial wetland.
the freeboard between the bypass spillway and the pond non overspill wall should be greater
than 1.5m (see Appandix G), using a manning n value of 0.025 a discharge capacity curve was
platted, see Figure 3. It should be noted that although the bypass spillway has the capacity to
divert the 1:25 year return period storm, storm water may still breach the non overspill crest
because of wind set up and wave run. This may cause damage to the attenuating structure.
A trapezoidal bypass channel with slopes of 1 in 1 was selected, because it increases capacity as
flow depth increases. Given that this a major system with regional attenuation, the typical
recurrence interval is between 10 and 20 year return period (Armitage et al,2013).
Spillway type:
Channel width
Freeboard water level:
Manning's n value
Spillway capacity at
Freeboard level:
Trapezoidal by pass channel
3.5 m
1.0 m
The n = 0.025
Q = (A/n)(R2/3)H3/2
26 m3/s ( see Appendix D)
10
DISCHARGE CAPACITY
REDUCED LEVEL (m)
1665.9
1665.7
1665.5
1665.3
1665.1
1664.9
1664.7
1664.5
0
5
10
15
20
25
30
35
40
45
50
DISCHARGE
(m3/s)
Series1
Series2
RMF
Figure 3: Spillway rating curve of the Attenuation Pond
7.2 Outlet pipe
Number of outlet pipes
Single outlet
Diameter of inlet pipe:
100 mm steel pipes
Maximum discharge capacity at FSL:
0.02 m3/s
Description of river outlet valves:
100 mm central stainless steel pipes: A stainless steel pipe has the
advantage of being very efficient, while capable of resisting damage
from trees, and human error.
11
8.
SEDIMENTATION CONTROL DESIGN
The South African Guidelines for Sustainable Drainage Systems and Sediment Yield Prediction for
South Africa - 2010 Edition was utilised to size the sedimentation pond .The storm water
sedimentation control is sized with the following qualifications and assumptions:

Particle size of sediments to be retained are larger than 0.02mm
 It is assumed that 30 % of the catchment is rural and vulnerable to erosion should the soil be
left bare.

Assume 1 ton of soil is 0.843 m3
 A sedimentation yield prediction will yield the depth sedimentation per year for the entire
catchment.
 Sizing of the sedimentation trap is also affected by the topography and availability of
machinery and staff to clean the trap. Depth greater than 1.5m are to avoided because bracing
will be required for labourers to dig lower than 1,5m, furthermore heavy duty tracks may cause
damage to the side slopes of the pond and the golf course.
 Basic design recommendation is to maintain the settling zone of a sediment basin free of
accumulated sediment for a depth of at least (0.61 m).
 The slope of the channel is more than 20% therefore the gabion berm should be greater than
1 m in order to increase the volume of sediments trapped.

The sediment basin should have a means of dewatering in after a storm
 Design flood used is 16m3/s (rational method 1:10 year return period recalculated), this
return interval is set on the program
 Sediment storage depth: The storage zone must be large enough to contain sediment
deposits without decreasing the settling volume. The sediment yield to the basin can be
estimated by using the Sediment Yield Prediction for South Africa method. The depth required for
storage can be determined by using the following equation: Estimated Annual Sediment Yield =
Required Basin Depth / Surface Area of the Basin,
12
Figure 4: General design of Attenuation pond (South African SuDS Guidelines)
8.1 Assessment of results
The results of the SDF method are smaller than both the Rational and alternative Rational
method in lower return periods, but results get closer to the rational method at the higher
return periods.

The catchment size is 2.3 km2 (rational method) which is equal to 230 hectares. The
catchment is only 30% rural (rational method), therefore effective catchment that will
be used to calculate soil loss is 69 hectares.

The soil lose is 11 tons/ha.year (according to Sediment Yield Prediction for South Africa 2010 Edition ).

Therefore soil loss is 1056 tons per year for the catchment, which equals to 887 m3 per
year

The height of the sedimentation trap is 1.5m and will be cleaned four times a year
13
9. LITTER TRAP
Urban development's also impacts on waterways by generating solid waste (litter), litter cannot
be treated with an artificial wetland or sedimentation trap. Bellevue and Yeoville are suburbs
upstream of the Observatory Golf Course, this high density suburbs contribute to a decrease in
water quality because they have a deteriorating stormwater and sewer system and a population
that generally litter its environment. The lined stormwater drains and channels transport
pollutants from Bellevue and Yeoville to Observatory Golf Course tributary. A litter trap design
necessary in order to trap solid waste upstream of the attenuation pond within the Observatory
tributary.2
A trash rack litter trap was selected as the most suitable option for the Observation channel
because:

Trash racks are practical and easy to construct

Cost less to construct and less to maintain

Cleaning frequency can be monthly

Off-line arrangements directs low and medium flows into the trash rack, while high flows
bypass the structure.

May be used to trap litter upstream of the sedimentation trap and attenuation pond.

Can be retrofitted into existing drainage channel
The dimensions of the litter trap are 35m length, 4 m width and 1m depth and this will yield a
capacity of 110m3. Further, additional overflow capacity is provided to increase the overall
capacity of the system to a capability of accommodating storms up to the 50 year storm event.
The location of the trap should be upstream of the artificial wetland in order to improve
efficiency of litter removal.
14
10. CONCLUSION
A hydrological and hydraulic assessment was conducted recommends an artificial wetland,
attenuation pond with a bypass spillway and a sedimentation trap. The pond wall height should be
kept below 2.5m with a freeboard of 1.5m. An additional bypass channel to accommodate storms up
to the 25 year storm event should constructed pond wall. A 100mm Outlet should be place in the
attenuating structure to slow down steady flow that may damage pants in the wetland.
The Attenuation pond will be coupled with an sedimentation trap. The sedimentation trap will need
to be cleaned four times a year or after flood, the height of the sedimentation trap is 1.5m
From an operational perspective a gross litter trap design is recommended, because it is likely to
lower the maintenance cost and improve removal efficiency.
It should be noted that this SuDs interventions are design to treat the effects of urbanisation on the
storm water drainage. There is likely a greater benefit in reducing production of pollution and
erosion from the sources, rather than trying to remove it from the drainage system. Initiatives like
planting indigenous grass to protect exposed hill slopes, using environmentally friendly garden
fertilizers, and maintaining or replacing damaged sewer pipes will reduce are likely to reduce the
pollution load in streams during rain storms.
It is important to note that a wetland with an attenuation pond may require authorisation under
National Water Act 1998, because of potential of impeding or diverting of flow characteristics of the
water course. This has been assessed in detail by environmental management reports within this
project, in order to ensure management of the water resource in a reasonable manner.
15
11. REFERENCE
Kruger E. 2006. The South African National Roads Agency, Road Drainage Manual (5th Edition)
Anhaeusser, C.R. 1999. Archaen crustal evolution of the central Kaapvaal Craton, South Africa:
evidence from the Johannesburg Dome. South African Journal of Geology 102: 303-322.
SANCOLD 2011 Guidelines on freeboard for dams volume II
Alexander WRJ. 1990. Flood Hydrology for South Africa. SANCOLD, Pretoria
Lynch SD. 2004. Development of a raster database of annual, monthly and daily rainfall for
Southern Africa WRC Report No 1156/1/04, Water Research Commission.
Wilson, S., Bray, R. & Cooper, P. (2004)Sustainable drainage systems: Hydraulic, structural and
water quality advice. CIRIAC609. London. ISBN 0860176096. Available from:
http://www.ciria.org.uk/suds/publications.htm
Woods-Ballard, B., Kellagher, R., Martin, P., Jefferies, C., Bray, R. & Shaffer, P. (2007). The SUDS
Manual. CIRIA 697. London. Available at: http://www.ciria.org.uk/suds/publications
16
12. APPENDIX A Hydrology
1
13. APPENDIX B
Detention Pond Volume Estimation - S.I. units
2
14. APPENDIX C
Attenuating Structure Outlet Flow Control Design - S.I. units
This may be a drainage pipe with valve control
1. Single Stage Pipe Control
Pipe Material:
reinforced concrete pipe
Inputs
Calculations
Manning roughness
coefficient, n =
Pipe length, L =
Kp =
0.04215
C=
0.462
0.013
3.05
m
Pipe diameter, D =
Water elevation at
design volume, Es =
2
m
0.02
m
0.02
m /s
100
mm
Pipe centerline
elevation, Ec =
Pre-development peak
runoff rate, qpb =
Pipe diameter, D =
3
3
100
mm
(trial value)*
* This requires an iterative (trial & error) solution, because a value is needed for D in order to
Calculate Kp, which is needed to calculate D …. The trial value of D in the inputs column is an
intial guess in order to start the process. When values are entered for all of the parameters in
the inputs column, the calculations column will calculate a value for D. If the calculated value
for D is different from the trial value, repeat with the trial value of D set at the next standard pipe
diameter less than the calculated value. Repeat again if necessary.
Volume of Pond
Time to Empty pond
Discharge flow
1000
m
3
12
hours
0.02
m /s
3
4
Equations for Single Stage Flow Control Design with a Pipe
Kp = 115,768 n2 D-4/3
C = 0.456 + 0.047(LKp) - 0.0024(LKp)2 + 0.00006(LKp)3
D = 1346 C qpb0.5 (Es - Ec)-0.25
Where:
n = Manning roughness coefficient for pipe
(n = 0.013 for reinforced concrete and 0.024 for corrugated metal pipe)
D = pipe diameter, mm
L = pipe length, m
qpb = pre-development peak storm water runoff rate, m3/s
Es = water elevation in pond when holding design storage volume, m
Ec = elevation of outlet pipe centerline, m
Standard S.I. diameters for storm water drainage pipe (all in mm):
100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 600, 750, 900, 1050, 1200, 1350, 1500
5
15. APPENDIX D By-Pass Spillway Capacity
Spillway discharge capacity calculation
1:25
=
1:25
=
= (A/n)(R2/3)H3/2
20 Q =
20 Soffit Level=
FSL =
b=
1664.5
1666
3.5
A
P
R
n
Slope
side slope of channel
NOC
1666
1666
1666
1666
1666
1666
1666
1666
1666
1666
1666
1666
1666
1666
1666
1666
RL
Q
1664.5
1664.6
1664.7
1664.8
1664.9
1665
1665.1
1665.2
1665.3
1665.4
1665.5
1665.6
1665.7
1665.8
1665.9
1666
=
b*y+(y^2)/tana
= b+ 2y/sina
= A/P
0.025
0.03
45 1:1
RMF
RMF%
0
0.4
1.3
2.6
4.4
6.7
9.5
12.8
16.6
21.0
26.1
31.7
38.1
45.1
52.8
61.2
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
6
0
2
6
13
22
33
47
64
83
105
130
159
190
225
264
306
16. APPENDIX E SEDIMENTATION TRAP
7
8
9
INPUTS
1
minimum particle size
0.02
post-developed flow
16
mm
m3/s
2
Vs = 0.0062 ft/s =
3
surface Area available if berm = 1.5m
w=
4
soil loss per year (SA Yield Map)
11
t/ha.year
catchment size
rural catchment (30% rural)
3.2
96
km2
ha
5
0.00029
m/s
230
15.16575
m2
soil loss per year
(assume 1t = 0843m3)
1056
890.208
t.year
m3
Basin depth required for once a year
cleaning
3.87047
m.year
10
17. APPENDIX F FLOODLINES
Job Title:
JUSKEI LINED CHANNEL ALONG BEZ VALLEY
Stormwater Discharge Calculations
Description
Symbol
Formula
Units
DISCHARGE AREAS(CATCHMENTS)
SUB 5
487
SUB 3
431
SUB 4
282
0.60
3328
134.5
25
750
2342
4
2.78
115.65
0.65
2020
102.5
25
750
1895
5
2.78
69.98
Catchment area measured
Am
State
ha
Catchment factor
Length of flow
Fall
Return period
Mean Annual Rainfall
Diameter of equal circle
Slope (as a percentage)
Constant
Cf
L
H
n
r
d
s
C
State
State
Coeff.
m
m
Years
mm
m
%
Const.
Time of concerntration
tc
Calc
mins
0.70
2263
53.5
25
750
2490
2.364
2.78
86.48
Catchment Factor
Rainfall Intensity
Cf
I
Calc
Calc
Coeff.
mm/hr
0.70
54.1
0.60
42.5
0.65
64.0
Catchment area measured
Am
Calc
ha
487.00
431.00
282.00
Runoff discharge
Q
C x Cf x I x A
l/sec
51261.9
30524.2
32617.9
State
State
State
State
Calc
Calc
11
OPEN DRAIN CAPACITY CALCULATIONS
Description
Drain depth
Top width
Bottom Width
Symbol
Formula
OPEN DRAINS
Units
SUB 5
SUB 3
SUB 4
3.4
6.00
6.069
0.0086
3.6
7.00
6
0.011
4
7.50
6.2
0.011
1/3
0.035
0.035
0.035
D
Wt
Wb
State
State
m
m
m
Slope
S
State
Ratio
Manning's n value
n
State
s/m
Sectional Area
A
Calc
m
2
20.52
23.40
27.40
Wetted Perimeter
P
Calc
m
12.87
13.27
14.30
Drain full Capacity
Velocity
Q
v
Calc
m /s
m/s
3
74.19
102.35
126.64
3.6
4.4
4.6
State
Drain full Capacity
Qfull
VxA
l/sec
74189.7
102351.3
126635.4
Runoff discharge
Q
CxIxA
l/sec
51261.91
81786.11
114403.99
Qfull%
Q/Qfull
%
69
80
90
% Pipe full
12
18. APPENDIX G PRE AND POST DEVELOPMENT VELOCITY
13
ObStream
Plan: ObStreamPstDvpPL
03/07/2016
ObStream R1
3.5
Legend
Vel Chnl 20yr
Vel Chnl 10yr
Vel Chnl 5yr
3.0
Vel Chnl 2yr
Vel Right 20yr
Vel Left 20yr
Vel Right 10yr
Vel Left 10yr
2.5
Vel Left (m /s), Vel Chnl (m /s), Vel Right (m /s)
Vel Right 5yr
Vel Left 5yr
Vel Right 2yr
Vel Left 2yr
2.0
1.5
1.0
0.5
0.0
0
200
400
600
800
Main Channel Distance (m)
14
1000
1200
1400
1600
PRE-DEVELOPMENT
ObStream
Plan: ObStreamPL
02/07/2016
RS = 510.0001
.15
.013
.15
1676
Legend
WS 100yr
WS 50yr
WS 20yr
WS 10yr
1674
WS 5yr
WS 2yr
Ground
Bank Sta
Elevation (m)
1672
1670
1668
1666
1664
0
20
40
60
80
100
120
140
160
Station (m)
ObStream
Plan: ObStreamPL
02/07/2016
RS = 540.0001
.15
.013
.15
1676
Legend
WS 100yr
WS 50yr
WS 20yr
WS 10yr
1674
WS 5yr
WS 2yr
Ground
Bank Sta
Elevation (m)
1672
1670
1668
1666
1664
0
20
40
60
80
100
120
140
Station (m)
15
160
ObStream
Plan: ObStreamPL
02/07/2016
RS = 480.0001
.15
.013
.15
1676
Legend
WS 100yr
WS 50yr
WS 20yr
1674
WS 10yr
WS 5yr
WS 2yr
Ground
1672
Bank Sta
Elevation (m)
1670
1668
1666
1664
1662
0
20
40
60
80
100
120
140
160
Station (m)
ObStream
Plan: ObStreamPL
02/07/2016
RS = 450
.15
.013
.015
1676
Legend
WS 100yr
WS 50yr
WS 20yr
1674
WS 10yr
WS 5yr
WS 2yr
Ground
1672
Bank Sta
Elevation (m)
1670
1668
1666
1664
1662
0
20
40
60
80
100
120
140
160
Station (m)
16
POST DEVELOPMENT
ObStream
Plan: ObStreamPstDvpPL
03/07/2016
RS = 540.0001
.15
.025
.15
1676
Legend
WS 100yr
WS 50yr
WS 20yr
WS 10yr
1674
WS 5yr
WS 2yr
Ground
Bank Sta
Elevation (m)
1672
1670
1668
1666
1664
0
20
40
60
80
100
120
140
160
Station (m)
ObStream
Plan: ObStreamPstDvpPL
03/07/2016
RS = 510.0001
.15
.025
.15
1676
Legend
WS 100yr
WS 50yr
WS 20yr
WS 10yr
1674
WS 5yr
WS 2yr
Ground
Bank Sta
Elevation (m)
1672
1670
1668
1666
1664
0
20
40
60
80
100
120
140
Station (m)
17
160
ObStream
Plan: ObStreamPstDvpPL
03/07/2016
RS = 480.0001
.15
.025
.15
1676
Legend
WS 100yr
WS 50yr
WS 20yr
WS 10yr
1674
WS 5yr
WS 2yr
Ground
Bank Sta
Elevation (m)
1672
1670
1668
1666
1664
0
20
40
60
80
100
120
140
160
Station (m)
ObStream
Plan: ObStreamPstDvpPL
03/07/2016
RS = 470
.15
.025
.15
1676
Legend
WS 100yr
WS 50yr
WS 20yr
WS 10yr
1674
WS 5yr
WS 2yr
Ground
Bank Sta
Elevation (m)
1672
1670
1668
1666
1664
0
20
40
60
80
100
120
140
Station (m)
18
160
11