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CHAPTER 7
BENEFITS OF CHECK DAM
7.1
GENERAL
Assessment of hydrological impact of the check dam in this area
was made and the areas that are very much benefitted were demarcated as
explained in the previous chapters. It is important to integrate these
observations so as to understand the region that are on the whole benefited by
this structure. It is also essential to assess the socio economical benefit to the
livelihood in this area. As many such check dams have been constructed
along this river, it is necessary to assess how this will modify hydrological
balance in the Arani river basin.
7.2
DEMARCATION OF AREA BENEFITTED BY CHECK
DAM RECHARGE
The impact of recharge from the check dam was understood by the
study of water level fluctuation, Electrical Conductivity (EC), major ions and
isotopic variations as well as estimation of recharge by different methods.
Impact of recharge on the quality of groundwater of this region was also
assessed by geochemical, trace, pesticides and herbicides and microbiological
analysis. These methods helped in delineating the area that are significantly
benefited by the recharge from this dam. Groundwater modelling was used to
assess the area that was benefitted by the recharge. The observations based on
these methods are integrated and shown in Figure 7.1. Hydrogeological and
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University, Chennai.
CHECK DAM
Low EC (323 µS/cm to 1180 µS/cm)
Suitable-drinking (D)& irrigation (I) (w.r.t ions)
High turbidity (T) ( 4.7 to 5 NTU)
High microbiological load (M ) (48 to 227 cfu)
January
III
II
July 2010
I
II
III
X
West
X'
2
HIGH (I)
Low EC (323 -1100)
Suitable for D & I (w.r.t ions)
Low T (0.1 to 3.5)
Low M (2 to 85 cfu)
0
1
2
Distance in Km from check dam
1
MODERATE (II)
Moderate EC (700 -1600)
Suitable for D & I (w.r.t ions)
Low T (0.1 to 3.5 NTU)
Low M (2 to 85 cfu)
East
LEAST (III)
High EC (781 -4073)
Not suitable for D
(w.r.t TDS, Ca, Mg, Cl)
Least
X
X'
Least
Figure 7.1 The region that are significantly benefited by the recharge
from this dam
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hydrological measurement shows that the wells located within about 1.25 km
are benefited by the recharge from check dam as there is no marked
difference was identified beyond this region. Result of the groundwater
modelling show that after construction of check dam the region up to about
3km is benefited by the recharge from check dam. The benefits acquired by
the livelihood due to this structure are discussed in the following sections.
7.3
SOCIO ECONOMIC BENEFIT
Outcome of any research study is expected to enhance the
livelihood of the people. The success of a technical solution based on a
scientific study can only be assessed based on the feedback from the user. The
feedback from the users is very vital for development or suitable modification
of the implemented technology. In this section, socioeconomic benefits of
check dam are discussed.
Survey on personal information mainly consists of location, age
group and occupation. Age group of the respondent varied from 30 to 60.
53% of the responded were in the age group between 51 and 60, 34% of the
respondent were between 41 and 50 and 13% are in the age group between 30
and 40. Occupation of the respondent includes farming (74%), own business
(16%) and labor (10%). Occupation of majority of the respondents were
farming and 87% of the respondents were in the age between 41 and 60
indicates that data was collected from the relatively old people who know
about the region very well. The responses of the persons for various questions
are given in Table 7.1.
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Table 7.1 Responses of the persons interviewed
Category
Sub questions
Agree
Awareness about Is check dam useful?
78%
the recharge
Is this the optimum
95%
structure
location for check
dam?
Water quantity Is there Improvement
82%
in water level?
Is there any increased
100%
discharge from pump?
Is there any
0%
upstream/downstream
dispute?
Water quality
Is the water stored by
71%
the check dam
contaminated?
Is there any
84%
improvement in
groundwater quality?
Is there any health
8%
issues related to usage
of water from check
dam?
Agriculture
Is the water suitable
100%
and sufficient for
irrigation?
Is there any change in
32%
cropping pattern after
check dam?
Is there any increase in
26%
irrigated land after
check dam?
Is there any increase in
29%
yield after check dam?
Economic status Is there any increased
53%
income after check
dam?
16%
Is there any new
employment after
check dam?
What is income from Not quantifiable
new employment?
Disagree
22%
5%
18%
0%
100%
29%
16%
92%
0%
68%
74%
71%
47%
84%
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7.3.1
Awareness About the Recharge Structure
In order to assess the awareness about the recharge structure,
respondents were interviewed with two questions about the purpose of check
dam and opinion about location of the check dam at this area. The reply based
on purpose gave various combinations of results as shown in Figure 7.2.
Agriculture in this area was practiced by pumping groundwater; 78% of the
respondent is aware that water stored in the check dam replenishes the
groundwater recharge. 47%, 48% of the respondents considered that the site
selected for the check dam is very good, good respectively. 5% of the
respondents opined that the site is not suitable as the water stored in the check
dam deteriorates quality fresh groundwater.
Recreation , cattle
5%
Bathing,
Agriculture,
Recharge
8%
Recreation,
cattle,
recharge
8%
Agriculture
combined with
other activities
Not used
5%
Industry
3%
Bathing
3%
Agriculture,
Recharge
5%
Agriculture
45%
Agriculture,
cattle
3%
Agriculture,
bathing
10%
Agriculture,
Bathing, recharge
5%
Figure 7.2 Use of water in the check dam for various purposes
7.3.2
Water Quantity
Assessment of impact of this dam on water quantity was made by
getting the opinion of the people on groundwater level, change in pumping
pattern, upstream and downstream disputes. Opinion of the respondents on the
change in water level after construction of check dam is shown in Figure 7.3.
16 % of the respondent state that water level has been increased to about 4.5
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University, Chennai.
m to 6 m after construction of the check dam. These respondents are from
Paleshwaram and part of Rallapadi located within 1 km from the check dam
towards the groundwater flow direction as shown in Figure 1. 11%, 55% of
the respondents state that groundwater level improved from 3 to 4.5 m, 1.5 to
3 m respectively. 18% of the respondents stated that they have not observed
any changes in the water level.
Figure 7.3 Improvement in water level after construction of check dam
All the respondents felt that the pattern of pumping has changed
after the construction of the check dam. 100% of the respondents, even those
who does not notice any change in groundwater level also stated that when
groundwater is extracted, water comes out high pressure and there is no
failure of pump after construction of the check dam at this location. Before
the construction of check dam they observed that pumps will discharge water
at irregular interval during summer period. There was no upstream and
downstream disputes observed on the study area as all the respondents are
benefited by the construction of check dam. 17 new tube wells were drilled by
the respondents within this three year (2010-2013) after construction of the
check dam for domestic and irrigation purposes.
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7.3.3
Water Quality
Impact check dam on water quality was assessed by considering
both water stored by the check dam and groundwater. If the respondent
indicate that the water quality is bad, then their opinion on a few more
questions to identify the reason for contamination and health hazard
associated when using the water for domestic purpose. Figure 7.4a and 7.4b
shows the percentage of responses on the quality of water stored in the check
dam and groundwater respectively. 66% of the respondents state that water
stored by the check dam was contaminated by the sewage waste disposal at 2
km upstream of the check dam and 5% states that this water was also
contaminated by the domestic waste disposal.
Figure 7.4 Quality of a) Water stored by the check dam b) Groundwater
after construction check dam
This type of contamination was also observed during initial field
survey apart from response from the questionnaire survey. Only 5% of the
respondents agree that water stored in the check dam was not contaminated.
10% and 74% of the respondents state that quality of groundwater is very
good and good respectively. They do not find any difference in groundwater
quality after construction of check dam. 16% of them state that groundwater
quality have changed due to the interaction with the contaminated water
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stored by the check dam. These 16% (6 people) of responded are also replied
that there is no remarkable health hazards observed by them after using this
water for domestic purposes, except cough (2 people) and itching (1 person).
7.3.4
Agriculture
Survey about impact of check dam on agriculture includes
questions about land information, cropping pattern at the time of interview,
suitability of groundwater for irrigation and availability during summer
period, change in cropping pattern after check dam, increase in irrigated land
after check dam, increase in yield after check dam. 45%, 34%, 5%, 5%, 11%
responded are having land less than 5 acre, 6-10 acre, 11-15 acre, 16-25 acre,
11% of land respectively. Green gram (2%), Jasmine (8%), Spinach (5%),
Paddy with combination of other crops (75%) were cultivated at the time
survey. 10% of the respondents left their land uncultivated due to lack of
financial resources. Before and after construction of the check dam they do
not observe any change in quality of water used for irrigation purpose and this
quality is suitable for irrigation.
Figure 7.5 Increase in area of
Figure 7.6 Increase in paddy yield
irrigation after
after construction of
construction of check dam
check dam
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Though 100% of them responded that after construction of check
dam groundwater is available even during summer period, only 13% and 19%
of them responded to change in agricultural pattern from one crop to two
crops and two crops to three crops in a year respectively. Figure 7.5 shows the
changes in irrigation practice after construction of check dam. 68% of them
does not observe any change in cropping pattern after construction of check
dam.
24% of the respondents aggress that the area of cultivation has
increased between 1 and 5, 2% of them say it has increased from 5 and 10.
75% of the respondent informed that there is no change in the agricultural
area and it is also not possible by everyone to go for additional area of land
for cultivation. Paddy is main source of income to the farmers in the study
area. Increase in yield in terms of number of additional paddy bags (75kg
/bag) was also observed during the survey is shown in Figure 7.6. 28%
responded that yield is increased between 1 and 20 bags. 71% does not
observe any change in yield and these responded belong to those who had not
practiced any additional cropping pattern. Few farmers have increased the
well depth so as change the gradient and draw more water from the check
dam.
7.3.5
Economic Status
Economic status of the people was assessed based on new
employment and additional income obtained in agriculture after construction
of check dam. New employment raised after construction of check dam is
shown in Figure 7.7.
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Figure 7.7
New employment after Figure 7.8
check dam
Increase in income rate
due to agriculture after
check dam
Availability of sufficient water resource is the main advantage to
increase the market in the field of real estate. Land values of this area are
increased from Rs. 300/cent to Rs. 700/cent (1 cent = 40.46 m2) after
construction of check dam. Fishing was done only for a month as it requires
time for the culture and maturity of fish. 50 to 100 kg of fishes was available
during the water storage period. Small scale business through tourists is also
increased only when there was water in the check dam. Quantification of
income based on this new employment requires census survey and it does not
provide income throughout the year. Figure 7.8 shows the increased income
from the agriculture after construction of check dam. Agriculture in this area
depended on the groundwater and water stored by the check dam increases the
groundwater recharge. Assured water supply for the irrigation has increased
the income to the respondent.
7.3.6
Suggested Management Strategies by the Respondents
Questions framed are restricted to collect data from the various
category listed earlier. Apart from this additional information are provided by
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the respondents during the survey. This information is mainly focused about
the maintenance and management options to improve the benefits of the
check dam at this location. The respondence are of the view that the
protection of water quality in the dam is very important and washing of meat,
bathing, disposal of sewage/domestic waste should be prevented. If the water
is clean then this can also be used for drinking purpose or income can be
improved through boating facilities for tourists. They also suggest that sign
board about the depth of water and fence should be provided in order to avoid
the accident during diving. They also wished to conduct awareness camps
highlighting the need for keeping the water clean in the dam. Respondent also
state that the strict law should be enforced through polluters pay policy. Even
though there are certain disadvantages they clearly understand the importance
of check dam across non perennial River.
This study indicates that more advantages are noticed in the entire
category except the agricultural category. Though water is available
sufficiently after construction of check dam, the farmers are not able to
improve the agricultural activities, due to the requirement of high initial
investment for buying seeds, fertilizers, manures, equipment and non
availability of labors. Hence, based on the survey it was identified check dam
constructed in this area is efficient in improving the livelihood of the people.
The results of the survey indicated that check dam at this location
provide respondent with better livelihood. The responded were also suggested
that proper protection against the contamination should be enforced to obtain
maximum benefit from this check dam. Hence, check dam is considered to be
an excellent method of MAR to be constructed across non perennial river as
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its harvest the excess runoff and water is available in the river even after the
monsoon over a period of four month after the rainfall.
7.4
ESTIMATION OF COST OF WATER RECHARGED BY
CHECK DAM
It is important to understand the benefit accrued due to the
construction of the check dam at this site. The estimation of quantum of
recharge by water balance method and groundwater modelling was about 3.4
Mm3 during the period from October 2010 to March 2013 (3 years). The cost
of construction of this dam was about Rs. 70.00 Million. Considering the
annual recurring expenditure for maintenance of this structure as Rs. 0.1
Million and life period of about 100 years that total cost comes to Rs. 80.00
Million. Assuming that the same quantum of recharge will take place for the
remaining years, and then total quantum of water recharged for 100 years will
be about 113.33 Mm3. Based on this calculation the annual expenditure to
harvest about 1.13 Mm3 would be Rs.0.8 Million. Hence, the cost of 1 Mm3
of water stored by the check dam would be Rs.7,00,000/- (Rs. 0.7/ m3 of
water). Even though, there are several factors that need to be considered for
estimation of coast incurred for recharge, in order to have a very approximate
cost of water, this simple calculation was made.
7.5
REDUCTION IN RUNOFF DUE TO CHECK DAMS
As discussed earlier, the Public Works Department, Government of
Tamil Nadu and the Chennai Metropolitan Water Supply and Sewerage Board
(CMWSSB), has initiated the construction of a series of check dams across
Arani river after 1990’s. Six check dams were constructed across Arani River.
Hydraulic particulars of these dams are given in Table 7.2. These dams will
thus store part of the runoff that otherwise will be discharged into the sea.
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Before construction of this check dams the runoff from this basin was
estimated to be 94.2 Mm3 (UNDP 1987).
Table 7.2 Hydraulic particulars of
1990’s across Arani River
check dams constructed after
Sl.
Location of
Height up to
Length
Storage
No
check dam
crest (m)
(m)
volume (Mm3)
1
Uttukottai
1.5
345
0.36
2
Panapakkam
1.2
100
0.28
3
Kalpatu
1.2
170
0.28
4
Sengothkalam
3
225
0.71
5
Paleshwaram
3.5
260
0.83
6
Reddipalayam
3
95
0.28
Based on the present study carried out at Paleshwaram check dam,
the volume of water that is likely to be stored in all the other check dams was
estimated from their height and river bed topography. It was assumed that the
check dams can conserve volume of water equal to two times of its storage
capacity (Table 7.2). Hence, the total volume of water conserved by this six
check dams will be about 5.5 Mm3. Thus, the proposed MAR through these
will result in harvesting about 6% runoff (Figure 7.9). Considering that the
potential evaporation of about 40 % to 50 % of total storage (5.5 Mm3) in the
check dams, a remaining quantum of about 3 Mm3 of water is expected to be
the groundwater recharge. As only a small fraction of runoff is harvested, due
to this there will not be any major changes in the hydrological balance.
However, construction of check dams may lead to reduction in sedimentation
near the mouth of the river which is a major cause for sinking of several
major river deltas of the world (Syvitski et al 2009).
Figure 7.9 Runoff into the sea with and without the check dams
12
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In the present study, accumulation of sediment in the dam was not
observed, which may be due to the absence of sediments in the inflow
probably due to the check dam on the upstream side. Over long period of
time, it is expected that the siltation may reduce the recharge. Hence, the
suitable change in the design of the check dam may be carried out such as the
provision of sluice gates. Further, these sluice gates may be opened for a
shorter period of time so as to release the sediment and also allow minimum
flow on the downstream site which is expected to improve the groundwater
recharge.