chapter 7 benefits of check dam -...

115Parimalarenganayaki, S 2014, Managed Aquifer Recharge: An integrated approach to assess the impact of a check dam, PhD thesis, Anna University, Chennai.

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


Figure 7.1 The region that are significantly benefited by the recharge from this dam

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)

LEAST (III)High EC (781 -4073)Not suitable for D (w.r.t TDS, Ca, Mg, Cl)

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)

X X'

CHECK DAMLow 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)

0 1 212 EastDistance in Km from check dam

West

I

January

July 2010IIII IIIIII

X X'

Least

Least


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.


Table 7.1 Responses of the persons interviewed

Category Sub questions Agree DisagreeAwareness about the recharge structure

Is check dam useful? 78% 22%Is this the optimum location for check dam?

95% 5%

Water quantity Is there Improvement in water level?

82% 18%

Is there any increased discharge from pump?

100% 0%

Is there any upstream/downstream dispute?

0% 100%

Water quality Is the water stored by the check dam contaminated?

71% 29%

Is there any improvement in groundwater quality?

84% 16%

Is there any health issues related to usage of water from check dam?

8% 92%

Agriculture Is the water suitable and sufficient for irrigation?

100% 0%

Is there any change in cropping pattern after check dam?

32% 68%

Is there any increase in irrigated land after check dam?

26% 74%

Is there any increase in yield after check dam?

29% 71%

Economic status Is there any increased income after check dam?

53% 47%

Is there any new employment after check dam?

16% 84%

What is income from new employment?

Not quantifiable


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.

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

Bathing3%

Industry3%

Not used5%

Recharge8%

Recreation , cattle5%

Agriculture 45% Agriculture,

bathing10%

Agriculture, Bathing, recharge

5%Agriculture,

cattle3%

Agriculture,Recharge

5%

Bathing, Agriculture,

Recreation, cattle,

recharge8%

Agriculture combined with other activities


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.


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


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 irrigation after construction of check dam

Figure 7.6 Increase in paddy yield after construction of check dam


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.


Figure 7.7 New employment after check dam

Figure 7.8 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


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


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.


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 check dams constructed after 1990’s across Arani River

Sl.No

Location of check dam

Height up to crest (m)

Length(m)

Storagevolume (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


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.

chapter 7 benefits of check dam -...

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