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5.7 Conjunctive Use of Surface and Groundwater - Krishna Delta,
In cases where a river system has been exploited to the maximum extent,
and where large, unmet demands for water continue to exist, it is often
necessary to exploit groundwater resources wherever they exist. However,
in the lower reaches of the system, it is also likely that seawater
intrusion will reduce the potential exploitation of groundwater resources
in the deltaic reaches of the system. In such situations, mixing of
groundwater with surface water can be used to augment water supplies.
The Krishna River flows through the states of Maharashtra, Karnataka and
Andhra Pradesh (AP), and has reached this state of maximum surface water
exploitation. In accordance with the Bachawat Award for the distribution
of river waters, Andhra Pradesh State has an allocation of 22 653 million
m3, most of which is currently being exploited or has been earmarked for
exploitation in the foreseeable future, leaving some areas of Rayalasema
without enough water to satisfy the minimum requirements. In view of this,
the Andhra Pradesh State Government has commissioned the Telugu Ganga
Project, a prerequisite for which is the conservation of the waters of the
Krishna River upstream of Nagarjuna Sagar Reservoir. The use of
groundwater in conjunction with surface water resources has been proposed
as part of these conservation measures. According to information published
by Andhra Pradesh State Irrigation Development Corporation (APSIDC), the
utilizable groundwater resources of the Krishna Delta are 4 568 million
m3, against an annual net utilization of 287 million m3. Hence there is
enough scope for utilization of groundwater in the delta provided it is
blended with available surface water to achieve an acceptable quality for,
primarily, agricultural use.
In order to meet the minimum water requirements of the Delta area, the
quality of groundwater and surface water in Krishna Delta ayacut was
considered in order to determine an appropriate blend of groundwater and
canal water to support their conjunctive use. The quality of groundwater
along the coastline is generally poor due to the intrusion of seawater
into the coastal aquifers. Chloride concentrations are generally found to
be in the range of 85 to 845 ppm. For this reason, crop irrigation mainly
depends on canal waters as the primary water source. Two methods of mixing
surface and ground waters were investigated; namely, supplying surface and
ground waters separately for alternate waterings in the required
proportions, and directly blending surface and ground waters by pumping
groundwater into the canals.
Extent of Use
APSIDC collected ground and surface water samples at Tenali, Duggirala,
and Pedavadlapudi in the Krishna Western Division, at Nidumole, Gudur and
Pamarru in the Krishna Central Division, and at Eluru, Gudlavalleru and
Mudinepalli in the Krishna Eastern Division, and analysed the samples for
Total Dissolved Solids (TDS) and chloride concentrations, hardness and
Electrical Conductivity (EC). Selected results are shown in Table 38.
These analyses, and related soil samples, collected at root zone depth,
suggested that the conjunctive use of surface and ground waters was
possible, as shown in Table 38, and that concerns regarding salination of
the soils were unfounded. Insignificant concentrations of chlorides were
present in the soil, probably due to leaching by rainwaters during the
Kharif season. The import of this finding was that no allowance
need be made for using additional canal waters to "sweeten" the
soils by leaching excess salt from the soil profile.
TABLE 38. Groundwater Quality in the Krishna Deltaa.
|| Total Dissolved Solids (ppm)
||Hardness ( ppm)
a In all the above samples,
sulphate concentrations were found to be below the limit of detection, and
the value of electrical conductivity was less than 1 000 microMhos/cm.
TABLE 39. Water Quality Standards for Irrigation
|Class of Water
||Electrical Conductivity (mhos/cm)
||Range of Hardness as CaCO3 (ppm)
||Excellent to good
||1 000-3 000
||Good to injurious
||Above 3 000
||Unfit for irrigation
The results of the analyses from the Krishna Western Division indicated
dissolved solids concentrations in groundwater and canal water samples of
1 364 ppm and 597 ppm, respectively. Blending these waters in a 1:1 ratio
by volume results in a final TDS of 981 ppm, which is below 1 000 ppm
threshold considered as the minimum quality for irrigation water.
Similarly, in the Krishna Eastern Division, a 1:1 ratio of groundwater and
canal water was found to produce a product water that is suitable for
irrigation use. In contrast, in the Krishna Central Division, blending
groundwater and surface water in ratios of up to 34:1 failed to result in
a product water with a TDS concentration of less than 1 000 ppm. Hence,
the utilization of groundwater is this Division was not considered
further. Finally, in the Krishna Delta ayacut system, a blend of
groundwater and surface water in a ratio of 28:72 was found to produce a
product water suitable for irrigation use.
Operation and Maintenance
The operation and maintenance requirements of this technology includes
the inspection and repair of pipelines, channels, and pumps, all of which
make use of existing skills present within the agricultural community.
Level of Involvement
The Andhra Pradesh State Irrigation Development Corporation is the
operator of the system. State Government agencies and financial
institutions have provided the funds required to develop the necessary
infrastructure to operate this technology.
Effectiveness of the Technology
The effectiveness of this technology in achieving the objective of
conserving water resources is evident from the fact that 28% of the total
water requirement of the Krishna Delta was met through the conjunctive use
of surface and ground waters, conserving 750 million m3 of surface water
which could be diverted to other uses. In subsequent phases of this
project, this savings is expected to reach 1 065 million m3.
The advantages of this technology include the conservation of large
quantities of good quality surface water in a very cost effective manner.
This technology may also have application in places where the good quality
surface water is not abundant.
Application of this technology requires additional infrastructure,
including a tubewell pumping system, which incurs additional costs. It
also requires additional monitoring of the operation of the system to
ensure the quality of the blended water, as some of the crops are
sensitive to salinity and changes in water quality. Also, soil quality may
be sensitive to the quality of the water applied, requiring that the ratio
of surface to ground water volumes should be closely monitored and
properly maintained to prevent salination of the soils.
Further Development of the Technology
In view of the large demands on the waters of the Krishna River upstream
of Nagarjuna Sagar Reservoir, it has become necessary to utilize the
groundwater supplies available in the Krishna Delta area to the extent
possible. Based upon water quality considerations arising from the
analyses of groundwater, canal water, and soil samples of the ayacut, it
is possible to conjunctively utilize groundwater and surface waters in the
Delta in blends of up to 28:72. Such use would conserve up to 1 016
million m3 of surface water for other purposes.
Vishwanadh, G.K. and D.V. Reddy 1995. Conjunctive Use of Ground and
Surface Water in Krishna Delta for Irrigation, Journal of Indian
Institution of Engineers, Civil Engineering Division, 75:197-202.