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The findings presented in Table 11 are entirely
consistent with other studies in the region that
have also reported reduced runoff as a result of
water harvesting along drainage lines and within
agricultural and forested areas (e.g. Rama Mohan
Rao et. al. 1993 and 1995). Soil water
conservation and construction of a large number
of check dams along the drainage lines is clearly a
major cause for reduced runoff. Groundwater
extraction in the vicinity of the drainage lines and
water harvesting structures is probably an
additional contributory factor because the
resulting groundwater depletion allows a larger
volume of water to infiltrate and be stored in the
aquifer. However, the relative importance of these
two causes and possible interactions between the
two could not be differentiated in this study.
Bearing in mind the fact that some of these
tanks are more than 200 years old, Figure 30
compares potential mean annual tank inflows
(i.e. the naturalised runoff that would occur if
there were no structures in the tank catchment
area), mean annual tank inflows approximately 15
years ago and mean annual tank inflows in 2002.
It can be seen that in all cases there has been a
reduction in mean annual inflows during both the
period from construction up until 15 years ago
and from 15 years ago up until 2002. In the case
of Chapari, the biggest reduction took place
during the period up until 1986 and, whereas for
Gundlur, the reduction was more marked during
the period 1990-2002. Table 12 summarises tank
inflow information that is specific to each tank.
Figure 30. Comparison of tank inflows with no structures in
catchment, and the situation 12-16 years ago and in 2002
400
350
300
Tank inflow (ham)
250
200
150
100
50
0
Gundlur Anabur Inchigeri Ya padinne Chapa ri
No structure s 12-16 years ago 2002
Table 12. Summary of tank inflow information specific to each
Tank
Specific characteristics relating to tank inflows
Chapari
Yapadinne
Gundlur
Anabur
Inchigeri
Major decline in tank inflow occurred approximately 100 years ago when two tanks were
constructed in catchment area to meet the domestic water needs of Kalyandurg town.
Although there has been a large reduction in tank inflows, this is not leading to
significant problems because the catchment area is very large in comparison to tank capacity .
Sand extraction along feeder canals and stone quarries in catchment have created
additional storage in the catchment area.
Original design of the tank relied on two feeder canals to fill the tank to full capacity.
Unfortunately, one feeder canal was blocked by water harvesting structures and the
other was poorly constructed and never functioned.
Inchigeri has a relatively small catchment area. Runoff from this area was reduced as
a result of farmers blocking feeder canals with large field bunds. These have enabled
these farmers to cultivate paddy and sugar cane. Reduced inflows to the tank and the
resulting reduced percolation to groundwater appears to be directly linked to the severe
drinking water problems now faced by people living in Inchigeri town.
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