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Runoff at the micro-watershed and
field scales
Micro-watershed and field-scale studies of
runoff have been carried out by the CSWCRTI
in Bellary and by CRIDA in Anantapur. These
studies have shown that average annual runoff is
typically 2% to 15% of average annual rainfall
and highly dependent on such factors as: soil
type, slope, land use and/or vegetative cover and
presence of in-field soil and water conservation
measures. Although average annual runoff figures
are low, it must be emphasised that runoff
resulting from individual or sequences of rainfall
events will often be much higher. Runoff will also
tend to be relatively high from small plots or
from certain features in the landscape (e.g. rock
outcrops, roads, urban areas, areas of hard pan
etc.). However, it is the annual average runoff
figure that provides an indication of the scope for
developing additional surface water resources at
any given point in a watershed.
Table 9 summarises runoff findings from
micro-watershed experiments that were carried
out by CSWCRTI (Bellary) at off-station
locations. The information from Chinnatekur
is particularly relevant because this experimental
watershed is located in Kurnool District
approximately 40 km from Dhone. It can be
seen from these findings that mean annual
runoff as a percentage of mean annual rainfall
is less than 10% regardless of the nature of the
land use or land surface conditions. It can also
be seen that runoff is relatively lower from
forested areas and from agricultural areas that
have received soil and water conservation
treatment.
Table 9. Summary of runoff from two
experimental micro-watersheds
4.3 Impact of water harvesting
on patterns of water availability
and use
For centuries, tanks have played an important
role in maintaining rural livelihoods in the semiarid
areas of South India. Until recently, they
provided a reliable source of water for irrigation
and, in many cases, they helped recharge shallow
aquifers that met drinking water needs during dry
seasons and periods of drought. As has been well
documented elsewhere, a shift towards centralised
government contributed to the breakdown of
traditional management systems as government
departments took responsibility for decisions and
tasks that had originally been the responsibility of
local people and/or elites. As a result of relatively
recent state government policy, most tanks in the
two study mandals have been converted into
percolation tanks (i.e. sluices have been blocked
and surface water is no longer released for
irrigation in the command area).
In recent years, people in the study mandals
have observed a reduction in both inflows to
many tanks and the frequency of spillage or
surplusing. In discussions, the reasons that are
often given for these changes are: i) A decline in
rainfall and ii) Deforestation in the tank
catchment area. Neither of these explanations is
convincing because: i) There has not been a
measurable decline in rainfall and ii) Although
deforestation has taken place, this occurred before
the phenomena of reduced inflows was observed
and, in any case, deforestation is more likely to
increase tank inflows.
Using the methodology described in Section
2.8, the impacts of water harvesting on five
traditional tanks systems were assessed. Chapari
and Yapadinne tanks are located in Kalyandurg
and Dhone respectively, whereas Gundlur,
Inchigeri and Anabur tanks are located in northeast
Karnataka in areas with similar agro-climatic
conditions to the study mandals. Physiographic
information relating to the tanks and their
catchment areas can be found in Table 10.
Experimental Mean No. Runoff (% mean annual rainfall)
watershed annual of
rainfall years Forest Treated Untreated Barren
(mm) Catchment agricultural Catchment area
Catchment
Chinnatekur 501 5 2 5 9
G R Halli 569 7 - 2 - 9
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