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4.2 Surface water resources
Runoff at the regional and large
watershed scale
Analysis of gauging data from the Central
Water Commission (CWC) showed that annual
surface runoff, at the macro-watershed or basin
scale, is somewhat lower than is often reported
or than accepted wisdom would suggest
(see Table 8). With the exception of one river,
the Kunderu at Alladapalle, the average annual
runoff values are within the range 4-35 mm
which is equivalent to between 0.8 and 7.5% of
rainfall. The main reason for the apparent higher
runoff in the Kunderu is the fact that this river is
used for inter-basin transfer of Krishna River
water. The relatively low runoff values observed
at most gauging stations challenge the
widespread assumption that runoff in this region
is always in the range 30-40% of annual rainfall.
Although significant volumes of water can drain
into the Bay of Bengal during periods or years
with exceptionally high rainfall, in general,
runoff represents a relatively small loss from the
region.
The runoff figures presented in Table 8
agree with the low runoff values reported in the
KAWAD Water Audit Report (Batchelor et al.,
2000) for large watersheds. They are also
consistent with the characteristics of the area
(e.g. semi-arid climate, extensive development
of water harvesting structures).
Figure 28 compares annual rainfall and
runoff at the CWC Tadapatri gauging station
on the Pennar River. This figure shows the
considerable inter-annual variation in rainfall
and surface runoff and that there have been long
intervals of virtually no surface flow during this
25 year period (e.g 1990-1996).
Figure 29 compares monthly rainfall and
runoff at Tadapatri. In addition to indicating
levels of variability, this figure shows that on
average 80% of annual runoff occurs during the
three months September to November.
In conclusion, the main points from the
runoff analysis using CWC data are:
. Throughout southern Andhra Pradesh,
average annual runoff values at the large
watershed scale, in the absence of interbasin
transfers, are in the range 1% and
8% of average annual rainfall.
. Rainfall and runoff are extremely variable
both within and between years.
Coping with seasonality in surface water
availability and droughts and floods is
therefore a key issue.
. Although scope for further development
of surface water resources along with
regulation of river flows is possible in
some areas, the scale of this development
is much lower than suggested by some
GoAP programmes.
Check dam near Golla, Kalyandurg
Table 8. Average runoff and rainfall for
study catchments
River Average Average Average
annual runoff catchment annual runoff
(mm) rainfall (mm) (as % rainfall)
Chinnahagari at Amkundi Bridge 6 451 1.3
Vadavathi at Bhupasamudram 4 450 0.8
Hundri at Lakshmipuram 35 468 7.5
Pennar at Nagalamadike 12 573 2.0
Pennar at Tadapatri 28 551 5.0
Chitravathi at Singavaram/ Ellanuru 20 549 3.6
Kunderu at Alladapalle 133 617 21.6
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