Abstract:
The primary use of many lowland reservoirs in Sri Lanka is to supply of water for
irrigation, and inland fishery has become a secondary use. In the present study, four
irrigation reservoirs in the Kala Oya river basin, namely: Dewahuwa, Kala Wewa,
Siyambalangamuwa and Usgala-Siyambalangamuwa were selected to investigate the
optimum water requirements for irrigation, fisheries and other small-scale economic
activities such as livestock farming and brick making. A cross section (from year
2014 to 2015) of household heads (n=756) adjacent to the four reservoirs were
interviewed to gather information on their degree of dependence on reservoir water
for those multiple uses. General Stochastic Production Frontier Model was employed
to evaluate the technical efficiency of water uses for various economic activities, and
to quantify the volume of water that can be saved through more efficient uses. Water
poverty index (WPI) was estimated to investigate accessibility and availability of
water for multiple uses. Water valuation and optimum level of water allocation
between uses were then calculated based on Marginal Value Product (MVP). The
results indicated that the highest technical efficiency of water uses was for fisheries
followed by livestock farming, rice farming and brick making, mainly due to nonconsumptive
use of reservoir water for fisheries. The lowest WPI was in Dewahuwa
reservoir situated in the upper region of Kala Oya river basin followed by Kalawewa,
Usgla-Siyambanagamuwa and Siyambalangamuwa, which were located in the lower
regions of the river basin where water uses for irrigation and other consumptive uses
are much higher. In terms of MVP, the value of product for a unit of water use was
higher for livestock farming and brick making. However, these economic activities
are less significant compared to agriculture and fisheries. As such, this analysis
highlights the need for concerted action of reservoir water management through
cooperation between irrigation and fisheries authorities.
