Impacts of land cover dynamics and shallow groundwater abstraction on sustainability of Hakwatuna Oya irrigation system

I P S K Pelpitiya,E R N Gunawardena,N D K Dayawansa

doi:10.4038/tar.v27i1.8150

I P S K Pelpitiya, E R N Gunawardena + Show 1 more

Open Access

https://doi.org/10.4038/tar.v27i1.8150

Copy DOI

Journal: Tropical Agricultural Research	Publication Date: Apr 5, 2016
Citations: 2	License type: cc-by

Affiliation: University of Peradeniya

Abstract

Deforestation, expansion of agriculture and over abstraction of groundwater in watersheds can influence the water yield. Hakwatuna Oya watershed area in Deduru Oya basin also faces a similar situation due to rapid land use/cover changes and associated impacts. This study was conducted to identify the land use change dynamics and their possible impacts on the inflow to the Hakwatuna Oya reservoir. Land use mapping was done using 1:50,000 topographic maps and Landsat TM, ETM+ and OLI satellite images of 1994, 2003 and 2014 and the changes were assessed using GIS. Measured pump discharges rates and duration of pumping was used to calculate the total groundwater abstraction per month based on the average hours of irrigation and the duration of cultivation. Secondary data on rainfall, evaporation, reservoir storage and water issues were used to calculate the inflow using a water balance study. Assessment identified that forest, home gardens and agricultural area changes are the most prominent during 1986 to 2014. Proliferation of agro-well irrigation was observed as a result of agricultural activities with an agro-well diffusion of 71/100 farmers and agro-well density of 110/km2 of agricultural land area; exceeding the recommended value of 100/km 2 . No statistically significant change was observed in reservoir inflow with time. Although the temporal changes of reservoir inflow was not statistically significant, even a slight reduction of inflow can have a considerable impact to the farmers due to sensitivity of water availability for agriculture. Therefore, it is important to manage the watershed area of Hakwatuna Oya to preserve the ecosystems and to maintain the water yield for the sustainability of the downstream irrigation system.

Highlights

Reservoirs are mostly built in dry areas for storing water to prevent wastage and increase availability during non rainy periods
Land use/cover dynamics in Hakwatuna Oya watershed area Hakwatuna Oya watershed has been subjected to changes since the period of reservoir rehabilitation in 1960s (Samaranayake, 2011)
Plantations and agricultural lands are scattered in other places of the watershed

Summary

Introduction

Reservoirs are mostly built in dry areas for storing water to prevent wastage and increase availability during non rainy periods. They are mainly used to support agricutural production by providing irrigation water (Abeysinghe et al, 2005; Biemans, et al, 2011). River runoff and direct rainfall occur during rainy season are the main sources of water stored in these surface reservoirs to be used during dry season (Güntner et al., 2004). Some of these reservoirs are built for hydropower generation, to reduce discharge variability, for improved navigation and other users (World Commission on Dams, 2000; International Commission on Large Dams, 2007). Climate change contributes to reduce the inflow to surface reservoirs, and simultaneously increases the requirement for irrigation water in the downstream (Van Oel et al, 2008)

Methods

Results

Conclusion