Watershed Management Prioritization in Paddy Land Uses: A Case Study in Hungamala Ela Sub-watershed of Mahaweli River Basin of Sri Lanka

Abstract

Prioritization of watersheds is important for proper planning and management of soil and water resources for sustainable development. Morphometric analysis has been commonly used to for prioritization of watersheds for management. Hence, Hungamala Ela sub-watershed of Mahaweli Basin where paddy is grown extensively was selected for this study to identify and prioritize soil and water conservation in the sensitive areas via morphometric analysis and GIS based approach. Stream network, stream order and micro-watersheds were extracted from the DEM derived from the 20 m contour interval in the Arc GIS environment. The spatial data required for morphometric analysis were derived from Arc GIS tools. Watershed prioritization was completed following the methods proposed in published literature. Paddy land use analysis was carried out for 2003, 2012 and 2020. The results of the study revealed that 14 micro-watersheds, HE1 to HE14, could be identified within the Hungamala Ela sub-watershed area and its stream network extends up to the 7th order showing a dendritic drainage pattern. The results of watershed prioritization revealed that HE6, HE7, HE9 and HE11 fall under the high priority category for soil erosion susceptibility. Moreover, paddy landuses have increased drastically, by 83% from 2003 to 2020, even in the identified sensitive micro-watersheds. Therefore, the Hungamala Ela sub-watershed management should be prioritized by introducing proper soil conservation measures especially within the identified highly sensitive areas for sustainable paddy cultivation.