WATERSHED MANAGEMENT PRIORITIZATION IN PADDY LAND USES: A CASE STUDY IN HUNGAMALA ELA SUB-WATERSHED IN MAHAWELI BASIN

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 prioritize watersheds for management. Hungamala Ela sub-watershed of Mahaweli River Basin was selected for this study. Stream network, stream order and micro-watersheds were extracted from Digital Elevation Model derived from 20 m contour interval using Hydrology toolset in ArcMap. 14 micro-watersheds namely HE1 to HE14 could be delineated for the selected sub-watershed. The spatial data needed for morphometric analysis were derived from ArcGIS. Linear aspects viz stream order, stream number, bifurcation ratio, stream length ratio, stream frequency, drainage density, drainage texture and length of overland flow and areal aspects viz basin area, perimeter, length, form factor, circulatory ratio and elongation ratio were calculated at micro-watershed level adopting the methods given in the scientific literature. Watershed prioritization was done by ranking and getting a compound value from those estimated linear and areal aspects of morphometric parameters. Paddy land uses were analyzed for 2003, 2012 and 2020. The results of the morphometric analysis revealed that Hungamala Ela has a 7th order stream network with a dendritic drainage pattern. The results of watershed prioritization revealed that HE6 falls under very high priority category and HE5, HE7, HE8 and HE9 fall under high priority category for soil erosion susceptibility. Moreover, paddy land uses have increased 83% from 2003 to 2020 drastically even in the identified sensitive micro-watersheds. Therefore, proper soil conservation measures are needed to be adopted by planners and policy makers for sustainable paddy cultivation especially, within the identified highly sensitive five micro-watersheds in Hungamala Ela sub-watsershed of the Mahaweli River Basin.