Degree of Erosion of Small Water Impounding Projects’ Watersheds in Cagayan Valley: An Assessment

Abstract

Small Water Impounding Projects (SWIPs) play a vital role not only in increasing agricultural production
but also in flood control. However, soil erosion decreases storage capacity and lessens the economic life of these
SWIPs. This research aimed to assess the degree of soil erosion of 19 SWIP watersheds in Cagayan Valley. The overall
methodology was done by integrating Modified Universal Soil Loss Equation (MUSLE) and Geographical
Information System (GIS) to calculate the annual erosion rate of these sites considering the parameters: rainfall, soil
type, topography, land use, and conservation practice. GIS data layers including rainfall erosivity (R), soil erodibility
(K), slope length and steepness (LS), cover management (C), and conservation practice (P) factors were computed to
determine their effects on average annual soil loss in the study sites. As a result, it was found out that 12 SWIP
watersheds assessed – four from Cagayan, three from Isabela, four from Nueva Vizcaya, and one from Quirino –
possess extreme high erosion (greater than 100 tons/ha/year). In addition, four SWIP watersheds possess very high
erosion (25-100 tons/ha/year), while three SWIP watersheds possess moderate to high erosion (10 -25 tons/ha/yr).
Thus, to lessen the soil loss and the deposition of sediments on SWIP reservoirs with very high and extremely high
erosion rate, human, financial, and physical support from the National Government Agencies, Non -Government
Organizations, Local Government and SWISA is urgently needed to prolong SWIP economic life. Furthermore, the
research output should serve as baseline information for watershed planning, development, management, and policymaking.