EFFECTS OF THE UPPER WATERSHED LAND COVER CHANGES ON THE FLOOD REGIME OF THE RIVER BASIN IN TANAY, RIZAL, PHILIPPINES

Abstract

Flood and land cover change analyses were used to assess the dynamics of flood in the floodplains of Tanay River. Flood simulation was carried out using the derived hydrograph under different land cover scenarios to analyze the effects of land cover changes on the flood regime of the river basin in Tanay, Rizal. The model was calibrated using the measured
water depths and discharge of the river cross-section. Land cover analysis revealed that the watershed is predominantly covered by orchard plants and grasses with an approximate area of about 2286.68 and 1157.4 ha, respectively. Reforestation of the grasslands in the upper portion of the watershed can considerably reduce the volume of floodwater in the floodplains of the river. Flood simulation using the land cover of the area predicted the flood depths and delineated the spatial extent of flooding in the floodplains of the river. The total area that may be saved from flooding if the grasslands in the upper watershed are reforested is about 16.4 ha. About 12.4 ha is located in Barangay Plaza Aldea. The two major environmental adaptive measures that need to be done are the development of a comprehensive community-based rehabilitation and management of Tanay watershed and the protection of the remaining watershed of the area.