Hydrologic Assessment on the Impact of Land Cover Change in the Streamflow of Davao River Basin using Hydrologic Modeling System

Rapid population growth and urbanization have led to changes in land cover, including the transformation of agricultural areas and forest land into built-up areas. This paper aimed to analyze and assess the impact of changing land cover on the streamflow of the Davao River Basin using Geographical Information System (GIS) and Hydrologic Modeling. The Davao River Basin watershed was created using the ArcGIS tool, allowing the stream and sub-basin boundaries to be constructed. The Hydraulic Engineering Center -Hydrologic Modeling System (HEC-HMS), a computer simulation software, was then utilized to simulate the rainfall-runoff and to develop the Davao River Basin's hydrologic model. The developed model was simulated for a one-year rainfall-runoff event using the daily rainfall data for 2003, 2010, and 2015. Parameter calibration was done by comparing simulated discharges from the model to the observed data of the Department of Public Works and Highways (DPWH). The discharge values obtained from the calibrated model were used to generate flood inundation maps to assess the extent of flooding and relate it to the change in land cover of the basin. Simulations show that an increase of 76.61% in built-up areas (from 2003 to 2010) resulted in a 53.45% and 64.04% increase in the maximum depth of flood for 50-year and 100-year return periods, respectively. Moreover, the 12.40% increase in built-up areas from 2010 to 2015 only increased 21.06% and 26.37% in the maximum depth. These findings show that the continuous increase in built-up areas and further reduction of agricultural and forest lands in the area resulted in the broader spread of floods and an increase in the maximum flood depth of the Davao River Basin. The findings of this study can help in the decision-making of stakeholders in balancing future development and watershed preservation.