Flood Assessment of Catchment Areas and Drainage Networks with Aggregate Quarrying in Angono, Rizal using GIS and Remote Sensing John Mclien Venadas
University of the Philippines Diliman
Abstract
Rizal Province consists of high-elevated and low-lying areas, with the latter being critically affected by floods during typhoons including the municipality of Angono. With an average of 20 typhoons annually, floods are widely experienced due to multiple contributing factors including the amount of rainfall, topographic changes, drainage network blockages and disruptive human activities. At least two quarrying activities in Rizal Province, primarily for construction materials, have been ongoing for decades. The study evaluated the periods in 2000 and 2024 to assess the overall transformation brought by these activities and its effects on the changing environment. Quarrying sites delineation and catchment modeling were done to determine the flow direction and discharge patterns of the surface runoff using RS and GIS techniques. Then, two flood simulations were done using the LISFLOOD-FP model and Typhoon Enteng rainfall to determine the difference between the flood behavior of the two test periods. Elevation data, manning coefficient and boundary conditions were the main distinguishing parameters in the flood simulations. The results showed significant flooding at the sub-catchments due to the topographic patterns that served as temporary basin causing water accumulation, and at the low-lying areas that serve as the outlet points of the discharged and overflowed floodwaters of the high-elevated catchments after reaching their maximum capacities. Another finding suggests an inverse relationship between drainage network flood capacity and flooding in lowlands. This means that greater floodwater volume in drainage channels can correspond to smaller flooded areas with reduced depths at the outlet points. This occurs because the drainages also serve as sub-catchment areas, lowering flood depths in low-lying areas and slowing the flood depth increase. However, in drainage networks with very steep slopes, water flows more quickly, leading to greater accumulation in receiving areas and potentially higher flood depths.
