Applying localized model in quantifying and valuing flood regulation service of loom river basin, Borongan City, Eastern Samar, Philippines

Date

6-2025

Abstract

This study assesses how forests in Samar Island Natural Park (SINP) regulate floods in the Loom River Basin, Borongan City, and quantifies associated economic benefits. Land cover and soil hydrologic groups were used from secondary data sources, and SCS-Curve Number (CN) values were calibrated against observed streamflow. The InVEST Urban Flood Risk Mitigation model simulated two scenarios, Baseline (existing SINP forest) and Degraded (forest replaced by cropland), for 5- and 25-year storms. Calibration achieved < 20 % relative error in 24-hour runoff. Under a 5-year storm, SINP headwaters recorded a mean Runoff Retention Index (RRI) of 0.962 (SD = 0.034) versus 0.869 (SD = 0.076) downstream (p=0.001). Forest degradation increased basin runoff volume by 4.5 % (p = 0.01 1) and lowered RRI by 0.27 % (p = 0.003). For a 25-year event, degraded conditions raised runoff by 56.6 % and reduced RRI by 7.13 % (both p < 0.001). Depth-damage functions and maximum damage values were localized using a market-price canvass and 84 depth--loss observations. Avoided Damage Costs (ADC) from preserving SINP forests amounted to PhP 2.55 M for a 5-year storm and PhP 35.03 M for a 25-year storm. Results highlight, albeit some model's simplications, forest ecosystem's cost-effective flood- regulation role; recommendations include headwater reforestation, integration of avoided costs into DRRM budgets, and refinement of hydrologic and damage-valuation methods.

Document Type

Dissertation

Degree

Doctor of Philosophy in Environmental Science

College

Graduate School (GS)

Adviser/Committee Chair

Nico C. Ancog

Committee Member

Patricia Ann J. Sanchez, Cristino L. Tiburan Jr., Margaret M. Calderon

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

En – AGROVOC descriptors

URBAN RUNOFF; FLOOD CONTROL; RIVER BASIN DEVELOPMENT; FOREST COVER; FOREST DEGRADATION; FOREST ECOSYSTEMS

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