Development and Performance Evaluation of Rainfall-Runoff and Soil Sediment-Measuring Instrument

During the rainy season, people experience floods, soil erosion in the uplands, and soil pollution in the lowlands caused by sediment from runoff flowing into the coastal area. Runoff happens when the rate of rainfall is higher than the rate of soil infiltration or when the soil is already saturated, and when the depth and rate of rainfall exceed infiltration, surface runoff occurs. The depth of rainfall was already monitored by the national weather monitoring agency. However, the depth (volume) of runoff in each area is still unmonitored, and even the volume (weight) of soil sediments carried by this surface runoff has not been evaluated and measured. The study objectives were to develop a rainfall-runoff and sediment-measuring instrument, evaluate the depth of runoff every rainfall-runoff event, and assess the volume of soil sediment caused by the rainfall-runoff event. This study was conducted at the Bataan Peninsula State University – Abucay Campus, Bangkal, Abucay, Bataan, Philippines (North 14°44'28.4" East 120°27'6.7") from October 2023 to October 2024. The type of soil in the study area was Antipolo clay (vertisols). The developed instrument was fabricated and calibrated. The instrument has a sediment and runoff trough 10x10x50 centimeters in dimensions. The runoff measuring device was attached to it upon overflowing of the trough. Since the repairs were corrected, it was evaluated. Instruments were laid out in 30, 25, and 18 percent land slope with a length of 15 meters and 100 percent vegetation. Environmental parameters like rainfall, temperature, humidity, and wind were considered in the study. The runoff depth of every rainfall event observed and monitored was significantly higher in the steeper slope area using the instrument. Concurrently, soil sediments eroded using the instrument were higher than using the revised universal soil loss equation in the steeper areas at 25 and 30 percent slope. The developed instrument was portable and could easily be carried and used by researchers, environmental planners, and policymakers in gathering rainfall-runoff depth and volume of soil sediments eroded.