Effect of Selected Climatic and Physiographic Factors on runoff coefficient by using Rainfall Simulator

Abstract

The research investigates the impact of selected climatic and physiographic factors on the runoff coefficient using a Rainfall Simulator. The simulator comprises components such as a pan with dimensions of 3 feet by 2 feet and a soil sample height of 0.7 inches. Flat fan nozzles with spray angles of 65, 73, 80, and 110 degrees, operating at 3 to 6 bar pressure, are utilized alongside a 12-volt single-stage booster pump. The pump selection is based on pressure calculations, ensuring efficient nozzle operation. The experimental setup follows the rational method in the hydrology lab at Bahauddin Zakariya University, Multan, for runoff coefficient (C) estimation. The trials involve varying the location and intensity of nozzles over a mixture of soil and sandy soil scenarios. The result obtained shows that the average C value is 0.5 to 0.9 for mixture of soil(slit + clay + sand) with no crop when nozzle located up-stream, down-stream & mid of the pan of rainfall simulator and the C value for sandy soil is zero. In sandy soil, with nozzles at different positions, the runoff coefficient consistently equals zero, indicating high infiltration due to large pore spaces. When intensity of rainfall is double at the mid of the pan of rainfall simulator lead to increase runoff, erosion, and compaction, impacting soil permeability and potentially causing flooding. With single rainfall intensity, the soil experiences a more moderate impact, allowing for better absorption and reduced runoff, promoting soil health and minimizing erosion concerns at the up-stream & down stream pan of the rainfall nozzle. These findings provide valuable insights into the factors influencing runoff in simulated conditions.