Effect of Slope on Infiltration Capacity and Erosion of Mount Merapi Slope Materials

Abstract

Infiltration which occurs on slope has a specific behavior that can be parameterized. One of the reasons is because the slope generates less ponding on the sloping soil surface. This condition affects infiltration rate and surface runoff proportion of water from any kind of rainfall distribution in time. Since surface runoff tends to be higher, erosion rate is also to be higher on slope. The slope steepness is the most important parameter of a slope. In this study, the effect of slope steepness on infiltration capacity and erosion rate of Mount Merapi bare slope material were tested in a laboratory using rainfall simulator. Three values of slope steepness of 36%, 47%, and 58% were used. The rainfall intensity was set constant and was found has rate of 116,312 mm/hour. The infiltration rate was measured by volumetric balance principle and the erosion rates were measured by collecting the eroded grains at the downstream end tank. Infiltration rate was evaluated by using Horton method and the average erosion were analyzed from the eroded grain data for each test. After fitting the recorded infiltration rate data to the Horton equation, the infiltration capacity was obtained. The results were the relationship between slope steepness and the affected the infiltration capacity and erosion for each test. Infiltration capacity is found to increase and the decrease with the increase of slope steepness while erosion rate is found to increase on the steeper slope. The increase of erosion range is between 15% to 33% for each 1o increase of slope steepness. In addition, polynomial and exponential equations were developed to express the relationship between slope steepness and infiltration capacity and also the erosion rate.