Peak Discharge in Jemelak Subwatershed, Sintang District

Abstract

Jemelak Sub Watershed is close to the junction of two big rivers, i.e., Kapuas and Melawi. Therefore, this location faces environmental issues such as a flood. To avoid its possible damages, information on peak discharge becomes critical, particularly in calculating the drainage structure. This study was aimed to predict the peak discharge in this area using a rational method. The maximum daily rainfall data from 1998 to 2017 were divided into two periods of 10 years and analyzed. In the first period, maximum rainfall rangesfrom98.6 to 176.3 mm, while the second period fluctuates from67.6 to 190 mm. Analysis of land cover described that 43.97% of secondary swamp forests turned into shrubs and swamp shrubs in the first period. Furthermore, about 800.71 ha of secondary swamp forest tuned into 582.80 ha of bare land, 181.04 ha of a plantation, and 36.88 ha of swamp shrubs in the second period. About 95.15% of shrubs were also turned into agricultural land mixed with shrubs in the second period. The result showed that the changes in the maximum daily rainfall and land cover simultaneously affected the improvement of the peak discharge by about 2.53% in the first period and 28.30% in the second period. If the peak discharge exceeds the river capacity, then the local flooding will occur along the river border. Keywords: land cover, peak discharge, rainfall, Jemelak

Investigation on Impact of Changes in Land Cover Patterns on Surface Runoff in Ayung Watershed, Bali, Indonesia Using Geographic Information System

“…The runoff coefficient was calculated by overlaying maps of the four parameters following the methods proposed by Risky et al (2017), Auliyani andNugrahanto (2020), andSudaryatno et al (2020). The data were analyzed using a quantitative descriptive research method.…”

“…The scores for each category for four parameters were assigned based on the Cook's scoring system that has been widely applied to calculate the runoff coefficient (C) (Indriatmoko and Wibowo, 2007;Auliyani and Nugrahanto, 2020;Sudaryatno et al, 2020).…”

“…The geographic information system (GIS) is a tool for analyzing the changes in the land cover and runoff coefficient, using the QGIS 3.20 software with a manual digitization method. The runoff coefficient can be calculated by Cook's method using the physical characteristics of the watershed: land cover, infiltration rate, slope of land, and drainage density (Auliyani and Nugrahanto, 2020). Obtaining the runoff coefficient by combining the physical characteristics of the watershed is a very effective method that uses limited data for mapping flood risk areas, and has yielded satisfactory results in several studies (Mahmoud et al, 2014;Asare-Kyei et al, 2015;Mousavi et al, 2019).…”