Morphometry Analysis of Sedayu Mountainous Catchment Areas from Detailed Aerial Photos

Abstract

Morphometric analysis is a powerful tool to understand the hydrological process quantitatively and the main requirement to determine the hydrological characteristics of a watershed. Morphometric analysis to determine the drainage characteristics of the Sedayu River Sub-watershed, Semaka District, Tanggamus Regency, Lampung Province was carried out using Digital Elevation Model (DEM) data. The primary data used is aerial photography using drones, the location of aerial photos representing watersheds of concern. The catchment area morphometrics were obtained from the extraction of the morphometric characteristics of the combined DEM data from the mountain watershed and the analysis of topographic maps by using ArcGIS software. Based on reports over a period of time, at several points in the area there are frequent river floods that overflow during heavy rains. Morphometric analysis in flood-prone areas with high rainfall is needed. The morphology of the Sedayu area has contrasting variations consisting of several gentle alluvial plains, some of which are Bukit Barisan hills with varying slope variations. The Sedayu watershed in this study is divided into 3 sub-watersheds, namely: sub-watershed A, sub-watershed B, and sub-watershed C. However, only sub-watershed A is the focus of morphometric analysis because its longest river, record flood disasters, landslide records, and has upstream to residential. Morphometric analysis was carried out on parameters such as watershed area (A), watershed length (Lb), main river length (Ln ), watershed width (W), drainage density (Dd ), bifurcation ratio (Rb ), and circularity ratio (Rc ). The results of morphometric calculations are the length of the watershed 4.82 km, the length of the main river is Sub-watershed A 8.996 km, the width of the watershed 0.686 km, and watershed area 4.861 km2 Based on these results can be calculated drainage density (Dd ) 2.719 km/km2 which means Sub-watershed A of a rough type with the inundated surface, permeable sub-soil, and resistant to erosion. Bifurcation ratio (Rb ) is 3.333 which means sub-watershed A has a rapid rise and fall in floodwater. Then, the circularity Ratio (Rc ) 0.32 which means Sub-watershed A is elongated so that the peak discharge and decrease flow quickly and causes a link with the hydrological response of rainfall-runoff. The results of this morphometric characteristic analysis are the right reference for planning strategies for soil erosion control and soil conservation.