Abstract
The Benanain Watershed is located in East Nusa Tenggara with an area of 3,181 km2 and is divided into 29 sub-watersheds. The East Nusa Tenggara itself is an eastern region of Indonesia with a unique climate condition called semi-arid. The high rainfall intensity occurring in short duration results in large surface runoff and erosion. Floods and erosion in semi-arid areas due to sensitive soils to drought and heavy rainfall extremely. This paper presents the application of the Soil Conservation Services-Curve Number (SCS-CN) real-flood flows through a digital map of soil type, land use, topography, and the heterogeneity of physical condition, especially for ungauged watersheds. The method used is an approach empirical to estimate runoff from the relationship between rainfall, land use, and soil hydrology groups. This watershed has a large area that must analyze every sub-watershed. The land-use of the Benanain watershed is secondary dryland forest by 44.26% and the hydrological soil group on the B group classification with medium to high absorption potential by 46.502% from the total area. The curve number value of the Benanain Watershed ranges from 56.54 to 73.90, where the mean CN value of 65.32. The rainfall (mm) for the 29 sub-watersheds in the Benanain Watershed has decreased by about 74.65% when being surface runoff or only 25.35% of water becomes surface runoff. The relationship between rainfall depth and CN is classified as standard response and trend line (flat slope) equilibrium occurs when rainfall depth value of 56.71 mm and CN is close to 66.30. The high variability of intense rainfall between the rainy season and the dry season had a significant influence on the curve number value in a large watershed area. Further analysis will be more accurate if it is supported by long rainfall data and observation runoff data as a control. Doi: 10.28991/cej-2021-03091711 Full Text: PDF
Highlights
A semi-arid region is an area that receives lower rainfall compared to potential evapotranspiration
This study aims to determine a Curve Number (CN) value based on a hydrogeological map diversified to the hydrologic soil group map and check its applicability to the ungauged watershed such as in the Benanain Watershed
The hydrological soil types in the Benanain watershed has classified into 19-types with three levels of permeability, namely, moderate to high permeability, moderate to low permeability, and low to very low permeability consisting of Hydrologic soil group (HSG) B, HSG C and HSG D
Summary
A semi-arid region is an area that receives lower rainfall compared to potential evapotranspiration. This semi-arid region covers 31% of the world's [1]. The climate in East Nusa Tenggara (NTT) is of type D with the rainy season (average of monthly rainfall > 200 mm) that occurred between 3-4 months [2]. The characteristic of semi-arid regions is the evapotranspiration is much greater than precipitation, and the intensity of rainfall is very high during the rainy season. The land surface temperature affected land use, land cover, vegetated areas, water resources, etc. East Nusa Tenggara which has semi-arid conditions, is affected by the land surface temperature
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