THE CHARACTERISTIC OF WATERSHED MORPHOMETRY DATA FOR SUPPORTING THE MODIFICATION MODELING OF NAKAYASU SYNTHETIC UNIT HYDROGRAPH

Abstract

This research aimed to investigate the characteristics of watershed morphometry that affect the main parameter that forms the Nakayasu Synthetic Unit Hydrograph (SUH). The result is will support the modification modeling of Nakayasu SUH. The formulation of time like (in the Nakayasu SUH) itself consists of the physical characteristic such as the main river length (L) that is limited regarding the category of main river length such as L > 15 km and L < 15 km. Due to the specific characteristics of the Nakayasu SUH formulation, this research will focus on the development of the Nakayasu SUH formulation by modification by adding the watershed characteristic parameter to the time lag (tg). This research was conducted in the 23 watersheds in Indonesia, which have the Automatic Water Level Recorder (AWLR) and Automatic Rainfall Recorder (ARR). However, this research is conducted on the 7 morphometry and time lag data that are watershed area (A), the length of the main river (L), river slope (I), river density (D), the river length to the eight point of watershed (Lc), the factor of H (H = L.Lc), watershed perimeter (O = O), and time lag. The time lag of each watershed is analyzed using the straight line method; however, the watershed morphometry data is analyzed by using the software of ArcGIS and analyzing the river/drainage density and the factor of river length and river length to the weight point of watershed. The results show five morphometry variables that very influenced the time lag (one of the variables in the Nakayasu SUH model): A, Lc, H, L, and O. The other two variables are not affected by the time lag: D and K.