A synthetic unit hydrograph model based on fractal characteristics of watersheds

Abstract

ABSTRACTSynthetic unit hydrograph (SUH) is one of the rainfall-discharge transformation models that are still popularly used today primarily for estimating flood discharge for water resources planning and management. The advantage of this model is that it is able to estimate the discharge based on the sequence of time in an occurrence of rainfall, and thus the correlation between time and discharge in the form of hydrograph can be obtained. The fundamental weakness of SUH is that they are likely to produce deviations for watersheds that do not have the hydrological characteristics similar to the watersheds used as the basis for the model’s development. These deviations are estimated as a result of the assumptions used to establish the concept of unit hydrograph and the complexity of the factors affecting hydrograph, particularly the nature of rainfall and watershed characteristics that are not accommodated in the model, including fractal characteristics of watersheds that are considered highly influential on the formation of a hydrograph. This research was conducted at eight watersheds in Central Sulawesi-Indonesia to develop and construct an SUH model. The model was constructed by using some parameters based on a combination of main fractal and morphometric characteristics of a watershed. This research successfully formulated a peak time equation (Tp) as a function of the length of the main stream (L), the ratio of stream length (RL) and the density of stream network (D) with a determination coefficient (r2) of 99.8%, a base time equation (Tb) as the function of area of a watershed (A) and slope of main stream (S) with a determination coefficient of 98.2%, a peak discharge equation (Qp) as a function of peak time and a simple single curve equation derived from Gamma Distribution Equation. The validation of SUH models at eight watersheds in Central Sulawesi shows that all the main hydrograph parameters evaluated showed a very good performance.