PENGARUH PERUBAHAN TATA GUNA LAHAN TERHADAP DEBIT BANJIR

Abstract

Bali as tourist destination has great impact to the change of land use. This is related to the development of tourism supporting infrastructures such as hotel, villa, restaurant and other facilities which are developed at strategic area with beautiful landscape. Generally in the area has mountainous area that is from upper course area to downstream and beach area. The impact of this development activity is the need of the area which is originally on open are and function as water absorption area, then changed into impermeable residential area. This condition has resulted toward the increase of surface run off which directly influence the flood discharge in the river. The discharge of flood due to the change of land use is calculated by using Rational Method. The Rational Method has three components i.e. coefficient of run off, C, rainfall intensity, I, and catchment area, A. The value of coefficient run off (C) is determined based on the condition of land uses. The result of flood discharge due to the change of land use from period of 1992 to 2000, at one of Sub Basin Tampus in Ayung Basin has resulted the trend of decrease of flood discharge 30,36 %. This concern is true as according to condition existing DAS Tampus. Explainable theoretically if with the same of rainfall value (analysis from year data 1992 - 2000) but with variation of land opening change therefore time from rain from farthest point to the observation point (tc) related also will change. In the consequence of increase of tc value thus with the same rainfall will causes the intensity of rainfall is decrease. Value of tc in DAS Tampus is increase which in the year 1992 = 116 minute become 121 minute in the year 2000, because of the process of land closing by vegetation that is the continuation of new cultivated area in location, so that the rain process to become the surface run off is more slowly. Keywords: discharge of flood, intensity of rainfall, coefficient of run off, and land use