Hydrograph separation method and baseflow separation using Chapman Method – A case study in Peusangan Watershed

Abstract

Base flow is the portion of stream that is not run off and results from seepage of water from the ground into a channel slowly over time. Base flow is considered to be the groundwater contribution to stream flow. Estimates of the amount of base flow can be derived from stream records. This study is about groundwater recharge condition at two sub watersheds in Krueng Peusangan: sub watershed of Lut Tawar and sub watershed of Teupin Mane (Krueng Teumbo). The Krueng Peusangan Watershed is one of priority for watershed management because this watershed is in a critical condition. The Krueng Peusangan Watershed is an important water catchment area in Aceh where there are one million people depend on life from the water source watershed, such as dringking water, agriculture, and fisheries. The Krueng Peusangan includes four regencies, an upstream Aceh Tengah, a midstream area in Bener Meriah and downstream area in Bireuen and Aceh Utara. This research aims to get groundwater recharge using Seasonal Recession Method and Base Flow Separation Method. Both of methods were used to estimate groundwater recharge for each peak in stream flow during the period of record (2008-2012). The results showed that the trend pattern of the stream hydrograph could be explained using the exponential function where the dots lowest discharge that is the end of the recession (y) than any period of time on stream hydrograph semi logarithmic (x). The regression formula for the watershed of Krueng Peusangan is: y=1.3x−0.12 (Lut Tawar - Wih Nareh) and y=1.94x−0.42 (Teupin Mane-Krueng Teumbo). The filtering method (Base Flow Separation Method) by Chapman (1999) gave a lower percentage of the low flow component (base flow) for Sub Watershed of Teupin Mane (Krueng Teumbo): 2008/2009 (18%), 2009/2010 (3%), 2010/2011 (1%), 2011/2012 (1%). For Sub Watershed of Lut Tawar (Wih Nareh): 2008/2009 (1%), 2009/2010 (1%), 2010/2011 (4%), 2011/2012 (1%). Estimates using the two methods define a reasonable range of the base flow contribution to stream flow in the watershed.