Lesti集水區位於印及爪哇島東部，面積為380平方公里。Lesti集水區流量為下游水資源需求之主要來源，然而集水區常受當地降雨之高度時間與空間變異性影響，流量呈現劇烈之年間變化，嚴重影響下游水資源之供應穩定度。有鑑於此，本研究嘗試提升上游集水區水文狀況之掌握程度，以增加下游水資源供應之效率與穩定程度。 本研究利用Lesti上游集水區之地下水位位線波動推估集水區之地下水出流量，並結合 AVSWAT ( Arc View Soil Water Assesment Tool)模式得到集水區之出流量。地下水位線波動是由Lesti集水區中4水井所測得，可獲得季節與年際之地下水位波動情形，用以推估集水區地下水出流量。而集水區中水井觀測資料顯示，2007年年際變化幅度為2800mm至5700mm，2008年變化幅度為3900mm至4700mm，2009年變化幅度為3200mm至5100mm，2010年變化幅度為2800mm至4600mm。而根據以上觀測結果，2007年之地下水出流推估量為736 mm，2008年之地下水出流推估量為820,9 mm，2009年地下水出流推估量為786,7 mm，2010年地下水出流推估量為306,4 mm，相關係數R-square大於0.7。而在本研究中2007年至2010年中Dv(%)則維持在23.32%-55.3%之間。 Upstream Lesti Watershed is one of the major watershed of East Java of Indonesia and it covers about 380,93 Ha. The basin has enough water resources to meet current demands but there are many challenges including high spatial and temporal variability in precipitation during one year. Good understanding of the water condition is very necessary to know the effect on streamflow of the Lesti river in each sub basin. This study investigated the contribution of sustainable management water resources in the Upstream Lesti Watershed by prediction the recharge of groundwater using water table fluctuation especially in dry season which can cooperating with the performance of the AVSWAT program ( Arc View Soil Water Assesment Tool) model by comparing observed streamflows with simulated streamflows at outlet. The water table fluctuation method from 4 well was used in the Upstream Lesti Watershed to evaluate the seasonal and annual variations in water level rise and to estimate the groundwater prediction (deep aquifer). The results show that annual water level rise with a range of 2800 mm - 5700 mm in 2007 3900 mm - 4700 mm in 2008 3200 mm – 5100 mm in 2009, and 2800 mm – 4600 mm in 2010. Based on standard values of specific yield and the measured water level rise, the prediction from area weighted that occur in sub basin 39 outlets in 2007 amounted to 736 mm in 2008, amounted to 820,9 mm in 2009 amounted to 786,7 mm, and the lowest was in 2010 are equal to 306,4 mm. Also, the correlation coefficient has a direct positive relationship range 0,7 < R <1 in the while Dv (%) in this study the smaller values of Dv were satisfied with the range of 23.32% - 55.3% in 2007 - 2010.
