DESAIN BENDUNGAN SOJOMERTO DI DAERAH BUKAN CEKUNGAN AIR TANAH (Design of Sojomerto Dam on the Non-Groundwater Basin Area

Abstract

Sojomerto adalah salah satu desa di Kecamatan Gemuh, Kabupaten Kendal, yang memiliki karakteristik hidrogeologis berupa daerah Bukan Cekungan Air Tanah. Air sungai kebanyakan berasal dari lepasan interflow daripada aliran air tanah. Lapisan tanah yang mampu menampung air hanyalah lapisan vadose dan lapisan root zone, dengan kondisi ini rawan terhadap kekeringan dan banjir ketika hujan hanya menjadi aliran permukaan saja. Pada tanggal 20 mei 2010 terjadi banjir di Sungai Blukar. Akibat dari banjir ini beberapa infrastruktur kecamatan-kecamatan di Kendal mengalami kerusakan, seperti jalan dan jembatan. Bendungan Sojomerto diharapkan mampu menangani masalah banjir dan kekeringan di daerah ini. Bendungan Sojomerto merupakan bendungan urugan tanah yang didesain dengan debit banjir rencana periode ulang 100 tahun dengan kapasitas sebesar 477 m3/detik. Volume tampungan sebesar 3,52 juta m3 diharapkan bisa memenuhi kebutuhan air. Material timbunan bendungan menggunakan tanah dari daerah lain, karena tanah disekitar lokasi memiliki sifat ekspansif. Wilayah berupa daerah Bukan Cekungan Air Tanah harus memiliki upaya konservasi lahan yang baik dan berkelanjutan, karena keberadaan dari lapisan tanah paling atas sangat penting bagi keberadaan air. Potensi interflow akibat infiltrasi hujan masih bisa diandalkan apabila daerah tangkapan pada wilayah ini masih terjaga dengan baik. Pembanguna Bendungan Sojomerto sangat bermanfaat bagi kelestarian dan keberlangsungan sumber daya air. Kata kunci: Bukan Cekungan air Tanah, interflow, bendungan urugan tanah, banjir rencana, kekeringan, tanah ekspansif, konservasi. vii DESIGN OF SOJOMERTO DAM ON THE NON-GROUNDWATER BASIN AREA By Candra Purna Saputra and Wahyu Widayanto ABSTRACT Sojomerto is one of the village in Gemuh District at Kendal Regency, which has hydrogeological characteristics of the Non-Groundwater Basin Area. The river water most come from interflow discharge rather than groundwater flow. Soil layer that is able to storage the water were Vadose or root zone only, so with this conditions prone to flooding and drought when it precipitations just a runoff. Dated 2010 May 20th, there were floods in Blukar River. Due to flooding there are some of Kendal District's infrastructure is damaged, such as roads and bridge. Sojomerto dam is expected to solve the problem of flooding and drought in these area. Sojomerto dam is an earth fill dam which designed to design flood by 100 years of return period for 477 m3/second. Storage volume of 3.52 million m3 is expected to meet the water requirements of the area. Dam’s embankment material use soil from another areas, because soil around the site have an expansive characteristics. The regions which has non-Groundwater Basin characteristics must have a good deal about the sustainable land conservation, because the existence of the top soil layer is very important for the availability of water. Interflow potential due to infiltration of precipitation can still be relied upon if the catchment area in this area is well preserved. Construction of Sojomerto Dam very beneficial to the preservation and sustainability of Water Resources. Keywords: Non-Groundwater Basin, interflow, earth fill dam, design flood, drought, expansive soil, conservation.