Penggunaan beberapa metode untuk prediksi laju endapan sedimen di Waduk PB Jendral Sudirman

DARMONO, Prof.Dr.Ir. H. Sudjarwadi, MEng

2001 | Tesis | S2 Teknik Sipil

Pengukuran sedimentasi wad& dengan metode echo sounding memerlukan biaya yang cukup mahal. Penelitian ini bertujuan mengkaji beberapa metode laii meliputk (1) penggunaan tabel Muddock, (2) metode Brune, (3) analiiis model, (4) pemilihan rumus empiris angkutan dasar, dan (5) tinjauan erosi lahan. Beberapa metode yang dikaji dimaksudkan untuk mengetahui sejauhmana laju endapan sedimen di wad& iJerdasar hitungan dengan rumus dan tingkat penyimpangaunya terhadap hasil pengukuran echo sounding. Sedangkan tinjauan erosi lahan dimaksudkan untuk mengetahui besarnya Sediment Delivery Ratio (SDR) dan tingkat erosi dari Daerah Aliran Sungai @AS) yang bersangkutan. Lokasi penelitian adalah DAS dan Waduk PB Jendral S u d m di Banjarnegara. Analisis dilakukan berdasar data sekurader, mencakup: (1) data pengukuran echo sounding, (2) data debit sediijnen suspemi, (3) data inflow, outjZow, dan kapasistas waduk, (4) data konsentrasi sedimen inflow dan outj7ow, dan (5) data penunjang. Hasil penelitian menunjukkan bahwa dengan menggunaan tabel Maddock nilai yang tendcur dengan echo sounding dapat didekati dengan anggapan bahwa sedimen dasar sebesar 229% dari sedimen tmspensi. Rumus empiris angkutan dasar yang paliig sesuai diterapkan di daerah penelitian adalah Meyer-Peter- MuZZer FIPM). Penerapan metode analisis menggunakan model yang dikembangkan dalam penelitian ini dim metode Brune memperoleh laju endapan sedimen pertahun sebesar 4,298 juta m3 dan 4,117 juta m3 dengan tingkat penyimpangan terhadap hasil pengukuran echo sounding masing-masing sebesar 3,3% dan 8,2%. Sedangkan tinjauan erosi lahan memperoleh nilai SDR rerata sebesar 40,6% dan laju erosi mencapai 1803 ton/ha/tahun yang dapat diklasifikasikan pada kategori tingkat bahaya erosi berat (kelas IV).

Measurement of reservoir sedimentation by echo sounding is expensive. Some other methods are tried in this research and among them are: (1) the use of Maddock table, (2) the Brune method, (3) the analysis using a model, (4) the selection of empirical formula for bed load transport, and (5) formula for surface soil erosion. Those methods have been studied to find out the rate of sediment disposition in the reservoir and to find out the discrepancy comparing with data obtained by echo sounding measurement. Then the application of surface soil erosion is used as an approach to calculate the Sediment Delivery Ratio (SDR) and to identifl the erosion level in the watershed. The research location are watershed and PB Jendral Sudirman reservoir at Banjarnegara, of central Java. The analysis is based on secondary data, comprise: (1) the data of echo soundq measurement, (2) the data of suspended load discharge, (3) the data of inflow, outflow, and reservoir capacity, (4) the data of inflow and outflow of sediment concentration, and (5) the supporting data. Using Maddock table, the result of this research shows that the value fiom echo sounding measurement can be approximated by an assumption that the bed load is 229% of the suspended load. The most appropriate empirical formula for this area is Meyer-Peter-Muller (MPM). The use of model developed in this study find out that the yearly rate of sedimentation is 4.298 million m3. While the formula of Brune give the rate of 4.1 17 million m3 annually. Their deviations fiom echo sounding measurement are 3.3% and 8.2% respectively. Using surface soil erosion formula reveals that the average SDR is 40.6% and the erosion rate is 180.3 ton/ha/year. It can be classified into the category of heavily critical erosion (at class IV).

Kata Kunci : Sedimen Waduk, Computation method, reservoir sedimentation, Jendral Sudirman Reservoir