Analisis Efektivitas Flushing Pada Bendungan Panglima Besar Soedirman Melalui Drawdown Culvert (DDC) untuk Mengatasi Sedimentasi
FITRIANA GALUH PUTRI PANGESTIKA, Muhammad Sulaiman S.T., M.T., D. Eng.
2024 | Tugas Akhir | D4 TEKNIK PENGELOLAAN DAN PEMELIHARAAN INFRASTRUKTUR SIPIL
Sedimentasi
menjadi permasalahan kompleks Waduk Mrica yang berdampak pada umur layanan
waduk. Hal ini akibat alih fungsi hutan menjadi lahan pertanian dan lahan
terbangun yang menyebabkan laju erosi meningkat. PT PLN IP telah melakukan flushing
melalui Drawdown Culvert (DDC) sejak tahun 1992 untuk mengatasi
sedimentasi, namun jumlah tampungan efektif masih berkurang setiap tahunnya.
Tujuan penulisan tugas akhir ini untuk menganalisis keefektifan pelaksanaan flushing
pada Waduk Mrica.
Analisis
dilakukan dengan membandingkan hasil hitungan kuantitatif flushing
efficiency (Fe) dan flushing feasibility (Ff)
dengan hasil pengamatan proses flushing dan pengolahan data
merujuk Surat Edaran Ditjen SDA Nomor /SE/D/2017 Tentang Pedoman Penilaian
Kinerja Bendungan.
Berdasarkan hitungan parameter Fe
diketahui pelaksanaan flushing 2020-2023 rata-rata volume air keluar
saat flushing (Vo) sebesar 616.122 m3, rata-rata
volume sedimen keluar saat flushing (Vso) sebesar 29.191,63 m3,
rata-rata berat sedimen yang keluar keluar saat flushing (Wso)
sebesar 39.625.959 kg, rata-rata konsentrasi sedimen keluar saat flushing (Co)
sebesar 49 kg/m3, rata-rata debit air masuk harian (Q) sebesar 151 m3/s,
rata-rata volume air masuk ketika flushing (Vi) sebesar
524.321 m3, rata-rata volume sedimen masuk saat flushing (Vsi)
sebesar 2.888 m3, rata-rata berat sedimen yang masuk saat flushing
(Wsi) sebesar 3.745.431 kg, rata-rata konsentrasi sedimen masuk saat
flushing (Ci) sebesar 4 kg/m3, dan rata-rata
volume sedimen mengendap (Vd) sebesar 17.512 m3. Hasil
analisis Fe ketiga metode di Waduk PB Soedirman pada tahun 2012-2014
didapatkan rata-rata 0,61 dan untuk tahun 2020-2023 didapatkan rata-rata 0,37.
Hal ini menunjukan penurunan keefektifan pelaksanaan flushing pada 4
tahun terakhir ditinjau dari nilai Fe. Nilai Ff melampaui batas persyaratan parameter uji awal Sediment
Balance Ratio (SBR) dan Long Term Capacity Ratio (LTCR). Namun,
nilai Flushing Width Ratio (FWR) belum memenuhi syarat kriteria, hal ini
menunjukan luasan cakupan flushing masih kurang efektif
dalam menggelontorkan sedimen. Hasil analisis
diharapkan menjadi bahan evaluasi pelaksanaan flushing dalam menjaga
laju sedimentasi dan segera dilakukan penormalan pintu DDC lalu dilakukan
perhitungan ulang nilai Fe dan Ff setelah pintu DDC
diperbaiki untuk menilai efektivitasnya.
Sedimentation is a complex
problem in the Mrica Reservoir which has an impact on the reservoir's
endurance. This is due to the land conversion from forest to agricultural and buildings
which causes the increase rate of erosion. PT PLN IP has carried out flushing
through DDC since 1992 to overcome sedimentation, but the effective storage is
still decreasing every year. The purpose of writing this final assignment is to
analyze the effectiveness of flushing in Mrica Reservoir.
The analyze is by comparing the results
of quantitative calculations of flushing efficiency (Fe) and flushing
feasibility (Ff) with the results of observations of the flushing
process and data processing referring to the Circular Letter of the Directorate
General of Natural Resources Number /SE/D/2017 concerning Guidelines Dam
Performance Assessment.
Based on the Fe parameter
calculation, it is known that the implementation of flushing in 2020-2023, the
average volume of water discharged during flushing (Vo) was 616,122
m3, the average volume of sediment discharged during flushing (Vso)
was 29,191.63 m3, the average weight of sediment discharged during
flushing (Wso) was 39,625,959 kg, the average concentration of
sediment discharged during flushing (Co) was 49 kg/ m3,
the average daily inflow of water (Q) was 151 m3/s, the average
volume of water discharged during flushing (Vi) was 524,321 m3,
the average volume of sediment discharged during flushing (Vsi) was
2,888 m3, the average weight of sediment discharged during flushing
(Wsi) was 3,745,431 kg, the average concentration of sediment
discharged during flushing (Ci) was 4 kg/ m3, and the
average volume of sediment sedimentation (Vd) of 17,512 m3.
The results of the 2020-2023 Fe analysis was 0.037 compared to the
2012-2014 Fe of 0.061, there was a decrease in the effectiveness of flushing
in the last 4 (four) years. The Ff value exceeds the limits of the
initial Sediment Balance Ratio (SBR) and Long Term Capacity Ratio (LTCR) test parameter requirements. However, the Flushing Width Ratio (FWR) value does not meet the criteria requirements,
indicating that the flushing coverage area is still less effective in flushing
out sediment. The results of the field survey showed physical and functional
damage to the building. It is hoped that the results of the analysis will be
used as material for evaluating the implementation of flushing in maintaining
the sedimentation rate and immediately normalizing the DDC door. And also
recalculating the Fe and Ff values ??after the DDC door
has been repaired to assess its effectiveness.
Kata Kunci : sedimentation, flushing, reservoir, flushing effectiveness
