Unjuk Kerja Alternatif Pengendalian Banjir Batang Anai dan Batang Kandis Sumatera Barat

ERIZA, Corri, Dr. Ir.Istiarto, M.Eng

2008 | Tesis | S2 Teknik Sipil

Hampir setiap tahun terjadi banjir akibat luapan Batang Anai dan Batang Kandis. Tahun 2001 dilakukan perencanaan pengendalian banjir kedua sungai tersebut yang tertuang dalam Anai-Kandis River Improvement dengan alternatif pengendalian banjir berupa penanganan terhadap alur seperti perbaikan dan pelebaran tampang sungai, dan alternatif untuk mengurangi debit puncak seperti pembuatan dam atau retarding basin. Unjuk kerja alternatif pengendalian banjir dilakukan terhadap 3 alternatif berdasarkan ketersediaan data. Alternatif 1 mensyaratkan perbaikan alur dan pelebaran tampang (dengan tanggul) dikedua sungai serta penambahan Floodway di Batang Kandis. Alternatif 2 serupa Alternatif 1 kecuali peniadaan tanggul di Batang Anai dan tambahan pintu air di Batang Kandis. Alternatif 3 untuk Batang Anai serupa Alternatif 2 dan tampang disepanjang Batang Kandis diperlebar. Analisis mencakup analisis kecukupan alur dalam mengalirkan debit rancangan dan analisis transpor sedimen untuk alternatif dengan unjuk kerja terbaik, yang keduanya dilakukan dengan alat bantu software HEC-RAS versi 4.0 Beta. Pengendalian banjir berupa perbaikan alur dan pelebaran tampang di sepanjang alur Batang Anai dan Batang Kandis (Alternatif 3) memberikan unjuk kerja terbaik dibandingkan alternatif lainnya, karena mampu mengalirkan debit rancangan Q50 (1471 m3/s) di Batang Anai dan Q25 (293 m3/s) di Batang Kandis. Simulasi transpor sedimen di Batang Anai dengan aplikasi Alternatif 3 memperlihatkan trend terjadinya erosi dan deposisi terbesar berturut-turut di lokasi sebelah hilir Jembatan Nasional (RS 108) dan tepat di hilir RS 108 yaitu RS 107.

Nearly every single year, flood is happening due to the fact of the floatation of Batang Anai and Batang Kandis. In the year of 2001 local authority made a plan to control the flood in both rivers, which was implemented in Anai-Kandis River Improvement with the alternatives of controlling flood by handling the river courses, such as improving and widening the river channel, and decreasing the peak of discharges by making dams or retarding basin. Performance of flood control structures are made of three alternatives based on the information gathered. First alternatives suggest for repairing the river course and widening the river channel (with levee) in both rivers and floodway in Batang Kandis. Second alternative is similar with the first alternative except negation the leeve in Batang Anai and replenishment of floodgate in Batang Kandis. Third alternative for Batang Anai is identical to the second alternative and also widening the river channel throughout Batang Kandis. The analysis includes the analysis of sufficiency of channel to drain the design discharge and sediment transport analysis for the alternative with the best performance, which both could be doing with auxiliaries of Software HEC-RAS version 4.0 betas. As the result, controlling river by repairing the river course and widening the river channel throughout Batang Anai and Batang Kandis (3rd alternative) gives the best performance comparing to the others alternatives, due to the fact that it could be able to canalize the design discharge of Q50 (1417 m3/s) in Batang Anai and Q25 (293 m3/s) in Batang Kandis. The simulation of transport sediment in Batang Anai with the 3rd alternatives implementation shows the biggest trend of erosion and deposition in a row, located next to National bridge downstream (RS 108) and precisely in downstream of RS 108 i.e., RS 107.

Kata Kunci : Banjir sedimentasi,Perbaikan alur,Erosi, Flood control stuctures, Sufficiency of channel, Erosion and deposition