ON THE PLANGWOT- SEDAYU LAWAS FLOODWAY CHANNEL IMPROVEMENT PROJECT LAMONGAN DISTRICT

• Main Author: Ulya Nur Utari, Khoirunisa
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/62676
• Institution: Institut Teknologi Bandung

One of the problems that occur in the Bengawan Solo watershed is the high flood discharge from upstream, causing flooding downstream, especially in Lamongan Regency and Gresik Regency. In order to anticipate this, BBWS Bengawan Solo is working on Plangwot-Sedayu Lawas Floodway Capacity Improvement from 640 m3/s to 1000 m3/s. This research was conducted to examine the effect of inlet gate additon to Bengawan Solo River flood discharge reduction and floodway ground changes. The analysis was carried out by modeling the existing operating manual with 3 (three) inlet gates (capacity 640 m3/s) and 5 (five) inlet gates (capacity 1000 m3/s). The flood modeling uses 50 years return period flood discharge, while the ground changes modeling uses the generated flow discharge using Sacramento Model. The modeling was carried out using Hec-Ras 5.0.7 software. Based on the results, it was found that the peak discharge of the 50-years return period of the Bengawan Solo River downstream was 4191.70 m3/s. Simulation using 3 (three) inlet gates shows that the flood discharge peak can be reduced to 3628.94 m3/s (reduced by 13.43%). For the simulation using 5 (five) inlet gates, it shows that the flood discharge peak can be reduced to 3298.6 m3/s (reduced by 21.31%). In the upstream and downstream sections of the floodway, erosion tends to occur with a maximum erosion of 2.02 m at Sta. 7+900 while the middle section tends to sedimentation with a maximum sedimentation of 1.03 m at Sta. 2+800. Erosion is caused by the slope of the channel on the upstream and downstream sections which tend to be steeper. The total sediment that comes out of the floodway to the estuary is 21.8 thousand tons/year. The sedimentation rate in the floodway watershed is classified as poor (>5 mm/year) with values between 583-817 mm/year.