COMPARATIVE ANALYSIS OF THE EFFECT OF PARAPET WALLS AND PENTAPOD DYKES ON FLOOD CONTROL AND SEDIMENT TRANSPORT IN THE LAMONG RIVER, JONO VILLAGE SECTION

• Main Author: Humaidi
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/87213
• Institution: Institut Teknologi Bandung

The Kali Lamong Watershed (DAS) is part of the Bengawan Solo River Basin, located administratively in Lamongan and Mojokerto Regencies for the upstream section, and Gresik Regency and Surabaya City for the downstream section. The upstream area of the Kali Lamong Watershed is characterized by hilly topography with natural basins that serve as water catchments. This region consists mainly of young teak forests and agricultural land, including rainfed crops and tobacco plantations. Kali Lamong is categorized as an intermittent river, with significant discharge during the rainy season (November–April) and almost no base flow in the downstream section during the dry season (May–October). The river's cross-section is relatively flat and meandering, especially in the downstream areas between Jono and Gandong villages. Severe bank erosion occurs, particularly in the middle reaches, leading to a wider and flatter river cross-section, with an average width of 20 meters in the upstream section and 80 meters in the downstream section. Jono Village is one of the areas heavily impacted by flooding due to overflow from the Kali Lamong downstream section. The riverbed in this area experiences sedimentation, and the existing embankments are eroded annually during peak floods, causing the river to overflow into residential areas, farmland, and aquaculture ponds. Flood control efforts for Kali Lamong have been ongoing since 2013 and are expected to continue until 2024, including the construction of earth embankments, CCSP installation as retaining walls, and parapet walls. This study aims to analyze the impact of parapet wall construction on flood control and sediment transport in the Kali Lamong River and compare it to alternative flood control measures using Pentapod Dykes. The analysis was conducted using HEC-RAS 1D and 2D software. Input data included topographical or DEM measurements, discharge data, and sediment data. The modeling scenarios did not account for river regime stability, hydraulic structure stability, or social and economic issues. The modeling scenarios were divided into three parts: tidal modeling, flood modeling, and sediment transport modeling. Tidal modeling using Q2 and Q25 flood discharges revealed no tidal influence in the study location, as seawater only enters the river’s estuary due to high river discharge. Flood modeling analyzed the effectiveness of existing embankments, parapet walls, and Pentapod Dykes. The Q2 flood discharge simulation indicated that the existing embankments in the Jono Village section of the Kali Lamong River overflowed, while no overflow occurred with parapet walls and Pentapod Dykes at a top elevation of +5.3 meters. However, Q25 flood discharge simulations resulted in overflows in all scenarios. Sediment transport modeling aimed to analyze the impact of Q25 flood discharge on river morphology. The simulation of existing conditions showed sedimentation on the riverbed and erosion of the riverbanks. Simulations using parapet walls or Pentapod Dykes demonstrated sedimentation on the riverbed, with the planned embankments remaining safe from erosion, although sedimentation occurred on the embankment sides. The recommended flood management for the Lamong River suggests raising the embankment to an elevation of +6.41 m, considering the river's proximity to residential areas and Surabaya City. Additionally, the alternative use of pentapod dykes is proposed as an innovation to expedite fieldwork implementation and reduce project costs.