STUDY ON THE IMPACT OF THE SIKAMBING-BELAWAN FLOODWAY IN MEDAN CITY ON FLOOD CONTROL AND RIVER MORPHOLOGICAL CHANGES

• Main Author: Jul Fachri, Fiqih
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/87255
• Institution: Institut Teknologi Bandung

From 2022 to 2024, flooding occurred in Medan City, primarily caused by the overflow of the Sikambing River during periods of heavy rainfall. To address this issue, the construction of the Sikambing-Belawan Floodway was implemented as a flood control measure for the Sikambing River. On the other hand, the performance of the floodway in conveying discharge from the Sikambing River is influenced by the discharge occurring in the Belawan River. To evaluate the performance of the floodway, hydrological and hydraulic analyses were conducted using 2D HEC-RAS modeling under flood conditions with return periods of 25, 50, and 100 years. The 2D HEC-RAS modeling can analyze the impact of the Belawan River discharge on the flow of the floodway in reducing flood discharge, flood inundation area, flood depth, and the timing of flood events occurring in the Sikambing watershed. The analysis results indicate that the floodway can divert flood discharge from the Sikambing River by 30,69 m³/s under Q25 conditions, 33,05 m³/s under Q50 conditions, and 34,65 m³/s under Q100 conditions, with the maximum influence of the Belawan River flow extending up to 36,51 m from the floodway outlet. Overall, the Sikambing-Belawan Floodway can reduce average flood discharge by 21,79%, decrease the average flood inundation area by 48,75%, shorten the average flood event duration by 35,56%, and reduce flood depth by up to 0,21 m. Two additional solutions analyzed for flood control, namely the addition of levees and retention ponds, can further mitigate flooding comprehensively up to Q100 conditions. Furthermore, a sedimentation study using 1D HEC-RAS modeling was conducted, highlighting that the box culvert of the spillway and the floodway inlet require special attention, with sedimentation needing to be normalized by 3,319.93 m³ for 1 year, 4,853.57 m³ for 3 years, and 5,907.46 m³ for 5 years. Additionally, sedimentation occurring over a 5-year period in the box culvert of the floodway spillway reached a thickness of up to 0,82 m, while sedimentation in the floodway inlet box culvert reached 0,55 m.