STUDY OF CAPACITY OF DELI RIVER IN MEDAN CITY, WITH THE FRAMEWORK OF FLOOD CONTROL PLANNING

• Main Author: Rezki Uli Simanjuntak, Indi
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/68252
• Institution: Institut Teknologi Bandung

The total length of the Deli River is ± 72 km, of the Deli River Basin (DAS) area is ± 472 km2. The located of Deli River is at the foot of Mount Berastagi in Karo Regency, and its downstream empties into the Malacca Strait. Based on previous studies, data on the Deli River flood was recorded as having a fairly serious flood problem. The flood inundation area that occurred was in the city of Medan. The heart of Medan City which is crossed by the Deli River is the cause of flooding. The flood inundation areas recorded include the sub-districts of Medan Polonia, Medan Baru, Medan Maimun, and Medan Barat. Floods in the city of Medan occurred due to the narrowing of the Deli River or siltation so that its capacity was only able to accommodate 272,669 m3/s equivalent to a 2-year return period of rain discharge. The capacity of the Deli River in Medan Polonia District is ± 207.335 m3/s, Medan Maimun District is ± 242.913 m3/s, Medan Baru District is ± 255.954 m3/sec, and West Medan District is 272.836 m3/sec. So that when the discharge exceeds 272,669 m3/sec, the Deli river will overflow and flood. However, the standard of the Deli River that crosses the city according to the regulations of the river PUPR must be able to accommodate the discharge at the 25-year return period. Therefore, the Deli River control planning is carried out using the planned flood discharge at the 25- year return period, which is 329,226 m3/s. Deli River hydraulic using HEC-RAS 6.1 for modeling, starting from the upstream to the outlet point of the flood event, with a catchment area of 250.01 km2 along ± 45 km. The results of the HEC-RAS search with flood discharge on a 25-year return period show the inflow discharge is 349,226 m3/s and the outflow discharge is 322,200 m3/s, meaning that the inflow to outflow hydrograph is only able to reduce peak discharge by ±10%. The peak time (Tp) inflow is 4 hours to outlet 5 hours, so the time difference is only 1 hour, meaning that with only 1 hour, the community is not enough to mitigate flooding of the occurrence. Therefore, the flood that occurred in Medan is categorized as sudden, so people must be aware or alert. Alternative countermeasures that can be carried out through structural efforts include: building parapets or embankments on the right and left sides of the river, normalizing the river to enlarge the existing river, and also constructing a retention pond. In this study, flood control modeling in Medan was carried out by constructing a parapet or flood control wall. The yield of parapet height required during the 25-year return period flood discharge is 1 m to 4 m high. During the 5- year return period, the height of the parapet required is 0.5 m to 1.5 m. Flood discharge at the 10-year return period required parapet height is 0.5 m to 2.5 m. The construction of a parapet or flood control wall is also required for a guard height or freeboard as the purpose of the guard height is to prevent the overflow of water level from rising to the river bank. The height of the guard or freeboard in this modeling is 0.5 m (minimum) to 1 m (maximum).