STUDY OF FLOOD AND SEDIMENTATION CONTROL OF THE BABON RIVER IN SEMARANG CITY

• Main Author: Jaya Putra Manurung, Eko
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/71450
• Institution: Institut Teknologi Bandung

The Babon River has quite high sedimentation so that the channel capacity is reduced. The Babon River is getting aggradation due to the low slope of the river bed. This results, thereby reducing the channel capacity of the Dolok Penggaron River System. The Babon watershed (DAS) is one of the watersheds in Central Java which is located on the northern slope of Mount Ungaran. Babon watershed covers areas of Semarang Regency, Semarang City, and Demak Regency. The location of this study starts from the upstream of the Babon River in the Pucang Gading Dam, Demak Regency to the downstream of the Babon River in Genuk District, Semarang City along 16.3 Km. This study creates the calculation and analysis of flood discharge and assesses the impact of sedimentation on changes in the morphology of the Babon River. There are 2 geometric data used, namely during the initial year where sedimentation has not occurred and the geometry after sedimentation has occurred for 10 years. Simulation of sedimentation uses daily discharge data of Babon River which is simulated for 1 year and 10 years while flood modeling uses flood discharge with a return period of 25 years, both of which are influenced by tides in the downstream part. River bed material data is also included in the model to simulate sediment transport. Furthermore, changes in river morphology will be obtained in the form of degradation and aggradation of the river bed. All modeling is conducted with the HEC-RAS 6.1 program. The results of the flood modeling show that there is flood runoff along the Babon River, especially in the upper and middle parts. Modeling was also carried out for extreme conditions with the Kanal Banjir Timur (KBT) is closed which resulted in increased runoff due to additional discharge from the upstream of the Penggaron River. The highest runoff occurs in the upstream with an average runoff as high as 2.5 meters. Sedimentation simulation results show that for 10 years the Babon River has sedimentation with an average of 63,000 tons every year and the total sedimentation that occurs is 636,892 tons/10 years. With the addition of this sedimentation, there is an increase in the elevation of the riverbed which has an impact on the higher runoff that occurs. The next is modeling floods when the Q25 discharge comes from upstream and still limited by tides with the latest geometry in downstream, namely the condition of the Babon River after being sedimented for 10 years. From the modeling results, it was found that there was an increase in the height of the runoff to 3.177 meters at Sta 13,550. This ascent occurs along the Babon River at varying elevations. The average height of sedimentation that occurred for 10 years is 0.782 meters. This result cause an increase in the flood water level with an average elevation of 0.194 meters. The presence of sedimentation in the Babon River results in morphological changes that reduce the capacity of the Babon River. From the modeling results was concluded that there was a reduction in river capacity due to sedimentation for 10 years with bankfull discharge conditions from 137.64 m3/s to 127.3 m3/s.