STUDY OF ENVIRONMENTAL FLOW IN UPPER CITARUM RIVER

• Main Author: Chumaedi, Irpan
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/81225
• Institution: Institut Teknologi Bandung

Changes in river discharge characteristics due to anthropogenic activities have a direct impact on all living things that depend on the river. Aside from humans, the river is a place for living aquatic ecosystem that need to be preserved. From a hydrological perspective, mitigation of the minimum need for water in this river has been stated in the form of an "environmental discharge" or "maintenance discharge", one of the methods suggested in PP No. 38 of 2011 is Q95. However, this method is only based on the minimum river discharge requirement, regardless of the response of the ecosystem in it. The aims and objectives of the study were to find out how much the discharge characteristics (discharge gap) changed in the upstream Citarum river, to identify the conditions of the ecosystem and to obtain the most optimum discharge probability and river hydraulic characteristic to accommodate existing ecosystem needs. In this research, three approach methods were used, namely: the hydrological approach, the hydraulics approach, and the optimum ecosystem conditions approach. For hydrological analysis, calibrated discharge simulation modeling at the PDA Nanjung was carried out at 8 (eight) sampling point locations along the Upper Citarum River, both from instantaneous discharge conditions, Q90, Q95, and Q97.5 conditions. These discharge values are then used as input boundary conditions for hydraulic modeling to obtain hydraulic characteristics such as velocitt and depth at each sampling location. Next, the optimum conditions of the identified ecosystem species are compared with hydrological and hydraulic parameters to conclude whether the existing environmental conditions are still in optimum conditions for the growth and development of the representative ecosystem species. The gap discharge was carried out for three observation year periods (2004-2009, 2010-2015, and 2016-2022). The results show that in PDA located upstream (Majalaya) there is a tendency to decrease discharge from January to April by 10.9%. For the period from May to August and September to October, there was a tendency for discharge to increase by 56.5% and 39.4%. The average maximum discharge at the Majalaya PDA decreased by 13.8%, while the average minimum discharge increased by 175.2%. In the downstream PDA (Nanjung) discharge conditions tended to increase from January to April by 16.8%, the period from May to August also experienced an increase of up to 6.3%. Likewise, the period from September to December experienced an upward trend of up to 27.9%. When compared with the average rainfall around the PDA location, the value of rainfall that fell did not change significantly. Thus, the land cover factor is an indication of an increase in river discharge but with almost unchanged rainfall characteristics. The results of the hydrology and hydraulics analysis show that from the 8 sampling point locations the Q95 discharge value varies from 0.002 m3/s in the upstream (Situ Cisanti) to 6.31 m3/s in the downstream (Nanjung). The flow velocity also varies from 0.007 m/s to 0.54 m/s. Likewise, the water depth in the river is from 0.17 m to 2.0 m. Ecosystem identification was carried out on 8 types of ecosystem around the upper banks of the Citarum River at 8 sampling locations. Found 126 ecosystem sampling types of plants (54%), benthos (13.5%), insects (10.3%), fish (9.5%), birds (3.2%), amphibians (1.6%), reptiles (0.8%), and molluscs (7.1%). Of the 12 types of fish found, 8 types (66.7%) were non-local species and the remainder (33.3%) were local species. By comparing the study with 2012 at the same location, it was concluded that the local fish ecosystem that was still found was the Wader Fish (genus binotatus). The optimum condition of the representative ecosystem at each sampling point is then compared with hydrological and hydraulic aspects. As a result, there are 4 locations whose environmental aspects are met for the growth and development of existing fish with several different discharge percentages. These locations are Cihawuk with Q90, Bojongsari with Q88, Rancamanyar with Q95, and Nanjung with Q97.2. For other locations, water velocity that is too slow causes the growth and development of fish ecosystem to be less than optimal.