Hydrodynamic Analysis at The Confluence of The Mahakam River and The Karang Mumus Tributary

  • A. Nur , D. A. Suriamihardja, M. A. Thaha, M. P. Hatta
Keywords: Tidal levels, Currents, Salinities, and Numerical Modelling.

Abstract

This study aimed to model the distribution pattern of water masses by considering the upstream discharge and the tidal elevation downstream. The method of this study carried out field observations as inputs required in numerical simulations. The field observations covered upstream discharge of Mahakam River and two-position of tidal levels, a river mouth of Mahakam River, and the river mouth of Karang Mumus. Upstream discharge is obtained about 83.74 m3/s by measuring the current velocity and cross-section of the river on July 25, 2018. The tidal measurements have conducted for 15 days from July 14 to 28, 2018 (1-15 Dzulqa'dah 1439) in two-position of observations, namely Muara Pegah and the lower reaches of the Karang Mumus River. The former position has a tidal range of 192.42 cm, and the latter is 114.32 cm. There were 12 positions along the Mahakam River to measure salinity covered the results in the range of 28 to 0.05 PSU (practical salinity unit). Along the Karang Mumus River, 22 positions to measure salinity covered in 0.14 to 0.03 PSU. The currents and salinities in the Mahakam River have been distributed as maps by numerical simulations using mike21 software. Comparison between observed maps and numerical simulations give a good agreement by validation error of 6.14 % in Mahakam River mouth (Muara Pegah), and lower reaches of the Karang Mumus River of 3.41% and 6.6%. The seawater turned brackish, detected 14 km from the open sea at a high tide during the spring tide. Horizontal spatial distribution of salinity for SE-1 ranges 28 to 18 PSU as far as 5.2 km, SE-2 12 to 18 PSU as far as 7 km, SE-3 10 to 12 PSU as far as 9 km, and SE-4 4 to 10 PSU as far as 14 km from the open sea. Further far from the open sea, SE-5 was nearly freshwater. Well-mixed in the SE-3 area was caught 6.5 to 9.8 km from the open sea during spring and neap tides. High salinity causes the suspended load to flocculate until it falls into bedload. So, it is known the appearance of bars from the spatial distribution of horizontal salinity. On the other hand, the salinity intrusion persisted at the confluence of the Mahakam River and the Karang Mumus tributary, which is 60 km from the open sea. The minimum value was in the range of 0.065 to 0.240 PSU, but the minimum salinity value is essential in research for early warning of future floods because freshwater affects salinity.

Published
2021-09-01
How to Cite
A. Nur , D. A. Suriamihardja, M. A. Thaha, M. P. Hatta. (2021). Hydrodynamic Analysis at The Confluence of The Mahakam River and The Karang Mumus Tributary. Design Engineering, 5186-5202. Retrieved from http://www.thedesignengineering.com/index.php/DE/article/view/3918
Section
Articles