Vol. 4, Issue 1, Part A (2022)

The purpose of this research is to model the flow pattern of water masses by considering the upstream discharge and the tidal elevation downstream. The research activity is conducting field observations as inputs needed in numerical simulations. Field observations included the upstream discharge of the Mahakam River and the ebb and flow of the Karang Mumus river estuary. The results showed that the tides at the confluence of the Mahakam River and the Karang Mumus River had mixed tidal types, which tended to be double daily. The current pattern at the confluence of rivers is strongly dominated by currents from the Mahakam River. Upstream one-way flow occurs at high tide and two-way downstream flow occurs when the tide is low. The two-way flow is caused by the slowing flow when the Mahakam River flows into a dam on the downstream flow of the Karang Mumus River which will come out.