THE IMPACT OF HYDRODYNAMIC FLOW INTO RIVERBED ALTERATION OF LOBAWANG RIVER, SITUBONDO

Abstract

Lobawang River situated in Situbondo regency. There was sand mining activity run by local villagers that causing riverbed degradation and was damaging of the retaining wall of Lobawang River. In this study, RMA2 and SED2D within Surfacewater Modeling System (SMS) were utilized to evaluate the water level, flow velocity and the sedimentation occurred in Lobawang River. The results of the simulation revealed that Lobawang River has undergone a change in elevation over a period of 25 years (1985-year 2010). This condition was due to the movement of the flow (hydrodynamic flow) triggered by the sedimentation and degradation processes of the entire sections. The maximum sedimentation value was occurred in section No.7 with an increase in the riverbed elevation of 1.55 m. Meanwhile, the deepest degradation occurred in section No.13 by 0.25 m. The degradation processes were continuously occurred in some areas downstream caused the damage of the retaining wall on the left side of the riverbank. The proposed countermeasure by groynes was examined. Results indicated the reducing flow velocities in the eroded area; causing degradation to turn into sedimentation. Finally, the erosion on the riverbanks of Lobawang could be minimized