Riverbed degradation in Progo River had caused the failure of Srandakan Bridge I, which is located in Bantul Regency, Yogyakarta Special Province, in April 2000. Simulations were performed to simulate the supercritical flow in one-dimensional model. As the velocity variation in the transverse are more important than the vertical direction, this work simulates the supercritical flow in two-dimensional depth-averaged using FESWMS module in the SMS software. Besides the river flow simulation, the pier scour depth was also predicted in FESWMS using CSU equations. The simulation shows that the existence of Srandakan Bridge I will not deepen the scour depth in Srandakan
Keywords: numerical simulation, FESWMS, pier scour
Problems in river hydraulic can be brought into either analytical or numerical solutions. Analytical solutions are more intellectually satisfying, but they are tend to be restricted to a simple boundary condition (simple geometry). Problems in natural channel are complex and require disproportional amount of effort to be solved analytically. Numerical method approximates the mathematical method or the analytical method in the form of computable set of parameters describing the flow at a set of discrete points using the finite element method.
Environmental Modeling Research Laboratory (EMRL) at the Brigham Young University has developed the SMS (surface water modeling system) software for a one-, two-, or three-dimensional hydrodynamic model in cooperation with the U.S. Army Corps of Engineers Waterways Experiment Station (USACE-WES), and the U.S. Federal Highway Administration (FHWA). The software includes the hydrodynamic models (RMA2, FESWMS, and HIVEL2D), water quality models (RMA4 and SED2D), and the coastal modelling (ADCIRC and CGWAVE).
This work introduces the FESWMS, which is applied as a hypothetic analysis of the local scour around Srandakan Bridge piers, which is located in Bantul Regency, Yogyakarta Scpecial Province, across the Progo River.
The scouring, the increasing traffic load, and the riverbed degradation had caused settlement of the two piers and failure of the three spans of Srandakan Bridge I in
April 2000. Bailey bridge was constructed above the failed spans keeping the two sides of the bridge connected. To prevent the worse effect of the riverbed degradation, the government built Srandakan groundsill in 2001-2003, and to accommodate the increase of traffic number, Srandakan Bridge II has been constructed since April 2006 to substitute Srandakan Bridge I.
The government predicted that the existence of Srandakan Bridge I would affect and deepened the local scouring around Srandakan Bridge II and they planned to demolish Srandakan Bridge I. The prediction has not been proven by the analysis and simulation performed in 2005. The simulation was undertaken using RMA2 in SMS and HEC-RAS software to compute the hydraulic parameters. The local scour around Srandakan bridges were then calculated using formulas according to CSU, Froehlich, Shen, Breuser, and Raudviki (Istiarto, 2006).
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