Modeling the Slippage of Mount Merapi Cold Lahar Flow Due to the Placement of Non-Permanent Broad-Crested Weir Structures Downstream of the Pabelan Bridge

The flow pattern that occurs in rivers due to the descent of cold lava often causes damage in various areas. This phenomenon is inseparable from the volume of water mixed with volcanic material flowing through the open channel, which results from input water supply or water storage passed by cold lava. Hydrology researchers study the water mixed with volcanic eruption material that remains on higher ground. River flow is influenced by the riverbed surface profile and varying river widths. When given a certain volume with specific viscosity, a dense flow may form, which can be observed on the water surface, while the denser viscosity underneath the surface remains invisible to the naked eye. If the runoff of cold lava material in these channels is not measured, it can lead to uncontrolled jumps. The structured form of such uncontrolled and dense jumps can be observed through the resulting flow patterns. To prevent undetected flow patterns, hydraulic measuring structures are needed, one of which includes a weir with a bottom opening—known as flow over a weir—along with surrounding bridge structures. This sluice gate is easy to operate, even manually. However, estimating water operat