Flow Behavior of Boyong River as Revealed by Long-term Hydro-monitoring System

Boyong River is one of many rivers originating from Mt. Merapi, flows across three autonomy administrative of Sleman Regency, Yogyakarta City, and Bantul Regency. The river experiences flood in the form of lava flow several times, and the 1994 and 2010 occurrences were considered the biggest ones along with the river history. In line with the rapid development of information and communication technology, efforts to develop the early warning system due to the Mt. Merapi disaster have been implemented by the Hydraulic Laboratory of Gadjah Mada University 2006. This paper presents the study results of Boyong River flow behavior by analyzing the data obtained from the monitoring system. The Gemawang Weir at Boyong River was selected as the river control point understudy; those include the catchment boundary, the catchment characteristics, and the hydraulic features. Monitoring equipment consists of an automatic water level recorder (AWLR), the flow visualization using a Brinno camera, and the hydrophone monitoring system. The flow hydrograph characteristics and its corresponding sediment transport rate are considered two parameters for identifying the flow behavior. The results show that the precursive and recession times of the flood hydrograph are about 1-3 hours and 3.5-5 hours, respectively.