Storm water management model to evaluate urban inundation in Lowokwaru and Blimbing sub-catchments in the city of Malang

In the city of Malang, which is a highland area, there are still floods, including Blimbing and Lowokwaru sub-districts. One of the causal factors is the change of undeveloped areas becoming relatively large built-up areas in the Upper Brantas sub-watershed, from initially 20.5% in 2000 to 69.6% 20 years later. This change also impacts the transformation of irrigation canals that once irrigated rice fields, causing them to shift their function into drainage channels that carry runoff water toward natural channels (natural drainage). Consequently, the existing canal conditions cannot accommodate the runoff water. The research employed an approach that involved analyzing floodwater management models using the Storm Water Management Model (SWMM 5.1) and surveying existing canal data. The analysis results revealed that, within the studied areas of Blimbing Village and the Blimbing Catchment Area, 10 out of the existing 170 drainage channels were incapable of handling the discharge associated with rainfall intensities designed for return periods of 5 years (112.48 mm/day) and ten years (117.09 mm/day). In the Lowokwaru Catchment Area, it was evident that 18 out of the 216 existing canals experienced overflow events with designed flood discharge for 5-year and 10-year periods.