Spatial Modelling for the Calculation of River Capacity: Case Study Downstream Area of Wanggu River Kendari

Spatial modelling of flood-prone areas will provide maximum results if it is supported by the accuracy of the data acquired, mainly related to elevation data or the area’s topography. Spatial modelling generated from accurate topographic data can estimate the river’s carrying capacity. This study built a spatial model using data from aerial, terrestrial, and hydrographic surveys. Aerial surveys were conducted using UAV corrected by terrestrial surveys, GCP, and ICP. Testing the accuracy of the spatial model is carried out by comparing the results of current field velocity with the results of 2D Hec-Ras numerical simulations using a variation of the manning coefficient. The combination of aerial, terrestrial, and hydrographic surveys produces a cross-sectional spatial model of the river, which is used in calculating the river’s carrying capacity. The river’s capacity is calculated using a 2D numerical simulation method using Hec-Ras software and verified by a mathematical approach based on the flood hydrograph curve. The results showed that the horizontal accuracy of the GCP was 2.8 cm and the vertical accuracy was 6.5 cm. The results of testing the vertical elevation accuracy of aerial photographs on terrestrial topographic data measured in the field (ICP) have a Mean Absolute Percentage Error (MAPE) value of 5.81%. According to the spatial model, the manning roughness value is 0.06-0.09. The river’s capacity based on numerical simulations is 1.700.766 m3, and the results of the verification using a mathematical approach are 1.683.433 m3 with a difference of 1.02%.