An Assessment of the Factors Affecting Flood Peak Discharge Reduction Due to the Retarding Basin

This research assesses the variables influencing flood reduction. The land use changes occur due to the residential demand and all supporting infrastructures and facilities. It is related to population increase, raising surface run-off and then resulting in flooding. The proposed methodology involves simulating various placements of retarding basins (RAk) and different maximum storage capacities (Vk) for several flood return periods (Qt). This research is conducted in the urban agglomeration area of Wonosari, Gunungkidul Regency, Daerah Istimewa Yogyakarta-Indonesia. The results show that the variable representing the maximum capacity of retarding basin (Vk) has a logarithmic relationship with the response of AQp, with a correlation value (R) of 0.7894 and an adjusted determination coefficient (adjusted R²) of 0.6207. In addition, the variable of the controlled watershed area ratio (Rak) has linear, quadratic, cubic, and quartic relations with AQp, with the average correlation value being 0.4563 and the average adjusted determination coefficient (average adjusted R²) being 0.2032. However, the variable of design flood for the T year-return-period (Qt) has the logarithmic correlation, with a correlation value (R) of 0.3987 and an adjusted determination coefficient (adjusted R²) of 0.1536. Finally, the three variables of Vk, RAk, QT have a multiple linear relationship with AQp, with the correlation value (R) being 0.7894 and the adjusted determination coefficient (adjusted R²) being 0.6207. These results are essential to support the reduction of flood peak discharge modeling.