Hari Yuwono

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 ΔQp, 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 ΔQp, 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 ΔQp, 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.

This research aims to develop a model for flood peak discharge reduction (ΔQ_p) through the placement of retarding basins within a watershed system, represented by the area ratio of the controlled watershed (R_Ak) and the maximum storage capacity of the retarding basin (V_k). The area ratio of the controlled watershed (R_Ak) is defined as the ratio between the catchment area of the retarding basin and the total watershed area (A_k/A). The methodology involves simulating various retarding basin placements (R_Ak) and different maximum storage capacities (V_k) for several flood return periods (Q_T). This study was conducted in the urban agglomeration area of Wonosari, Gunungkidul Regency, Special Region of Yogyakarta, Indonesia. The placement and utilization of retarding basins result in varying levels of flood peak discharge reduction (ΔQ_p) at the downstream control point (Taman Pancuran), depending on the maximum storage capacity of the retarding basin (V_k) and its placement within the watershed (R_Ak). The resulting empirical equations for flood peak discharge reduction (ΔQ_p) using the retarding basin method are as follows: ΔQ_p = 0.105654 − 0.014593 V_k − 0.029251 R_Ak + 0.011089 Q_T for V_k values in the range (V₁–V₄) = 36.4–208.8 × 10³ m³, and ΔQ_p = 1.374989 − 0.003702 V_k − 0.338381 R_Ak + 0.004773 Q_T for V_k values in the range (V₄–V₂₀₀) = 136.2–7039.1 × 10³ m³. An observed anomaly was identified, where ΔQ_p became positive at small values of V_k and R_Ak, indicating an increase in peak discharge (Qp).