Influence of budget allocation and design rainfall intensity on cost-effective LID strategy for urban flood mitigation

The use of combinations of low-impact development (LID) measures is more effective than the individual measures in mitigating runoff under different design storms. The runoff reduction rate (3R) of LID measures is mainly influenced by budget constraints and the intensity of design storms. These factors ultimately influence the determination of optimal combinations. In this study, a cost-effective approach was developed to determine the optimal LID combinations for maximizing the 3R under constrained construction budgets and design storms. The proposed approach was applied to 31 urbanized subcatchments within a mixed land use basin in South Korea. As a result, the cost-effective LID combinations achieved total runoff reduction rates ranging from 9 % to 39 % and peak runoff reduction rates from 17 % to 43 % under 10-, 30-, and 50-year design storms. In the final combination results, retention-based measures such as bioretention cells and raingardens were assigned higher weights under generous budget conditions, whereas infiltration-based measures such as permeable pavement and infiltration trenches were prioritized under low budget conditions. Furthermore, as the intensity of the design storm increased, the runoff reduction performance of individual LID measures decreased, resulting in different combinations even under the same budget conditions. The findings of this study offer valuable insights for establishing effective stormwater management plans within urban subcatchments and emphasize the influences of constrained LID construction budgets and design storm characteristics on determining cost-effective LID combinations.