A simplified geospatial model to rank LID solutions for urban runoff management.

Studies have shown the usefulness of low impact development (LID) in runoff management in urban areas; however, there is a limited number of systematic decision-making models for ranking LID solutions (i.e., the location and type of LID required). This research proposes a physics-based GIS Multi Criteria Decision Making model (GIS-MCDM), which we refer to as the LID Solution Evaluation and Ranking ApproacH (SERAH). This model integrates the hydrological and socioeconomic-environmental benefits of LID with the subcatchment-level demand of LIDs - this has been traditionally overlooked in previous research. Specifically, SERAH integrates key the contributing criteria, including LID benefits, cost, feasibility, and subcatchment demand to rank LID solutions. To demonstrate the applicability of SERAH, a highly urbanized catchment in Toronto was used as a case-study and three types of LID: rain gardens, infiltration trenches, and porous pavements were considered. The hydrological performance of the ranked solutions was estimated using the stormwater management model, PCSWMM. The resulting LID ranking from SERAH corresponded to the best hydrological performance and LID co-benefits. Runoff volumes were reduced by 8.9-11.3%, and peak runoff values were reduced by 1.3-19.9% compared to the base scenario. The infiltration trench was ranked the highest in 16 of the 19 subcatchments where the cost was identified as a key factor. For the remaining three subcatchments, the rain garden was ranked the highest due to its socioeconomic-environmental benefits outweighing the higher cost. The effect of different rainfall durations, frequencies, and temporal patterns on the performance of the highest-ranked LID solution suggested that LID provide higher performance (runoff volume reduction) in more severe events. SERAH is useful for strategic planning for sustainable infrastructure. Future research is needed to better quantify the socioeconomic and environmental benefits of LID to improve SERAH.