Abstract
Urbanization alters natural hydrology, leading to increased stormwater runoff volumes, higher peak flows during storm events, and greater pollutant discharge into local waterways. These changes are primarily driven by the increase of impervious surfaces that accompany urban development. However, unpaved urban surfaces also pose challenges. During heavy storms, sediment from unpaved surfaces is eroded and carried away, adding to pollutant loads in local waterways. In areas like alleyways, unpaved surfaces often become compacted due to traffic, which reduces their infiltration capacity. This compaction further increases stormwater runoff and peak flows, exacerbating sediment transport and pollution issues.
Low-Impact Development (LID) strategies, such as permeable pavements, provide effective alternatives to mitigate these impacts. This study focuses on the hydrologic benefits of permeable interlocking concrete pavers (PICP), particularly in urban alleyways. The study is based on the Dixieanne Clean and Green Alleys project, a pilot initiative by the City of Sacramento aimed at beautifying alleys in Old North Sacramento while improving stormwater management through the installation of PICPs.
A hydrologic model was developed using the EPA Stormwater Management Model (SWMM), incorporating 30 years of historical precipitation data from the Sacramento Executive Airport rain gage. The model simulated various scenarios, including different soil types, side yard widths, imperviousness levels, and alley treatments. The treatments analyzed included asphalt, unpaved, PICP No Storage, PICP with 8 inches of Storage, and PICP with 16 inches of Storage.
The analysis showed that PICP treatments consistently increased infiltration compared to both asphalt and unpaved surfaces even eliminating runoff completely in some scenarios, for loam and sandy soils. PICP with 8 inches of Storage significantly enhanced infiltration compared to PICP with No Storage. However, increasing the storage depth from 8 inches to 16 inches did not yield proportional gains in infiltration, although it further reduced hourly discharge rates and delayed peak flow times.
The simulation results were used to develop the PICP Infiltration Benefits Tool, enabling planners and engineers to estimate infiltration improvements and pollutant load reductions associated with PICP installations. This tool is applicable for grant applications, providing estimated benefits to support funding requests for future projects. Additionally, it provides city planners the necessary information regarding different PICP options, and the estimated benefits associated with them to optimize alley rehabilitation efforts, prioritize future sites for LID installation while aligning with stormwater management strategies and sustainability goals.