Water Sensitive Urban Design - Hydrological Effects of an Infiltration Trench with a Permeable Kerb in an Urban Streetscape

Abstract

Urbanisation and climate change have intensified stormwater runoff and urban flooding, demanding effective and sustainable water management solutions. Water Sensitive Urban Design (WSUD) systems, like infiltration trenches, are promising solutions for effective stormwater management. However, current literature reports limited retention performance in some systems, partly due to inlet restrictions, contributing to increased maintenance demands. Hybrid systems that combine infiltration trenches with inlet configurations such as permeable kerbs – designed to enhance the infiltration area while spreading sediment, litter and debris accumulation across a wider area and reduce blockage risk – remain unexplored. This study evaluates the hydrological effects of an infiltration trench paired with a permeable kerb inlet. Over a 7-month period in northern Melbourne, Australia, the research examines the system’s capacity to retain runoff, reduce peak flows, and enhance soil moisture through passive irrigation. Volumes of stormwater inflow, retained inflow, and outflow were calculated. Exfiltration into surrounding soils was modelled using an exponential decay model. Soil moisture was measured with sensors surrounding the trench. Rainfall events were defined using a 3-hour minimum inter-event time. To account for unusually dry conditions during the study period, the average rainfall distribution for the same months was derived from a 10-year dataset and compared to observed rainfall. The system achieved a runoff retention of 77.4% and an average peak flow reduction of 90.6%, outperforming similar systems. Most events up to 6 mm were 100% retained, highlighting the system’s ability to manage frequent, small rainfall events. Soil moisture surrounding the passively irrigated permeable kerb site was similar to the control site at 0.5 m from the trench and lower at 1 m away from the trench. Retention and peak flow reduction were likely overestimated as the system only received 56% of the typical rainfall depth for the same period of the year. Nonetheless, findings highlight three key reasons for higher performance compared to other WSUDs: i) increased system-catchment ratio, ii) enlarged storage volume, and iii) unrestricted inlet configuration via the permeable kerb. Substantial limitations in the soil moisture data prevented clear conclusions regarding passive irrigation effects. Further research should quantify the impact of these factors and assess performance under larger storms, the kerb’s susceptibility to clogging, and effects on water quality. This study contributes to the understanding of scalable, low-maintenance WSUD strategies by demonstrating how a combined infiltration trench and permeable kerb can approach stormwater reduction and infiltration targets set by the state of Victoria, Australia.