Where and When Soil Amendment is Most Effective as a Low Impact Development Practice in Residential Areas

Improving the infiltration capacity of urban soil is critical for effective stormwater management, but existing guidance on soil amendment in residential areas typically calls for tilling and amending soil throughout the entire yard, an approach that is most feasible during development or redevelopment. To develop guidance on less‐extensive soil amendment interventions which a homeowner could implement postconstruction, we designed a modeling study to compare four scenarios targeting soil amendment in a single‐family yard (1) at disconnected impervious features, (2) at locations with large upslope drainage areas, (3) at locations with a high topographic wetness index (TWI), and (4) randomly (control). We find that soil amendment may be ineffective at reducing runoff from residential areas with high near‐surface infiltration rates (e.g., Ksat > 1 × 10−2 m/hr), but can reduce runoff by 46%–73% (up to 15% of precipitation) on yards with lower near‐surface infiltration rates. We find that targeting amendment at interfacial hotspots near disconnected impervious surfaces can reduce runoff by over 10× more than amending a random equivalent area and by at least 2× more than targeting amendment by drainage area or TWI. We suggest including this intervention in the suite of low impact development practices promoted to residential property owners since it effectively and efficiently reduces runoff and may appeal to homeowners who are wary of maintenance needs of other practices.