Field Performance of Rain Garden in Red Soil Area in Southern China

Sponge City, as a new concept in urban stormwater management, utilizes on-site or local hydrologic processes for runoff control and therefore is highly dependent on the geographical location (soil type) and site-specific climatic conditions. Field studies are valuable because of the insufficient quantity of field performance data in low-impact development (LID)-related research. Rain gardens are recommended for LID to manage stormwater. A rain garden was designed as a pilot project in Nanchang city, which is one of the typical red soil areas in southern China. Red soil is usually not conducive to runoff infiltration due to its low organic carbon, strong acidity and low permeability rainfall characteristics, but the permeability of the filter media layer is an important parameter in LID design. The construction depth of the rainwater garden was 600 mm, and 30% sand, 10% compost and 60% laterite were used as combined matrix; the permeability coefficient of medium layer was 1.48 × 10−5 m·s−1. Rainfall runoff control and pollutant removal efficiencies were studied based on the on-site conditions. The analysis of almost 2 years of field data showed that volume capture ratio of annual rainfall was 78.9%, the mean load removal of TSS, NH3-N, TP, TN, COD and NO3-N were 92.5%, 85.3%, 82.9%, 80.5%, 79.8% and 77.5%, respectively, which could meet the technical guidelines for sponge city construction in Nanchang. The research results could provide a basis for sponge city design in low organic carbon and low permeability areas.