| Description |
Bioretention is a structure which captures runoff from small catchments and stores it in porous vegetated areas with the intent of infiltrating all or a large fraction of the annual runoff volume. The effects of bioretention on potential groundwater recharge are oftentimes unknown because of variable infiltration rates. This study examined the performance of a field site on the University of Utah campus in Salt Lake City, Utah. Data were collected between March, 2012 and November, 2012. The site demonstrated improvement in volume retention and infiltration over the preexisting conditions. The average storm event produced 5.6 mm (0.22 in) of precipitation. For all storm events examined, nearly all inflow volume was retained and either infiltrated, lost through evapotranspiration, or utilized by plants. Average vertical and horizontal infiltration rates ranged between 0.5 cm/hr and 20 cm/hr for the sandy loam subsoils. The wetting front took 1 to 2 days (24 to 48 hrs) to reach the 1.8 m (6 ft) depth and 7 to 14 days to reach the 3.7 m (12 ft) depth depending on the spatial location. At depths of 1.8 m (6 ft), 3.7 m (12 ft) and 4.6 m (15 ft) outside the basin, the wetting front progressed at least 3 m (10 ft) laterally in three days (72 hrs), but without additional sensors located at larger lateral distances, it remains unclear exactly where the lateral extent of the wetting front ceases. Without additional engineering to protect infrastructure such as building foundations and retaining walls, it is recommended that bioretention cells constructed in semiarid climates and with similar subsoils be located at least 6.1 m (20 ft) from infrastructure. Overall, this research indicates that bioretention is a viable stormwater best management practice in Utah. It was shown that with proper design and sizing, nearly all annual runoff volume can be controlled on site and either infiltrated or utilized by native plant species. As measured infiltration data were limited to the vadose zone, the infiltrated volume was considered potential recharge; future work may include modeling and installation of deeper sensors as a means of approximating recharge. |
