Vacant Lot Bioretention Systems: Characterizing Performance and Identifying Broader Implications Through Monitoring

Four bioretention practices were constructed in 2015 on vacant lots as a set of projects aiming to integrate vacant lot identification and utilization with small-scale stormwater management systems. The general layout of the systems is consistent amongst the four sites and includes diversion of water from the street to an off-line bioretention system. The bioretention system incorporates an engineered soil over an open graded aggregate reservoir. An underdrain is provided but is controlled in a manhole with two valves at different elevations to offer a range of control schemes.Monitoring of the projects was conducted throughout 2016 to quantify the change in runoff entering the combined sewer due to the presence of the bioretention systems. The rate, volume and duration of infiltration was monitored by carefully measuring the inflow and outflow of each bioretention system. The extent, rate and duration of groundwater mounding was monitored at 3 groundwater wells located 1.5-, 3- and 6-m (5-, 10-, and 20-ft) from the edge of each practice along with one water level in the middle of the practice. And modeling parameters unique to the residential neighborhoods in Detroit were assessed by monitoring the rainfall at each site along with the inflow to each practice. The use of four replicate sites constructed and monitored affords us a unique opportunity to compare site conditions and gives us a level of confidence on the results.