As subconsultant role, Lu was responsible for all engineering to reconfigure two parking lots, each over eight acres in area, to direct stormwater flow to large rain gardens capable of treating the “first flush” storm runoff. The objective of the project was to evaluate the hydrologic behavior of the parking lots to quantify stormwater runoff and capture the higher frequency rain events on the site to infiltrate this water back into the ground, thus removing it from the runoff leaving the site. This project requires reconfiguring the stormwater patterns of the lot surface to capture the runoff in structures that direct target storm events to the “off line” rain gardens. Larger volume storms are shunted past the rain gardens to avoid damage to them.

The soils underlying the rain gardens accommodate the infiltration measures proposed, having well-drained to excessively well-drained sub soil conditions. Significant challenges on this project include preserving the existing closed drainage system to permit flows from outside the subject lot to continue unobstructed through our site, and to regrade the parking lots to redirect runoff flow to the desired collection points for distribution into the rain garden system or the accompanying overflow system.