A majority of sites requiring stormwater detention will use an earthen berm or a concrete basin for storage. However, sometimes that is not feasible. If there is no public storm infrastructure adjacent to the subject site using traditional detention, storage could be challenging.
This is one scenario where it makes a lot of sense to use parking lot detention. In fact, Austin’s Drainage Criteria Manual even has a code section that allows a parking lot to be used to meet stormwater detention requirements.
Per the Drainage Criteria Manual Section 8.3.3.I., the ponding depths in a surface parking lot during a 100-Year storm event are limited to an average depth of eight (8) inches and a maximum depth of twelve (12) inches.
It’s important to note that using a parking lot for detention can cause an inconvenience to both pedestrians and traffic, so going this rout will need to be studied carefully by a qualified engineer. Detention areas should be placed in low traffic areas and as far from a building as possible to minimize any negative impacts of using this strategy.