Civil engineers and stormwater equipment manufacturers often plan for the 100-year storm. Yet few of their designs are ever put to the test. But what if a 100-year storm did happen? Could the Filterra bioretention system endure and perform as expected?
A 100-year event dumping six inches of rainfall over a two hour period created flash flooding and washed large amounts of debris and sediment into a Filterra system in Ellicott City, Maryland.
Shortly after the storm a crew from Stevens Maintenance, Inc. was dispatched to inspect and maintain the Filterra system, which is customary after a major storm event. The inspection revealed the Filterra system performed as expected and no damage was done to the system; the tree grate, box structure, media, tree, and bypass were all in proper working order.
The essential mulch layer of the Filterra system retained sediment and debris as it was designed to do, and protected the media from contamination. The maintenance crew noted there was a 16" deep layer of sand, rocks and debris in the unit; sediment that would have made its way into the nearby Chesapeake Bay Watershed if not for the Filterra.
The maintenance crew removed 40, 5-gallon buckets of debris to get to the Filterra media layer. Once revealed, the media layer showed no sign of compromise. After the debris was removed, the tree was inspected and pruned, and new mulch was added. The tree, a 5’ Red Bud, was in good health, indicating the media was performing as expected. Lastly, new replacement dissipation stones were added to the opening of the system to provide energy dissipation of flow entering the system.
“We were quite impressed with this unit to still be working properly despite the flood and its impacts,” stated Pat Cleary from Steven’s Maintenance.
The Filterra system installed on this project was part of a larger Low Impact Development retrofit project in Ellicott City. The project received First Place in the Best Ultra-Urban BMP category of the 2017 Best Urban BMP in the Bay Awards (BUBBA's) by Chesapeake Stormwater Network. The BUBBA's are intended to promote the implementation and adoption of LID practices in the Chesapeake Bay watershed.