Stormwater Management and Wetland Mitigation: Platts Creek

Client: St. Lucie County Public Works Department
Location: St. Lucie County, Florida

The Platts Creek drainage basin is a suburban mixed use drainage area located in St. Lucie County, Florida. The Platts Creek Stormwater Management and Wetland Mitigation Area project, in accordance with both the Indian River Lagoon SWIM Plan and National Estuary Program Plan, includes restoration of the natural storage and water purification functions along the river’s floodplain. Hazen and Sawyer is the prime engineer on all major aspects of the project, including preparation of construction plans and technical specifications and preparation of the Environmental Resource Permit (ERP) application and Mitigation Banking Instrument.

Project Outcomes and Benefits

  • The project provides water quality treatment for the 1,000-acre drainage basin.
  • Restores 80+ acres of wetlands and habitat directly adjacent to Platts Creek and the North Fork of the St. Lucie River.
  • Provides overall reduction in freshwater released to the North Fork of the St. Lucie River.
  • Attenuates flow so that basin discharge is slower and less detrimental to critical salinity level.
  • Eliminates agricultural runoff from citrus grove directly adjacent to the North Fork of the St. Lucie River.
  • Restores natural storage and purifying functions along the river’s floodplain.
  • Creates a mitigation bank that the county can use to offset impacts on other projects or sell credits into offset impacts by other parties.

Runoff from a mixed use drainage basin of more than 1,000 acres contributes to the Platts Creek facility, which helps protect the North Fork of the St. Lucie River from the adverse impacts of otherwise untreated stormwater runoff.

Platts Creek discharges into the highly protected North Fork of the St. Lucie River.

Primary treatment is provided through the 15 acre wet detention pond. Alum treatment facilities are located at the stormwater pump station for improved floculation and settling of suspended solids. Subsequent phases will include the addition of constructed wetlands to replace remnant citrus groves. The created wetlands will provide natural habitat and perform polishing treatment for runoff routed through the facility.

The stormwater pump station is utilized to divert flow offline from Platts Creek for treatment in the stormwater facility and hydrologic restoration in the created wetlands.

Construction of stormwater pump station was completed in 2005.

This view shows the pump discharge outlets into the vegetated conveyance canal which carries runoff to the 15 acre detention pond.

A carefully designed weir was constructed on Platts Creek in order to create an inlet sump area for the stormwater pump station.

This area provides for settling and removal of large floatables. The weir provides for passage of baseflow during normal conditions and full bypass during critical / extreme storm event conditions.

Major project elements include the purchase and decommissioning of approximately 102 acres of existing citrus groves, construction of stormwater detention facilities and a stormwater pumping station, sump and discharge channel and construction of approximately 80 acres of created wetlands.

Hazen and Sawyer prepared both the construction plans and technical specifications and the Environmental Resource Permit (ERP)/Mitigation Bank application. Hazen and Sawyer’s team of experienced ERP permit specialists worked closely with St. Lucie County, the Army Corps of Engineers, the South Florida Water Management District, and other agencies to obtain a permit.

In order to facilitate movement through the detention area and wetlands, a pump station was constructed at the head of the system. A storm water sump area of a little less than half an acre was constructed to receive flow from the adjacent neighborhood stormwater systems. The sump is equipped with a weir that is specially designed to allow for base flow in the lower reaches of Platts Creek and to provide for bypass flows at flood stages associated with extreme storm events.

A detention area of approximately 15 acres was designed to receive flow from the pump station. This detention area provides a slowdown in velocity to permit settling to occur to treat and remove pollutants from the stormwater prior to flowing into the wetlands. The created wetlands will provide polishing treatment for stormwater runoff as well as restoration of the natural system.

Alum facilities were added to provide coagulant to encourage settling of stormwater contaminants in the detention area. Six 1/3 Hp metering pumps are provided on two separate skid systems. The metering pumps draw from a 5,000 gallon storage tank and inject the alum at each pump. The addition of alum occurs simultaneous with the start of the stormwater pumps.

For more information on this project, or to discuss a similar project in your area, contact

Rob Taylor, P.E. at rbtaylor@hazenandsawyer.com