Water bodies, watersheds and storm water

Regional stormwater treatment areas

An agricultural ditch carries agricultural stormwater runoff in the TCAA.

For generations, the tri-county agricultural area (TCAA) — located in Flagler, Putnam and St. Johns counties — has been farmland, producing mostly potatoes and cabbage. The 28,000 acres of irrigated cropland contain many old canals that transport irrigation and stormwater runoff directly into natural waterways.

Runoff from the TCAA is nutrient-rich from fertilizers that are applied to the farms and make their way into the Lower St. Johns River Basin. This encourages algal blooms that deplete oxygen from the water and block sunlight from reaching underwater vegetation critical to fish and wildlife habitats. It is estimated that human activities have increased nutrient levels in the lower basin by six-times their natural level.

What’s being done

In 2002, the St. Johns River Water Management District began designing two regional stormwater treatment areas to reduce the amount of phosphorus, nitrogen and suspended solids flowing into the river.

The Deep Creek West Regional Stormwater Treatment Area has been operational since February 2006. The facility consists of a 15-acre wet detention pond and a 38-acre treatment wetland on 1,136 acres of land in the Deep Creek Conservation Area, situated at the confluence of Deep Creek and Sixteen-Mile Creek in southern St. Johns County.

To offset wetland losses from the widening of State Road 207, the Florida Department of Transportation (FDOT) has partnered with the District to fund the $3.8 million project.

The second project, the Edgefield Regional Stormwater Treatment Area, consists of a 25-acre wet detention pond and a 56-acre treatment wetland and has been operational since October 2007. It is located on 212 acres of land adjacent to Dog Branch Creek in eastern Putnam County.

Funded with assistance from the National Oceanic and Atmospheric Administration’s Coastal Impact Assistance Program, FDOT and special legislative appropriations, the projects are very similar. The projects each cost approximately $3.8 million to complete ($1 million less than anticipated for each).

The projects also have the same goals: to reduce the total nutrients by 60 percent for phosphorus, 50 percent for nitrogen and 70 percent for total suspended solids in water routed through them.

How it works

In each project, irrigation and stormwater runoff from fields flow to the regional stormwater treatment area through canals and are pumped into the first component, a stormwater pond. Much like a neighborhood stormwater pond, these wet detention systems allow nutrients to settle to the bottom, where they are deposited.

Water then slowly flows into the projects’ second component, the created wetlands. Again mimicking natural processes, the wetland vegetation further absorbs dissolved nutrients before the water empties into the St. Johns River.

The stormwater treatment areas in St. Johns County (top right) and Putnam County (bottom right) are both located in the tri-county agricultural area (left). The areas each have filled with water to make wetlands and a deep pond, which filter pollutants from rain and irrigation runoff before they flow into the St. Johns River. Blue shading has been added to the above photographs to show the location of the deep ponds; yellow shading represents the wetlands.