What’s Happening with the C-43 Reservoir

by Jim Metzler & Sarah Ashton

Map of Calooshahatchee Watershed

Last week the Coastal & Heartland National Estuary Partnership (CHNEP) (formerly the Charlotte Harbor National Estuary Program) hosted an all-day workshop on the C-43 reservoir. The workshop had sessions that covered topics ranging from key scientific issues to the current plan to add a water treatment component to the reservoir. When assessing the workshop, Sanibel Councilman Richard Johnson said that “What has been missing in the past was broad widespread public engagement and that the workshop was valuable because it brought a lot people together to share ideas and help all of us make better plans for the future.”

As shown in Figure 1, the C-43 reservoir is being built on 10,700 acres of former farm land in Hendry County, Fla., just west of Labelle. The reservoir was first envisioned in the early 2000s and the South Florida Water Management District (SFWMD) began construction in 2015. When it’s completed in 2023, the reservoir, which will measure 6 miles by 3 miles in size, will hold approximately170,000 acre-feet of water, and it will have a depth of water that ranges from 15 feet to 25 feet. This video depicts the massive scale of the reservoir.

The SFWMD has identified the following as goals and benefits of the reservoir:

  • Capture and store stormwater runoff from the Caloosahatchee River basin, reducing excess water flow to the Caloosahatchee Estuary.
  • Capture and store water that is released from Lake Okeechobee, reducing the discharges to the coastal estuaries.
  • Improve the salinity balance for the Caloosahatchee Estuary by controlling peak flows during the wet season and providing essential flows during the dry season

One of the most insightful scientific presentations was given by Dr. JoAnn Burkholder from North Carolina State University. Dr. Burkholder stated that scientists have just recently begun to understand that while the total amount of nitrogen and phosphorous in a waterbody are important indicators of the health of the waterbody, so is the ratio of nitrogen to phosphorous. She stated that this ratio controls the food quality of the water and hence it controls which algae are in the waterbody and how well they are doing.

Dr. Burkholder also pointed out that in spite of the fact that there has been a major reduction in the amount of phosphorous entering Lake Okeechobee, the total amount of phosphorous in the Lake continues to rise. She attributed that phenomena to the fact that the sediment on the bottom of Lake O contains massive amounts of phosphorous which is being released back into the water. She also said that the rate of release is impacted by the ratio of nitrogen to phosphorous in the Lake. One of Dr. Burkholder’s conclusions was that in many of Florida’s waterbodies, it is important to co-manage nitrogen and phosphorous.

Until earlier this year, there was no water treatment associated with the C-43 reservoir. As such, the reservoir was going to store and release dirty water and potentially serve to incubate algal blooms similar to what happens in Lake O. In January 2019, Governor DeSantis signed executive order 19-12. Part of the executive order calls for the Florida Department of Environmental Protection (FDEP) to work with the SFWMD to add stormwater treatment to the C-43 reservoir with the goal of improving the quality of water leaving the reservoir.

In response to the executive order, an inter-agency group was formed. That group, which is comprised of the SFWMD, FDEP and local governments including Lee County and the City of Sanibel, was charged with using the best available science to identify at least three feasible ways to add water quality treatment to the C-43. The group plans on holding public meeting starting in the fall and it has the goal of completing the study within 18 months.

CHNEP has posted all the slides from the workshop and has stated that they intend to also post a video of the workshop.

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