Seepage wall proposed to protect 8.5 square mile area and keep water in Everglades National Park

Posted 2/17/21

The South Florida Water Management District plans to spend about $20 million to build an underground wall to stop seepage

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Seepage wall proposed to protect 8.5 square mile area and keep water in Everglades National Park


WEST PALM BEACH – The South Florida Water Management District plans to spend about $20 million to build an underground wall to stop seepage from Everglades National Park from impacting the Las Palmas community.

At their Feb. 12 meeting, the SFWMD governing board once again tackled the problem of the 8.5 square mile area, also known as the Las Palmas community. The 8.5 square mile area is located between Everglades National Park and the L-31 levee that separates the natural areas from the developed areas in Dade County. The area is south of the Tamiami Trail and south of Water Conservation Area 3 (WCA-1).

A key goal to the Comprehensive Everglades Restoration Plan (CERP) is to move more water under the Tamiami Trail to Everglades National Park. Billions of dollars of infrastructure will make that possible. However, increased flow to the park also increases the problem of seepage of water into the 8.5 square mile area. In the 2020-21 water year, even though some of that infrastructure was ready to increase flow, the volume of water that was moved under the Tamiami Trail was limited in order to protect the 8.5 square mile from flooding.

Jennifer Reynolds, SFWMD director of Ecosystem Restoration and Capital Projects, said the seepage wall solution:
• Mitigates high water levels in the water conservation areas (WCAs);
• Mitigates high water level in the 8.5 square mile area; and,
• Increases flow to Florida Bay.

Extreme high water in the WCAs is critical in years there is a lot of rainfall, she explained. Currently, water control structures stack up water north of the Tamiami Trail when that water needs to flow south. “We’re building billions of dollars of infrastructure in order to do just that,” she said.

She said the 8.5 square mile area has poor drainage. Even with normal rainfall there is standing water. Seepage of water from Everglades National Park complicates the problem. Increasing the water flows into the park increases the problems of the seepage in this area, she said.

“As we restore flow into Everglades National Park, we have a seepage effect,” she explained. Some of the water seeps through the earth into the developed areas.

Reynolds said they ran computer models for a partially-penetrating seepage wall (about 45-50 feet deep) and at a fully penetrating seepage wall (close to 65 feet deep in many areas.)

The model results showed that for a very wet year, using conditions from 2017, the 8.5 square mile area saw water above ground 152 days of the year. With a partially-penetrating wall, that would have been 142 days, according to the computer models. With a fully-penetrating wall, that would be reduced to 5 days.

She said the fully-penetrating curtain wall would allow increased flow to Everglades National Park while helping to prevent seepage into the Las Palmas community. Even a fully-penetrating wall will not completely prevent seepage, she warned.
Should they buy the land?

Reynolds said the area of Las Palmas most impacted by current conditions includes 119 properties. Eighteen of the those properties have homes. Estimated cost to buy the 119 properties is $25 million. At a previous meeting, the SFWMD governing board asked if it would be better to just buy the land, since Las Palmas is on the Everglades side of the levee that was built to divide the natural area from the urban area.

Letters were sent in both English and Spanish to the property owners. SFWMD Real Estate division also started calling property owners. They were able to reach about 59% of the property owners. Of those they reached, about 30% were interested in selling; about 15% said “no”; and, another 15% said “maybe.”

A land acquisition strategy would be complicated and would probably take some time, Reynolds said.

She said as restoration continues, and more water goes into the park, the seepage impacts will continue to move farther east. A seepage barrier “not only prevents the land impacts but it keeps the water in the park, where we want it,” she said. “Not just in terms of flooding but in terms of seepage loss, so all of the water that is impacting land farther and farther east from the park is water that is lost to the natural environment.”

A full-penetrating curtain wall of about 2.3 miles will meet both the current and future seepage management needs at the 8.5 square mile area, she said.

She said without a seepage wall, increased flow to Everglades National Park could create seepage problems farther east, past the 8.5 square mile area.

“When CERP was designed and the South Dade Conveyance System was designed, there were not 9 million people in South Florida and the developed area did not reach all the way to Krome Avenue,” she explained. The buffer area that used to exist between the developed area and the levee is no longer there.

“We’d like to construct the wall,” she said. The fully-penetrating wall will cost around $20 million. It can be constructed in 12 to 18 months.

She said staff will continue outreach to property owners and officials in that area.

Col. Andrew Kelly, commander of the U.S. Army Corps of Engineers Jacksonville District, said the seepage wall could have an immediate impact in the day-to-day operations in that area and allow the corps to move more water into Everglades National Park.

“They are still going to have a problem with direct rainfall,” said Governing Board Member Ron Bergeron. He said the Las Palmas area does not have positive drainage and will still have seasonal flooding from direct rainfall. He said he supports the seepage wall plan but after the wall is built, they should not have to shut down flow to Shark River Slough when there is flooding from direct rainfall in the 8.5 mile area.
Governing Board Member Cheryl Meade said she is in favor of buying land from willing sellers in addition to building the seepage wall.

Governing Board Member Charlette Roman said she is convinced the seepage wall is needed not only to protect the 8.5 square mile area but also to keep the water in the park. She said she also supports the idea of buying land from willing sellers in that area as it becomes available.