From trickle to torrent: why Everglades water levels rose among the highest on record

The Everglades never used to hold much more than about three feet of water. In fall 2020 the national park's water levels climbed among the highest on record, and the reason is part weather and part plumbing. An Everglades National Park science communicator wrote the article, which explains both.

Shark Valley Loop Road had to be closed because of the extremely high water levels. This picture was taken Nov. 24, 2020. Shark Valley later reopened after water levels fell. NPS photo.

A dry start, then a flood

South Florida gets about 70% of its annual rainfall in the six-month wet season, May to October. Before September 2020 total wet-season rainfall was below average, then so much fell in the last two months that the season finished average compared with other wet seasons. Water in the park, which had arrived as a trickle before September, became a torrent. Late in the season, Tropical Storm Eta dumped up to 16 inches of rain on parts of South Florida in mid-November, giving the dry season, which starts on paper on Nov. 1, a very wet beginning.

Monthly rainfall in the South Florida Water Management District, April to December 2020. When the solid line rises above the dashed line, the district got more rain than average. NPS figure.

In October, deep water stood on both sides of the road at the park entrance and flowed over it in places. The park temporarily closed some access roads and the Shark Valley Loop Road to keep visitors and resources safe. At a staff gauge in Taylor Slough, north of Main Park Road, the water read 5.18 feet above sea level on October 10, 2020. Fourteen days later it read 5.66 feet.

A staff gauge shows water level in relation to something else. This one, in Taylor Slough, read 5.18 feet above sea level on October 10, 2020. NPS photo.

Why three feet?

A park ecologist told the author that the historic Everglades could hold only about three feet of water, because the region's physics and geology prevented deeper water. Today the Everglades is compartmentalized: levees, canals, locks and pumps contain and move water between separate basins, and the only places where levels can rise above three feet are those where people have intervened. Everglades National Park is not one of them. Apart from a few roads that may alter its course, water there flows naturally, gradually downhill from the north, where it enters or falls as rain, toward the ocean, spreading out and soaking into the porous bedrock on the way. So levels relative to sea level generally decrease from north to south, as they did historically.

Sloughs are deep sections of a wetland that are flooded periodically. Shark River and Taylor Sloughs carry and spread water through the Everglades, and many plants and animals, including spikerush and American alligators, rely on them. NPS photo.

Managing water for the park

Before Everglades Restoration began, the park was often an afterthought in water management: a place to send water in floods and to cut off in droughts. Now its ecosystem is a consideration. A water plan put in place in 2020, the Combined Operational Plan, calls for more flow to the park in the dry season, when its supply was often shut off. New infrastructure from the Central Everglades Planning Project South is also reopening a historic flow path, Northeast Shark River Slough.

At the time of writing, water levels were expected to fall gradually over the next five months, which were expected to be fairly dry. The author reported very high bird activity and outstanding fishing in the marine areas of the park.

Sources

• National Park Service, Everglades National Park, "From trickle to torrent: What's up with water levels at Everglades National Park," by Michelle Collier, Science Communications Liaison (https://www.nps.gov/articles/000/from-trickle-to-torrent-what-s-up-with-water-levels-at-everglades-national-park.htm); part of the series on water levels at the end of 2020; the author's personal anecdotes and the ecologist's name are left out; rewritten in hubnx's own words.