Most rain that falls on the Everglades Agricultural Area never leaves the farm.
Runoff from the Everglades Agricultural Area (EAA) Basin is sometimes blamed for water problems in South Florida, but data collected by the South Florida Water Management District (SFWMD) and U.S. Army Corps of Engineers (USACE) shows runoff from the EAA to the stormwater treatment areas (STAs) was only about 15% of the flow to the Water Conservation Areas north of the Tamiami Trail this wet season.
Farms are vast open fields, with nothing to block water from percolating into the earth. Some of the rain never even reaches the ground because it is absorbed by the plants through their leaves.
“How much runs off depends on how fast it comes down and how wet the soil already is,” explained Tom MacVicar, of MacVicar Consulting South Florida Water Resource Specialists.
The Best Management Practices (BMPs) developed by the Florida Department of Agriculture try to keep the rich muck soil of the EAA moist. If the muck soil dries out too much, it can oxidize and be lost.
“There’s a fine line between wet enough and too wet for plants,” said MacVicar. The type of crop also makes a difference. “Cane is very tolerant of water, but vegetables aren’t.”
Rice, used as a rotation crop with sugar cane is very tolerant of water, as rice is grown in flooded fields. Depending on the variety planted, sugar cane is two-, three- or four-year crop. At the minimum, sugar cane is grown for two years, and harvested twice. Most varieties of sugar cane are grown for three or four years, harvested once each year. After the last crop is harvested, the field is switched to rice or a vegetable crop.
About 25,000 acres of rice are planted every year in the EAA, MacVicar explained.
In times of heavy rainfall, farmers can and do pump water off flooded fields, he said. However, the BMPs do not allow pumping until the field has received at least 1 inch of rainfall per rain event.
“A lot of times it rains, and the water will come up, but they don’t pump it down,” said MacVicar. “Most have BMPs that require they measure 1 inch of rain before they can turn on the pumps, even if the fields are already wet.”
Based on the rainfall figures for the current wet season, about 60-70% of the rain that has fallen in the EAA basin stayed on the farms.
Most of the water in the Water Conservation Areas comes from direct rainfall. This wet season, about 70% of the water in the WCAs is from direct rainfall.
The EAA STAs are north of the WCAs. Water also flows into the WCA-3 from the west and from the east for flood control.
MacVicar said on average about 13% to 16% of the water that flows into the WCAs originates with rainfall in the EAA Basin.