Water being discharged from the western areas is the primary cause of heavy sedimentation that has destroyed the Lake Worth Lagoon, according to experts who made a presentation Tuesday to the Palm Beach County Commission.
Rob Robbins, director of Palm Beach County’s Department of Environmental Resources Management, said the start of this year’s rainy season was the wettest on record since 1932. He added that there is still not enough storage in the drainage system, which was designed in the 1930s and 1940s.
“Those floodwaters make their way to estuaries, where they have an adverse impact, including the Lake Worth Lagoon,” Robbins said.
Dr. Yongshan Wan with the South Florida Water Management District said the Lake Worth Lagoon received a lot of fresh water this year, especially from May to August, from the western parts of the county, which is a very large watershed that includes many residential areas. “Those kinds of land uses are mostly in the Lake Worth Lagoon areas,” he said.
Those areas are primarily the C-51 east and west basins that include Wellington, Royal Palm Beach, Loxahatchee Groves and The Acreage, which are in the C-51’s western basin, separated from the C-51 east by a gate just west of State Road 7. However, that gate is opened during heavy rainfall in the west.
“A different land use is like a person,” Wan said. “They have different personalities when it comes to runoff generations.”
Urban areas have large impervious spaces that do not allow water to percolate into the soil. In those areas, more than half of the rainfall will become stormwater runoff, he said, whereas in wetland or forested areas, a majority of the water will be held on site and either evaporate or percolate into the ground.
“The point is that we are in a very special watershed [in which] over 50 percent of the watershed is urban high, medium residential, so when you have rain, you can expect that you’re going to get a lot of discharge” he said.
The amount of rainfall and discharge over the past year was a record for Palm Beach County, Wan said. “It is 26 percent more than the average,” he said.
Asked whether that is a trend, he said South Florida seems to be having wetter wet seasons and drier dry seasons. “That is the difficulty of water management, that we are facing the problem of during the dry season we don’t have much water, and in the wet season we have too much,” Wan explained.
He said the issue is reflected in the Lake Worth Lagoon, where for four months beginning in May, large amounts of runoff typically have to be released, but it was much more this year.
He said the wet season appears to be over, and that now, the SFWMD must do what it is able to stave off a water shortage.
Robbins said the Lake Worth Lagoon has been adversely affected by those discharges. It can bounce back, but does not recover easily from the accompanying sediment, which destroys oyster beds and prevents sea grass from growing.
Robbins said sea grass is a natural filtering plant and cover for marine life that the county monitors to measure the health of the lagoon.
“Sea grasses are one of the primary producers in an estuarine system, converting sunlight energy into food energy, and form the basis of a complex food chain, so it’s an important component to monitor,” he said.
Monitoring over the past year showed a sea grass decline of about 20 percent near the inlets but about 80 percent around the discharge point of the C-51 Canal, Robbins said. “There has been an interruption in that complex food web,” he said. “That does have lasting effects, but it can bounce back.”
Even with all the restoration efforts in the Lake Worth Lagoon, there has been an overall downward trend in the amount of sea grasses in the lagoon over the past several years.
“If we can moderate those abnormally high discharges, if we can provide other discharge opportunities across South Florida on a very large scale, this could easily be an upward moving trend for sea grasses,” Robbins said.
As high volumes of water move down the C-51 Canal at a high velocity, it picks up dirt along the way. That dirt is held in suspension by the energy contained in high-velocity water. It passes through the system with the dirt still in suspension, and then it hits the lagoon. The water velocity slows down, and the sediment settles into the lagoon, which over the years has created a muck in that area where nothing much can grow.
Robbins said that most of the developments since the 1980s have stormwater ponds that trap much of the sediment. Farther west in the agricultural areas, much less of the sediment is caught, and it is subsequently transported to the lagoon.
The county, in cooperation with the SFWMD, built a sediment trap upstream as an experiment. “This was an attempt, and we didn’t know how well it was going to work, to get some of those sediments before it hit the lagoon,” Robbins said.
He said the trap has captured a significant amount of the sediment but, judging by recently dead oyster beds in the lagoon, not all of it.
Robbins congratulated the SFWMD for the efforts it has made to reduce discharges, but urged that more storage needs to be added to the system. “We should be able to hold on to those fresh waters and slow discharge into the dry season,” he said.
There are some projects on the horizon that give hope that there will be storage opportunities in the future.
Commissioner Priscilla Taylor asked about the effect of new development planned in the western areas, and Robbins said those developments are required to provide their own on-site water storage.
“When we’re talking about storage needs of the lagoon, we’re talking about tens of thousands of acre-feet of storage to be able to make a difference, not something that an individual development project will be able to make a dent in,” he said.