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Study: Dredging would make St. Johns saltier
« on: April 06, 2009, 12:22:16 AM » the St. Johns River to expand Jacksonvilles port could raise salt levels in parts of the river by about one-fifth, a new state report forecasts.Thats bad news for some of the rivers underwater grass beds and for dozens of kinds of fish that find food or shelter in them.The grass beds grow better in fresh water, but researchers cant tell for sure yet how much damage the extra salt would do, scientists at the St. Johns River Water Management District said.\"We think this is potentially important, and thats why we continue to look at it,\" said Ed Lowe, director of environmental science at the management district.A draft report by the agency compares the effects of dredging to create a 45-foot-deep shipping channel against the impact of withdrawing 262 million gallons daily from the river for use by utilities far upstream. The management district has talked with utilities in Central Florida about whether to allow large withdrawals from the river to help meet growing water demands.Facing strong criticism of that idea in Northeast Florida, the management district has been re-examining whether the river withdrawals could hurt the St. Johns. The review will continue for almost two years more, but the early findings estimated the dredging would have a far greater impact on the river in Jacksonville.Dredging would also raise salinity in Jacksonville more than the rise in sea levels forecast for coming decades, another early finding said.Local port officials have advocated deepening the river for years, saying theyll need to accommodate bigger ships once a project to enlarge the Panama Canal is finished in 2014. But any decision to do that rests with the U.S. Army Corps of Engineers, which is studying how the deepening would impact shipping.The rivers shipping channel is 40 feet deep now.Dredging down to 45 feet would keep the port competitive with others in the Southeast, said Jacksonville Port Authority spokeswoman Nancy Rubin.Scientists from a National Research Council committee are meeting this week in Jacksonville with management district scientists to examine how the review of withdrawals is being done and what the initial findings have been.During a talk with that committee Thursday, a scientist from the management district, Peter Suscy, pointed out that there are parts of Northeast Florida where the river withdrawals would affect salinity more than dredging. But as the river flows toward the ocean at Mayport, dredging had a bigger influence, Suscy said.The greatest total change in salinity would happen near the Talleyrand area, about 18 miles from the rivers mouth, but some effects would be felt much farther south, the draft report said.Because the river gets saltier as it heads toward the ocean, the southern half of Duval County is about as far downstream as the grass beds grow. Beds between the Buckman and Fuller Warren bridges already are strained by salt levels and would be the most vulnerable if the salt level rose, Lowe said.Many kinds of fish depend on the grass beds at some stage of life, either hiding from larger species when theyre young or catching and eating small fish, crabs and snails that cluster there. Endangered manatees also use the grass beds as food.In most of Northeast Florida, salt levels in the St. Johns change throughout the day as tides carry seawater in and out. Plants and sealife there all have their own ways of adapting, but that ability to cope may depend on salt levels dropping below a certain level periodically.The report projects the impact of dredging and other changes in terms of increases in \"practical saline units,\" a measurement used to count salt in water. Seawater has about 35 saline units. In the Talleyrand area, the average salt level is 12.5 units now, and would gain another 2.2 units from dredging, the report said. That would represent an 18 percent increase from current levels, a little less than one-fifth.In some areas farther south, the salt increase would have a larger proportional effect, for example representing about a 23 percent increase near the Fuller Warren Bridge.The management district has no authority over whether the river is dredged, but it is studying possible effects because they could influence whether the district will let utilities in Central Florida to take water from the river.The Port Authority has argued that deepening the rivers shipping channel would have huge benefits for Northeast Florida.\"We see that channel improvement having a direct impact on both jobs and the financial future of our region,\" said Tim Murphy, senior director of engineering and construction at the port.The Corps of Engineers could decide two to three years from now whether deepening the river channel is justified, said Jerry Scarborough, chief of the agencys Coastal/Navigation and Antilles Branch in Jacksonville.The Corps will focus on weighing the benefits to commercial shipping against the project costs, and environmental issues and local economic effects will be considerations, he said. That analysis will likely weigh costs and benefits for different river depths from 41 feet to 45 feet, working in one-foot increments, he said.If it decides to deepen the river, the Corps would act as the lead agency in designing and contracting out the project. Murphy said the project might cost anywhere from $500 million to $1 billion, which would be split between federal and locally based agencies


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Re: Study: Dredging would make St. Johns saltier \"BentHook\"
« Reply #1 on: January 30, 2009, 01:58:11 PM »
Other than posting an article from this source, whats your point?


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Re: Study: Dredging would make St. Johns saltier \"Poolbiz\"
« Reply #2 on: January 30, 2009, 02:29:30 PM »
I doubt if the saltwater inshore fishermen  \"trout, reds, flounder, jack, etc ....\"would complain. The largemouth bass fishermen might be upset.  I suspect most of them go towards Platka and south anyway.

They say grass in the river would be affected.  But the mouth seems salty/brackish back to the Mathews Bridge to me.  They don\'t say how far up stream the dredging would make salty.  Or how far up stream they plan to dredge.

The withdraw of water by Central Florida will make the lower st Johns more \"salty\" by diluting the Platka paper mill water less.
Modified by Bakerman at 5:32 PM 1/30/2009