Watershed Planning for Dona and Roberts Bays

VeniceInlet2004cover

What happens when we dig canals to drain our lands to the sea?? A lot. Precious fresh water which is becoming a scarcer resource is wasted. Salinity balance in estuaries is altered disrupting the life cycles of both estuarine and marine organisms. Freshwater habitats on the landscape are deprived of the water needed to function. The excess water delivers higher loads of nutrients to our bays and streams causing algal blooms, depleted oxygen levels, and low visibility, which in turn disrupt our fisheries. These realizations have spurred restoration efforts of previous drainage activities throughout the state of Florida. Charlotte Harbor National Estuary program has supported numerous restoration efforts within the confines of its study area. One such project is the Dona Bay Restoration Program in Sarasota County.   The historic Dona Bay watershed was significantly smaller than it is today.  The original Cow Pen Slough was a large natural slough that meandered south and east towards the Myakka River. In the 1960’s the United Stated Department of Agriculture’s Natural Resource Conservation Service (now known as the Soil Conservation Service) embarked on one of the most significant drainage works in the history of Sarasota County.  A large canal system with water level control structures was constructed from Shakett Creek, through Cow Pen Slough and north to Manatee County.  This canal system introduced excessive amounts of freshwater to Dona Bay and enlarged the watershed from 15 square miles to about 75 square miles. Sarasota County completed a watershed management plan for Dona Bay in 2007. The watershed plan established the following objectives. 1) Providing a more natural freshwater/saltwater regime in the tidal portions of Dona Bay by removing a portion of the excess flow; 2) Provide an opportunity for alternative water supply development along with environmental restoration; 3) Provide some flood protection through storage; 4) Provide pollutant load removal and 5) Provide rehydration of wetlands by rerouting flow to the original slough path. Through cooperation from the Southwest Florida Water Management District and State Legislature appropriations as well as other potential partners, Sarasota County is currently in the design and permitting stage of complex projects aimed preliminarily at improving water quality while laying a foundation that will meet the other program objectives. The current project under design uses a treatment train approach by diverting excess freshwater through County owned lands, borrow pits, and wetlands which will provide attenuation and treatment. The project replaces an aging weir structure in the Cow Pen Slough canal. Water will be diverted off the canal close to this structure into an adjacent former citrus grove and floodplain area. Excavated areas in the former grove will provide wet detention as well as floodplain relief. The excess fresh water then passes through a series of existing borrow pits and wetlands providing further attenuation and water quality treatment before being released back into the system. Future projects and phases will further reduce excess freshwater volumes from entering Dona Bay through alternative water use such as irrigation or even potable supply. Full implementation of the program project(s) will be a win/win/win situation by improving the environment, eventually providing a water source, as well as offsetting ground water withdrawal.

 

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