jaxweb.gif (11739 bytes)

 

 

PALM RIVER RESTORATION
(TAMPA BYPASS CANAL)

 

        Palm River is located in east central Hillsborough County, flows into McKay Bay, and is adjacent to the most northeasterly tip of Tampa Bay.  The river is a portion of Canal 135 of the Four River Basins Project.  The specific reach considered for this project is the 2.5-mile segment between McKay Bay and Structure 160.

        Prior to its’ channelization in the 1960’s, Palm River was a relatively shallow, slow moving, meandering river subject to tidal flow.  Straightened, widened and deepened with steep riverbanks, its purpose was to divert flows from the Lower Hillsborough Flood Detention Area away from the cities of Tampa and Temple Terrace, into McKay Bay.   Structure S-160 serves as a tidal/salinity barrier and outlet control structure for canal discharges into Palm River and McKay Bay.  Material dredged downstream of S-160 was deposited at several nearby disposal sites resulting in detrimental effects on those ecosystems. Dredging did not occur in the immediate vicinity of the U.S. Highway 41 bridge located just upstream of McKay Bay.  Due to concerns of undermining the bridge pilings, the material was left under the bridge creating an underwater berm.

        The Tampa Bay estuary of which Palm River is a part has suffered significant habitat losses; the estuary contained approximately 24,831 acres of historical intertidal wetlands, of which only 14,079 acres remain; a 43 percent loss.  Prior to construction of the canal, the mouth of Palm River was an oligohaline environment where tidal flows mixed with freshwater.   The flows were sluggish and the mostly saline environment provided hatchery and nursery environments for small fish and shrimp.  At the mouth, the saltmarsh vegetation also provided nursery habitat for small fish and shrimp as well as shoreline protection from wind and wave action.  Inland of the saltmarsh was mangrove wetlands, which provided shade and cover for small mammals and roosting and nesting habitat for pelicans and cormorants.

        Today, oxygen depleted waters are trapped in the lower part of the water column upstream of the raised berm beneath the U.S. 41 bridge all the way up to S-160.  Littoral areas along both sides of the river/estuary system, which provided habitat for shoreline birds and small fish, were eliminated.  Destroyed was all the aquatic and emergent vegetation which provided cover for fish and aquatic organisms and which directly improved water quality through nutrient uptake.

        Project features include:

1) Modifications to Corps dredge material management areas.  These sites would be excavated to an elevation more typical during pre-canal construction, approximately 1-foot National Geodetic Vertical Datum (NGVD) and then contoured by creating several meandering inlets (tidal channels) which would allow tidal flushing of the sites.  The typical tidal channel will have; a bottom elevation of approximately -1.5 feet NGVD, a top width of approximately 23 feet, and a channel bottom width of approximately 3 feet.  The land will also be cleared of exotic vegetation and succession of native species will be assured.

2) Construction of a littoral zone.  A littoral ledge would be constructed adjacent to the north shoreline of the canal.  The exact width and length of the littoral zone will depend on the amount of suitable material available and the constraints required to insure the canal’s authorized flood control capability.   A backwater analysis will be performed to verify that the littoral zone and any associated filling of the channel prism would not adversely impact the flood control capability of the canal.  The littoral zone will be constructed of tested, select material from the three upstream sites and the berm beneath the U.S. Highway 41 bridge.

3) Removal of underwater berm.  The berm beneath the U.S. Highway 41 bridge spans the length and width of the bridge (approximately 600 feet by 100 feet); the top elevation is at -5 feet NGVD.  Approximately 400 feet or two-thirds of the length of the berm will be removed down to -20 feet NGVD.  The bridge piers will be stabilized with riprap if necessary.

        The above project features will provide benefits as follows:

1) The restoration sites will be restored to create viable saltmarsh and mangrove habitat. Vegetation through natural succession should allow for an exchange of aquatic organisms between the Bay and the marsh.  It will also provide additional nursery habitat for fish and shrimp as well as areas for shorebirds.  The emergent wetland vegetation will help local water quality by providing for nutrient uptake from circulating tidal flows.

2) The construction of the littoral area will create an aquatic habitat along the shoreline and a ledge in the water column.  Aquatic vegetation will be given the opportunity to inhabit the shallowest areas within the photic zone.  This vegetation will provide cover for fish and surfaces for organisms to attach to.  It will also improve water quality by allowing nutrient uptake of pollutants from the water column.

3) Dredging of the berm under the bridge will allow improved flushing and mixing of the water column upstream of the bridge.

Point of Contact:  [Martin Gonzalez] (904) 232-1117
E-mail:  martin.t.gonzalez@usace.army.mil
Page Created:  11/97
Page Last Updated:  06/26/03