Project Summary

1. Project ID
Name	Construction of Bridges to Restore Circulation and Provide Ecological Enhancement in the Ft. DeSoto Park Aquatic Habitat Management Area
Region	Gulf of Mexico Region
State	FL
Location	St. Petersburg
Date of this update	8/24/00

2. Problem(s) addressed (check one or more)

Habitat Restoration/Protection
Wetlands
River systems
Beaches/Dunes
Offshore areas
Mangroves
Assisting Species at Risk
Pollution Mitigation
Non-Point Source Pollution
Other (describe)

3. Project description (100 words or less)

A. Description of the Issue to be Resolved by the Project

The objective of this project is to restore circulation to the inner portion of the bay that was severed during the dredging and filling activities that occurred in the late 1950's. Summertime temperatures become extremely elevated in these areas leading to very low dissolved oxygen levels as well as severe seagrass stress resulting in blade necrosis. Restored circulation patterns will lead to improvement in water quality parameters and a healthier seagrass and faunal community. The improved health and viability of seagrasses will result in continued seasonal uptake of nutrients and sediment trapping instead of adding pollutant load to the water body due to decaying seagrasses.

B. Description of the Proposed Project

The project will include the construction and performance evaluation of 40' span bridges to replace portions of the filled causeways at Ft. DeSoto Park in Pinellas County. The Park was once a group of separate islands. During the Park's development in the late 1950's and early 1960's, the main island was connected to the smaller islands by dredging and filling two causeways, one to provide access to the mainland and the other to create a maintenance area and Park Manager residence. This activity cut off circulation between the back bays.

Data obtained during a 1985 study of water quality, circulation and benthic fauna of the area support the theory that the causeways are restricting flow and reducing water exchange within the back bays of the Park. This study was conducted as a result of the less than optimal operation of the four sewage treatment plants located at the park. Water quality was poor due to the incomplete treatment of sewage during peak use and suspected entrapment in the back bays.

Tidal surge and flow patterns were mapped to determine if the back bays were flushing or if they were stagnant. As expected, although the tidal flux travels from east to west, the flow patterns merely fill the bays then empty them in a very slow manner not conducive to flushing which led to elevated water temperatures, water quality degradation and sea grass mortality.

Although the plants were dismantled and the sewage pumped to mainland treatment plants, water quality still was poor in comparison with surrounding waters. Field visits confirmed stagnant conditions and at times one can observe differences in the tidal and wind driven water levels between the cells of Mullet Key. If water could pass between the cells, pocketing and stagnation would be reduced. Opening the causeways by partial replacement with 40' span bridges will restore east-west circulation to the semi-enclosed embayments and will improve ecosystem health.

Pinellas County has started to perform pre-construction water quality monitoring to document the improved conditions. Allowing the natural tidal flux and wind driven gulf/bay water to pass between the cells will help modulate water temperature and improve water quality by restoring the historic circulation patterns that existed prior to the filling of the passes. Preliminary modeling predicts a 100% exchange of water in the smaller bay and 25% for the larger bay. The bridges will be designed to allow non-motorized vessels to travel between the bays and provide a canoe trail within the park as an added public benefit.

The project directly affects a SWIM priority water body and a high priority TMDL water body. It affects water quality and habitat value at a regional park facility. The Southwest Florida Water Management District has committed $150,000 to this project. The project is consistent with the Pinellas County Comprehensive Plan, SWIM, the goals of the National Estuary Program and the CCMP. It is also contained within the Pinellas County Capital Improvement Project Program.

Pinellas County is designing the project in-house. Pinellas County proposes to design and permit the project during F.Y. 98/99 with construction to follow. Discussions with permitting personnel revealed that the project is very desirable and that permitting should pose no problems.

4. Goals/Benefits (quantify where possible using measures of success list) Was a cost-benefit study conducted for this project? yes/no If yes, provide a summary of findings.

5. Partners (include each participant's responsibilities - funding, permitting, etc.)

6. Funding/Contributions (organization and amount)

Cash

Federal

Non Federal

State government
Local government
Private industry
Public interest groups

Total


In-Kind Services (hours, equipment, or other forms of assistance and estimated dollar value)

Volunteers (number of people and hours, and estimated dollar value)

7. Legislative authorities used by each participant

8. Value added by Coastal America Partnership including Government Performance and Results Act (GPRA) goals achieved through this collaboration (500 words or less)

9. Project Status

• Initiation date:
• Completion date:
• Current stage (Initiated - I, Underway - U or Completed - C)

10. Contacts

11. Any additional information/comments