Blind Pass Project Update

Bayous Preservation Assoc.February 9, 2011

Project Goals Provide a stable pass opening with a 5

Year maintenance schedule

Increase water circulation in Clam & Dinkins Bayou (4 Day Flushing Cycle in Clam Bayou)

Improve habitat for Mangroves, Seagrasses, Shorebirds, Benthic Invertebrates, and Fisheries.

Enhance recreational opportunities in the Pass and along the adjacent beach on Sanibel Island.

Supplement storm protection along Sanibel Island and Bowmans Beach.

Continue a long term management program to maintain Blind Pass and the surrounding ecosystem.

Stable Pass OpeningWhat is the Definition of Stable Opening

Relative to Blind Pass?

Maintenance Dredging scheduled on an average 5 yr interval.

Water mixing sufficient to allow aquatic animals egress and ingress thru Blind Pass and water quality supports seagrass and mangrove habitats.

The Path Here Pass Opened July 31, ‘09. 148,000 cyds Removed at a cost of $2.5 M. Initial Infilling did not Warrant ‘Resweep’. Instigated a 6 Month Monitoring Event

Six Month Monitoring Results

Parameter Predicted(ECE 2006)

Measured(CEC 2009)

% Difference

Peak Flood Velocity*

3.8 ft/s 2.7 ft/s 41%

Peak Ebb Velocity*

4.1 ft/s 2.9 ft/s 41%

Cross Section Area

1,500 ft2 1,165 ft2 29%

Spring Tidal Prism

100*106 83*106 20%

*Values are listed as daily averages

Six Month Monitoring Results

6 Month Monitoring Conclusions

Project is Performing Well but Maintenance Schedule is

UnknownAdditional Monitoring is required to identify

if dredging is necessary to maintain an ‘open’ pass thru the initial 5 year

schedule.

6 Month Management Steps

Evaluate design parameters and modify permit as required.

Repeat monitoring efforts at 1 Year time frame to further identify stability parameters and shoaling trends.

Continue Joint Management Effort w/ CEPD, City of Sanibel and Lee County.

Proposed Sediment Basin

Additional Fill Area(s)

1 Year Monitoring

Parameter Predicted(ECE 2006)

6 Month Measured

(CEC 2009)

1 Year Measured

(Lee Co. 2010)

Peak Flood Velocity*

3.8 ft/s 2.7 ft/s 1.5 ft/s

Peak Ebb Velocity*

4.1 ft/s 2.9 ft/s 1.5 ft/s

Cross Section Area

1,500 ft2 1,165 ft2 932 ft2

Spring Tidal Prism

100*106 83*106 41*106

*Values are listed as daily averages

2009 Stability Curve

1 Year Management Steps

Continue to monitor the pass stability and shoaling and evaluate if cost / benefit supports a maintenance event in summer 2011.

Repeat monitoring efforts at 2 Year time frame to further identify long term stability parameters and shoaling trends.

Continue Joint Management Effort w/ CEPD, City of Sanibel and Lee County.

Coordination Moving Forward

• Weekly updates posted to Lee-County.com

• CEPD will be main point of contact for residents.

• Lee County staff will attend CEPD meetings to address any questions when requested.

Common Questions

• 1. Who is responsible for maintaining the pass? No one is required to maintain the pass.

• Lee County has agreed to be the lead in a 3 way interlocal agreement to maintain the pass. The other partners are the City of Sanibel and the CEPD. The Florida DEP also participates in maintenance activities.

Common Questions

2. Did removing the ebb shoal in Redfish Pass decrease tidal flow and increase shoaling in Blind Pass?

The opening of Redfish Pass in 1921 is believed to have played a significant role in reducing the tidal prism for Blind Pass.

Common Questions

3.Why did the maintenance dredging not connect to PIS?

Engineering justifications did not support the connection. Only the area required to establish necessary flows / velocities was included in final design.

Initial Design

Concept

Final Design Concept

Common Questions

4.Is the jetty on Captiva the problem with the pass closing?

No, the jetty is slowing the transport of sand off Captiva .

Common Questions

5. Why was the dredging not completed as designed?

A private property owner objected to what they considered the dredging of their land.

Based on 6 month monitoring results, this modification is not believed to have created significant impacts. (Less than 3% of volume avoided by change)

Common Questions

Common Questions

6. Would a jetty on Sanibel’s side solve the problem of shoaling and closure?

It is believed a structure on the Sanibel side would create or add adverse impacts to the sediment transport and is not justifiable.

Common Questions

7. If beach nourishment was stopped for Captiva Island, would Blind Pass stay open?

Stopping sand placement on Captiva would create impacts to both Captiva and Sanibel and is not believed justifiable.

Probable Impacts w/ NO Nourishment

Photo Provided by CPE

Common Questions

8. Where is the sediment coming from that is filling in Blind Pass?

Generally in the winter months the transport is from north to south, (Captiva); and in the summer months from south to north (Sanibel).

Volumetric Changes Aug ‘09 to Oct ‘10

Graphic provided by CEC

Common Questions

9.Why can’t the sand from Blind Pass be placed on Sanibel or Captiva?

It is currently being placed on Sanibel. The option to place it on Captiva is being investigated, however this is considered ‘Backpassing’ by State DEP and not generally permitted.

Common Questions

10.Is there a more efficient way to keep the pass open with permitted maintenance dredging, prop-dredging, or removal by backhoe of the sand bars as they build up, not after they block the pass?

The design goal of any project is to have it naturally maintained.

Common Questions

11.What needs to be done to improve the project design so that the pass stays open as long as possible?

We need gain an understanding of the hydraulic behavior of the pass through continued monitoring.

Common Questions

12. Are there funds available to complete a maintenance event?

This is questionable. Probably not to clean the anticipated 90,000 cyds. However with a dredge in the area, a ‘competitive’ price may be obtainable.

Common Questions

13. When should the permit be approved?

Expected by June 2011.

14. When should the dredge be available?

Expected September 2011.

Common Questions

15. Are the City of Sanibel, CEPD, and Lee County in general agreement about what needs to be done to maintain the pass?

Each party recognizes the benefits of having an open pass. Activities necessary to accomplish this will be on-going and costs must be analyzed accordingly.

Special Thanks to Coastal Engineering Consultants Inc.

Aerial Dated October 2009

Thank you!