Dingley Island Tidal Flow Restoration Project
Feasibility Studies
Hydrodynamic and Geologic Sedimentation Studies and Biological Survey
June 2001
Project Purpose:

Hydrodynamic Study: Prediction of flow velocity will be based on the width of opening and alternative depths to which sediment might be removed beneath the bridge span. Based on prediction, recommendation will be provided on the appropriate depth to which sediments should be removed in order to minimize excessive erosion. Bedrock depth has already been determined to be at 20'. Chart from 1870s shows tidal flats in this area.

Provide recommendation on best width and depth of opening based on reasonable cost effectiveness (since entire causeway cannot be removed to achieve best biological effect).

Provide bathymetric contour map and contour map of causeway area.

Examine the sediment composition on either side of causeway and out as far as projected effect based on recommendations above.

Predict rates of erosion/deposition.
Predict where existing silt will move and its depth.
Predict how long it may take to be moved and how it will affect habitat for soft-shell clams
Predict the long-term effect on these clam-flats if tidal flow is not restored.

Biological Survey: Provide baseline data on shellfish population on either side of causeway as far as current population boundaries (about 300'). Post-construction, shellfish data may be collected by Bowdoin College students and Harpswell shellfish harvesters.

Notes: Site will be visited at high tide to measure different levels/depth of water on either side of causeway. Clam-flats are exposed for about 2 hours on either side of low tide. Depth of water at high tide is about 6'. Tide predictions are the same as for Portland.

Point of Contact: Elsa Martz

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