2.0 - WORKSHOP TERMS OF REFERENCE

Title of workshop:

Petitcodiac River and Estuary Technical Workshop:
Modelling of Hydrology and Sediment in Support of an Environmental Impact Assessment

Date:

Location:

Objective:

The purpose of the Workshop is to identify technically feasible and cost-effective modelling approaches that could be used to evaluate movement of water and sediment in the Petitcodiac River and estuary under existing conditions and under a range of openings in the Petitcodiac River dam/causeway. The results of these models would be required for an environmental impact assessment.

Expected Outcomes:

1. An exchange of information on field measurement, data collection and modelling of hydrology and sediment in relation to the Petitcodiac River and estuary and lessons learned from case studies in other parts of the world that would be pertinent to the Petitcodiac.

2. A summary of expert opinions with regard to the existing situation: has the estuary reached equilibrium and what would occur if there were no further changes to the Petitcodiac dam/causeway?

3. A summary of expert opinions with regard to field measurement and numerical modelling of the Petitcodiac estuary, for existing conditions and for several possible openings in the Petitcodiac dam/causeway. The summary should include the advantages and disadvantages of differing modelling approaches and the constraints and limitations of different methodologies.

4. Assuming that one or two best approaches can be identified, provide an estimate of the range in cost, time and money to collect associated field data, to conduct model calibration, to carry-out model runs and analyze model predictions for various scenarios.

5. A summary of the Workshop, including an annotated agenda, an audio recording and copies of workshop presentations for use primarily by environmental planners and the proponents to be prepared by March 20, 2002.

Issues to be addressed by modelling:

The modelling must be able to simulate the existing conditions, and two or more scenarios of opening the dam/causeway up to a maximum 300 metres in width for which 20 to 50 year forecasts may be required depending on the issues. The primary issues are:

1. Estimates of the changes to the hydrodynamics in the estuary below the causeway and in the river above the causeway including: - changes to the tidal range or tidal constituents/characteristics - changes to the tidal bore within 5 km downstream of the causeway - the increase or decrease in the potential and magnitude of storm surges 10 km above and below the causeway - increase or decrease in potential for flooding of lands above and below the causeway due to freshwater runoff, mud buildup or erosion, tidal and storm surge effects, ice buildup, ice damming, the hydrodynamics of flow, supercritical to critical flow transitions, through gates or around possible bridge piers

2. Estimates of the local changes in the sediments within 5 km above the causeway and 10 km below the causeway and the resulting predicted bathymetry including erosion or/and accretion of the mudflats and location of the channel. Predictions for the fate of the accumulated sediment in the region of the causeway. The process of freeze and thaw must be considered.

3. Estimates of sediments composition and sedimentation rates, 40 km below the causeway in lobster fishing areas and shorebird migration stopovers in inter-tidal areas of Shepody Bay.

4. Estimates of the erosion or accretion of riverbanks up to 40 km below the causeway and 20 km above the causeway. Where will shore protection be needed and where are salt marshes likely to develop or diminish? Are there areas where bank erosion will be a wave dominated process and does this need to be modelled?

5. Estimates of dilution rates and fate of effluent from the primary sewage treatment plant downstream of the causeway. Dilution rates to be established for all options, including existing conditions.