Introduction

The objective of this task is to determine a sediment budget, on a lakewide basis, which can be updated to keep track of sediment supply to various reaches around the Lake Michigan shoreline. This analysis includes information for various reaches, such as: potential alongshore transport rates; fraction of beach size sediment made available through erosion; other sources of sediment; and, sinks of sediment. This analysis provides important information for predicting the sand cover on cohesive shores, and changes, which may effect future recession rates. Essentially, a predictive system will be developed to evaluate changes to sand cover on cohesive shores (or erosion of sandy beaches) where the sediment budget has been influenced by natural or human factors. This will introduce a feedback mechanism in to the modeling system as changes to sand cover may influence recession rates which in turn will influence yield of eroded sand (and sand cover), which in turn effects recession rates. This feedback mechanism will be addressed in the overall Flood and Erosion Prediction System through iterative model runs. It is likely that the fully interactive predictive system involving both sediment budget and coastal process modules (i.e. complete with feedback) would only be applied on a littoral cell basis (i.e. not on a lakewide basis). The sediment budget system for predicting changes to sand cover is currently being checked against the recent changes that have been experienced downdrift of New Buffalo.

An important task in the development of the sediment budget aspect of the Flood and Erosion Prediction System by Baird has been creating an automated approach for assessing bypassing at all partial and full littoral barriers around the lake. The influence of dredging operations the sediment budget has also been incorporated. The system will therefore be ideally suited to the estimation of the cost (potential damages) of increased dredging requirements under low water scenarios.

In 1998, Baird & Associates completed the development of the sediment budget module of the Flood and Erosion Prediction System. Testing of the system was completed at some of the eight study sites and required information to implement the model on a lakewide basis has been obtained and included in the system.

1999-2001 Activities

In 1999, assessments were made of the influence of sediment budget on the evaluation of historic and prediction of future recession rates for each of the five prototype counties. The sediment budget module of FEPS is being applied to complete this assessment. Sediment budget assessments were completed for the historic period of record corresponding to the available recession rate data. Due to the lack of complete SHOALS data at the harbor mouths, complete sediment budget analysis could not be performed. Further data is necessary.

This assessment will be used to assess impacts of sediment budget changes on recession rate predictions. Tests of sediment budget outcomes using the FEPS are being completed for each of the alternate water level scenarios to test the influence of different wave and lake level conditions on sand transport rates and sediment budget. The new SHOALS data was insufficient at the harbor mouths. Hydrographic surveys will be conducted to provide the data necessary to complete the sediment budgeting. This work will be completed in 2001.

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