Many of America's urban beaches today are threatened due to sand loss caused by human activities including harbor dredging and shore armoring. Attempts to mitigate these problems are often too little-too late. Cumulative impacts of activities that reduce the supply of sand to coastal beaches is sometimes difficult to assess but should be considered in any shore management plan. A detailed "sediment budget" that identifies sinks and sources for sand can provide a useful starting point. Sediment budgets are approximations of the yearly balance of sand entering a self-contained coastal system (coastal cell) through rivers and shore erosion, and exiting the system through loss to deep water, entrapment in an embayment and upland loss.
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