traffic to pass over or through the dunes without causing further damage. Concentration of runoff Beaches provide a filter for runoff from the coastal plain. If the runoff is naturally dispersed along the beach, water borne silt and organic matter will be retained on the land and will feed the flora in the coastal area. Runoff that is dispersed along the beach will tend to percolate through the beach and may emerge from the beach at low tide. The retention of the freshwater may also help to maintain underground water reserves and will resist salt water incursion. If the surface flow of the runoff is diverted and concentrated by drains that create constant flows over the beach above the sea or river level, the beach will be eroded and ultimately form an inlet unless longshore flows deposit sediments to repair the breach. Once eroded, an inlet may allow tidal inflows of salt water to pollute areas inland from the beach and may also affect the quality of underground water supplies and the height of the water table. Deprivation of runoff Some flora naturally occurring on the beach head requires freshwater runoff from the land. Diversion of freshwater runoff into drains may deprive these plants of their water supplies and allow sea water incursion, increasing the saltiness of the groundwater. Species that are not able to survive in salt water may die and be replaced by mangroves or other species adapted to salty environments. Inappropriate beach nourishment Beach nourishment is the importing and deposition of sand or other sediments in an effort to restore a beach that has been damaged by erosion. Beach nourishment often involves excavation of sediments from riverbeds or sand quarries. This excavated sediment may be substantially different in size and appearance to the naturally occurring beach sand. In extreme cases, beach nourishment may involve placement of large pebbles or rocks in an effort to permanently restore a shoreline subject to constant erosion and loss of foreshore. This is often required where the flow of new sediment caused by the longshore current has been disrupted by construction of harbors, breakwaters, causeways or boat ramps, creating new current flows that scour the sand from behind these structures and deprive the beach of restorative sediments. If the causes of the erosion are not addressed, beach nourishment can become a necessary and permanent feature of beach maintenance. During beach nourishment activities,