Integrated WEB GIS coastal planning

The main anthropogenic interventions causing coastal erosion are the following one.

1. DAMS

Thousands of dams have been constructed on rivers worldwide, creating reservoirs which retain a large part of the sediment discharge from the catchment areas. The best-known example of coastal erosion related to sediment trapping behind a river dam is the erosion of the Nile Delta coast after the construction of the Low and High

Aswan Dams in the 1960´s and 1970’s. The coastal erosion reached a level of 42 m/year during the period 1969-1971, mainly because of the reduction in the river discharge and the construction of the Low Aswan Dam, whereas a drastically increased erosion rate of 129 m/year after 1971 was caused by the construction of the High Aswan Dam.

2. SAND MINING IN RIVERS AND BEACHES

Sand mining in rivers is a major cause of coastal erosion in many Countries. Sand mining in a river lowers the riverbed, causes bank erosion and reduces the supply of sand to the coast. Beach sand mining directly reduces sand volume.

3. AGRICULTURAL DRAINAGE SYSTEMS

They cause redistribution of sediments in the longshore making the littoral cell adapt to the new sediment budget status.

4. CONSTRUCTIONS CLOSE TO THE COAST

Coastal constructions on beaches may destroy sand dunes or lose their stability.

Sand-dunes are a natural defense of beaches against erosion; buildings on the beach, on the other hand, act as seawalls making waves erode their foot until they collapse.

5. HARD CONSTRUCTIONS FOR COASTAL PROTECTION

Hard constructions, like ports, groynes, detached breakwater, seawalls/ roads and revetments cause landform migration interruption. Changing the sediment fluxes to the sea, stabilizing sand formations or altering the sediment transport pathways through hard constructions leads to local changes in the sediment budget and forces the ecosystem to adapt, usually not in favor to man.

6. DREDGING IN ACCESS CHANNELS AND PORT ENTRANCES

This technical operation also reduces sand volume in the coast changing the local sediment budget causing erosion in nearby areas.

7. SEA LEVEL RISE DUE TO CLIMATE CHANGE

Climate change is widely considered as a response of nature to anthropogenic interventions and it leads to sea level rise and to changes in annual rain frequencies as well as in river supplies. The above changes directly disturb sediment diet at the coasts and may lead to extensive erosion of the most affected areas.

8. LOSS/DEGRADATION OF AQUATIC AND COASTAL HABITATS

Anthropogenic changes in ocean oxidation, water temperature, and nutrients changes, as well as mechanical abrasion leads worldwide to degradation, or even loss of aquatic habitats. Aquatic habitats, especially seagrasses (e.g. Posidonia oceanica in

Mediterranean) act as natural submerged breakwaters, minimizing the wave energy reaching to the beach. Moreover, their dead leaves and roots are stranding on the beach, offering an extra mechanical protection against erosion. In the same way, coastal habitats, such as the sand-dune vegetation, stabilize coastal sediments and are considered a very effective self-protection of beaches.

2.3. CONSEQUENCES OF COASTAL EROSION

Coastal erosion typically results in a landward retreat of the coastline. This can increase the risk of coastal flooding and result in loss of land and damage to buildings, infrastructure and agricultural land. Sudden coastal erosion events, particularly those in the vicinity of coastal cliffs, may directly endanger the lives of people. The movement of salt-water into freshwater areas (saline intrusion) can occur during coastal flooding and can impact upon the biodiversity of previously freshwater or terrestrial ecosystems. Coastal erosion may cause damage to buildings, infrastructure and utilities and any resulting debris may enter the coastal system, potentially endangering humans and coastal ecosystems. Disruption to gas utilities may also provide a fire hazard, disruption to water pipes, a flooding hazard and disruption of the sewerage network a health hazard. Moreover, beaches and coastal wetlands are normally in equilibrium with the dynamic longshore sediment transport alongside the provision of ecosystem goods and services. Wetlands are in most cases utilized for agriculture, water abstraction and livestock rearing with the associated changes in land use linked to clearing of vegetation cover and conversion of land to its current use. This has led to an influx in sediments from the catchment into the rivers, and this suspended sediment loading increases turbidity and siltation. During heavy rains, coastal and river flooding occurs with notable impact on the coastal ecosystems: coral reefs and seagrasses are destructed, or their growth is retarded due to sediment retention. These ecosystems are natural stabilizers keeping the coast in equilibrium with the dynamic waves and tides that dominate the coastal waters. Frequent flooding of rivers and coastal wetlands degrade coastal marine ecosystem by the increase in sediment loading in the recent past.

Figure 1: Examples of hazards regarding coastal erosion. Top: Loss of buildings, infrastructure facilities, middle: decrease of sand volume to compensate the natural littoral processes in the Nile delta and bottom: Degradation or loss of coral reefs due to deposition of silt and increased water turbidity. Source: The Web