Caspian Sea beach erosion hazard assessment with use GIS modeling

Although seasonal and natural changes in hydrodynamic energy levels can lead to changes in sediment dynamics and accumulation rates, human activities also have the potential to modify beach sedimentary morphodynamic and structure. Clear links between human activities andsedimentary system response occur in areas where coastal construction like ports or harbors andrestricted area through hard coastal engineering structures. The main problems posed by humanintervention arise partly from construction inside the active profile of the coastal zone for example removal of foredunes and their replacement with solid infrastructure renders that infrastructure vulnerable to erosion during storm condition (passive intervention). Human alteration of sediment movement (active intervention) occurs through structure intended to alter wave and current patterns and intercept sediment in transport (e.g. groynes and jetties), and prevent sediment from being eroded (e. g. seawalls). Human activities may also impede theability of shoreline to adjust to rising sea-levels. Previous experiences show that there have been historical changes in human use of the coastline (Nordstorm2000). The first impact was probably vegetation destabilization in coastal dunes. Navigation posed the next major human treat tonatural coastal morphodynamics. Increases levels of human utilization and occupation of the coast are the other human interventions in the coastal region. Therefore human interventionscontinue with harbours construction, coastal lands reclamation and seawall construction. At now each one of these or combination of them have been developed in studied area. The degrees to which beaches are modified by human beings related factors depend on the degree to which theyin turn to modify the primary parameters of wave height, wave period, sediment size and currents condition. Human impact on wave height is normally related to structures that causeadditional wave breaking, shoaling and refraction. Structures designed to lower or eliminate wave height, as in harbor construction, will substantially reduce wave height at the shore and change the consequent beach morphodynamics and sediment size distribution. Horikawa (1988) provides an excellent overview of morphological changes caused by the construction ofstructures. The structures provide an insight into the modification of beach processes and platform that take place following the placement of the structure. In this research we are attempting to evaluate Amirabad coastal zone response to beach modification by human activities. In fact the measuring of beach morphodynamic changes, sediment dynamic variation and beach geometry structures have been the most vital targets in this research. Portimplementation, power plants unit, fishery harbor, sediment dredging and extraction, constructing oil and gas reservoir tanks and urban buildings are the most important human activities at the coastal zone of the study area. The above mentioned coastal engineering constructions which were built in the study area have unfortunately caused some morphodynamic problems such as: beach lowering, edge erosion, potential grain size changes, separation of dune and beach system and new littoral currents and sediment transport mechanism.

Keywords:

Caspian , GIS , Beach , erosion , hazard