Module 8 Geology: Coastal Processes and Terrain
Sediments are transported along coastlines by several processes. Rivers deposit sediments as they enter wetlands and oceans. Tidal fluxes are constantly depositing and eroding sand while waves erode sand and deposit it somewhere else. Wetland and coastal dune vegetation retains sediments. Storm surges can dramatically erode coastal sediments.
Coastal sand transport by all these methods are complex. But, the issue has become more complex with human impacts on the natural processes. Flood control measures and the damming of rivers decreases the downstream deposition of sediment. Sediment starvation of these areas typically results in our replacement of sand on our beaches. These replenishment methods are typically short-lived and very expensive. The development of coastal properties is also having a dramatic impact. The construction of groins to trap sediment as it moves down the coast leads to sediment starvation further down the coast or offshore deposition. Construction of seawalls to prevent beach erosion is problematic in that they concentrate wave activity to a localized area and result in more acute erosion. To further exacerbate the problem, the bulldozing of sand dunes for development or to provide better sea views disturbs the delicate equilibrium. Finally, the dredging of ship channels and inlets disturbs crucial flows of sediment. The anthropogenic impacts on coastal sand transportation have not necessarily been wise either environmentally or economically.
Hurricanes and Coastal Areas
Storms along the coast result in significant movement of sand. High storm surges move large amounts of sand seaward and off the coastline. The calmer spring and summer months will help the sand move back to shore, but large storm events result in a net loss of sand along the coastlines.
The federal government has historically used many measures to counteract the loss of sand from the coastline. Construction of levees and seawalls prevent storm surges from moving inland and prevent some of the loss of sediment to the ocean. History shows not all of these protective measures have been successful. Hurricane Katrina in New Orleans is a good example. The levees were not built to withstand a category 5 hurricane and resulted in the devastation and flooding of thousands of acres of urban habitat and wetlands. This displaced thousands of residents from their homes and it resulted in a significant loss of life. The United States Army Corps of Engineers was faulted for their design of the flood control and levee system in New Orleans.
Hurricane Katrina is not the only casualty of poor response by the federal government. The Flood Control Act of 1928 has pardoned many agencies and private entities from liability from inadequate planning and preparation for extreme storm emergencies. More stringent regulations need to be put in place to reduce the vulnerability of our valuable coastal cities and ecosystems.
Hess, D., & D. Tasa. (2010). McKnight's Physical Geography: A landscape appreciation (10th ed.). Location of Publisher: Prentice Hall.
USGS. (n.d.). Coastal Change. Retrieved from http://pubs.usgs.gov/circ/c1075/change.html
Wikipedia. (n.d.) Hurricane Katrina. Retrieved from http://en.wikipedia.org/wiki/Hurricane_Katrina