Erosion

About Coastal Erosion

Coastal erosion is a natural process that continually affects the Oregon coast. Erosion becomes a hazard when human development or public safety is threatened. Beaches, sand spits, dunes, and bluffs are constantly affected by waves, currents, tides, and storms, resulting in chronic erosion, landslides, and flooding. Changes may be gradual over a season or many years. Changes may also be drastic, occurring during the course of a single storm event. Erosion may be caused by large waves, storm surges, rip cell embayments, high winds, rain, runoff, flooding, or increased water levels and ocean conditions caused by periodic El Niños. Coastal dunes and bluffs comprised of uplifted marine terrace deposits are especially vulnerable to chronic and catastrophic erosion. Coastal erosion processes create special challenges for people living near the ocean, requiring thoughtful planning in order to minimize the potential dangers to life and property. Attempts to stabilize the shoreline or beach are often futile, because the forces that shape the coast are persistent and powerful. Poor understanding of a coastal system can result in dramatic problems, such as those documented in the story of Bayocean Spit.

Investigating Coastal Erosion

How do we know if a particular beach is affected by erosion, and if it will continue to get worse or improve? Scientists at the Oregon Department of Geology and Mineral Industries are conducting research to answer these sorts of questions. They have been using a variety of technologies to quantify the changes in Oregon beaches that have occurred over the last 10 years.

One DOGAMI project used three different USGS LIDAR surveys (from 1997, 1998, 2002) to see how beach morphology has changed over time. LIDAR is short for "Light Detection And Ranging" and is an active sensor technology, similar to radar that transmits laser pulses to a target and records the time it takes for the pulse to return to the sensor receiver. Very detailed beach height or topography data can be collected by LIDAR sensors placed on small aircraft. You can see where areas have eroded or accreted sand by comparing the same cross section of a beach in two different LIDAR surveys. To browse the results of the LIDAR Beach Morphology study via a map for all north coast Oregon beaches click here.

Another DOGAMI research project involves on-site monitoring of the Rockaway littoral cell for changes in beach morphology. This segment of coast was chosen because it contains a combination of pristine shoreline, engineered structures (jetties and riprap revetments), and densely developed shorelands. This project incorporates backpack GPS surveys of specific beach profiles with larger scale "surface mapping" of beaches using a 6 wheel amphibious ATV vehicle. The cross-shore backpack GPS surveys of the 25 beach profile sites are carried out approximately bimonthly and/or after major storms, and can reliably detect elevation changes greater than 4-5 cm. The ATV along-shore survey follows transect lines that are spaced approximately 15 - 20 m (50 - 65 ft) apart and extend for some 3 - 4 km (1.9 - 2.5 miles) in length along the shore. Preliminary data and further information about this study can be found here.

Planning for Coastal Erosion

So how does an Oregon coastal community plan around coastal erosion? Typically, local governments will use the best information available, from DOGAMI’s efforts or from littoral cell management planning projects (see below). This information is then used to assist coastal residents and builders in making decisions about development.

Public Education - Understand before you Build!

 Detailed, current maps and data are available for many areas of the coast, but not all. However, good sources of information about coastal hazards are available. One excellent resource is a video which is designed to help coastal residents and prospective property buyers understand how coastal processes may affect their choices and opportunities. This video, titled “Living on the Edge: Buying and Building Property on the Oregon Coast”, was produced by Oreogn Sea Grant and the Oregon Coastal Management Program. The video is intended for developers, lenders, buyers, builders and coastal homeowners. 25 minutes long, the video also provides information about wave, winds and rain on coastal beaches and bluffs. It is available for $9.95 from Sea Grant Communications, Oregon State University, 322 Kerr Administration, Corvallis, OR 97331. Include $2.00 for shipping and handling of the first DVD, and $1.00 each for additional copies. Or, click here to order online.

 

 

What is a Littoral Cell Management Plan?

A littoral cell management plan is a comprehensive hazards management strategy focused on the reduction of risk to new and existing oceanfront development from coastal hazards. A littoral cell management plan typically includes: littoral cell inventories, a chronic hazards management strategy, and implementing mechanisms. The plans are built as map and inventory projects using Geographic Information System [GIS] software.

  • The Littoral Cell Inventory is a collection of information describing physical, biological, and cultural characteristics within a given littoral cell or subcell. This inventory information, which can be in map, database, and text formats, forms the basis for decision-making.
  • The Chronic Hazards Management Strategy is a description of preferred management measures and the policies and procedures needed to implement them. Two parts of an overall chronic hazards management strategy can be identified:
    • The Hazard avoidance strategy, which focuses on policies and procedures pertaining to the siting and design of new development, and
    • The Beach and shore protection strategy, which focuses on policies and procedures pertaining to hazard alleviation for existing development.
  • Implementing Mechanisms include local ordinances, coordination agreements, memoranda of understanding, or other similar types of documents which adopt policies and procedures prescribed in the management strategy. These materials, together with monitoring and maintenance programs, are needed to ensure the success of a littoral cell management plan.

Where are they being done?

Littoral Cell Management Plans have been developed for the Newport, Netarts \\ Oceanside, and Bandon areas.


Information provided by Oregon Department of Geology and Mineral Industries and the Oregon Coastal Management Program
 

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