BEACH NOURISHMENT BASICS

Don Barber, Geology Dept., Bryn Mawr College

(originally written as guideline for Surfrider Foundation activists)

 

WHAT IS BEACH NOURISHMENT (aka beach replenishment) ?

Beach nourishment is the process of dumping or pumping sand from elsewhere onto an eroding shoreline to create a new beach or to widen the existing beach. Beach nourishment does not stop erosion, it simply gives the erosional forces (usually waves) something else to "chew on" for awhile. The waves erode the nourished sand instead of destroying houses, roads or parking lots. Because nourishment doesn't stop erosion, nourishment must be repeated to maintain the beach. This is called "beach renourishment". It's helpful to imagine that each nourishment project (i.e., an addition of a batch of sand) has a "lifetime". The project's lifetime is simply the time it takes for all the nourishment sand to be eroded away. After that time, the beach would be back to its pre-nourishment width, and would need to be renourished with sand.

WHEN IS BEACH NOURISHMENT AN OPTION?

Beach nourishment is often proposed when beach erosion threatens to remove an existing beach, make it too narrow to be used, and/or when property behind an eroding beach is threatened. Publicly funded beach nourishment is worth considering only if the general public will have good access to the "new" or restored beach, AND when all parties have been informed that this solution is temporary, and will have to be repeated. Publicly funded beach nourishment is foolish if only a few beachfront property owners stand to benefit.

ADVANTAGES:

  1. Nourishment restores and widens the recreational beach.
  2. Structures behind beach are protected as long as the added sand remains.
  3. When erosion continues, beach nourishment does not leave hazards on the beach or in the surf zone. This is a big advantage when compared with "hard" beach stabilization structures like seawalls or groins. Seawalls may protect structures behind the beach, but they almost always cause the beach in front of the wall to become narrower. If erosion breaches the seawall, then debris from the wall will be left on the beach and in the surf. Since beach nourishment only puts sand on the beach, no debris is left when it erodes.

DISADVANTAGES:

  1. Beach nourishment sand often (in fact, usually) erodes faster than the natural sand on the beach. A good rule of thumb is that nourished beaches erode two or three times faster than natural beaches. Erosion rates can differ widely, however. The biggest factor for the lifetime of a nourished beach is the number of storms that affect the beach. Storms are unpredictable, so nourished beach lifetimes are unpredictable too. The amount of sand added per yard of beach length and the sand placement design determine the new beach width. Wider nourished beaches last longer.
  2. Beach nourishment is expensive, and must be repeated periodically. Except on very small beaches, the minimum expenditure is usually $1 - $2 million dollars; larger, longer-lasting projects often cost much more (e.g., $100 million - 1 billion).
  3. The beach turns into a construction zone during nourishment.
  4. The process of nourishment may damage, destroy or otherwise hurt marine and beach life by burying it, squishing it under bulldozers, changing the shape of the beach, or making the water near the beach too muddy. In recent decades, a variety of plants, insects, turtles, shorebirds, and other animals have become threatened or endangered as a result of human alteration of beach environments. Many of these organisms rely on storms and other natural beach processes (such as dune formation by wind) for the creation and/or maintenance of their habitats. Because of their dependence on natural beach processes, nourishment projects can affect the survival of certain species. For example, beach nourishment can modify a beach by making it too steep and/or too compacted for sea turtles to climb up and bury their eggs. Another example involves filter-feeding marine organisms, such as certain species of clams, that are accustomed to relatively clear water. These organisms can be particularly hard hit by the extreme muddiness produced by nourishment, and they can die-off in large numbers.
  5. The sand added to the beach is often different from the natural beach sand. It can be hard to find a perfect match. This means that the new material may have smaller or larger diameter sand grains than the natural beach. Such differences in "grain-size" affect the way waves interact with a beach. This will affect surf conditions and bars on the submerged part of the beach, and will also change the shape of the "dry beach", which is where people spread their towels and go for strolls. Fine-grained sand generally erodes faster than coarse-grained sand, so grain-size influences the replenished beach's "lifetime" (see point 1, above).

HOW TO REACT TO A BEACH NOURISHMENT PROPOSAL:

I. WHILE PROJECT IS BEING CONSIDERED

  1. Find out who's paying for the whole project. Funding is usually a mix of local, state, and federal money. A major cost objection to beach nourishment projects is that people who experience no benefit from the project end up paying for nourishment with tax dollars. A typical and often-used example is the federal taxpayer in Iowa who never visits the nourished beach in Delaware that he helps pay for. There is not much that can be done to help person, but publicly funded beach nourishment should not be acceptable unless the public is going to have good access to that beach. This might mean changing beach-use ordinances, building some new free parking areas, or starting a beach-user shuttle bus. Be creative, but demand access!
  2. A second major objection to beach nourishment projects is that the project engineers tend to over-estimate how long the beach will last. This skews the cost-benefit analysis, because town and state officials think, "OK, if the new/improved beach will provide a tourist attraction for 8 or 10 years, then I guess it's worth spending ten million dollars of taxpayer funds," whereas if the local officials could know that the beach will likely last only 2 years, they might reject that expenditure. Studies of past beach nourishment projects on the U.S. East Coast show that very few nourishment projects last longer than 5 years without significant (= costly) renourishment. One should be skeptical when folks when the contractors make big promises regarding beach durability.

II. DURING PLANNING STAGES

  1. Ask the project engineer about the grain-size characteristics of the sand being used for nourishment. Where is it coming from? Grain-size data should include average grain-size and the degree of sorting, which tells whether most of the grains are about the same size (well-sorted), or that there is a wide range of different sizes (poorly sorted). The goal is always to match grain-size characteristics of the source sand with your beach's natural sand. Considering any sand differences between the source and your beach, ask how the replenished beach will differ from the present beach (besides being wider due to the added sand).
    It's important to know how much mud will be brought onto the beach along with the new sand, so also inquire about the "percent mud" analysis of the source material (mud, composed of silt and clay, is any sediment particle smaller than sand; this analysis should be included with the grain-size data). Generally, mud is not found on natural ocean beaches because waves wash it away rapidly. During nourishment, however, if the source material contains a significant amount of mud (more than 5%), then organisms living in the nearshore zone just off the beach can become smothered by mud.
  2. Ask where the sediment is coming from. Sand dredged from marina basins, boat channels, or reservoirs may contain toxic material, especially if the sediments are muddy. When requesting the grain-size data noted above, it's usually a good idea to also ask for a sediment toxicity analysis.
  3. Ask what the "design beach slope" is going to be, e.g., how will the beach profile change? In other words, how steeply or gradually will the beach be sloping when the nourishment is finished? As noted above, this can be important for the survival of organisms that use the beach. Also ask how and where the sand is going to be placed on the beach. Common approaches involve either pumping sand in a watery slurry through pipes to the beach or carrying it in dump trucks. To avoid rapidly losing the sand offshore, the sand is usually then spread out on the dry beach (above the high-tide line) using bulldozers.
  4. Consider all local biological life, particularly any fragile, endangered, or threatened species. Before a project begins work to eliminate or minimize the impact on all resident species. An example would be birds that nest seasonally on part of the beach. In this case, nourishment might be carried out while the birds are away, during a non-nesting season.

III. WHEN PROJECT BECOMES IMMINENT

Before nourishment begins, take photographs of the beach from various locations. Try to find some locations that you can re-occupy during the project and after it is finished (groins, seawalls, and fishing piers are good spots to stand). Include people or buildings in the photos for scale. Don't just take photos after storms. Try to shoot them at regular intervals: like every 3 - 6 months, or at the end of the winter and the end of the summer. If done carefully, such photos can be extremely useful in describing the behavior of your beach. It also makes a great science fair project or term paper! You might also find a local earth science teacher who can show you how to measure the beach profile using the simple but effective Emery method (html link) / Emery method (MS Word .doc).

THUMBS UP or THUMBS DOWN?

The bottom-line for is that nourished beaches hardly ever perform as well as advertised. Nevertheless, in terms of recreational beach use, nourishment is always preferred over "hard" beach stabilization methods, such as building new seawalls or groins. The most important thing to remember is that none of these methods stops erosion. Erosion will continue, but a nourished beach allows continued normal beach use, while a seawall sacrifices a recreational beach to save property or structures behind the beach.

We do well to keep in mind that nourishment projects are never proposed where human structures don't exist. This is because on natural beaches, erosion does not endanger the beach itself. Shorelines eroded for thousands of years, yet beaches remained, because they could change their shape and position. Erosion only becomes a problem when we place stationary buildings, parking lots and roads too close to the beach. Thus the best course of action is to crusade against additional development of our beaches and, wherever possible, encourage people to retreat from the beach. If we get out of the way, the beach will take care of itself, and we can continue to enjoy it at a much lower cost.

 

Beach Profiling Reference: Emery, K.O., 1961, A simple method of measuring beach profiles. Limnology and Oceanography, v. 6, p. 90-93.


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