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 COASTAL CURRENTS |
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| Summer 2008 |
Engineering News and Information |
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Assessing the Value and Cost of Shoreline
Stabilization Methods
It is a well documented fact that beaches along our shorelines are eroding not only from loss of sand due to the forces of coastal storms, but also from the relative rise in sea level. With 50% of the U.S. population residing by or near coasts and seaports - and visits to beaches the #1 tourist destination in America - the effects of rising sea levels are of major concern to all.
Although most scientists agree that the melting of continental glaciers through global warming is contributing to this rise in sea level, there are differences of opinion regarding the predicted amount of rise and the timeframe in which it will occur. A recent report from the Intergovernmental Panel on Climate Change (IPCC) predicted the rate of sea level rise for this century to be twice the rate of increase during the 20th century.
Regardless of the actual rate of increase, it is evident that the near-term effects of tidal changes due to nature's modification of coastal beach systems are far more likely to have adverse effects on our shorelines than the longer-term sea level rise due to global warming (see below). |
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The value of protecting our shorelines
Faced with rising sea levels, shoreline stabilization and protection measures not only provide a sense of security for waterfront homeowners, but also maintain our beaches for recreational purposes, restore natural wildlife habitat, and provide storm protection for the infrastructure that supports significant portions of the American economy.
With both public and private shoreline properties gaining in value over the past years, these properties will only become more valuable in the future as proper erosion control and stabilization measures are put in place. But, these higher values also come with greater environmental risks. For this reason, a shoreline evaluation assessment - of both existing conditions and longer-term risks that may impact property values - can be a worthwhile investment. |
 How to assess shoreline risks
A shoreline property's risk assessment profile looks at a number of conditions and risk factors, including:
- Geographic location (i.e., whether the property is on a barrier beach, the ocean, a bay, or an estuary);
- Mapped flood zone profile;
- The proximity of any coastal structure to the shoreline, and its condition; and
- The historic frequency of episodic storms and storm surge levels in the area - and the future probability for occurrence and/or re-occurrence of these events.
For a nominal cost investment, this type of evaluation report can provide valuable information to assess a shoreline property's level of risk for experiencing adverse environmental conditions, such as coastal erosion and predicted storm surge. The report can also be used to assess the condition of any existing coastal structure and to estimate its remaining useful life - or to evaluate the possibility of moving those structures further away from any coastal threats. |
 What can be done?
There are a number of shoreline bank stabilization methods that can be designed and implemented, although some options may be limited by various state and local regulations. In Massachusetts, any shorefront stabilization projects need to be designed by licensed engineers to meet local and state performance standards. Also, wetland regulations do not allow protection of a property unless it is deemed to be threatened by coastal erosion by the local Conservation Commission. Aside from areas under federal jurisdiction (such as in the National Seashore), if a coastal dwelling is considered to be in jeopardy from erosion, then some degree of shoreline protection can be considered - provided it can be demonstrated that the proposed protection method will meet the wetland protection performance standards. |
| What will it cost?
In addition to evaluation and design costs, the up-front construction costs for protecting 100' of shoreline on a 10' coastal bank are currently in the range of:
- Rock revetment: $800/l.f. = $80,000
- Sand for nourishment (trucked in): $25/cy = $12,500
- Fiber rolls: $60/l.f. = $6,000 - $18,000 (for 1-3 tiers)
- Drift fencing: $50/l.f. = $5,000
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Beach nourishment (in conjunction with a county dredge project): $6.5o/cy = $3,250
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Turf reinforcement mats (natural or synthetic): $2-$3/s.f. = $2,000 - $3,000
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Beach grass planting: $1/s.f. = $1,000.
Beyond these initial costs for shoreline protection, there are also long-term beach nourishment costs to replace sand that erodes from the beach. And, since sand placed on a beach does not remain in its original location - migrating as wind and waves allow - the beach must be monitored periodically, with more sand added as needed. |
What works best?
Though many different shoreline stabilization approaches have been tried, it often takes a combination of solutions to work best. These combination approaches generally involve either a "soft" solution (plantings or fencing) or harder "armoring" (a revetment or bulkhead) - plus the addition of sand for ongoing nourishment purposes.
The shoreline stabilization methods that work best involve a combination of approaches.
Depending on the scale and complexity of the project, federal, state, and/or local environmental permits may be required. Although all shoreline projects must obtain local approval, a proactive approach that keeps projects at the local level only can make the permitting process less costly and less cumbersome.
While the costs for shoreline stabilization projects are not insignificant, if properly maintained, this adds value to the property by protecting our shorelines - and that's worth the cost, both economically and ecologically. |
 About Chatham's North Beach Break
Breakthroughs are a normal occurrence in barrier beach systems and are part of the natural process of the ocean and its shoreline. Over the past century, North Beach in Chatham has experienced many changes, including breaks and overwashes. In some instances, the breaks close up again; in others, the breaks stay open for extended periods of time, thus changing the channels and shoreline behind them.
The most recent break occurred in April 2007 as a result of a very active winter storm season. Located east of Chatham Light, the barrier beach break caused by this nor'easter created a new inlet directly across from a group of shorefront property owners - and caused an immediate 1' sea level rise!
The April 2007 barrier beach break caused an immediate 1' sea level rise! |
A number of the property owners who were directly impacted by this break recognized that if nothing were done, their coastal banks would continue to erode when higher water levels scoured the bottom of the banks. So, a comprehensive survey and feasibility analysis was undertaken - outlining the existing conditions and potential options for shorefront protection for each property - to determine what preventive measures, if any, could be taken to best ensure that the existing properties and structures would be preserved.
As a result of this analysis, a phased approach to shoreline protection was designed to stabilize the coastline and protect against further coastal bank erosion. This approach utilized a variety of solutions, including beach nourishment, native plantings, sand drift fencing, and turf reinforcement matting. In addition, ongoing monitoring surveys will be conducted at least once a year and after any significant storm event. Aerial photos will also be utilized to look at how other shoreline features, such as shoals, sand bars, and channels, may be affecting the area. These efforts will help predict what tidal changes will likely occur in this newly-created coastline area over the next 100 years. | |
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