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 COASTAL CURRENTS |
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| December 2009 |
Engineering News and Information |
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Sea-Level Rise: Washing Away Cape Cod's Precious Resources
There has been much in the news lately about global warming and its effect on sea-level rise. Although there is still considerable debate on the cause or causes of these general trends, the observance of relative rise in sea-level is fairly well documented in the field of coastal engineering. Sea levels have risen and fallen for centuries. In our most recent history, global temperature has increased approximately 0.6°C over the last 100 years resulting in a half foot of sea-level rise. Couple that with a half foot of geological rebound of the continental plate and the result is a relative sea-level rise of about a foot over the last century. State-of-the-art climate models suggest that global temperature could continue to rise between 1°C -5°C over the next century. Although estimates at best, based on this type of data, analysts predict a continued, strong correlation between general global warming trends and sea-level rise (SLR).
Changes in sea level since 1880 with a rise in sea level of about 18.5 cm (7 1/4") during the 20th century. Data obtained from 23 tide gauge stations on geologically stable land. Tide gauge date for each year was averaged. Thick black line is an average that shows trend.
Source: Bruce C. Douglas (1997). "Global Sea Rise: A Redetermination". Surveys in Geophysics 18: 279-292. doi:10.1023/A:1006544227856. | |
Surrounded by Ocean, Surrounded by Risk
Consequences of SLR are apparent to anyone who lives near the coast. It is evident to even the casual observer that our shores are eroding. During winter months, there are more frequent storm-surge flooding events. As a result, we are losing our precious wetlands to salt water intrusion and, in some areas, our beaches have disappeared altogether, putting many coastline homes and commercial properties in jeopardy. Facing potentially catastrophic losses, the emotional, environmental, and financial impact can be staggering for property owners.
Economically
speaking, Cape Cod's tourism industry faces this ongoing challenge as
our beach-going vacationers are affected by the loss of some beach
areas. Our shrinking coastline affects the future of one of the Cape's
primary revenue sources, the tourism industry.
Waterfront
hotels, restaurants and the Cape's commercial boating and fishing
industries should take note as SLR threatens their livelihood.
Consider the 40+ marinas located on the Cape's shores: structures like
boat docks, fishing piers and boardwalks are closer to the water than
in previous years; some close to being submerged.
Due
to winter weather conditions, entrances to harbors narrow to the point
of becoming unsafe to pass. The annual cost of dredging harbor
channels continues to rise, but is vital to the operation of any
marina. Owners of fishing vessels depend on passable waterways; they
must be able to dock or moor safely to maintain their trades.
Waterfront property owners around the world are facing the challenges
of SLR; the potential impact it has on their lives is dramatic.
Property
damage along our shores is undeniable. Generally speaking, the
average erosion rate is 1'-3' per year on exposed shoreline. However,
some properties on Cape Cod have seen erosion of almost 15' after only one
winter. It is evident that erosion will increase as SLR
continues. Waterfront properties are at risk of damage due to
SLR. To protect valuable real estate assets, property owners must compare the cost of providing meaningful shorefront protection versus the cost and feasibility of moving a building to higher
ground. The call goes out to property owners: be proactive; evaluate the alternatives and make an investment in stabilizing your
shoreline.
The
first step is to engage the services of a reputable engineering company
to evaluate the property and to develop structural alternatives for
protecting the property. The selected firm should be familiar with
coastal construction and regulatory permitting requirements.
Experience in understanding the coastal process and the engineering
design options for shorefront protection is a prerequisite to
developing sound plans.
The
next step is to develop a sound strategy for implementing shorefront
protection. These strategies need to be appropriate for the site and
sensitive to protecting the environmental concerns of a stable
ecosystem as well as the vested interests of the private property
owners.
Afterwards,
plans and supporting documentation for the project are assembled for
submission and review by environmental regulatory agencies.
Depending on the complexity of the project, this process can take a few weeks to several months, sometimes years, to
obtain the necessary approvals to implement project plans.
Being
well-informed about the vulnerabilities of the coast is an important
step in protecting valuable property assets, lifestyles and
livelihoods. Humanity cannot prevent disasters from occurring, but we
can plan ahead and take steps to minimize the loss when natural
disasters occur. |
Coastal Engineers and Planners Strategize to Minimize Loss
Traditional coastal management methods include soft and hard engineering solutions.
Soft engineering solutions use ecological principles and practices to "soften" the land-water interface, thereby reducing erosion without compromising the integrity of shorelines. Soft solutions work with existing natural resources to reduce the effects of erosion while also enhancing wetland habitat value. Some commonly used soft solutions include fiber rolls, sand bags, and drift fences put in place to slow down the effects of SLR. Fiber rolls remain useful if they are located above the water line; if not, they eventually decompose and are no longer effective. For the most part, soft solutions are eco-friendly, but may not be dependable or durable, and may become cost prohibitive over their serviceable life if installed in the wrong location.
Hard engineering solutions include structures made of concrete or stone designed to absorb the energy of incoming water. Breakwaters, revetments and bulkheads are designed and constructed using longer-life materials. These engineered structures provide a longer-term solution to shorefront protection. In aggressive erosion areas, supplemental beach nourishment is required to maintain the sediment transport budget.
Beach nourishment on a localized level will help to maintain existing properties. On a large scale, channels can be dredged for significant area maintenance.
Locally, engineers and planners are looking at SLR projections for the Cape's coastlines. Beach nourishment strategies on a localized level help to maintain existing properties. Many towns now require beach nourishment as mitigation to shorefront protection projects. |
American Society of Civil Engineers Update (ASCE.ORG)Civil
and coastal engineers and planners have been called to action to revise
engineering standards for the future and to research new materials and
construction methods. In June of this year, a Civil Engineering and
Climate Change Protocol was adopted at the triennial conference of
ASCE, the Institute of Civil Engineers and the Canadian Society for
Civil Engineering. Key-note speakers at this gathering cited recently
updated ASCE policies that prompt engineers to adapt our infrastructure
to manage climate change. Coastal engineers will need to make design
adjustments due to climate change as it relates to SLR. |
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Shoreline 'Savvy': A Must for Property Owners
Homeowners can protect their properties by being well informed about current building code requirements and permit regulations. Buildings that were constructed after 1978 have a major challenge in that hard engineering solutions such as sea walls, revetments, or breakwaters are generally not allowed. (Potential future changes in legislation that allow owners of structures built after that time to invest in shoreline protection may aid in the Cape's struggle against the effects of SLR.) As real estate generally appreciates over time, coastal property owners should note that proper erosion control and stabilization measures will add to their property value. The importance of being proactive is paramount. A shoreline evaluation assessment of existing conditions and longer-term risks, executed by a certified professional, is therefore, a worthwhile investment.
 As the effects of SLR escalate on Cape Cod, protecting and maintaining shorelines using traditional coastal management methods is likely to become more challenging environmentally and economically. The cost of protection can be significant, but the reassurance that results is worth the investment economically and ecologically.
Coastline protection measures that are in place today may not be effective going forward. They will not be high enough nor run deep enough to thwart damage due to the effects of sea-level rise. |
 Storm Stories: Pleasant Bay, Chatham
Breaches in barrier beach systems are natural occurrences on Cape Cod. These breaks and overwashes are occurring at increased intervals due to the effects of sea-level rise (SLR). The coastal community has seen sea levels all over the world rise in response to global warming.
For decades, North Beach, Chatham has been affected by SLR. Breaks have occurred and have remained open for extended periods of time, resulting in repositioned channel openings and modified shorelines. Property owners on Pleasant Bay, which sits across from North Beach and includes shorefront in the towns of Chatham, Harwich, Orleans, and Brewster, used to be protected by the existing barrier beach and by sea walls and bulkheads already in place. In 1987, an inlet into the bay developed. The area's erosion rate increased from 1.5 feet annually to 4 feet annually, thus bringing high tide levels up by as many as 5 feet. While some area homeowners were already in the process of securing permits to refit their shoreline structures, this new path for sea water brought the topic of shoreline protection to the forefront.
Fast forward to 2007 - a very active winter storm season pounded the outer shore and created another breach, resulting in a new inlet into Pleasant Bay. Homeowners on Pleasant Bay went on alert as they noticed higher than normal tides and increased erosion on the banks of their properties. With experience gleaned from the development of the inlet of '87, the response plan for the '07 inlet called for a combination of preventive measures including beach nourishment and sand drift fencing as well as increasing the height of current sea walls. These formidable hard structures were beneficial for some time but, with two inlets allowing water to move readily into the bay, these protectors had started to fail.
To monitor conditions, a system of benchmarks was put in place to assist in measuring the amount and direction of sand movement. Both visual and digital markers become visible when sand levels drop below an acceptable level. Additionally, the coastal engineering community conducts surveys on an annual basis and after any significant storms to track changes in the Pleasant Bay area.
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The Future of Pleasant Bay
 The last two years have brought additional changes to Pleasant Bay. With more erosion anticipated, proactive property owners are having assessments performed now. As we enter the 2009 storm season, it is probable that we will see further changes to what remains of the barrier beach. As sediment moves and settles, some of the additional sand could help to stabilize the shoreline, but may also clog area channels.
As for the future of Pleasant Bay, it is clear that the area will continue to evolve. According to Chatham Coastal Resources Director, Ted Keon, water resource officials are proceeding on the assumption that the new inlet (2007) will ultimately dominate and replace the original inlet (1987). Currently, the configuration of the two inlets is causing a more efficient tidal exchange between the inner estuary and the Atlantic Ocean, causing both higher high tides and lower low tides than were previously occurring. For property owners, it is clear that they, too, must evolve with enhanced measures to armor their shorelines and protect their properties. |
John Z. Demarest Joins Coastal Engineering Company
Coastal Engineering Co., Inc. is pleased to announce that John Z. Demarest, Jr., PLS, has joined the firm in our Land Surveying Division. John has more than twenty-six years of land surveying experience on Cape Cod and was a partner in the land surveying and civil engineering firm of Demarest & McClellan Engineering, Yarmouth, MA for over ten years.
John brings a wealth of expertise in all facets of land surveying including property boundary surveys, existing conditions and topographic surveys, subdivision design and plans, easement and right-of-way plans, construction surveys, ALTA/ACSM land title surveys, and Massachusetts Land Court.
508-255-6511. He looks forward to assisting you with any of your land surveying needs. | |
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