Dredging Cape Cod's Waterways
Cape Cod is populated with many harbors, channels, and estuaries th
at offer access to Nantucket Sound and Cape Cod Bay. Within their watershed live abundant fish and plant life. At the end of the aquatic life cycle of plants and fish, their remains break down and settle to the bottom. This naturally-occurring, organic material is called silt. While silt levels can fluctuate seasonally and with tidal flow, at some point the amount of silt can become excessive affecting the ecological health of the environment and hindering safe boat navigation.
Silt accumulates on a continual basis with the natural break down of organic matter. As organic matter settles to the bottom, it gives off nitrogen, which in turn encourages invasive growth of vegetation. Fluctuating nitrogen levels in the water have a direct effect on silt production. As the level of nitrogen increases, it creates an environment conducive to algae growth. Algae blooms, dies, and then becomes part of the silt material. Nitrogen introduced into the water, whether naturally or via septic system effluent or lawn run off from nitrogen-rich fertilizer, encourages algae blooms, and results in degradation of the water quality through a process known as "eutrophication". The effect is increasing amounts of silt in the water.
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Eutrophication - an increase in the concentration of phosphorus,
nitrogen, and other plant nutrients in an aging, aquatic ecosystem
that results in an increase in organic material. The organic
material breaks down, enters the ecosystem, and results in large
concentrations of blooms of algae and microscopic organisms on
the water surface.
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Some say let nature take its course while others vie for strong intervention in managing waterways. Midway between these two viewpoints lies the most tenable option - periodic dredging to deepen waterways and, when possible, use the removed organic sediment in an environmentally-responsible way such as part of a beach stabilization or a beneficial re-use effort.
Dredging inner harbors is defined as removing accumulated underwater silt. It is a labor and time intensive undertaking that requires manpower, state-of-the-art equipment, precise timing, and knowledge of the dredging process.
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Case Study: Allen Harbor, Harwich Port
Allen Harbor is a manmade basin that was created in 1926. The Town of
Harwich and commercial property owners on the harbor depend on the
harbor's safe navigation to meet the boating public's needs. Residents
along the harbor need to maintain the waterway to preserve deep-water
boating access. The public wants to protect water quality and the ecological
environs around the waterway.
Since the harbor's inception, there has been limited localized dredging.
The most recent major dredging of the inner basin took place in 1952.
Today, the harbor is unsafe to navigate in some areas. Private and
commercial boat owners run their engines afoul through the silt.
The silt gets churned up and settles anew resulting in a limiting depth
of only 3-4 feet at low tide.
Current conditions in Allen Harbor warrant a dredging project. But,
suppose no intervention was made. How would Allen Harbor evolve
if it were not dredged?
Predictions are that the harbor would continue to fill in with silt, stifling
water quality and rapidly degrading environmental conditions. Boats
would operate in unfavorable, silty conditions restricting access during
full tide cycles. Commercial fishermen, who depend on safe passage in
and out of the harbor, would not be able to enter the harbor to dock
and their livelihoods could be jeopardized. Vessel owners, no longer
able to navigate the channel nor use the Town Boat Ramp, would need
to dock elsewhere or in other towns if their boating time were dictated
by limited deep water mobility.
The loss of the harbor has a trickle-down financial effect to other business
and economic interests in the town as well affecting retailers, restaurants,
and lodging businesses.
Waterfront homeowners invest in premier real estate because of location
and because of reliable deep-water access for boating. If not maintained,
a channel and harbor can fill in and eliminate that access for boating. As
a result, property values may be adversely affected by as much as 10-15%.
Environmentally speaking, deferred maintenance of the harbor may have
undesired consequences. Decades of settling sediment result in:
- Loss of shellfish and ground fish due to high turbidity levels
and low oxygen - Limited navigation that will cause large amounts of silt to be
put back into the water column - Lack of flow resulting in increased flood issues
- Loss of bird feeding habitat.
Eventually the harbor will revert to a marsh. A productive waterway for
boaters and aquatic life will be lost.
For the past three years, the Town of Harwich has worked diligently to
get regulatory approvals to dredge, dispose of the dredge spoils taken
from Allen Harbor, and to gain support from the town to share in the
cost of this betterment project. At the 2011 annual Town Meeting,
residents of Harwich approved a $2.6 million, 10-year debt exclusion
to dredge Allen Harbor. That cost will be shared among the Town of
Harwich, businesses surrounding the harbor, and abutting residents.
The Town of Harwich has illustrated the power of a cooperative public-
private endeavor and may serve as a model for other Cape towns whose
harbors are in jeopardy. The stakeholders in the Allen Harbor dredging
project realized the importance of returning Allen Harbor to a healthy
state. Concerned taxpayers, business owners, and residents came together
to work toward a common goal. In doing so, they have engineered a
positive outcome for Allen Harbor.
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Conclusion
Dredging is a proactive and environmentally responsible method of nurturing and protecting Cape Cod's waterways. The benefits of dredging include returning a waterway to a healthy ecological state; preserving an economic asset for the Town; and securing the boating public's safety. The cost to dredge can be quantified, budgeted for, and managed over the long term.
In contrast, the decision not to dredge carries a risk of harming aquatic fish and plant species, losing precious waterways, negatively impacting Town revenue, and completely altering our marine landscape - an environmental and financial price tag that is too expensive for Cape Cod.
Roy E. Okurowski, P.E.
Mr. Okurowski is the Marine Division Manager of Coastal Engineering Co., Inc. He is a registered professional engineer and a certified hydrographer with over 20 years of experience.
Send e-mail to Roy Okurowski
COASTAL ENGINEERING COMPANY, INC.
