Shoreline
Erosion - Impacts of Boating and Waves
Introduction
Shoreline erosion is a major source of non-point source pollution entering our rivers and streams. Shoreline erosion is defined as the process by which soil particles located on or along riverbanks or lakeshores become detached and transported by water currents or wave energy (Asplund 2000). Shoreline erosion may affect water clarity, shade submerged aquatic plants, interfere with fish use of shallow water habitat, and negatively affect property values. Shoreline erosion can be expensive to prevent and control.
Shoreline erosion is influenced by the intensity or energy of the movement of the water (waves) and the characteristics of the bank material. Water currents, waves, and fluctuating water levels are the primary factors that cause shoreline erosion, although overland runoff can also contribute to the problem. The erosive characteristics of the shoreline also affect erosion rates - materials such as sand erode at a much higher rate than do clay soils. The amount of vegetative cover, slope, and the degree of human disturbance also affect shoreline erosion.
Shoreline erosion is a natural process; however, human activities exacerbate the rate. Erosion does occur naturally with storm and flood events but is usually minimal and localized.
Among the main causes of shoreline erosion on navigable rivers are the waves generated by river traffic and wind (Bhowmik 1982). There is anecdotal evidence from around the world of the impacts of river traffic, particularly powerboats:
In conducting a comprehensive shoreline assessment, the Tennessee Valley Authority (TVA) finds that 8% of their 11,000 shoreline miles are in poor condition. This may seem a small percentage; however, 880 miles of TVA’s shorelines are highly degraded. TVA biologists attribute three factors to the poor condition of these shorelines: highly erodible soils; more intensive land use; and extensive wave action from wind and watercraft. (TVA River Neighbors May 2002)
Kayakers on the Charles River, Cambridge, Massachusetts, witness excessive shoreline erosion, with the worst occurring on the Boston side of the river. “Scallops” in the shoreline are visible where chunks of land are falling into the river weekly.
Much of the problem is attributable to boat wakes...the wash from one or two of the many power boats cruising the river may not amount to much, (but) the continual force created by thousands of craft passing up and down the river exerts a powerful force on the shore. (The Charles River Conservancy)
In a Final Environmental Impact Statement, the TVA reports that they attempt to preserve the shoreline “that is being affected by deep-hulled boat traffic and recreational activities.”
The Wantastiquet Region web site (www.crjc.org/wantastiquet.htm) reports on activities and problems associated with the Wantastiquet River, among them,
The estuaries of New South Wales, Australia, are reportedly used for recreational and commercial boating. The New South Wales Department of Natural Resources dnr.nsw.gov.au/care/water/estuaries/factsheets/humanimpacts/human_activities.html#boating reports that adverse effects of boating include:
Little or no empirical data are provided in these and dozens of other references to document specifically the problem and the degree of shoreline erosion due to recreational powerboats, or whether boats are even a significant cause. While empirical evidence may suggest a cause-effect relationship between boating activity and shoreline erosion, it is important to examine scientific reports to determine whether there is support for the visual and intuitive evidence. A number of studies have been conducted that document the shoreline erosion that occurs from barge traffic, powerboats, and jet skis.
