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Shallow water habitats rank among the most important components of the Chesapeake Bay ecosystem. The operation of watercraft in these sensitive environments increases the hydrodynamic energy of the site through the generation of surface wakes and propeller wash. When this energy exceeds the shear force of sediment material, sediment resuspension occurs. The degree and pattern of resuspension determine the impact to resident biota. In this study, a variety of common recreational watercraft were operated in the navigable headwaters of seven creeks in the mid-Chesapeake Bay area. The craft were operated according to existing regulations and the rules of good seamanship along an established course that ranged in depth from 0.3 to 1.8 m. Bottom sediments from the courses on each creek were analysed for texture prior to testing. During testing, turbidity was measured in Nephelometer Turbidity Units (NTU) at the surface, middle, and bottom of the water column at each of the depths. No significant differences in turbidity were found among the 10 watercraft (ranging from a personal watercraft to a 235 hp displacement hull vessel) tested on the different creeks; however, when resuspension was intentionally induced, only turbidity at the lower portions of the water column was significantly increased. This suggests that studies of this type require sampling throughout the water column in order to fully evaluate potential adverse effects on sediment stability, regardless of the source.
Author: Ailstock, MS, Hornor, SG, Norman, CM and Davids, EM
Year: Undated
Document Source: Database
Avalability: Digital
Interaction: Erosion
Confidence: Good
Quantified: Quantified
Interaction significance: The study was designed to assess the impacts of watercraft on shallow water creeks in Anne Arundel County, Maryland. It focused on the effects of recreational watercraft that are operated according to existing regulations and under the rules of good seamanship. The conclusion of the study was that there was no significant increase in turbidity due to resuspension under these restricted operating conditions. The combination of an 11 kmph no wake limit and its effect on reducing navigational errors is significant since every craft tested could produce forces capable of resuspending the natural sediment of the tributaries.
Context: Th study focused on a specific water body and acknowledged that site specifics could effect the outcome, such as extant environmental conditions including water depth, current, tidal flow, bottom contour, creek width and volume, sediment characteristics, time of year, and potential activity by resident bottom dwelling biota.
Mitigation/Best practice: Speed and no-wake restrictions were found to be effective in relation to disturbed sediment.
Download the report: Resuspension of sediments by watercraft.pdf (129.64 KB)
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