VI. B. 4. Management Recommendations |
Light reduction, which affects the growth, distribution, and abundance of submerged aquatic vegetation, is one of the most significant impacts associated with an overwater structure, and should be avoided if possible. When avoidance is not an option, light penetration can be enhanced by increasing structure height over the water’s surface (in the case of docks), increasing pile spacing, modifying structure orientation (a north-south orientation maximizes solar penetration), and minimizing the structure’s surface area and number of pilings (Short and Burdick 1996; Nightingale and Simenstad 2001b). Floating dock designs that allow minimal light penetration and ground at low tide should be discouraged. Light penetration can be enhanced under many dock structures by using grating as surface material, glass blocks, reflective material, or artificial lighting (Blanton et al. 2001).
Other considerations include placing mooring buoys and floating docks in deeper water to avoid grounding on low tides, substrate modification, and light limitation from vessel props and scouring. Properly installed mooring buoys have the least impact when midline floats prevent the anchor line from contacting the bottom substrate (Nightingale and Simenstad 2001b). Other considerations include the use of proper line lengths relative to maximum water depth, as well as the size and type of line and anchor used.
Alternatives to the proliferation of docks and pilings for residential and commercial use are the establishment of carefully placed community-use docks in areas of low potential impact. The use of treated wood pilings should be minimized where possible; a variety of alternative materials exist, including concrete, metal, or composites. Sleeves may also be placed over pilings to isolate the structure and prevent direct exposure to attached organisms or their eggs. Another approach would be to remove the pilings, although consideration should be given to the additional dispersal of contaminated sediment near the piling.
Design and placement studies should be conducted for proposed marinas to maximize current and circulation patterns and to minimize habitat loss. Other ideas include upland boat storage as an alternative to in-water moorings, excavation of upland basins rather then shallow nearshore areas, and placing marinas in areas of low biological abundance and diversity that will not interfere with littoral drift processes or natural wave energy. Existing water quality issues associated with the operations of docks and marinas can also be minimized via catchment systems, which collect runoff and divert it to treatment facilities.
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