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PDFWAC 220-660-410

Dredging in saltwater areas.

(1) Description: Dredging includes the removal of substrate to improve vessel navigation and to maintain navigation channels. Dredging is also used to clean up contaminated sediments.
(2) Fish life concerns: Dredging may result in changes in bathymetry, habitat conversion, and changes to nearshore zone ecosystem dynamics such as salinity intrusion. As a result, dredging may convert intertidal and shallow subtidal habitat to deeper subtidal habitat. Dredging may affect the plant and animal communities that are uniquely adapted to the particular light, current, and substrate regimes of intertidal and shallow subtidal areas. In addition to changing the habitat, dredging equipment can injure or kill fish and shellfish during the uptake of sediments and water. Suspended sediments released into the water column by dredging can affect fish by interfering with breathing and feeding, and by changing predator-prey relationships.
(3) Dredging – Generally:
(a) The department may require hydrodynamic modeling to assess changes in salinity, turbidity, and other physiochemical regimes for new dredging projects and expansions.
(b) The design and expansion of dredging projects must follow the mitigation sequence to avoid or minimize converting intertidal to subtidal habitat.
(c) The department prohibits new dredging in sand lance, surf smelt, and herring spawning beds; rockfish and lingcod settlement and nursery areas; and Olympia oyster settlement areas.
(d) The department requires a seagrass/macroalgae habitat survey for all new dredging. A survey is not required for maintenance dredging or deepening the channel within the original dredged footprint.
(e) Dredging must avoid adverse impacts to seagrass and kelp beds, intertidal wetland vascular plants, and geoduck tracts.
(f) Limit the depth of the maintenance dredging to no deeper than the channel depth at the seaward end. The department may authorize dredging to depths deeper than the channel at the seaward end only in berthing areas and turning basins for commercial shipping.
(g) In addition to those timing limitations listed in WAC 220-660-320, the department may further restrict dredge timing to protect other fish life.
(4) Dredging construction:
(a) Conduct dredging with dredge types and methods that cause the least impacts to fish life.
(b) Operate a hydraulic dredge with the intake at or below the bed surface. Raise the intake up to three feet above the bed only for brief periods of purging or flushing the intake system.
(c) Operate a dragline or clamshell to minimize turbidity. During excavation, each pass with the clamshell or dragline bucket must be complete. Dredged material must not be stockpiled waterward of the OHWL.
(d) Dispose of dredged bed materials at an approved in-water disposal site or in an upland location so the materials will not reenter waters of the state. The department may allow dredged material placement for beneficial uses such as beach nourishment or capping of contaminated sediments.
(e) To minimize turbidity, hopper dredges, scows and barges used to transport dredged materials to the disposal or transfer sites must completely contain the dredged material.
(f) Whenever feasible, limit dredging operations to daylight hours to avoid attracting fish to lights.
[Statutory Authority: RCW 77.04.012, 77.04.020, and 77.12.047. WSR 15-02-029 (Order 14-353), § 220-660-410, filed 12/30/14, effective 7/1/15.]
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