Current through Register Vol. 24-18, September 15, 2024
(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 inter-tidal
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.
