Current through Register Vol. 24-18, September 15, 2024
The requirements of this section do not apply to suction
dredging for mineral prospecting covered in WAC
220-660-300, or to diver-operated
dredging for aquatic plant control covered in WAC
220-660-290.
(1)
Description: Dredging
includes removing substrate or sediment from rivers and lakes to improve vessel
navigation and to maintain navigational channels and flow conveyance. Dredging
is also used to clean up contaminated sediments.
(2)
Fish life concerns:
Excessive deposition or aggradation may interfere with land use, hydraulic
flow, and fish passage, and may cause stranding of fish. However, dredging can
alter multiple fundamental channel processes, and effects can propagate
upstream or downstream of the modified channel reach, or into tributaries, and
may affect channel stability, habitat features, and flood plain interactions
within and beyond the project area. Direct impacts include mortality,
physiological stress, or displacement of fish and other organisms, increased
sediment transport downstream, damage to riparian zone vegetation, and
temporary loss or imbalance of nutrients and food supply. This activity usually
decreases the complexity and diversity of habitat that supports fish
life.
(3)
Dredging
design:
(a) The department may not
authorize dredging in fish spawning beds unless it creates or improves the
access or quality of fish spawning beds as part of an approved restoration
project.
(b) The department will
evaluate the potential impacts of dredging and the disposal of dredged
materials in eulachon spawning areas and provision these projects based on
project location, seasonality, scale, frequency, and duration and on run
timing, run size, and presence/absence in the work area.
(c) The department may require a preproject
channel survey or assessment by a qualified professional to determine the root
causes of a sediment deposition problem and the potential channel changes that
may result from dredging. This provision does not apply to maintenance dredging
of navigational channels and berthing areas, boat ramp and boat launch
approaches, and hydroelectric dams.
(d) The department may require pre- and
post-dredge project bathymetric data for dredging of navigational channels and
berthing areas.
(e) Use the dredge
types and methods that minimize adverse impacts to fish and the habitat that
supports fish life.
(4)
Dredging construction:
(a)
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.
(b)
Operate a dragline or clamshell to minimize turbidity. During excavation, each
pass with the clamshell or dragline bucket must be complete. Stockpile dredged
material in the location shown on the approved plan.
(c) To avoid fish stranding, the bed must not
contain pits, potholes, or large depressions upon completion of the
dredging.
(d) The department may
require a person to use a boom or similar device to contain floatable materials
when dredging a lake or pond.
(e)
Dispose of dredged bed materials at a department-approved in-water disposal
site or outside the flood plain so materials will not reenter waters of the
state. The department may allow dredged material to be used for beneficial
projects such as beach nourishment or capping contaminated sediments.
(f) 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.
