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.