An individual HPA shall be required for water level manipulation. The use of water level manipulations (drawdowns) to remove or control aquatic noxious weeds or aquatic beneficial plants by exposing plants and root systems to extreme temperature and moisture conditions may be appropriate under specific circumstances. Accurate plant identification is important to ensuring any degree of success. Water level manipulation projects shall incorporate mitigation measures as necessary to achieve no-net-loss of productive capacity of fish and shellfish habitat. The following technical provisions shall apply to water level manipulation projects for both aquatic noxious weed or aquatic beneficial plant control or removal except where otherwise indicated:
(1) If at any time as a result of project activities or water quality problems, fish life are observed in distress or a fish kill occurs, operations shall cease and both the department and the department of ecology shall be notified of the problem immediately. The project shall not resume until further approval is given by the department. Additional measures to mitigate impacts may be required.
(2) Water level manipulation shall be conducted to cause the least adverse impact to fish life.
(3) Water level manipulation shall occur gradually and in a controlled manner to prevent a sudden release of impounded water or sediments which may result in downstream bed and bank degradation, sedimentation, or flooding. Water levels shall be drawndown and brought back up at rates predetermined in consultation with and approved by the department. Instream flow requirements shall be maintained as water levels are brought back up.
(4) Disturbed bank areas shall be protected from erosion. Erosion control methods may include, but are not limited to, filter fabric and immediate mulching of exposed areas. Riprap, or other bank hardening/armoring method, shall not be allowed.
[Statutory Authority: RCW 75.08.080
. WSR 97-13-001 (Order 97-84), § 220-110-338, filed 6/4/97, effective 7/5/97.]