18.65.380 Streams – Specific mitigation requirements

18.65.380 Streams – Specific mitigation requirements.

In addition to the requirements in CMC 18.65.130, the following applies to mitigation to compensate for the adverse impacts associated with an alteration to a stream or stream buffer:

(1) Mitigation measures shall be addressed in the critical area report and must achieve equivalent or greater stream functions including, but not limited to:

(a) Habitat complexity, connectivity and other biological functions;

(b) Seasonal hydrological dynamics, water storage capacity and water quality; and

(2) To the maximum extent practical, permanent alterations that require restoration or enhancement of the altered stream, stream buffer or another stream or stream buffer must consider the following design factors, as applicable to the function being mitigated:

(a) The natural channel or shoreline reach dimensions including its depth, width, length and gradient;

(b) The horizontal alignment and sinuosity;

(c) The channel bed or lake bottom with identical or similar substrate and similar erosion and sediment transport dynamics;

(d) Bank and buffer configuration and erosion and sedimentation rates;

(e) Similar vegetation species, diversity, size and densities in the channel or lake bottom and on the riparian bank or buffer; and

(f) Include all conditions in State and Federal permits or approvals;

(3) Mitigation to compensate for adverse impacts shall meet the following standards:

(a) Not upstream of a barrier to fish passage;

(b) Is equal or greater in biological function; and

(c) To the maximum extent practical is located on the site of the alteration or within one-half mile of the site and in the same stream reach at a 1:1 ratio for the length of mitigation to area of alteration; or

(d) Is located in the same stream drainage sub-basin and attains the following ratios of area of functional mitigation to area of alteration:

(i) A 3:1 ratio for a Type S stream;

(ii) A 3:1 ratio for a Type F stream; and

(iii) A 2:1 ratio for a Type Np or Ns stream;

(4) For purposes of subsection (3) of this section, a mitigation measure is in the same stream reach if the length of stream bank meets the following criteria:

(a) Similar geomorphic conditions including slope, soil, aspect and substrate;

(b) Similar processes including erosion and transport of sediment and woody debris;

(d) Equivalent or better biological functions including mating, reproduction, rearing, migration and refuge; or

(e) For tributary streams, a distance of no more than one-half mile;

(5) The City may reduce the mitigation ratios in subsection (3) of this section to 2:1 for Type S or F streams and 1.5:1 for Type Np or Ns streams if the applicant provides a scientifically rigorous mitigation monitoring program that includes the following elements:

(a) Monitoring methods that ensure the mitigation meets the approved performance standards identified by the Director;

(b) Financial guarantees for the duration of the monitoring program; and

(6) For rectifying an illegal alteration to any type of stream or its buffer, mitigation measures must meet the following standards:

(a) Located on the site of the illegal alteration at a 1:1 ratio of area of mitigation to area of alteration; and

(b) To the maximum extent practical, replicates the natural pre-alteration configuration at its natural pre-alteration location including the factors in subsection (2) of this section;

(7) The City may modify the requirements in this section if the applicant demonstrates that, with respect to each stream function, greater functions can be obtained in the affected hydrologic unit that the Director may determine to be the drainage sub-basin through alternative mitigation measures. (Ord. 09-19 § 9 (Exh. D); Ord. 06-17 § 4 (Exh. B))