The following performance standards shall be applicable to all design, construction, implementation and maintenance of stormwater management systems pursuant to the jurisdiction exercised through this chapter:
A. Increase In Rate: There shall be no increase in the peak rate of runoff from the site when compared with the dissipation of stormwater in the undeveloped state for a 25-year storm of two (2) hour duration. Within project boundaries, sufficient retention capacity shall be constructed to detain surface flow to meet the performance standards established by this section.
B. Collection Or Concentration: No stormwater shall be collected or concentrated, except within a channel protected against erosion and containing energy dissipation measures to prevent further erosion on adjoining lands. Existing unprotected channels shall be protected against further erosion in the course of site development. Any site development or construction shall preserve installed components of a stormwater management plan. All disturbed soils shall be protected during the course of construction to prevent exposure to stormwater and to contain eroded materials should contact be made.
C. Directed To Infiltration Areas: Any and all collected stormwater shall be directed to infiltration areas which shall be established with grass and other approved plant materials or to an acceptable alternative stormwater management design. In general, grass infiltration areas or their acceptable alternatives shall be sized to hold and treat the first one-half inch (1/2") of stormwater runoff from all impervious surfaces. The overall stormwater disposal system shall have a capacity to handle a 25-year storm based upon the appropriate Idaho Transportation Department IDF curve, without damage to the stormwater management system or adjacent land and improvements. (Ord. 542, 1-27-2015; amd. Ord. 596, 5-24-2019)