Chapter 6 —
6.1 Introduction
This chapter describes the requirements for meeting Minimum Requirement #8. See Vol I–4.2.8 Minimum Requirement #8: Wetlands Protection for a description of this minimum requirement.
6.2 Applicability
The requirements below apply only to projects with stormwater discharges into a wetland, either directly or indirectly through a conveyance system. These requirements, where applicable, must be met in addition to meeting Minimum Requirement #6 and Minimum Requirement #7.
6.3 Thresholds
The thresholds identified in Minimum Requirement #6 and Minimum Requirement #7 shall also be applied to determine the applicability of these requirements to discharges to wetlands. If the project discharges stormwater runoff to a stream that leads to a wetland, or to a wetland that has an outflow to a stream, Minimum Requirement #8 applies.
6.4 Standard Requirement
In addition to meeting requirements for runoff treatment and flow control (Minimum Requirements #6 and #7, respectively), discharges to wetlands shall maintain the hydrologic conditions, hydrophytic vegetation, and substrate characteristics necessary to support existing and designated uses. Projects shall comply with Volume I, Appendix I C of the Ecology Manual. The hydrologic analysis shall use the existing land conditions to determine the existing hydrologic conditions unless directed otherwise in the Critical Areas Ordinance codified as Title 19 KCC.
6.5 Coordination with Minimum Requirement #7
In most cases, if wetland hydroperiod protection is required per MR #8, then the flow control performance standard is also required per MR #7 (see Vol I–4.2.7 Minimum Requirement #7: Flow Control). In these cases, the designer must attempt to meet the requirements for both minimum requirements. This may prove to be infeasible in some situations because MR #7 will seek to adjust the flow in small time intervals and MR #8 looks to maintain daily flow volumes.
If the designer is unable to meet both requirements, then the requirement to maintain the hydroperiod of the wetland becomes the overriding concern and the designer must show compliance with MR #8. If this is the case, the designer must also provide documentation detailing why they are unable to meet both requirements, and is subject to director approval.