Ordinance 2910-06 - Laserfiche WebLink

improvement function on or immediately offsite in the same drainage basin. The habitat functions for these wetlands can be mitigated off-site. The basis for these recommendations is that the maintenance of stormwater/floodwater control and water quality control functions, especially in upper watershed wetlands within developed areas, is critical to the maintenance of the habitat functions of downstream wetlands. Many of the upper watershed wetlands will have over 20% of their contiguous basin developed in impervious surfaces. In fact some drainage basins are anticipated to have 60 - 80% of the portion of the basin in the Subarea in impervious surfaces. Therefore, it is likely that these wetlands will have water level fluctuations that significantly reduce species richness for plants and amphibians. Additionally, these wetlands are isolated and located several thousands of feet from adjoining wetlands, wildlife corridors and riparian corridors and have, therefore, limited importance to wildlife and low performance of habitat functions. In these circumstances, it may be acceptable to move the habitat function to a larger offsite or out of basin wetland ecosystem that has a higher potential to provide significant gains in the habitat function. When the water quality improvement and stormwater control functions of a wetland are required to be maintained on or immediately adjacent to the site, they can be incorporated into wetpond design for a proposed development. These existing functions, however, must be provided in addition to what is required to treat and detain stormwater per City standards for a new development or redevelopment. (SEPA Plant and Animal, Water, and Land and Shoreline Use Policies) 3. When an applicant proposes to fill or alter all or a portion of a wetland, the wetland replacement ratios shall be per the requirements of Chapter 37 of the Zoning Code unless otherwise described below. Conceptual and detailed mitigation plans must be approved by the Planning Director per the requirements of Chapter 37 of the Zoning Code. The following potential mitigation sites/activities shall be considered: • Creation or enhancement of wetlands and buffers where the mitigation would result in connection of isolated habitat or widening narrow riparian or wildlife corridors. Where significant additional upland buffers/wildlife corridors and connections are created and the overall habitat function is increased beyond what would have occurred with the creation and enhancement by itself using Zoning Code replacement ratios, the Planning Director shall have the discretion to reduce wetland replacement ratios down to a minimum of 1:1. • Table 4-1 provides a summary of potential wetland mitigations by basin. Note that where mitigation measures include raising the elevation of outlets in flow through riparian systems, the mitigation will be subject to site-specific analysis addressing the feasibility of the mitigation. The mitigation shall not be used for meeting on-site stormwater detention requirements. The intent is to create additional wetlands and increase the range of water depths to approximately .5 to 2 feet so that a mosaic of