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three options) in that it protects what remains of the waterways/setback areas that drain to water quality <br /> impaired waterways, even though some of them maybe quite impacted with impervious surfaces. <br /> Option 2 -Combination of Standard Setback and Removal of Some Waterways from "Protect" Status <br /> This option would apply a standard setback to all water quality waterways that do not exceed the ISC <br /> thresholds for all management zones, and, utilize the parceUcorridor impact evaluation to eliminate from <br /> "protect" status those waterways that exceed the ISC thresholds for one or more management zones. In <br /> other words, waterways that do not meet the threshold criteria of impervious surface area within all three <br /> management zones (u to 10%ISC streamside zone; u to 25%ISC middle zone; u to 40%ISC outer <br /> P P P <br /> zone) would be deemed too impacted to have adequate water quality function to warrant protection. This <br /> approach involves not only looking at individual waterways, but also at the corridor as a whole, to <br /> evaluate existing ISC against the threshold criteria. The result would be that a standard setback would be <br /> applied to Amazon Main Stem for instance, but that the Roosevelt Channel, the north Beltline Floodway, <br /> <br /> j Debrick Slough (including Delta Ponds), and the west Beltline floodway would be taken out of the "water <br /> quality protect" designation and no protections would be applied. With this option, 60.5 of the 85.3 (71 <br /> water quality waterways would be protected. While this approach acknowledges the presence of <br /> significantly impacted areas and becomes the basis for no protection, it does not account for the presence <br /> of water quality function within waterways that have earthen bottom with side-slope vegetation -even at <br /> high levels of impact -and the role they play in helping to address TMDLs on a system-wide basis. <br /> Option 3 - Combination of Standard Setback and Customization of Buffer Widths for Some Waterways <br /> This option would apply a "standard setback" to all water quality waterways that do not exceed the ISC <br /> thresholds for all management zones, and, utilize the parceUcorridor impact evaluation to refine buffer <br /> widths for waterways that exceed the ISC thresholds. In other words, for waterways that exceed the <br /> threshold criteria of impervious surface area within one or more of the three management zones (10% ISC <br /> streamside zone; 25%ISC middle zone; 40%ISC outer zone), aerial photos and the GIS tool would be <br /> used to determine more specifically the location, nature and concentration ofthe-impervious surface area. <br /> This "look-back" included a review of the "Total ISC" data to determine if the percent impervious surface <br /> cover of the overall waterway corridor was below the 25% threshold. Results from this closer evaluation ` <br /> would be used to customize the buffer widths to something that recognizes existing impacts up-front. For <br /> example, where we know there are significant impacts due to adjacent roadways (e.g. Upper Amazon <br /> between East and West Amazon Drive, Roosevelt Channel, west Beltline Floodway, etc), reduce the <br /> buffer to something more in-line with where the impervious surface area currently starts (e.g. 25 feet, 50 <br /> feet). Using this approach all of the 85.3 miles of water quality waterways would be protected, with <br /> varying degrees of protection for 24.8 miles of the waterways. <br /> Stormwater Management Team Recommended Option <br /> The SWMT recommends, by unanimous consensus, proceeding with Option 1: apply a standard 75 foot <br /> setback to all water quality waterways and exempt existing development through provisions in the <br /> ordinance. The team believes that Option 1 is the most defensible, the most reasonable, and is clear and <br /> simple. Option 2 was supported by a couple SMWT members as an alternative to Option 1, for its use of <br /> the parceUcorridor evaluation data and for its simplicity. Option 3 was the staff team's recommendation <br /> to the SWMT, however it was not very well supported given the "look back" and apparent subjectivity in <br /> customizing buffer widths. It was thought by the SWMT that Option 3 would leave the city open to <br /> challenge, and that it would be simpler to exempt existing development through ordinance provisions <br /> rather than customized buffer widths. <br /> 3/28/06 6 <br /> _ _ <br /> <br />