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.: . . . . . -Many methods and models are available to measure existing ecosystem resource conditions and to estimate future conditions of those resources.. Habitat.models developed for individual species may have limitations when used to assess ecosystem restoration problems and objectives. They do not consider communities of organisms and typically consider habitat in isolation from its . . ecosystem context. Single.sp'ecies habitat mQdels may be limiting if used to optimize for a . particular species,. but they can be useful when.carefully applied in the ecosystem context.in . which the habitat is situated. They can be helpful in identifYing important influential functions or structural components for ecosystem projects to address. The 'assessment methodology chosen for . a study should be governed by how well the technique meets the needs of the study 20als and. obiectives and level of detail fora ~iven study. The assessment methodology may include habitat models, or infonnation derived from community or ecosystem assessments using other . . sCientifically based methods that are generally accepted bystate or Federal resoti~e.agencies. . . An asseSsment methodMrilrV that involves outputsin ecosystem units (acres x quality i~dex) or- - .' stream habitat improved to a less degraded cOildition and riparian habitat improved to a less degraded condition is desirable. The Corps will first determine if FWS or toow have a . preferred ecosystem assessment methodology. It is anticipated that these agencies may have a preferred assessment methodology, such as IFl.M.PHABSlM (In-streamflow incremental methodology - physical habitat simulation). The Corps will also suggest for consideration the following.: . . . ..... . . The simplest. least costly method that would give an approximation of ecosystem units would be to use existing HEC-RAS modeling: efforts.. Stream cross-sections and HEC-RAS modeling . developed either by the Corps for flood damage reduction studies or by the In-'stream Issues GrouplUDFCD (see pages 33 and 37 of South Platte River Corridor Project, In~st~am Issues Report, November 14. 1996) would be used~ The.HEC-RAS modelimz would enable a . .. calculation of channel top width surface area for any given flow, which is a quantification of. stream habitat. . , For a more detailed and accurate approach, and also because of the age of the cross sections~. stream geometry data would be collected at low flow by means of digital topographic surveys, and then entered into a geo-referenced HEC-GeoRAS model and ArcGlSex.tension.. This method . would then translate the information into a depth grid of inundated area. . For either method. an ecosystem function model (HEC-EFM) would be used that would input flow and stage time series and ecO-hydro relationships data: .An example ofeeo-hydro relationshipsdata would be wintertime target flows of 60to 85 cfs. Relationships regarding summertime target flows sh~~ld also be developedbya fish and wildlife stakeholder workgroup. . '. . For the more detailed approach,' relationships regarding depths and ecosystem indicator species should also be developed. The moredetailed and accurate modeling effort would be used to .. visualize existing ecologic conditions, highlight promising restoration sites, and assess and rank alternatives according to the relative enhancement (or decline) of ecosystem aspects. . '-. . . Either approach will also involve outputs in quality. Omtlitv indexes will need to be developed . that relates existing and forecasted in-stream flows and stream bank conditions to the stream . habitat/riparian habitat river ecosystem quality. The eco-hydro relationships would be used in the development of the quality index. A GIS vegetation survey completed in1996-1998 by the Denver Audubon Society would also be used. The resulting assessment will likely result in acres of a habitat type multiplied by a Quality index rROlzing from 0.25 (poor) to 1.00 (excellent) in order to obtainhabitator ecosystem units. . 3