ࡱ> WYV%` +bjbj"x"x 4@@@#$H H H H ,t $$32 s3u3u3u3u3u3u3$&5h733 3F  s3s3c02 RH I/1s3303I1:P8_^P842P82i 33 3$$$$ H $$$H $$$ Environmental flows characterization for the Nonconsumptive Needs Assessment (version: August 7, 2007) As part of the nonconsumptive needs assessments (NCNA) for the 1177 Basin Roundtables, the NCNA Workgroup and Basin Roundtables have set a goal of identifying flows attributes necessary to maintain priority stream reaches. Stream sizes included in this effort are expected to be, at minimum, major tributaries of Colorados mainstem rivers, and may include tributaries to these tributaries. The NCNA Workgroup recognizes that some streams may not require flow characterizations, and others will require highly specific flow quantification. Between these to types are streams that would benefit from flow guidelines, yet are not a sufficiently high priority to merit resource-intensive, site-specific flow quantification. The development of environmental flow characterizations that can be applied across broad spatial scales is a central challenge facing instream flow programs. In an effort to provide generalized flow guidance to priority reaches without site specific flow assessment, The CDM Technical Team, with the assistance of outside expertise such as The Nature Conservancy and Colorado State University, will develop a generalized characterization of flow needs for major stream types. Stream types will be based on gross differences in hydrology and function. For example, three major hydrologic regimes present in Colorado are snowmelt, ground water discharge, and monsoonal rain. These major hydrologic types may be subdivided based on stream elevation, gradient, size or other factor that impacts stream function. For example, there may be characterizations for high mountain headwaters (e.g., the Fraser River), plains groundwater fed streams (e.g., the Republican River), or low elevation monsoonal streams (e.g., the Purgatoire River below Trinidad). We anticipate flow characterizations for around 10 stream types. Flow characterizations are expected to specify which flow parameters are important for supporting specific environmental (and probably also recreational) attributes, as well as criteria for each parameter that indicate the degree of hydrological/ecological alteration. The flow characterization will be similar to a synthetic unit hydrograph in the sense that it will be generic and thus applicable to a range of streams within a class. We expect these characterizations to extend the scientific basis for water management in areas that have not received site-specific environmental flow consideration. The characterizations will provide objective guidance for evaluating trade-offs among alternative management scenarios. They will offer a means to evaluate the ecological status of a stream, but there is no expectation that streams will be managed for pristine ecological status at the cost of established water uses. The process of developing environmental flow characterizations is expected to follow the highly-anticipated Ecological Limits of Hydrologic Alteration (ELOHA) methodology. The components of this methodology will likely include: Hydrology Baseline conditions The ideal foundation from which to develop broad-scale flow characterizations is to have an estimation of at least 20 years of natural (i.e., unaltered) flows for any reach in the state. This flow time series could be used to calculate various flow statistics of ecological significance. For the NCNA, we do not envision development of this baseline. Instead, we expect to employ existing hydrologic data, with only minimal extrapolation or additional modeling. As we understand it, the only basin with a relatively complete set of naturalized flow estimations is the Colorado. As such, the Colorado may be the only basin where a complete flow characterization by stream type can be accomplished. For other basins, it will be necessary to determine if existing gage or modeled data can be used to estimate natural flows at specific sites. If so, characterizations can be developed for these sites. Anticipated task: Determine status of data, both CDSS modeled data and relatively unimpaired gage data. Assemble data that will be necessary for next steps. Altered conditions A complete analysis for environmental flows would ideally include a hydrologic data set of altered (current and possibly future) conditions for all reaches. This data set is useful for two important reasons. First, by contrasting this data set with the baseline data set, degree of alteration can be determined. Second, knowing degree of alteration, it may be possible to discern some ecological or geomorphological responses as a function of alteration; or, it may be possible to conduct a study of responses. As with the baseline data, we anticipate that this step will use only existing data. Anticipated tasks: Determine status of and assemble data. Classifying streams Applying a generalized flow characterization broadly requires a stream classification. Multiple ways exist to classify streams. Since hydrologic processes are fundamental drivers of stream processes, the primary basis of classification should be based on flow characteristics. Given the availability of baseline flow data, tools exist for classifying streams (e.g., Hydrological Integrity Assessment Process). Geographic and geomorphic characteristics also influence stream ecology, so characteristics such as stream gradient, elevation, or other factors may further subdivide the hydrologic classification based on known or expected ecological responses. Methods for classifying based on catchment characteristics (e.g., drainage area, geology/lithology, precipitation) may allow classification based on readily available factors irrespective of the availability of flow data. Anticipated tasks: Develop classification using a to-be-determined method. This task will require interplay with the ecology component. Ecology: Defining Instream Flow Criteria Identify biological (or geomorphic) targets The goal of ecological flow recommendations is to support the natural functioning of the entire stream ecosystem, including aquatic organism, riparian communities, nutrient cycling, and geomorphic processes. Within each stream class, it is useful to identify biological (or possibly geomorphic) targets that represent or indicate important ecosystem components. For example, native fish habitat might be used as an indicator of adequate low flows, and regenerating cottonwoods might be used as an indicator of adequate flooding. Anticipated tasks: Identify targets/indicators for each stream class. Determine which flow parameters are most essential to maintaining these targets. It can frequently be assumed that flow management can focus on a subset of the total possible flow metrics, specifically, those key flow parameters that are fundamental to supporting stream processes within a class. Key flow parameters that support that above targets will be determined based on scientific literature, biological databases, and expert opinion. Anticipated tasks: Identify key flow attributes supporting stream function, as related to the above targets. Determine flow-ecological response relationships, and specify flow criteria With key flow parameters determined, defensible flow criteria require must be developed. These criteria are based on relationships between metrics of flow alteration and metrics of ecological integrity (i.e., the targets identified in the previous step). It is clearly recognized that flow-ecology relationships entail a potentially high degree of uncertainty. We expect to deal with this uncertainty by (a) indicating our confidence in the relationship, and (b) presenting the relationships as hypotheses to be tested in either a research or monitoring/adaptive management context. Once flow response relationships are determined, criteria will be defined to specify the degree of flow alteration the leads to a given ecological condition (e.g., good, fair, or poor). The criteria will be specified for each flow metric. It may be possible to combine metrics into an overall rating. Limits/uncertainty in these criteria will be specified. Anticipated tasks: Compile relevant literature and databases to inform flow-ecology relationships. Determine flow alteration criteria (i.e., benchmarks). Assess if alteration criteria can be rolled up into an overall index of alteration. Workshops We anticipate that after developing initial characterizations, we will convene a 1- or 2-day workshop to peer-review the initial flow characterizations (from classification through criteria). Components then will be modified as necessary. Possible additional task, not reflected in budget For reasons identified above, it would be useful to identify the degree of alteration by stream reach across the state. This would be a large task that is probably only possible given complete sets of baseline and current flow data. However, it may be possible in a sub-region of the state (perhaps the Colorado basin). 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