Selecting Methods
It is critical that stakeholders and Technical Teams consider the implications of assessment framework customization on the methods available for and/or best suited to the characterization of river health. A wide variety of assessment methodologies exist for characterizing different Drivers or Components of river health. No effort is made here to provide an exhaustive list of assessment methodologies. However, some commonly employed methods are listed in the table below.
| Health Driver | Potentially Relevant Data Sources | Example Assessment Tools, Techniques, & Methods |
|---|---|---|
| Flow Regime | USGS/CDWR streamflow gauge records, StateMod simulations, Hydrobase diversion and reservoir records, CBRT data dashboards | Indicators of Hydrological Alteration, Watershed Flow Evaluation Tool, StreamStats, trends analysis |
| Sediment Regime | Soil Survey Geographic Database, historical water quality sample results, aerial imagery, Wolman pebble counts | Network connectivity analysis, effective discharge analysis, WEPP model, BAGs and other sediment transport models, rapid field assessments |
| Wood Regime | Aerial imagery, site surveys | Field surveys, GIS mapping, review of aerial imagery |
| Water Quality | EPA STORET, USGS NWIS, Colorado Data Sharing Network, CBRT data dashboards | Colorado Water Quality Control Division regulatory assessment methodologies, trends analysis, weighted regression on time, discharge, and season |
| Riparian Habitat | Aerial imagery, local vegetation surveys, FEMA flood hazard mapping, Colorado LiDAR imagery repository, CPW riparian vegetation mapping, CNHP vegetation mapping, National Wetlands Inventory, National Land Cover Database | Rapid-assessment, field mapping/transects, aerial imagery review and/or GIS mapping, recruitment box model, vegetation succession model, 1D/2D hydraulic models (e.g., HEC-RAS) |
| Channel Dynamics | Aerial imagery, FEMA flood hazard models, FHZ mapping, local engineering studies, dike/levee mapping | Channel migration and sediment transport simulation models, rapid field assessments, fluvial feature mapping, repeat aerial image change detection |
| Aquatic Habitat | USFWS habitat suitability criteria, FEMA FIS hydraulic models, USFS and BLM rapid assessment reports, CDWR water diversion structure GIS dataset | 1D/2D hydraulic models (e.g., HEC-RAS, River2D, FASTMECH), channel-scale and reach-scale meso-habitat mapping, habitat suitability modeling (HABSIM-derivatives, etc.), dendritic connectivity index, aquatic organism passage analysis, bioenergetic habitat suitability modeling |
| Aquatic Food Webs | USFS/BLM/CPW aquatic species survey results, macroinvertebrate MMI Scores published by state and federal agencies, CPW fisheries reports, Upper Colorado River Recovery Program research reports | Macroinvertebrate health index scores, functional feeding groups distribution, fish biomass, fish age class distributions, fish species diversity indices |
Methods selection will also be influenced by the data resources available. Reviewing the CoRHAF Drivers in light of your known data sources and the factors that are important to the river(s) in your watershed will help you understand how involved an assessment is likely to be. Where river health conditions are not well understood and previous studies and relevant data are generally lacking, significant effort may be required to evaluate the condition of one or more Drivers that are important to stakeholders. Conversely, if current river health data is abundant and issues/areas of concern are already identified, the need for new data collection and analyses may be minimal. As a rule of thumb, assessing conditions at a high spatial resolution requires significant data collection and analysis and will be expensive on a unit length/area basis. If a project is constrained by limited budget and/or data, assessment activities will need to mainly rely on rapid methods, a coarser spatial resolution, and/or be limited to a modest geographic scope. In any case, the geographic scope of your assessment should weigh heavily in your consideration of which assessment intensities are best for the individual Drivers and/or Components in your assessment.
Assessment intensity refers to the amount of time and resources that are devoted to assessing a given unit length of river
Methodological Intensity
In CoRHAF, the different Drivers can be evaluated at different levels of intensity to allow you to dial in assessment rigor according to circumstances in the watershed, stakeholder interests, likely budget, and geographic extent. To aid with planning and communication, CoRHAF stratifies assessment intensity into three levels. Remote (Level 1) assessments are low-intensity. Rapid (Level 2) assessments are moderate-intensity. Focused (Level 3) assessments are high-intensity. Each assessment level is discussed below. Different assessment intensities can be used across Drivers and intensity may be varied among streams or reaches. For example, important Drivers or key locations can be assessed with high intensity approaches, whereas lower priority areas or Drivers can be evaluated at a lower intensity. Selection of methodological intensity reflectws how much study time and resources should be devoted to assessing a unit length of stream or area of the watershed for each of the Drivers.
Level 1 – Remote Assessment
Remote assessments are generally the most efficient means for characterizing conditions across large areas. Remote assessments can be qualitative or quantitative in nature. A qualitative remote assessment may rely on aerial imagery in mapping web applications or a geographic information system (GIS) to gather visual impressions of local conditions and identify the variety and distribution of likely stressors to river health. These impressions may become the basis for assignment of functional condition grades to Drivers or Components across long stream segments or entire subwatersheds. A quantitative remote assessment may use hydrological simulation modeling tools to characterize characteristics of the Flow Regime in great temporal and spatial detail and provide a Technical Team with an opportunity to objectively characterize the role of water diversions and reservoir storage on a multitude of flow behaviors.
Level 2 – Rapid Assessment
Rapid assessment occurs in the field. Like remote assessment, these assessment activities rely heavily on visual inspection and may or may not include data collection. Rapid assessments are commonly used to directly assign functional condition grades to Drivers or Components based on best-professional judgement. Rapid assessment may produce quantitative data, such as a visual estimation of shrub coverage in the riparian zone. However, but those data are estimated visually rather than by way fo systematic vegetation sampling. Walking or floating a river reach and recording observations of substrate embeddedness, coarse bed structure, and other characteristics of river form is a common form of rapid assessment. Some degree of standardization may be imposed on rapid assessments by developing questionnaires that cue the observer to certain characteristics of the system.
Level 3 – Focused Assessment
Focused assessments generally produce quantitative outputs. These methods assess conditions at single point or across a relatively small floodplain area or stream reach. Examples of focused assessments include characterization of riparian community structure by way of recording vegetation species distributions along fixed transects, development of 1-dimensional or 2-dimensional habitat suitability models for evaluating the response of aquatic species to changes in flows, sampling macroinvertebrate populations to generate indices of community robustness, or collection of streambed substrate data to characterize bed composition and the likelihood of bedload transport. The characteristics or processes revealed through application of these methods at the local scale may or may not represent conditions across larger areas.
Potential Assessment Intensities for Various Drivers
Flow Regime For a coarse analysis of hydrology, understanding of the general patterns and large-scale alterations or modifications to a river’s flow regime may be all that is needed. More detailed assessments may include detailed investigations of flow alteration including hydrological simulation modeling, statistical characterization of regime behavior, and/or trends analysis.
Sediment Regime High-level evaluation of sediment regime may involve rapid assessment techniques to characterize patterns of local and watershed-wide impacts to sediment supply, erosion, deposition, and transport such as clear-cut logging operations or widespread clearing of bankside woody vegetation. Detailed investigations may focus on site-specific relationships between channel hydraulics and lateral channel migration rates, the frequency and duration of significant streambed mobilization, relationships between sediment regime and spawning habitat quality, or modeling of hillslope processes in priority areas.
Water Quality Coarse investigation may rely on general examination of existing datasets, reports, and agency assessments from CDPHE or EPA. For streams lacking existing water quality data, stressors (e.g., point and non-point sources of pollution) can be identified and their effects on water quality inferred and subjectively rated. Detailed technical investigations may include new sample collection, statistical analyses of historical trends, or modeled interpolation of conditions between sample points
Wood Regime Coarse- or moderate-scale analysis may involve rapid field assessments and floating or ‘windshield’ surveys. Detailed investigations may involve modeling of wood recruitment, storage, and transport. Additional work may also explore the nexus between wood regime and fishery habitat condition.
Riparian Habitat Remote riparian assessments may rely primarily on aerial photo interpretation of land cover and land uses within the riparian zone and the amount of remaining riparian habitat. Rapid field assessments relying on float or walking surveys where access is possible may augment or field verify remote sensing data. Focused investigations might create high resolution imagery using drone-based photography and image analysis, or permanent sampling points to quantitatively benchmark riparian condition.
Channel Dynamics Channel dynamics might be assessed remotely by considering factors like watershed-scale stressors such as burn-scars or reservoirs that alter sources and sinks of sediment, alterations of streamflow, and reach-scale stressors like bank armor, woody vegetation clearing, channel spanning structures, and encroachment, and then interpreting how the interplay between those factors likely degrades processes including aggradation, incision, or the ability of the river to move across its floodplain. Detailed evaluations may include quantitative estimates of bed sediment transport, historical mapping and/or modeling of channel migration rates, or development of quantitative regional relationships between rates of channel change and other environmental variables (e.g., riparian vegetation extent, metrics of hydrological regime behavior, etc.).
Aquatic Habitat Coarse investigations may rely on rapid field assessments, aerial photography and other remotely sensed data, and reviews of existing habitat studies. Detailed investigations may utilize channel surveys and hydraulic modelling that relates different streamflow conditions to micro- or meso-habitat quality and availability for a species and/or life stage of interest. Alternatively, detailed assessments may include techniques like snorkel surveys of organism habitat use, quantification of embeddedness, habitat mapping, or bioenergetic habitat suitability modeling
Aquatic Food Webs Coarse assessments may rely on basic first-principals in freshwater ecology, rapid field surveys, and existing reports from CPW or other agencies. Detailed investigations may include macroinvertebrate sampling or targeted fish shocking. Alternative techniques may attempt to quantify energy, nutrient, or carbon inputs from riparian zones and/or upstream areas or may measure processes like whole stream metabolism.
