Assessment Implementation
River health assessment activities should occur only after stakeholder groups and Technical Teams produce a customized CoRHAF organizational structure, select assessment methods, and develop a set of Grading Guidelines uniquely suited to the needs of the project. The specific approach to, and success of, assessment implementation will largely be the responsibility of the Technical Team.
Field assessment can take various forms, but it is always a good idea to incorporate it into a health assessment. In large-scale studies, relying heavily on remote, desktop evaluation, fieldwork may be limited to basic ground-truthing, commonly “windshield surveys” with occasional stops for further consideration. In moderately sized studies (e.g., 20 stream miles) a common objective is to inspect all or as much of the river as possible. This often be done by floating or walking the river.
The wide array of considerations for data acquisition and analysis are too numerous to describe here. The specific approach to various assessment tasks will vary based on the level of intensity selected for each Driver and the unique geographical characteristics of the study area. Technical teams are encouraged to look to existing river health assessments to get a feel for how other groups approached assessments. Several important framing considerations are included below.
In remote or desktop approaches, it is helpful carry out an initial reconnaissance assessment across the study area and develop a list of ambiguous or confusing situations and then evaluate those in the field to understand the circumstances. Following this initial field-based familiarization, remote assessment can proceed with far greater confidence and efficiency.
Delineating Reach Breaks
In most applications, the river should be split into reaches for the purpose of organizing field assessment activities and reporting results. Delineating relatively short reaches as unique study units helps ensure that assessment results reflect somewhat homogeneous river conditions. Highly heterogeneous river segments, reported as a single unit, may produce information that lacks sufficient resolution to answer study questions. For example, performing assessment activities and combining assessment results from a highly impaired reach with an adjacent reach in excellent condition may obscure important details regarding river health impacts.
In general, reach breaks should be delineated where characteristics or conditions change to a significant degree. Reach break delineations may respond to a shifts in surficial geology, channel morphology, valley confinement, management regime, and/or stressor severity. Reach breaks do not need to be consistent across all Drivers, Components, and Metrics. For example, reach delineations for performing assessments of Sediment Regime or Channel Dynamics might be designated at landscape positions where significant changes in channel slope occur. Delineation fo reaches for the purpose of water quality assessment might correspond to historical water quality sampling locations or to major tributary confluence points. After assessments activities are completed, varying reach lengths can be accommodated using weighted averaging approaches or by further subdividing all reaches into short (e.g., 1/10th mile), fixed length units (see the Results Aggregation section for further discussion).
Assessment Timing
Literature and data reviews, GIS-based and remote data analyses, and simulation modelling on existing datasets can start and finish at any time. A number of practical considerations apply to field-based assessment work. These considerations are due both to data representativeness issues, as well as personnel safety. Collection of water quality samples, assessments of riparian condition, and other techniques are best applied during restricted seasonal periods or hydrological conditions. As you plan your assessment, be mindful of potential time constraints for field-based activities and ensure that you include sufficient margin in your timelines for completing those activities. Be sure to take private land access into account. Securing access to a private parcel often takes longer than assessing the parcel and it can be a substantial hurdle that shapes how you assess various Drivers or stream reaches.
Hydrology
Unpredictable weather and flow conditions will invariably challenge field staff throughout the year on many rivers in Colorado. Field work in high-elevation settings may be impossible before April due to iced river conditions or road access challenges. As these conditions begin to relent, high snowmelt runoff can make rivers too dangerous for wading or boat surveys. It may not be feasible to implement some data collection exercises until flows recede. For example, surveying channel cross sections or conducting Wolman pebble counts are activities better suited to low flow conditions in the late summer and fall. On the other hand, high flows can provide excellent opportunity for verifying bankfull discharge conditions, documenting floodplain and side channel or backwater connections, and assessing connectivity of tributaries to mainstem channel reaches. The snowmelt recession period after peak flows may be a great time to schedule float-based assessment activities on rivers large enough to support them. During this period, flows are still capable of supporting boating but have retreated from the peak period when safety issues may exist or the ability to eddy-out and focus on a particular reach may not be available.
Riparian Vegetation
Riparian assessments can begin in spring, with opportunity for vegetation assessment between leaf out in early summer and the first heavy frost in the fall. During this time, taxa identification is most reliable and community structure and composition can be readily observed. By mid- to late-fall, depending on elevation and location, riparian assessment becomes increasingly difficult due to leaf loss, color changes, lack of flowers or fruiting parts, etc.
Water Quality
Many aspects of water quality are influenced by adjacent landscape and watershed processes that exhibit distinct seasonal patterns. Concentrations of some water quality constituents may be highest during the spring first flush phenomenon, when new snowmelt rapidly moves along the land surface, carrying sediment, organic material, etc. to the river. The diluent effect of elevated streamflows may depress concentrations of metals and nutrients during peak snowmelt runoff. Concentrations of many constituents are highest during low flow periods in the late summer and fall months.
Aquatic Food Webs
Collecting data to characterize aquatic food webs frequently involves sampling benthic macroinvertebrate communities or performing fish community surveys. Macroinvertebrate data collection should generally occur in the late summer or early fall (e.g., August to late September) when the best presentation of taxa is available in samples. The fall period is also well-suited to wading the river for sample collection. If your assessment includes fish survey work, you will need close coordination and engagement with CPW staff. Organizing and scheduling such efforts can require significant lead time and will typically be performed in the spring or fall months.
Documenting Stressors
The evaluation, documentation and interpretation of stressors is of the utmost importance to the health assessment. Stressors provide the ultimate explanation of degradation in river health and form the rationale supporting expert interpretation and functional condition grades.
This is because quantitative data or analyses can be used to describe a characteristic of the river, but alone they usually provide little direct information about river condition or health. For example, consider quantitative data from a flow gauge used to make a hydrograph. It is usually not possible to infer the condition the hydrograph represents without either historical data or knowledge of water management and how it alters flow regime from its reference standard condition. In most cases historical data is not available, so interpretation leans heavily on stressor assessment.
Stressor evaluation is also a means of circumventing data gaps such as in the case of an ungauged stream or one lacking water quality data. When a stream lacks stressors such as diversions or sources of pollution, Flow Regime and Water Quality can be assumed to be in the “A” range. In other situations, the more stressors and the greater their severity and extent, the greater the departure from reference standard “A” grade.This is why grading guidelines are often largely based on description of the stressor regime. In assigning grades based on stressors or anything else, keep in mind that stream reaches that are truly bereft of stressors are very rare in Colorado, and A+ grades should be assigned with similar infrequency. In general, the highest quality streams in Colorado rank in the “A” range, and likely few or none of the Drivers on Colorado’s mainstem river reaches would warrant “A” grades.
Climate change and wildfire are two factors that warrant further discussion. Climate change is altering the fundamental character of Colorado’s rivers and there is overwhelming evidence that some or all of the shift is human caused. But, in a river health assessment, including it as a stressor is generally not informative because climate change acts in a contextual fashion and affects all river Drivers.
Wildfire represents a different assessment challenge, although it is exacerbated by climate change. Wildfire is clearly a disturbance to a watershed, and oftentimes a massive one, yet wildfire is a natural part of Colorado’s landscapes. On the other hand, fires are often started by humans, and it can be convincingly argued that historical forest management practices have greatly increased the severity of these inevitable events. It will be up to your technical team to frame wildfire in a manner that is useful to your assessment.Because the river health assessment is done to inform management and also for public outreach, the most helpful way to handle wildfire is usually to treat it as a stressor. This can help prioritize management actions and promotes monitoring that can track system recovery while also tracking the outcomes and benefits of response actions.
Private Land Access
There are two critical points to keep in mind when carrying out the field portion of the assessment. First, when a reach flows through private land, the bed of the river is the private property of the landowner, and it must not be touched without the permission of that landowner. Floating over the bed is fine, however. Second, securing access from private owners can be a major task. It is not uncommon for obtaining access to take more time than assessing the river on their property, so be sure to budget and plan accordingly.
Record Keeping
Documenting the rationale or evidence that supports the assignment of functional condition grades to Drivers, Components, and Metrics helps ensure transparency and, in the case of quantitative methods, repeatability of assessment results.
Clear and comprehensive documentation provides stakeholders with confidence in assessment outcomes. Where documentation is lacking, stakeholders, community members, or elected officials asked to use assessment results to support decision-making may question the reliability or accuracy of a river health assessment results.
In the case where qualitative assessment methods are employed, the documented rationale for an assessment grade should reflect the criteria laid out in the grading guidelines. The provided rationale should help stakeholders understand how observations in the field supported the formation of an expert opinion regarding functional condition. For example, functional condition grades assigned during a rapid field assessment of Corridor Dynamics can be supported by a narrative rationale that discusses the presence of bank armoring, evidence of fill material on the floodplain, and other stressors present in the landscape expected to promote or limit fluvial geomorphic processes. Photographs are an important means of record keeping for qualitative assessments. Geotagging all photographs or otherwise attributing photos with metadata that includes location, view angle, subject, and observational notes is highly recommended. Establishment of monumented photo points can support efforts to collect comparitive photographs during future monitoring phases.
In cases where quantitative assessment methods are used to evaluate functional condition, documentation of the evidence used to arrive at an assigned grade is required. This documentation may include the method applied and the numerical outcome of a statistical evaluation, simulation modeling exercise, etc. For example, functional condition grades assigned to average annual 3-day maximum flow (a Metric of Peak Flow) can be supported by documentation of the data set used to characterize that statistic of flow regime behavior (e.g. historical records for the previous 30 years from a particular stream gauge) and the numerical analysis result. This type of documentation provides a clear mapping between a specific quantitative outcome and the numerical thresholds or intervals defined in Grading Guidelines.
Users can download an example Assessment Result Data Sheet on the Resources page. This Data Sheet provides a structure for documenting the following:
- the geographical bounds of a particular assessment,
- the Driver, Component, or Metric that the assessment is responsive to,
- the method used in the assessment of functional condition,
- the assigned functional condition grade, and
- the rationale or evidence supporting the assigned grade.
