RPS Methodology, Step 1: Define the Scope
Although it is always possible to go straight to the Recovery Potential Screening (RPS) Tool and ‘play with the data’, good projects begin with good planning. Getting started requires a clear sense of the screening purpose, key participants, the basis for how watersheds will be compared and the products needed from this comparison. If these elements are clearly addressed in the beginning, the screening will be better targeted, more efficient and less subject to confusion or conflict later on. The following elements are essential:
Define the geographic area of interest. It is crucial to clearly delineate the geographic area within which watersheds will be screened and compared. RPS was first designed and is still often used at whole-state scale, but it can be used on subwatersheds of a larger watershed, whole river basins, ecoregions or regional to national scales as well. Further, RPS projects can target and compare a subset of the watersheds scattered throughout a larger area (such as only the cropland-dominated watersheds throughout a large ecoregion, or only the watersheds within a specific state that contain tribal lands). If the data are available, screening can take place on any scale geographic area that contains multiple smaller watersheds that you would like to compare and contrast. Note, however, that comparing just a few watersheds to one another is not recommended.
Define the targeted units whose recovery potential will be assessed and compared. RPS was designed to target watersheds, but there are many types of watersheds. Choice of targeted watersheds is most often based on scale, but may also consider land use setting or other factors that are relevant to the screening purpose.
Scale may be the most important factor: do you wish to compare whole river basins, or small drainage catchments? These extremes should not be compared to one another in the same screening, but screenings of multiple river basins (or catchments) at one consistent scale are appropriate. Watersheds can be custom-delineated for any area or type of area (e.g., all watersheds with native or stocked trout, or watersheds custom-delineated for all point-source-impaired water bodies), but there are also pre-delineated watershed units available at several scales available nationally in the Watershed Boundary Dataset (WBD) Exit. These nested watershed scales are organized by Hydrologic Unit Codes (HUCs) at several levels. The most commonly used and data-rich HUC level for RPS is HUC12, whose watersheds average roughly 36 square miles in area. The larger HUC8 level, whose watersheds average 1400 square miles, is also sometimes used in RPS for broad, first cut screenings across large areas. RPS Tools with lower 48 states coverage and embedded pre-made datasets for HUC12 and HUC8 watersheds are found in the RPS Tools section. At the small end of watershed-like units are the NHDPlus catchments Exit, which average about a square mile in area.
The targeted units for a screening may also address other factors if a smaller group of more similar watersheds is desired. For example, do you plan to screen all your watersheds, or specifically your watersheds with impaired waters? Or, are you targeting a set of watersheds of reasonably similar size, land use pattern, or other trait in common? Next, are there subsets of the unit that you specifically want to compare to one another? For example, do you plan to compare sub-groups of watersheds with similar land uses (e.g., urban settings) or impairment types (e.g. pathogens, nutrients)? Furthermore, are there other factors (e.g., public vs private landownership, Environmental Justice areas) that could define a subset of particular interest for screening and comparison? Although subsets of interest can be identified at any time, defining them up front makes a screening assessment easier to design and ensures that the members of a subset can be compared more meaningfully to one another. Some screenings even use a two-stage design, screening larger watersheds statewide and then screening and comparing the subwatersheds within each watershed for more localized purposes. Refining the RPS screening’s target group of watersheds based on common characteristics is further described in the Scenario Development(PDF) (12 pp, 150 K) document.
It is also possible to use the RPS Tool and methodology to compare waters, not watersheds, if appropriate data are available on a water body basis. As the watersheds of individual waters are still so influential, it remains useful to have watershed data along with data from the water bodies themselves. Screening on a water body level is often more difficult than screening watersheds because of the custom watershed delineations and individual water body data requirements involved.
Identify the purpose for the screening. Most generally, users carry out Recovery Potential Screening to compare watersheds and identify differences in likely level of restoration effort in order to inform their actions or decisions. Often, participants begin their RPS projects with this general approach, and working groups easily agree on the general purpose stated above. But, the purpose(s) for a specific screening can and should be stated more narrowly because a clear, specific purpose reveals more about the information that will be needed for a meaningful comparison. As they look closer, workgroups often refine their screening purpose. They may also identify additional purposes for other future screenings. This is a very important part of step 1 and should be given all the time it requires. RPS project planners should consider these factors, at a minimum:
- What statutory program or programs and requirements help define the purpose?
- What if any performance measures or goals help define the purpose?
- What types of information are needed?
- What types of decisions and actions must this information support?
- What are the relevant time frames?
- Will data be available to address more specific purposes of specific participants in the screening?
Identify participants and their respective roles. Defining a clear purpose also helps to reveal who should be involved in the screening. Users who are simply screening informally, just to gain insights for themselves, can focus on using the RPS Tool directly and need not consider participants and roles. One user can do a statewide screening with the RPS Tool in an hour… but buy-in on its findings requires more involvement. For a larger, group effort, consider that the participants can fill three basic roles: designers, assessors and appliers. The designers should include people that are essential to defining the scope and purpose, but not necessarily the methods. The assessors should be able to compile and analyze the data, develop the outputs and communicate effectively about them. Key skills for assessors usually include detailed knowledge of the watersheds and problems being assessed, ability to use geospatial data and spreadsheets, and the ability to communicate scientific information to more general audiences. The appliers are the users of screening assessment results and thus also often play an important designer role. Although involving many participants in these roles may seem complex, broader involvement of others generally increases buy-in and relevance to more program activities.
Identify the type of findings and specific products desired. The scoping stage should also clearly describe the intended products of the screening and how these will exemplify your watershed comparison in a useful way. For example, do you wish to identify some proportion of the watersheds with greater recovery potential? Can you quantify the size of the group of watersheds (e.g., top 50%, 10%, 2%; top 5, top 100 watersheds) you would want to target? Is a numerically rank-ordered list desirable, or is a preferred group of watersheds adequate? Are percentile-based groups appropriate? Further, is your screening tasked to provide a final selection or rank-ordering, or is it expected to identify alternative choices and communicate these to decision-makers? Will you want a single interpretive map, or several maps (or graphs, or rank-ordered lists) showing alternative interpretations? Work back from the desired products to be sure your screening design will get you there.
When you have a firm sense of screening purpose, participants and desired outputs, you are ready to move on to the next stage of designing the approach.