Base Indicators
This web page describes example base indicators for Recovery Potential Screening’s Social Index category. Unlike the ecological, stressor, or social indicators, this category’s metrics do not have a positive or negative influence on RPS index scores – they are value-neutral. Base category indicators are not used in any index calculations. These are reference parameters that are useful for tracking watersheds and use as an organizational structure for relating other indicator values to specific watersheds. The most essential base indicators are Watershed ID number and Watershed Name.
The base indicators category is also sometimes used to store indicators that actually can influence watershed condition as ecological or social positive features, or as stressors, in some cases. Their storage in the base category keeps them available to add to the RPS Tool’s appropriate category when they are appropriate to the screening purpose. For example, the attribute Watershed Area is normally value-neutral and a typical Base indicator, but it could be used as a Social indicator in a screening that intends to prioritize smaller watersheds because of limited restoration funding. In order to use a Base indicator in another category, follow the RPS Tool directions for ADD INDICATORS and copy (do not delete) the Base indicator and its values over into the new category location.
A few example base indicators are summarized below. These example indicators have been compiled on HUC12 watersheds at a national scale for the lower 48 states, and are all publicly available at that scale, but using the RPS Tool at other watershed scales will require compiling that scale’s Watershed ID and Watershed Name data at a minimum. Check the WSIO Indicators Master List to determine availability of other Base indicator data.
Watershed ID
Why relevant: One of the few mandatory metrics, without which the RPS Tool will not function. This field must be included in the Tool’s data table because it is the primary basis for linking the individual watershed to its many indicator attributes.
Data sources and measurement: US Geological Survey (USGS) Hydrologic Unit Codes (HUCs) provide the best-known, widely used existing source of watershed ID numbers at a national scale, through the Watershed Boundary Dataset (WBD). RPS, Watershed Index Online (WSIO) and many other EPA projects extensively use HUC12 scale watershed IDs based on this system. Because the USGS allows continual minor updating of HUC IDs and boundaries, however, RPS, WSIO, the EPA EnviroAtlas and many other projects use a WBD snapshot from 2014 that does not undergo the minor updates, thereby ensuring that the HUC12 data are fully consistent across all users' projects. The WBD snapshot is identical to the current WBD in most states, but users are advised to check for minor inconsistencies due to state-level minor updates in some areas.
Watershed Name
Why relevant: Also considered a mandatory RPS metric, although the RPS Tool will function without this field. Name is most useful in providing a more familiar informal reference to actual locations than the ID number and can be used in RPS bubble plots to label specific watersheds on the graph.
Data sources and measurement: USGS Hydrologic Unit Codes (HUCs) provide the best-known, widely used existing source of watershed names at a national scale, through the Watershed Boundary Dataset (WBD). RPS, Watershed Index Online and many other EPA projects extensively use HUC12 scale watershed names based on this system. Because the USGS allows continual minor updating of HUCs, however, RPS and other projects use a WBD snapshot from 2014 that does not undergo the minor updates, thereby ensuring that the HUC12 name data are fully consistent.
Watershed Total Area
Why relevant: Many additional indicators are calculated as a percent of total watershed area, thus area is an important Base indicator to have available for future indicator development. In addition, some projects may target larger or smaller groups of watersheds as a subset of interest.
Data sources and measurement: Total area of the HUC12 watershed. Value calculated from 30 meter grid of HUC12s. Units Square Meters.
Watershed Stream Length
Why relevant: Many RPS indicators involve calculating a stream attribute as a percentage of the total stream length within the watershed, thus stream length is an important Base indicator to have available for future indicator development. Some projects may target watersheds with higher or lower than average stream mileage as a subset of interest.
Data sources and measurement: Length of medium-resolution National Hydrography Dataset (NHDPlus version 2) stream features in HUC12 (kilometers). Calculated from the "NHDPlus2 NHD Snapshot" dataset. Includes all NHDFlowline features with FTYPE (feature type) equal to StreamRiver, CanalDitch, or Connector. NHDFlowline features with FTYPE equal to ArtificialPath are only included if they pass through a NHDArea feature with FTYPE equal to StreamRiver.
Watershed Waterbody Area
Why relevant: Many RPS indicators involve calculating an open waters attribute as a percentage of the total water body area within the watershed, thus it is an important Base indicator to have available for future indicator development. Some projects may target watersheds with higher or lower than average open water area as a subset of interest.
Data sources and measurement: Area of medium-resolution National Hydrography Dataset (NHDPlus version 2) waterbody features in HUC12 (square kilometers). Calculated from the "NHDPlus2 NHD Snapshot" dataset.
Percent Watershed in Riparian Zone (RZ)
Why relevant: The percent of the HUC12 that is in the Riparian Zone, measured as a standard width-per-side buffer around water features. Many additional indicators are calculated as a percent of total watershed riparian zone, thus it is an important Base indicator to have available for future indicator development.
Data sources and measurement: The Riparian Zone dataset in WSIO is determined using grid analysis to combine two surface water indicators and then place an approximate 100 meter buffer around these features. First, the surface water features from the National Land Cover Database (NLCD). Features included are 'Open Water' (code 11), 'Woody Wetlands' (code 90) and 'Emergent Herbaceous Wetlands' (code 95). Second, the flowline and waterbody features as represented in the catseed grid from the National Hydrography Dataset (NHD) Plus version 2. Source data used was NHD Plus Version 2.1. The combination of these two datasets represents surface water and is referred to as the ‘Water Mask’ (see metadata for more information). Last, distance from surface water is calculated using the ArcMap Spatial Analyst Euclidean Distance tool. All cells with a distance of 108 meters or less are included in the riparian zone. The combination of these two datasets and all cells with a distance of 108 meters or less from surface water are included in the Riparian Zone (RZ). Equation used: (Riparian Zone area/ HUC12 area) x 100.
Percent Watershed in Hydrologically Connected Zone (HCZ)
Why relevant: The percent of the HUC12 that is in the Hydrologically Connected Zone, measured as described below. The HCZ is essentially an irregularly shaped zone of areas within the watershed that are either contiguous with surface waters (e.g. active river floodplains) and/or topographically flat with high soil moisture. Many additional indicators are calculated as a percent of total watershed HCZ, thus it is an important Base indicator to have available for future indicator development.
Data sources and measurement: The Hydrologically Connected Zone (HCZ) dataset in WSIO is determined using grid analysis to combine surface water features from NLCD2011 and NHD Plus version 2. It also includes areas contiguous to surface water that also has a wetness index value of 550 or greater. The combination of these three datasets represents the Hydrologically Connected Zone.
Dominant Ecoregion
Why relevant: Omernik Level 3 Ecoregions are commonly used to identify zones in the landscape that share many terrain, vegetational, and hydrologic similarities. Dominant ecoregion is the Level 3 Ecoregion name with the highest percent of HUC12 area. Dominant ecoregion can be an important basis for identifying and targeting subsets of watersheds with similarities.
Data sources and measurement: Determined by percent of total HUC12 area in Omernik Level 3 Ecoregions.
States in Watershed
Why relevant: State or states occurring per watershed can be an important basis for sorting either in-state watersheds for a specific state’s projects, or targeting interstate watersheds specifically. This metric lists all states with any area within the watershed, comma-delimited.
Data sources and measurement: Due to errors found in the official Watershed Boundary Dataset (WBD) states attribute field, the states per HUC12 metric was re-processed in 2014 by the RPS project and is now used in all RPS Tools and the Watershed Index Online to determine all state-specific HUC12 watershed lists.
Percent Tribal Lands
Why relevant: This subset of HUC12 watersheds was produced to enable Tribes to identify subsets of HUC12 watersheds that contain any amount of Tribal lands, and then run RPS Tool screenings on just those watersheds if desired. Additional data has been compiled that enables the Tribe name to be identified, and to also identify HUC12s that border the HUC12s with Tribal lands.
Data sources and measurement: Percent of total HUC12 area that is Tribal land. Value is left blank for HUC12s with no Tribal land identified in the source dataset. Calculated using EPA tribal land data for the conterminous US and the WBD snapshot. Tribal land data includes all lands associated with Federally-recognized tribal entities— Federally recognized Reservations, Off-Reservation Trust Lands and Census Oklahoma Tribal Statistical Areas.