watershed % natural cover

  Why relevant to recovery: Large-scale land use change often provides nonpoint pollution (e.g. from urban areas, agriculture, transportation, mining) as well as altering runoff and infiltration patterns in ways that can destabilize stream channels and flow regimes. The percent of watershed area that is not transformed to non-natural cover types is generally associated with runoff and flow dynamics within normal range of variability, as well as reduced opportunity for pollutant runoff. Natural cover categories from land cover mapping mainly include forest, shrubland, wetlands, grasslands and in some regions desert or barren land categories.

  Data sources and measurement: Measured as total percent of land area (not including water area) in the watershed within several mapped natural land cover categories, as listed above. For land cover data, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is available; numerous statewide land cover mapping datasets are also available from state-specific sources. The natural categories (or if desired, also semi-natural categories, given a lower weight) from the land cover data are summed to create this indicator. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

watershed % forest (PDF) (4 pp, 59K)

  Why relevant to recovery: More watershed forest cover reduces risk of numerous impairment types, thus lessening the relative complexity of restoration of impaired waters from forested watersheds. Mollifying effects on runoff and recharge, temperature and overland pollutant transport are associated with more forested watersheds and help ensure that several primary natural processes are or can become functional once stresses are removed.

  Data sources and measurement: Percent of the total land area of a watershed mapped with a land cover classification of "forest" (i.e. deciduous forest, evergreen forest, mixed forest). For land cover data, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources. For watershed boundaries, numerous watershed scales have been delineated nationally as part of the Watershed Boundary Dataset (WBD) in the Natural Resources Conservation Service Geospatial Data Gateway. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

watershed % wetlands (PDF) (5 pp, 86 K)

  Why relevant to recovery: Wetlands are key features in watershed processing of nutrients in runoff, detention of excessive runoff during extreme weather events and acting as sinks for sediment and pollutants. In addition, wetlands provide vital recharge, detention and release in their role within groundwater/surface water interactions. Absence of wetlands degrades natural processing of the pollutants mentioned and results in greater direct transport to the receiving water body of the watershed, increasing or perpetuating impairment. The rationale is that greater proportion of wetland area in the watershed positively influences recovery potential in that watersheds with more wetlands have greater resilience concerning the types of impairments mentioned. If possible, current wetlands abundance can be contrasted with estimated pre-settlement wetlands abundance to develop an indicator more sensitive to wetland loss rather than wetlands total alone.

  Data sources and measurement: Percent wetland area within the selected watershed scale. Data sources may vary considerably in source, date and accuracy of wetland/upland delineation. For land cover data including generalized wetland categories, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources. NLCD or state land cover datasets are generally available but less accurate than wetland-specific mapping efforts such as National Wetlands Inventory (NWI) Exit. NWI data are partially available as digital coverage, are likely more accurately interpreted but may be out of date in selected areas. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

watershed % woody vegetation (PDF) (2 pp, 16K)

  Why relevant to recovery: This metric is relevant for reasons similar to watershed forest and watershed natural cover, and provides a more appropriate indicator choice in regions that are not naturally forested. More watershed forest and shrub cover reduces risk of numerous impairment types, thus lessening the relative complexity of restoration. Mollifying effects on runoff and recharge, temperature, and overland pollutant transport are associated with more naturally vegetated watersheds and help ensure that several primary natural processes are or can become functional once stresses are removed. Broad array of influences on capacity to recover including intercepting and moderating the timing of runoff, buffering temperature extremes (which can also reduce certain toxicities), filtering pollutants in surface or subsurface runoff, providing woody debris to stream channels that enhances aquatic food webs, and stabilizing excessive erosion.

  Data sources and measurement: Land cover mapping typically contains forested and shrub categories, which are added to calculate this metric. For land cover data, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

watershed topographic complexity (PDF) (2 pp, 44 K)

  Why relevant to recovery: Although likely not a strong causal influence on ecological condition, topographic complexity is associated with higher biodiversity, better water quality and reduced nutrient pollution in some studies. The metric may be indirectly related to limiting the extent of some forms of land use that may degrade aquatic condition, also associating it with greater recovery potential in general.

  Data sources and measurement: Watershed elevation range, mean watershed slope and relief ratio are measurable from elevation datasets and are closely correlated with topographic complexity. The USGS National Elevation Dataset (NED)Exit is adequate for generalized differences in elevation. High resolution elevation data should be used for any assessment units at HUC12 level or smaller. The Elevation Derivatives for National Applications (EDNA) Exithas been derived from the NED and is hydrologically conditioned to improve hydrologic flow representation. The NHDPlus Value-Added Attributes dataset Exitcontains information on maximum and minimum elevation for each flowline.

watershed forest patch mean area

  Why relevant to recovery: Patch size is a direct indicator of how fragmented a watershed's natural cover is. Larger average patch size is likely to be associated with less fragmentation in a watershed. Forest fragmentation and its land use causes are associated with runoff changes and potentially greater pollutant loading. Larger forest patches containing parts of the stream network are also more likely to harbor functionally intact waters.

  Data sources and measurement: Calculated as the total forested land area of a watershed divided by forest patch count. For land cover data, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources.

watershed soil resilience (PDF) (6 pp, 135 K)

  Why relevant to recovery: Soil texture and slope characteristics affect the degree of nitrogen retention, bank stability, overland flow and erosion potential, and soil characteristics can even completely override land cover effects. Higher stream slopes increase soil erosion potential, and thus, phosphorus transport potential in overland flow. Soil texture has been called the single most important watershed characteristic affecting water quality of the Great Lakes. Stream nutrients can be associated with soil properties, and fine-textured soils with higher runoff potentials appear to limit the transport of leached nitrogen.

  Data sources and measurement: Measured from mapped soil survey data within a selected corridor width, e.g. 30 meters, 90 meters. Based on selection of specific soil types documented as better for nitrogen processing, stability/erosion resistance and other factors as appropriate to the study area. Assigning scores to different soil types based on the properties discussed should be done specifically for the area undergoing assessment, as national generalizations are limiting. Another option is to measure % area within the corridor that has soils with high resilience properties. Digital soil survey data varies from State to State in availability. States with fully digitized county soil survey-level information can use this metric most effectively. Physical and chemical properties of soils are available for most areas as part of the Natural Resources Conservation Service (NRCS) Soil Data Access Exit. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

watershed % streamlength unimpaired

  Why relevant to recovery: From the standpoint of watershed-scale condition and functionality, the proportion of waterbodies reported as impaired is likely associated with the difficulty and complexity of a watershed-wide restoration. Functionally healthy stream reaches upstream of impairments may aid the recovery of impaired segments via dilution and through recruitment of aquatic biota. Caution should be taken that streams not reported as impaired aren't simply unassessed waters that could be impaired.

  Data sources and measurement: Measured as a proportion of total stream length per watershed. Geospatial data on impaired waters reporting (CWA section 303(d) impaired waters listing) is available from states directly or from EPA national geospatial data downloads, which are updated periodically with the most recent finalized spatial data from the states. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

watershed shape (PDF) (1 pp, 38 K)

  Why relevant to recovery: A more circular watershed shape has been associated with degraded water quality primarily due to greater risk of a more frequently destabilized channel. Runoff from rounder watersheds tends to concentrate and reach the mouth more quickly and with greater erosive power and velocity. Further, the shortened channel length associated with rounder watersheds enables less travel time to naturally process excess nutrients. Elongate watersheds tend to lessen the effects described above, which would lower the risk of repeated destabilization during recovery efforts.

  Data sources and measurement: Uses watershed boundary data. Watershed boundary datasets are available from the Natural Resources Conservation Service Geospatial Data Gateway Exit. Locate the watershed centroid, measure the axis (A) through the centroid most nearly parallel to the main channel, measure three additional axes (B, C, D) in 45 degree increments, then calculate the variability in length of these axes as A divided by the mean of the four axes. Nearly round watersheds approach a value of 1, elongate watersheds have higher values.

watershed size (PDF) (3 pp, 54 K)

  Why relevant to recovery: Related more to rate of recovery than absolute capacity to recover. As a general principle, smaller ecological systems are known to recover faster than larger ones if all else is equal. Also, size is correlated with many additional, directly and indirectly contributing recovery factors: for example, increasing complexity of larger systems delaying full recovery, larger systems' restoration often being more complex and expensive, larger watersheds usually having more complex ownership and multiple jurisdictions, larger lakes' far longer residence time, and larger river systems affected by more upstream factors that are less easy to isolate and address as part of a smaller system's restoration can often do.

  Data sources and measurement: Direct measurement of watershed area, with smaller size scoring higher. For digital data on watershed boundaries, numerous watershed scales have been delineated nationally as part of the Watershed Boundary Dataset (WBD) in the Natural Resources Conservation Service Geospatial Data Gateway Exit. Custom watershed boundary delineation can be done by aggregating NHDPlus catchments Exit or WBD HUC12 watersheds. This metric requires the watershed defined by the impaired segment's downstream terminus (e.g., not necessarily coincident with standard HUC units). ArcGIS tools can be used to derive area measures for any set of polygons of interest. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

bank stability/soils (PDF) (8 pp, 179 K)

  Why relevant to recovery: Specifically at the banks of rivers and streams as well as lakes, soils that are unstable are prone to continual erosion and greater likelihood of excess sediment load. Destabilizing forces can include the absence of woody and/or herbaceous vegetation, an unstable channel form (e.g. cut banks), or the soil type itself may be erosion-prone. Continual erosion and excess sediment are often linked to instream habitat degradation and diminished spawning success of lithophilic spawners, and may also add to other impairments involving nutrients or water temperature.

  Data sources and measurement: Metric reflects bank, not corridor, soil characteristics. Depending upon soil survey data available, specific soil types are rated as 'highly erosive'. This metric would be based on % of stream length passing through highly erosive soil types. Alternatively for lakes, use % of shoreline with highly erosive soil types. If a small buffer (e.g., 1 meter) is applied to the streams and lakes, then the measurement can be based on the % of area in the buffered corridor that contains highly erosive soil types yet still represent the land/water interface. Physical properties of soils are available for most areas as part of the Natural Resources Conservation Service (NRCS) Soil Data Access Exit. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

bank stability/woody vegetation (PDF) (4 pp, 75 K)

  Why relevant to recovery: Specifically at the banks of rivers and streams as well as lakes, areas that are unstable are prone to continual erosion and greater likelihood of a continuing excess sediment load. Destabilizing forces can include the absence of woody and/or herbaceous vegetation, an unstable channel form (e.g. cut banks), or the soil type itself may be erosion-prone. Continual erosion and excess sediment are often linked to instream habitat degradation and diminished spawning success of lithophilic spawners, and may also add to other impairments such as elevated nutrients or water temperature. River and stream banks without woody vegetative cover may be particularly prone to erosional damage during extreme high flow events and slower to recover in the aftermath. The prevalence of streambank stabilization projects involving woody plantings in restoration practice reflects the widespread opinion that the relative proportion of stable banks and woody vegetation needs to be high for the system to recover.

  Data sources and measurement: Land cover datasets coarsely identify woody vegetation (e.g forest, shrub, forested wetland, shrub wetland) that can be assessed as % of bank length with woody cover along the reach being assessed, calculated for both banks: Lwoody / 2 Ltotal X 100. Making this a linear metric (i.e. length of woody cover actually in contact with both stream/river banks, as mapped) discerns this metric from the "Riparian % woody cover" which is areal and relates to additional recovery relevant factors. GIS algorithms may be used to set buffer = 0, or if a small buffer (e.g., 1 meter) is applied to the streams and lakes, then the measurement can be based on the % of area in the buffered corridor yet still represent the land/water interface. Land cover datasets are available through the National Land Cover Database. Land cover for coastal areas is available through the National Oceanic and Atmospheric Administration (NOAA) Digital Coast website Exit. Orthophoto maps or remote imagery can be a good source for detailed local information. The NHDPlus Value-Added Attributes dataset contains flowline attributes on % for each land cover type from the National Land Cover Dataset. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

corridor % forest (PDF) (10 pp, 114 K)

  Why relevant to recovery: Broad array of influences on capacity to recover, including intercepting and moderating the timing of runoff, buffering water temperature extremes (which can also reduce certain toxicities), filtering pollutants in surface or subsurface runoff, providing woody debris to stream channels that enhances aquatic food webs and stabilizing excessive erosion.

  Data sources and measurement: Simplified calculation involves defining a standard corridor width on both sides of a watercourse (e.g. 30 meters, 90 meters) and calculating % area within the corridor. Also possible to calculate area within a variable-width corridor (e.g., an estimated flood return frequency zone). For land cover data, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

corridor % woody veg (PDF) (4 pp, 67 K)

  Why relevant to recovery: Broad array of influences on capacity to recover, including intercepting and moderating the timing of runoff, buffering temperature extremes (which can also reduce certain toxicities), filtering pollutants in surface or subsurface runoff, providing woody debris to stream channels that enhances aquatic food webs and stabilizing excessive erosion. See also corridor percent forest.

  Data sources and measurement: Requires medium to high resolution land cover mapping with shrub and forested classes included. Simplified calculation involves defining a standard corridor width on both sides of a watercourse (e.g. 30 meters, 90 meters) and calculating % area total of forested and shrub categories within the corridor. Also possible to calculate area within a variable-width corridor (e.g., an estimated flood return frequency zone). Different results from forested % possible when land cover data include a shrub class as well. Land cover datasets are available through the National Land Cover Database. Land cover for coastal areas is available through the National Oceanic and Atmospheric Administration (NOAA) Digital Coast website Exit. Orthophoto maps or remote imagery can be a good source for detailed local information. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

corridor % wetlands

  Why relevant to recovery: Wetlands are key features in watershed processing of nutrients in runoff, detention of excessive runoff during extreme weather events and acting as sinks for sediment and pollutants. In addition, wetlands provide vital recharge, detention and release in their role within groundwater/surface water interactions, particularly in stream corridors. Absence of wetlands degrades natural processing of the pollutants mentioned and results in greater direct transport to the receiving water body, increasing or perpetuating impairment. Presence of wetlands in the corridor may imply a more functionally connected and active floodplain.

  Data sources and measurement: Percent wetland area within the selected corridor width. Data sources may vary considerably in source, date and accuracy of wetland/upland delineation. For land cover data including generalized wetland categories, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources. NLCD or state land cover datasets are generally available but less accurate than wetland-specific mapping efforts such as National Wetlands Inventory (NWI)Exit. NWI data are partially available as digital coverage, are likely more accurately interpreted but may be out of date in selected areas. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

corridor slope (PDF) (2 pp, 45 K)

  Why relevant to recovery: Mainly relevant as low-gradient land surfaces near waters tend to develop less gullying and destabilized floodplain features that may perpetuate some impairments or make restoration more difficult, complex or expensive. These low-slope areas may also have superior water retention and favor more stabilizing vegetative growth. Note that corridor slope and channel slope are different metrics that do not have identical implications for recovery potential.

  Data sources and measurement: Digital elevation model (DEM) data from the National Elevation Dataset (NED)Exit or topographic data in many cases have already been mapped into slope classes, which can be merged with a selected corridor width to yield % in selected slope classes or a mean % slope for the corridor lands overall. Slope information can be obtained through the Elevation Derivatives for National Applications (EDNA) Exit. For finer resolution, use local Digital Elevation Model (DEM) data.

corridor soil erosion potential

  Why relevant to recovery: Soil types can vary substantially in erosion potential, with implications for the ease and frequency of siltation as well as for delivery of associated pollutants. Corridor soils have potentially greater influence than erosive watershed soils in general due to proximity.

  Data sources and measurement: Measured from mapped soil survey data within a selected corridor width, e.g. 30 meters, 90 meters. Assigning scores to different soil types based on the properties discussed should be done specifically for the area undergoing assessment, as national generalizations are limiting. Another option is to measure % area within the corridor that has soils with high resilience properties. Digital soil survey data varies from State to State in availability. States with fully digitized county soil survey-level information can use this metric most effectively. Physical and chemical properties of soils are available for most areas in Natural Resources Conservation Service (NRCS) Soil Data AccessExit. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

corridor soil type

  Why relevant to recovery: Soil texture and slope characteristics affect the degree of nitrogen retention, bank stability, overland flow, erosion potential and soil characteristics can even completely override land cover effects. Higher stream slopes increase soil erosion potential, and thus, phosphorus transport potential in overland flow. Soil texture has been called the single most important watershed characteristic affecting water quality of the Great Lakes. Stream nutrients can be associated with soil properties and fine-textured soils with higher runoff potentials appear to limit the transport of leached nitrogen.

  Data sources and measurement: Measured from mapped soil survey data within a selected corridor width, e.g. 30 meters, 90 meters. Based on selection of specific soil types documented as better for nitrogen processing, stability/erosion resistance and other factors as appropriate to the study area. Assigning scores to different soil types based on the properties discussed should be done specifically for the area undergoing assessment, as national generalizations are limiting. Another option is to measure % area within the corridor that has soils with high resilience properties. Digital soil survey data varies from State to State in availability. States with fully digitized county soil survey-level information can use this metric most effectively. Physical and chemical properties of soils are available for most areas in Natural Resources Conservation Service (NRCS) Soil Data AccessExit.

shoreline % forested

  Why relevant to recovery: Broad array of influences on capacity of lakes and reservoirs to recover, including intercepting and moderating the timing of runoff, buffering water temperature extremes (which can also reduce certain toxicities), filtering pollutants in surface or subsurface runoff, providing woody debris that enhances aquatic food webs and stabilizing excessive erosion.

  Data sources and measurement: Similar to corridor % forested measurement, but adapted for lakes and reservoirs to measure forested area within a shoreline buffer of specified width. For land cover data, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

shoreline % woody veg

  Why relevant to recovery: Broad array of influences on capacity of lakes and reservoirs to recover, including intercepting and moderating the timing of runoff, buffering water temperature extremes (which can also reduce certain toxicities), filtering pollutants in surface or subsurface runoff, providing woody debris that enhances aquatic food webs and stabilizing excessive erosion.

  Data sources and measurement: Similar to corridor % woody vegetation measurement, but adapted for lakes and reservoirs to measure wooded area within a shoreline buffer of specified width. For land cover data, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

natural channel form (PDF) (2 pp, 17 K)

  Why relevant to recovery: Helps flow regimes, sediment transport dynamics to occur within a natural range of variability, and for native and healthy biotic communities to become established. Although a wide variety of natural channel forms exist and some may be unstable or impaired for other reasons, the absence of any natural channel form (i.e. channelization) provides no generally preferred habitat as a starting point for biotic or natural fluvial process recovery. See also Channelization under stressor indicators.

  Data sources and measurement: Because channelization may occur in straight-line segments that join at angles, original detection is best done manually by visual ID on mapped or remote data (high resolution preferably). Once detected, the linear % of total reach length in natural channel form can be measured with common GIS software in a two-step process. Some monitoring programs note channel form among other field-gathered data and this is occasionally adaptable to a metric. Data sources include the high resolution National Hydrography Dataset Exit, state/locally compiled channelization metrics from previous studies, or other digital source.

corridor groundwater level (PDF) (2 pp, 116 K)

  Why relevant to recovery: Potentially related in multiple ways to waterbody recovery. Shallower vadose zone depth is likely to be related to the retention of alternating influent and effluent reaches along stream corridors, implying greater likelihood that groundwater/surface water interactions and exchanges are functional rather than isolated and disconnected. Also related to the likelihood of successful reestablishment of riparian vegetation and the greater bank stabilization that is implied.

  Data sources and measurement: Potentially related in multiple ways to waterbody recovery. Shallower vadose zone depth is likely to be related to the retention of alternating influent and effluent reaches along stream corridors, implying greater likelihood that groundwater/surface water interactions and exchanges are functional rather than isolated and disconnected. Also related to the likelihood of successful reestablishment of riparian vegetation and the greater bank stabilization that is implied.

channel slope

  Why relevant to recovery: Restoration practice implies that specific channel gradients are often more dynamically stable than others, and thus less prone to the instability that frequently causes channel restoration failure. Often, moderately sloped (e.g. 2 to 3%) channels are more stable than either lower or higher gradient channels. Note that corridor slope and channel slope are different metrics that do not have identical implications for recovery potential.

  Data sources and measurement: Measured as change in elevation over channel length for a specified segment or interval; can be averaged for longer segments or watersheds. High-resolution data over longer horizontal distances will produce better results. Generalized slope information can be obtained through the Elevation Derivatives for National Applications (EDNA) Exit. For finer resolution, use local Digital Elevation Model (DEM) data or LIDAR if available.

sinuosity

  Why relevant to recovery: Highly sinuous channels generally are more prone to longer-term sediment problems if they are impaired by excessive sediment loads. On the other hand, sinuous channels appear to allow for more nutrient processing. Relevance to recovery can vary with the impairment type and whether the sinuosity is human-altered.

  Data sources and measurement: Channel gradient can be field-measured very accurately at selected points. Topographic information or elevation datasets are less accurate but allow for coarse estimates of gradient anywhere. Sinuosity is better measured from high resolution National Hydrography Dataset or similar source than medium-resolution NHD. Expressed as channel segment length divided by straight line length between A and B, for a segment involving at least several meanders.

confinement ratio

  Why relevant to recovery: Confinement indicates the relative narrowness of a stream valley in comparison to stream width; more confined channels (i.e., low confinement ratio) tend to be more highly sensitive and prone to high-energy bank erosion and channel destabilization. This sensitivity can make the banks of confined channels with sediment impairments more difficult to restore through establishment and management of vegetated buffers. Relevance to other impairment types is unknown.

  Data sources and measurement: To calculate the confinement ratio, divide the valley floor width by the stream channel width. Very confined segments may have values around 1 to 2; very broad unconfined valley types with abandoned terraces may have a ratio of 10 or more. Measurement can require field work or be performed using aerial photography.

channel evolution status

  Why relevant to recovery: Many stream channels evolve in form after a significant disturbance, and the stage of this evolutionary process is relevant to recovery potential. The tendency of rivers is to seek their own flow-related and sediment-related stability. Following disturbance, streams will try to reestablish the dimension, pattern and profile of a pre-disturbance morphology. Channels in a highly destabilized state undergoing channel evolution may be more difficult to restore temporarily until approaching a more stable condition.

  Data sources and measurement: The existing stream type must be compared to the potential stable form it is likely to take on in time. Widespread spatial data on this factor are not likely to be found, but helpful guidance on evaluating successional status is available in the literature.

fine sediment transport capacity (PDF) (2 pp, 40 K)

  Why relevant to recovery: Moderate- to high-gradient streams and rivers are normally coarse-bedded and have aquatic communities adapted to coarse sediments. Fine sediment inputs commonly impair those communities. A system's capacity to move fine sediment and reestablish dynamic equilibrium affects how quickly it can recover from excess fine sediment loading.

  Data sources and measurement: Channel gradient can be field-measured very accurately at selected points. Topographic information or elevation datasets are less accurate but allow for coarse estimates of gradient anywhere. Sinuosity is better measured from high-resolution NHD or similar source than medium-resolution NHD.

natural flow regime

  Why relevant to recovery: Stream condition is largely dependent not only on 'enough' water but on naturally dynamic changes in the flow regime. Streamflow is strongly correlated with water temperature, channel form and habitat, thus acting as a primary factor that determines their aquatic communities instream and affects numerous human uses near streams. Five components of the flow regime include magnitude, frequency, duration, timing and rate of change; significant alteration of any of the five can affect stream ecosystem condition and strongly influence the potential for recovery from impairments of many kinds.

  Data sources and measurement: Data on flow regime may be limited but are extremely valuable to recovery potential screening where available. Using specific measures of one or more of the five flow regime components is more feasible than a single metric to summarize flow regime overall.

median flow maintenance

  Why relevant to recovery: See also natural flow regime. Depending on geographic region, median flow during specific times of the year influences stream and biological community condition. Surplus flows or deficits during crucial times of year may influence salmonid egg development, spawning, growth rates and survival, among many other effects. Although stream flow naturally varies, degree of departure from median flow on a monthly basis has been associated with significant biological impacts to current condition, and higher departure from expected flow range would likely work against recovery.

  Data sources and measurement: Typically measured as the median monthly flow for a selected month throughout a period of record, and departure from median monthly flow is estimated with reference to natural streamflow regimes calculated from gauging stations in the area. Typically a departure threshold such as less than +/- 10% difference from reference flow can be considered maintenance within natural variability.

low flow maintenance

  Why relevant to recovery: See also natural flow regime. Seasonal low flow is a vulnerable time for stream communities due to greater risk of elevated water temperature, lower dissolved oxygen, predation and more concentrated pollutants. As such, metrics that address the maintenance of low flows above harmful levels are useful in addressing whether flow volume might sustain or repeatedly interfere with stream recovery.

  Data sources and measurement: A number of different metrics can address low flow. Annual 7-day minimum flow is a commonly used statistic in water monitoring. Also, the number of times and duration of each time that flows drop below a given threshold make useful measures from which to examine how well flow is maintained under low-flow scenarios.

Strahler stream order (PDF) (6 pp, 76 K)

  Why relevant to recovery: Stream size is strongly related to many condition-relevant attributes but the recovery potential of different stream sizes varies with the attribute. The smallest headwater streams appear to be most sensitive to riparian stresses, suggesting lower recovery potential, yet their small size and high disturbance regime may imply greater resiliency and more rapid recovery than larger orders, as well as less complex and expensive restoration needs. Generally higher biodiversity associated with small to moderate orders (2nd to 4th order) may imply a more complex and resilient biotic community structure that may respond well to restoration efforts. Another recovery factor favoring a focus on the recovery of smaller orders is their favorable downstream influence on the condition of larger order streams.

  Data sources and measurement: Strahler stream order is manually calculable from topographic maps as well as available as a feature of the NHDPlus Value-Added Attributes dataset Exit.  NHDplus value-added attributes include stream order based on 1:100,000 NHD, which misses many finer order streams; thus orders may be lower than field-measured data, but may show relative rather than absolute differences in order adequately for general comparisons. If high resolution DEM is available it is possible to use ArcGIS tools to derive the stream raster network and run "Stream Order" tool within Spatial Analyst toolbox to calculate Strahler Order for the network. Local datasets may also be available. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

biotic community integrity (PDF) (4 pp, 70 K)

  Why relevant to recovery: The very complex concept of natural processes integrity is difficult to impossible to represent well using generalized geographic or impaired waters assessment data in a screening process. Nevertheless, several primary natural processes are exceedingly important influences on the prospects of recovery. As a substitute for measuring them all, biotic integrity integrates all other processes reasonably well. This recovery potential metric orients toward Karr's five major factors determining the condition of the water resource: flow regime, chemistry, habitat structure, biotic factors and energy. Severe degradation in any of the five likely represents severely reduced recovery potential. Many other more narrowly defined recovery metrics relate to one or more of these factors; this concept as a metric presents an opportunity to capture any other severe limiting factors that may be known but are unaddressed by the other recovery metrics in use. The increasing use of biotic integrity indices in state biomonitoring provides an important source of at least the biotic component of natural structure and process.

  Data sources and measurement: Index of Biological Integrity (IBI) data on fish or benthic invertebrates are available in some state monitoring program datasets (for example, the Benthic IBI for the Puget Sound LowlandsExit). Also, NatureServe Exit provides ecological integrity assessments for wetland mitigation in some regions of the country.

rare taxa presence (PDF) (2 pp, 52 K)

  Why relevant to recovery: Rare taxa have repeatedly been associated with more diverse and functionally intact ecosystems, including aquatic ecosystems. Rare taxa are also often more sensitive to stressors, and their presence in an impaired water may imply that the impairment is not severe. Increased eligibility and options for protection or restoration, elevated public and scientific concern and motivation to act, and other social factors may also be associated with rare taxa. These reasons support a probable association of the presence of rare aquatic taxa with generally higher recovery potential.

  Data sources and measurement: Species rarity has been organized and categorized for most major taxonomic groups as part of Natural Heritage Programs in most states and through NatureServe Exit conservation status assessment methodologies. National datasets can be found through the NatureServe Explorer or the USDA Plants DatabaseExit. In addition,  the Critical Habitat Portal Exithas GIS data for threatened and endangered species. More detailed datasets can be found through Natural Heritage Programs available in most states. It is possible to score the presence/absence of rare taxa with corresponding values of 1 and 0. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

trophic state

  Why relevant to recovery: Trophic state is often associated with water body condition relative to nutrients, with highly eutrophic systems frequently considered nutrient-impaired. Beyond nutrients, trophic state also has implications for biological impairment, oxygen depletion, sediment and other impairment types, the recovery from which can be hindered.

  Data sources and measurement: Standard data sources usually do not exist unless compiled through state monitoring programs or special studies. Measurement can be categorical with weights assigned between eutrophic and oligotrophic extremes.

NFHAP fish habitat condition index

  Why relevant to recovery: In a national assessment of fish habitat condition by the National Fish Habitat Partnerships (NFHP)Exit  17 metrics related to fish habitat condition were calculated at the NHDplus catchment level. Better-scoring catchments with better habitats represent less of a departure from fully functional systems, generally implying greater likelihood of restorability.

  Data sources and measurement: Data are publicly available for browsing and download through the NFHP map viewer. Scores have been calculated at the watershed scale of NHDplus catchments, HUC12 and HUC8. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

confluence density

  Why relevant to recovery: For impairments affecting biological communities in streams, recruitment from tributaries, particularly those large enough to support similar species assemblages, is one factor influencing speed of recovery. Tributaries per linear mile of impaired stream represent possible recolonization sources. On a watershed basis, confluence density is a measurement of this property.

  Data sources and measurement: Measured as the count of confluences per mile of watershed total stream length.  Strahler Order if used is available from NHDPlus Value-Added Attributes dataset Exit. Confluence count can be manual or automated. Where available, dam locations can be used to further assess and verify accessibility. Note that NHDplus data are at 100K resolution, missing many finer order streams.

unimpaired confluences density

  Why relevant to recovery: Impaired waters with unimpaired tributary confluences or bracketed by unimpaired upstream and downstream segments may be good prospects, as are listed waters where species of concern are reduced in number but not totally lost. In contrast, impaired waters isolated from similar systems may have poor prospects for recruitment or even be dependent on manmade reintroductions to recover fully, even if physical conditions have become suitable.

  Data sources and measurement: Measured as the count of confluences (optionally within + or - 1 Strahler stream order) with unimpaired tributary channels per mile of impaired segment on a watershed basis (also counts both up and downstream of segments within longer watercourses). Impaired segment shapefiles are available from EPA through the Assessment and TMDL Tracking and Information System (ATTAINS) and can be measured for length. Strahler Order is available from NHDPlus Value-Added Attributes dataset  Exit for both impaired segments and their tributaries. Where available, dam locations should be used to further assess and verify accessibility. Note that both the ATTAINS dataset and NHDplus are at 100K resolution missing many finer order streams.  When possible, high resolution data on Strahler order should be used.

watershed stream density

  Why relevant to recovery: Stream density is a surrogate measurement related to opportunities for biotic recruitment from tributaries. For impairments affecting biological communities in streams, recruitment from tributaries, particularly those large enough to support similar species assemblages, is one factor influencing speed of recovery. Tributaries per linear mile of impaired stream represent possible recolonization sources.

  Data sources and measurement: Measured as the total stream length per watershed total land area. Note that NHDplus data are at 100K resolution missing many finer order streams. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

contiguity with green infrastructure corridor (PDF) (4 pp, 61 K)

  Why relevant to recovery: Based on extensive documentation of the importance of connectivity among suitable habitats and habitat size/extent supporting more diverse and resilient ecological communities. Corridors increase effective habitat size and access, afford migration and movement to avoid temporary stressors and aid recruitment and recolonization into impaired areas. Basically, impaired water segments near, or hydrologically connected to, functionally intact waters identified as important corridors by a green infrastructure (GI) mapping effort have greater recovery potential than isolated impaired waters for the reasons above. Generally, GI corridors have relatively unimpaired aquatic systems and relatively uninterrupted, naturally vegetated riparian corridors.

  Data sources and measurement: This factor can be measured on a watershed-specific basis as corridor length, but that does not address connectivity. Measured on a stream segment basis, one example system for scoring would be:

• 0) no surface hydrologic connection to green infrastructure corridor;
• 1) no proximity to green infrastructure corridor (e.g., connected hydrologically but >2 km from corridor terminus);
• 2) proximate to green infrastructure corridor (e.g., connected hydrologically and < 2 km from corridor terminus);
• 3) connected to green infrastructure corridor;
• 4) Connected to and bridging two or more green infrastructure corridors.

Green Infrastructure (McMahon and others) mapping at statewide and other large scales has established criteria by which the more intact and ecologically functional stream corridors and larger natural habitat 'hubs' are identified. Examples of available state data include Maryland (See: http://www.dnr.state.md.us/greenways/gi/gi.html Exit.

proximity to green infrastructure hub (PDF) (3 pp, 58 K)

  Why relevant to recovery: Based on extensive documentation of island biogeographic principles and the importance of habitat size/extent supporting more diverse and resilient ecological communities. Green hubs and connected corridors increase effective habitat size and access, afford migration and movement to avoid temporary stressors, and aid recruitment and recolonization of impaired areas. Basically, impaired water segments near, or hydrologically connected to, functionally intact waters identified as parts of hubs and important corridors by a green infrastructure (GI) mapping effort have greater recovery potential than isolated impaired waters for the reasons above. Generally GI hubs contain major or multiple unimpaired aquatic systems and constitute larger, relatively uninterrupted, naturally vegetated communities with connections to multiple, naturally vegetated riparian corridors.

  Data sources and measurement: This factor can be measured on a watershed-specific basis as GI hub % of watershed or measured on a stream segment basis. Green Infrastructure (McMahon and others) mapping at statewide and other large scales has established criteria by which the more intact and ecologically functional, larger natural habitat 'hubs' are identified. Examples of available state data include Maryland (See: http://www.dnr.state.md.us/greenways/gi/gi.html Exit. Relative differences in this metric can be summarized as follows. If a categorical scheme is used, each impaired water segment could fall somewhere in the following classes (worst to best):

• 0) no hydrologic or watershed connection to a GI hub;
• 1) limited proximity to GI hub (e.g., within GI watershed and connected hydrologically but > 2 km from GI hub);
• 2) proximate to GI hub (e.g., connected hydrologically and < 2 km from GI hub);
• 3) continuous with GI hub.

recolonization access (PDF) (7 pp, 164 K)

  Why relevant to recovery: Loss or degradation of aquatic life, usually affecting a more sensitive subset of the resident fish or stream invertebrates, is an impairment whose recovery can be highly influenced by access and proximity to the nearest appropriate source for recolonization after conditions improve. Same or similar-sized streams within the same drainage are more likely to support similar aquatic life and act as biotic refugia and recruitment sources for recolonizing the impaired segment. Most relevant where aquatic life use support is impaired (many, perhaps most listed waters). Impaired waters with unimpaired tributary confluences or bracketed by unimpaired upstream and downstream segments may be good prospects, as are listed waters where species of concern are reduced in number but not totally lost. In contrast, impaired waters isolated from similar systems may have poor prospects for recruitment or even be dependent on manmade reintroductions to recover fully, even if physical conditions have become suitable.

  Data sources and measurement: Count # of confluences with + or - 1 Strahler stream order unimpaired channels per mile of impaired segment; impaired waters data from ATTAINS and stream order from NHDplus value-added attributes. Impaired segment shapefiles are available from ATTAINS and can be measured for length. Strahler Order is available from NHDPlus Value-Added Attributes dataset Exit for both impaired segments and their tributaries. Confluence count can be manual or automated. Where available, dam locations should be used to further assess and verify accessibility. Note that both the ATTAINS dataset and NHD plus are at 100K resolution missing many finer order streams. When possible, high resolution data on Strahler order should be used.

maintenance of % natural cover

  Why relevant to recovery: The relative proportion of land cover in a watershed that is not human-made (e.g., urban, agricultural, mining, or other altered cover types) influences watershed and water body condition in a number of ways. A high proportion of natural land cover is associated with better retention and infiltration of precipitation, less likelihood of damaging overland flow and erosion, and less transport of pollutants in runoff. This metric also incorporates the lack of rapid change in the proportion of natural cover, which generally implies low prospects for future loss of natural cover.

  Data sources and measurement: Natural cover categories from land cover mapping mainly include forest, shrubland, wetlands, grasslands and in some regions desert or barren land categories. Maintenance of natural cover is measured as change in total percent of land area (not including water area) in the watershed within the total of these several mapped natural land cover categories. For land cover data, the National Land Cover Dataset (NLCD) for 2011, 2006, 2001 and 1992 is accessible; the NLCD has already made available a land cover change dataset that can be used to generate this indicator. Numerous statewide land cover mapping datasets are also available from state-specific sources, but would require equivalent classification categories for two different dates. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

ratio current/historic % forest

  Why relevant to recovery: It is possible to consider a watershed's estimated pre-settlement natural vegetation cover as the original baseline for its general land-water interactions. For naturally forested regions the pre-settlement percentage of watershed forest cover can be reasonably estimated based on general terrain characteristics, soils and geologic data. When the current land cover proportions closely approximate original land cover, there is less likelihood of altered recharge, runoff and other land/water interactions that may impede recovery.

  Data sources and measurement: For land cover data, the National Land Cover Dataset (NLCD) for 2011, 2006, 2001 and 1992 is accessible. Studies of potential natural vegetation cover have been produced for most states, providing an approximation of pre-settlement vegetation types and distribution. One or more forms of this indicator has been measured at the HUC12 scale for all lower 48 states and data are available from Watershed Index Online (WSIO).

ratio current/historic % wetlands

  Why relevant to recovery: It is possible to consider a watershed's estimated pre-settlement natural vegetation cover as the original baseline for its general land-water interactions, and the similarity of current to historic wetlands extent provides insight into current condition relative to watershed hydrologic processes. Wetlands are key features in watershed processing of nutrients in runoff, detention of excessive runoff during extreme weather events and acting as sinks for sediment and pollutants. In addition, wetlands provide vital recharge, detention and release in their role within groundwater/surface water interactions particularly in stream corridors. Absence of wetlands degrades natural processing of the pollutants mentioned and results in greater direct transport to the receiving water body, increasing or perpetuating impairment.

  Data sources and measurement: Measure of the watershed's current percent wetland area divided by an estimated historic percent area, based on hydric soils with very low slope. Current data sources may vary considerably in source, date and accuracy of wetland/upland delineation. For land cover data including generalized wetland categories, the National Land Cover Database (NLCD) for 2011, 2006, 2001 and 1992 is accessible; numerous statewide land cover mapping datasets are also available from state-specific sources. NLCD or state land cover datasets are generally available but less accurate than wetland-specific mapping efforts such as National Wetlands Inventory (NWI)Exit. NWI data are partially available as digital coverage, are likely more accurately interpreted but may be out of date in selected areas.

historical species occurrence (PDF) (2 pp, 29 K)

  Why relevant to recovery: Although single-species oriented, this metric is appropriate where a restoration target or even a water quality criterion directly addresses a species of concern (e.g., naturally reproducing salmon or trout populations), or indirectly alludes to an aquatic condition exemplified by a keystone species (e.g., Eastern Brook Trout exemplifying a coldwater biotic community target). Verified historical occurrence does not necessarily ensure recovery potential due to the many additional factors that may interfere, but should provide a starting point for comparative evaluations of numerous potential restorations involving that species as a target. Verified historical absence is valuable for avoiding inappropriate restoration investments due to low recovery potential.

  Data sources and measurement: Limited to individual species of concern that have been researched sufficiently to establish historical presence/absence data. Assuming the probability that historical data are incomplete or imperfect, this metric at a minimum allows for the following three ranking categories (lowest to highest):

• 0) historically not found;
• 1) unknown historical occurrence;
• 2) known historical occurrence.

Distributional information on historical presence/absence of the species of interest may not exist for many species. Threatened and Endangered Species Habitat can be found through the Critical Habitat Portal Exit.  Historical information may be available through State Fish and Wildlife Service, as is the case in Oregon (See: http://www.fws.gov/oregonfwo/Species/Data/ Exit). Biodiversity organizations and state natural heritage programs may have data on other major aquatic taxa of interest.

species range (PDF) (2 pp, 41 K)

  Why relevant to recovery: Although single-species oriented, this metric is appropriate where a restoration target or even a water quality criterion directly addresses a species of concern (e.g., naturally reproducing salmon or trout populations), or indirectly alludes to an aquatic condition exemplified by a keystone species (e.g., Eastern Brook Trout exemplifying a coldwater biotic community target). The rationale regarding recovery is that a waterbody occurring in marginal habitat that approaches an extreme of species range generally represents greater stressors and higher risks to restoration efforts than non-marginal range locations. Marginality concepts may be numerous (e.g., northern or southern extremes; elevation; waterbody traits such as size, channel gradient, substrate; precipitation regime) and need to be selected appropriately for the species of interest. Climate change effects - both global processes and local, man-induced processes that approximate global effects (e.g. water temperature regime changes due to development and vegetation removal) - may act to make marginal range areas additionally unsuitable and difficult to restore.

  Data sources and measurement: Dependent upon species range maps, which are often very generalized. Modification may be necessary by consulting with local experts on the species of concern. Threatened and Endangered Species Habitat can be found through the Critical Habitat Portal Exit.  Historical information may be available through State Fish and Wildlife Service, as is the case in Oregon (See: http://www.fws.gov/oregonfwo/Species/Data/ Exit).  Biodiversity organizations and state natural heritage programs may have data on other major aquatic taxa of interest.