Reconnaissance basics
The IWWI database is structured by sixth-field hydrologic unit boundaries (HUB), which are watersheds that generally range in size from 5,000 to 50,000 acres. The project also utilized a common stream network layer. Watershed vulnerability data reflect the inherent risk for watershed conditions to become degraded if certain sensitive lands are disturbed. Sensitive lands are defined as having highly dissected slopes, highly erodable soils, or landslide deposits and potential for landslides. Watersheds rated as high vulnerability have more than 50% of their area in sensitive lands; watersheds rated with moderate vulnerability have 20–50% of their area in sensitive lands; and watersheds rated low vulnerability have less than 20% of their area in sensitive lands.
Stream segments identified as crucial have especially high resource values. They can include reaches that possess any of the following characteristics:
• being classified as an outstanding fishery;
• having an instream flow water right;
• having a public water supply diversion;
• providing outstanding recreation value;
• having a water-based cultural use;
• being in a water-based Research Natural or Special Interest Area; or
• having a self-propagating population of, or potential to support any designated endangered, threatened, or sensitive species.
Stream segments identified as damaged are those in which physical, chemical, or biological impacts have caused any water-related resource value to be seriously degraded. They can include segments exhibiting any of the following impacts:
• bank damage;
• sediment loading;
• channel modification;
• flow disruption;
• thermal change;
• chemical contamination; or
• biological stress.
Geomorphic integrity data provide information on soil–hydrologic function as a sponge-and-filter system to absorb and store water, and on geomorphic resilience of streams. Watersheds with high integrity are those in which the following criteria occur:
• soil–hydrologic function is judged to be excellent or good throughout the watershed;
• all streams are judged to be in dynamic equilibrium relative to their potential; and
• all riparian areas are judged to be in properly functioning condition.
Watersheds with moderate integrity are those in which any of the following are apparent:
• soil–hydrologic function is judged to be degraded in isolated areas (less than 20%) of the watershed;
• a minor percentage of the stream miles (less than 20%) are judged not to be in dynamic equilibrium; or
• a minor percentage of the riparian miles (less than 20%) are judged to be functioning at-risk or non-functioning.
Watersheds with low integrity are those of which any of the following is true:
• soil–hydrologic function is judged to be degraded over much (more than 20%) of the watershed;
• a major percentage of the stream miles (more than 20%) is judged not to be in dynamic equilibrium; or
• a major percentage of the riparian miles (more than 20%) are judged to be functioning at-risk or non-functioning.
Water quality integrity data provide information on whether designated beneficial uses are being supported or water-related resource values are being protected. Watersheds with high integrity are those in which no stream segment is damaged by physical, chemical, or biological impacts. Watersheds with moderate integrity are those in which only a minor percentage (less than 20%) of stream segment miles are damaged. Watersheds with low integrity are those in which a major percentage (more than 20%) of stream segment miles are damaged.
For both the geomorphic and water quality integrity data sets, the premise is that watersheds of high integrity are relatively pristine; watersheds of moderate integrity can recover in the short term, either naturally or through revised management with minimal capital investment; and watersheds of low integrity cannot recover without major capital investment and revised management that complements the recovery.
Reconnaissance limitations
The IWWI work was conducted in a very short timeframe to provide a reconnaissance-level estimate of geomorphic and water quality conditions. Protocols for conducting the assessment were developed; however, they were imprecise. Thus, the ratings are subjective and should be recognized by the user as such. To that end, it is assumed that the protocols were applied consistently within an administrative unit; it is probable they were applied inconsistently across units. Furthermore, the ratings apply to vast areas of land, using existing, readily available information that varied in detail both within and across administrative units. Therefore, comparison between units may be tenuous at best.
Inland West Water Initiative summary of ratings for the GYA
Summary ratings for the national forests in the GYA were originally completed in the spring of 1998, and updated in November 2000. Yellowstone National Park ratings were completed during April 2000. The watershed vulnerability GIS layer was then updated in December 2001, in order to account for the several major cross-administrative boundaries (Shovic and Urie 2001). The update required development of a consistent stream dissection coverage for the GYA, integration of new land type data, and linkage of results to the spatial data using 53 structured queries to make results repeatable and upgradeable when the base data change. Maps displaying geomorphic integrity, watershed vulnerability, water quality integrity, crucial segments, and damaged segments were prepared during the assessment but are not displayed in this paper due to scale issues. Though individual units varied, the proportion of highly sensitive watersheds in the GYA was reduced by the watershed vulnerability update from 47% to 27%. This was likely due to a combination of more detailed data, more land area included, and more consistent application of criteria used for defining sensitivity, but could also be from the conservative application of the rather general criteria given in the IWWI documentation.
The Shoshone National Forest had the highest amount (55%) of highly sensitive watersheds. Yellowstone National Park had the lowest, with 9%. The Shoshone National Forest contained the most highly dissected land area (30%), while the Beaverhead-Deerlodge and Caribou-Targhee national forests had the highest percent of watersheds with landslides (14% and 12%, respectively). The Custer National Forest and the National Elk Refuge had the highest proportion of highly erodable soils (46%), primarily due to large areas of shallow soils and silty, erodable soils.
Landscape data were missing from only about 2% of the entire GYA. Watershed data were missing from the Caribou-Targhee National Forest (46%) because they were unavailable at publication time. However, Grand Teton National Park and the National Elk Refuge were added. This model can be re-programmed to include these missing data at a later date. The new watershed data are highly consistent across administrative boundaries.
Only 34% of the watersheds in the GYA had a high geomorphic integrity rating. This low percentage was primarily a function of the stringent high geomorphic integrity rating criteria, which required excellent soil–hydrologic function throughout a watershed; that all streams be in dynamic equilibrium; and that all riparian areas be in properly functioning condition. Most watersheds in which multiple use activities occur will have at least some soil–hydrologic function degradation, some stream segments not in dynamic equilibrium, or some riparian areas not properly functioning; hence, the preponderance of moderate geomorphic integrity ratings. Yellowstone National Park had a high percentage (75%) of high geomorphic integrity watersheds due to the relatively undeveloped and undisturbed nature of the park.
The 6% of GYA watersheds with low geomorphic integrity ratings were areas with considerable watershed disturbance and/or function disruption. They comprise some of the highest priority areas for watershed rehabilitation and management improvement. Watersheds with ratings of moderate geomorphic integrity also have considerable potential for watershed rehabilitation. Range and road impacts were the most frequent cause of low or moderate watershed geomorphic integrity ratings. Grazing was the predominant cause on the Madison Ranger District of the Beaverhead National Forest, on the Bridger-Teton and Caribou national forests, and on the Beartooth Ranger District of the Custer National Forest. Roads were the primary cause on the Gallatin and Shoshone national forests. In Yellowstone National Park, fire was the primary cause of downgraded geomorphic integrity ratings due to several watersheds in the eastern part of the park (Absaroka Range) with high watershed vulnerability ratings and a significant amount of 1988 canopy burn.
Water quality integrity ratings are a direct function of the damaged stream GIS layer, which includes stream segments with one or more human-caused damaging factors including bank damage, sediment loading, channel modification, flow disruption, thermal change, chemical contamination, or biological stress. Damaged streams are frequently listed on state 303(d) lists. The IWWI damaged stream layer displays damaged stream segments by cause. The highest percentages of damaged streams occur on the Madison Ranger District of the Beaverhead National Forest, on the Bridger-Teton and Caribou national forests, and on the Beartooth Ranger District of the Custer National Forest. They also have the highest percentages of impaired watershed conditions, with grazing as the primary cause.