Introduction 1999 2005 2005 2000 2005 1984 1998 2005 2005 1984 1990 2003 1995 1997 1995a 1995b 2000 1984 1984 1995 1998 2003 1997 2005 2005 1994 2001 1984 2000 1995 2000 2003 2000 2005 1991 1 Fig. 1 Map of the study region showing rivers and dams of the Hells Canyon Complex  Methods 1 Table 1 Recent studies that include multiple comparisons for investigating ecological impacts from dams above river canyons of western North America (north to south) and the Snake River Author (year) River(s) Location 1. Upstream versus downstream 2. Progressive downstream 3. Dammed versus free-flowing 4. Pre- versus post-dam 5. Sequential post-damming 6. Flow modification 7. Process-based modeling 1995 2000 2005 a St. Mary River through Box Canyon Alberta X X X X X X  1986 1995 2000 2000 2002 2003 2004 a Green and Yampa rivers through Dinosaur Monument Colorado  X X X X   1995 2001 1995 1996 1997 2001 a Grand Canyon of the Colorado River Arizona X X X X X X X 1995 1999 Snake River, upstream of Hells Canyon Idaho     X  X 1995 Snake River, Hells Canyon Idaho, Oregon  X   X   Proposed composite study Snake River, Hells Canyon Idaho, Oregon X X X X X ? X a 1 River channel and valley characteristics were assessed by field visits and float trips along all of these reaches and from 1:24,000 scale USGS quadrangle topographic maps. From these maps, channel widths were measured at 1.6 km intervals from the left to right bank and incorporated islands if present. Longitudinal profiles were determined from elevational contours and calculated as both river and valley gradients. Historic hydrologic data were accessed from regional USGS gauges along the Snake and Salmon Rivers. Statistical comparisons of the river channel characteristics were undertaken with Kruskal-Wallis nonparametric comparisons with JMP 5.0 (SAS Institute Inc., Cary, North Carolina). Following from the consideration of different research strategies, we compared the different spatial and temporal study approaches relative to the similarity of the proximal, or local, rivers and landscapes, and the distal, headwater environments. We considered: (1) climate and hydrology and especially the seasonal river flow pattern; (2) aspects of fluvial geomorphology, with the geomorphic context for the local comparison, and sediment inputs for the distal comparison; and (3) biological aspects and especially the composition of the riparian vegetation communities. We applied a quartile scaling with: 0 = very different; 0.25 = different; 0.5 = somewhat different; 0.75 = very similar; or 1.0 = same. The local environment was considered most critical for riparian vegetation and, consequently, we doubled the weighting of this component and subsequently added the proximal and distal scores to produce the comparability index that could range from 0 (entirely different) to 4 (identical). Results 1 2 Table 2 Research strategies to analyze ecological impacts downstream of dams and their suitability for the Snake River through Hells Canyon Research strategy Study design Consideration / complexity Suitability for Hells Canyon I. Comparative studies A. Spatial comparison 1. Upstream versus downstream Paired comparison: upstream = control, downstream = treatment Dams are not randomly situated and are often at geomorphic transitions Low - an extreme geomorphic transition exists 2. Progressive downstream Quantitative comparison suitable for pattern analysis Inflowing tributaries can mitigate impacts of damming but also introduce system complexity Medium - the inflow of the Salmon River provides considerable system recovery 3. Dammed versus free-flowing Paired or multiple comparison: free-flowing = control or reference, dammed = treatment Although regional rivers have biophysical similarities, each river is somewhat unique High - in biophysical condition, the Salmon River Gorge is very similar to Hells Canyon B. Temporal comparison 4. Pre- versus post-dam Paired comparison: pre-dam = control, post-dam = treatment Comprehensive biophysical inventories were seldom undertaken prior to damming Medium - historic descriptions and archival photographs are available 5. Sequential post-damming Multiple comparison that may be suitable for pattern analysis Other coincidental changes complicate interpretation Medium - sequential aerial photographs permit comparison of large-scale features II. Manipulative experiments 6. Flow or sediment modification or dam removal Pre-determined paired or multiple comparison A specialized post-damming comparison that may test causal association Uncertain - following recent relicensing , there may be slight, but probably not major, changes in dam operations III. Biophysical modeling 7. Process-based modeling Quantitative modeling with hydrogeomorphic foundation (i.e., hydrology & geomorphology ➔ vegetation ➔ wildlife) Requires defined and deterministic relationships but some processes remain poorly understood High - the physically rigid landscape simplifies hydrogeomorphic modeling and riparian vegetation is limited Spatial Comparisons Spatial comparisons involve assessments of different reaches along a particular river or comparisons with nearby reaches of different rivers. Scientific interpretation is based on the general assumption that regional river reaches will demonstrate ecological similarities because they often share hydrologic and geomorphic contexts, have similar climatic regimes, and at least prior to damming, share some ecosystem communities. Correspondingly, the strength of comparison within or across rivers relies on environmental similarity without damming. Upstream Versus Downstream Concept 2 1 2 1980 1995a 1995b) 2000 1997 2 Fig. 2 Schematic showing general spatial comparisons to analyze environmental impacts downstream from dams. Triangles represent dams and reservoirs  2005 Application 3 4 4 4 Salix exigua Populus trichocarpa 2006 Fig. 3 Typical views of the Snake River upstream (top, near Weiser, July 1997) and downstream (bottom, below Hells Canyon Dam, July 1997) from the Hells Canyon Complex of three dams and reservoirs  Fig. 4 n n n p  3 1998 1991 1998 4 3 th 4 2 Progressive Downstream Concept – 2 1 2 2005 1984 1997 1986 1999 While the upstream versus downstream comparison represents a paired comparison, the progressive downstream or synoptic comparison involves a sequence of river segments to reveal quantitative patterns that are suitable for regression or other trend analyses. The progressive downstream approach also overlaps with temporal comparison because impacts such as sediment depletion may extend downstream over time. Application – 1995 2003 1 2 2 Dammed Versus Free-Flowing Rivers Concept – 2 1 2 2005 Application – 5 Fig. 5 Schematic showing the proposed spatial comparisons to analyze environmental impacts downstream from the Hells Canyon Complex of dams  4 4 3 Table 3 Hydrological characteristics of river reaches in the Hells Canyon region a Years of record 2 3 3 Ave Max Min Ave Max Min Snake River at Murphy 1914–1998 108,521 314 543 191 706 1339 306 b 1914–1998 70,707 198 488 48 593 1053 116 Snake R. at Weiser 1914–1998 179,228 513 1031 239 1299 2393 422 a 1965–1997 189,847 585 1035 276 1356 2777 578 Salmon R. at Whitebird 1914–1998 35,095 316 506 165 1798 3681 617 a b 1 The Snake and Salmon rivers also vary considerably in accessibility and the extent of human impact. The Snake River corridor has been the focus for agricultural development and human settlement in Idaho. In contrast, much of the Salmon River flows through the Frank Church River of No Return Wilderness Area, one of the least developed areas of the contiguous United States. Only about 150 km of the Salmon River flows through lands with developed agriculture and these areas are minor compared to agricultural developments along the Snake River. Because virtually all land uses within a watershed impact hydrology, sediment and nutrient fluxes, the different human histories of the watersheds would result in different inputs into the Snake versus Salmon River systems. 1991 2 Temporal Comparisons 1 1 1994 2001 1984 1995 1998 1989 2005 2007 Pre- Versus Post-Dam Concept – The second impediment is the nature of research funding. Because funding is generally limited in duration, it is more practical to seek funding for a limited-term project with a short-term “deliverable” than for a long-term study, potentially with an uncertain duration and outcome. The nature of academic study also favors a shorter-term comparison because research projects often involve two or three-year intervals to suit graduate student and post-doctoral projects. 1 Application Sequential Post-Damming Concept – 1999 2005 1984 1995 Application – 1995 1995 Flow Modification Concept – 2000 2001 2001 2003 2005 Application – Process-Based Biophysical Modeling Concept – 1994 1995 1999 1998 2000 2002 2002 2003a 1994 1998 2002 1994 1996 2003 2006 1994 1996 2003 Application – 1994 1998 1995 Comparative Validity Across Study Approaches 4 Table 4 Assessment of different comparison studies for analyzing impacts of damming and flow regulation on the Snake River through Hells Canyon  Proximal score (P) local landscape (weight = 2) Distal score (D) watershed conditions (weight = 1) Comparability index = P + D Upstream vs. downstream (Weiser vs. Hells Canyon) Different (0.5) (almost the) Same (1) 1.5 Dammed vs. free-flowing (Hells Canyon vs. Salmon) Very similar (1.5) Different (0.25) 1.75 Pre- vs. post-dam (Hells Canyon) Same (2) Very similar (0.75) 2.75 We applied a quartile scaling of: 0 = very different; 0.25 = different; 0.5 = somewhat different; 0.75 = very similar; or 1.0 = same; and multiplied this value by the weight to produce the P and D score Discussion 1 1984 1984 1995 2004 2 4 2 Natural Variation 2000 2005 2005 1989 1996 1994 Coincidental Influences 2005 Cumulative and Sequential Impacts 1999 2005 1991 Threshold Effects 2002 1994 Latent Effects 1995 Multiple Comparisons 2001 2 1 1995 1 A Composite Study Strategy for Hells Canyon 4 1995 5 2002 2005 5 1 2 2000 2005 5 1 5 1995