Final Project: Riverscapes of the Middle Salmon River in ID, USA
Final Project: Riverscapes of the Middle Salmon River in ID, USA
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Project Objectives
Project Objectives
Conduct a brief analysis of three unique reaches in a riverscape of interest
Provide a summary of catchment characteristics and geologic/ecological setting
Intercompare reaches along the selected riverscape based on information about the catchment and the analyses of selected reaches
All maps are projected in NAD83 UTM Zone 12N.
The Salmon River flowing through the Salmon River Canyon at Middle Fork. Photograph by Rex Parker.
Watershed Characteristics
Watershed Characteristics
General Location and Catchment Map
General Location and Catchment Map
The Salmon River is located in East-Central Idaho north of the Snake River Plain. It is the longest river without dams in the contiguous United States, with a mainstem length of 425 mi. The Salmon River has headwaters in the Sawtooth mountain range and is the largest tributary of the Snake River. Ultimately, the water from the Salmon River drains to the Pacific Ocean as it is part of the larger Columbia River system in the Pacific Northwest.
Fun fact: the Salmon River is also affectionately known as the River of No Return.
Catchment map of the Salmon Watershed, the Middle Salmon-Panther Watershed, and the Salmon River.
Catchment Characteristics
Catchment Characteristics
Map of the Middle Salmon-Panther catchment.
The catchment length of the Middle Salmon-Panther catchment, taken as the distance from the northernmost to southernmost point of the catchment, is 111 km. The area of the Middle Salmon-Panther catchment is 4719 sq. km. Elevation of the city of Salmon, ID, which is located in the center of the Lemhi Valley (large valley in the east-center of the catchment) is 1203 m.
The Middle Salmon-Panther catchment is moderately elongate and has low circularity. The low relief ratio indicates that the slopes in this catchment are relatively low.
Climate and Flow Regime
Climate and Flow Regime
Climate in the Middle Salmon River features cold, snowy winters and hot, dry summers. Hydrology of the Salmon River is largely dominated by snowmelt. Peak flows of the Salmon River typically occur during the mid-summer months (June/July), when snowmelt rate is highest (right). The river experiences low discharge from late summer through early fall, then increases to steady discharges between 1000-1500 cfs from mid-fall to early spring. Discharges are highly variable from mid-spring to mid-summer, but do consistently increase overall, culminating in the peak flows of mid-summer. The average discharge of the Salmon River overall is 11,100 cfs, indicating that this catchment has considerably lower discharges than larger, downstream portions of the Salmon.
Daily discharge (cfs) from 01/01/2024-01/01/2025 taken at USGS gage no. 13302500 (Salmon River at Salmon, ID).
Geologic Setting
Geologic Setting
Geologic units in the Middle Salmon-Panther catchment.
The Salmon River watershed was anciently covered in an inland shallow sea that deposited numerous limestone formations in the region. More recent volcanic and fault activity deposited igneous rocks, leading to a unique mixture of sedimentary, limestone, and igneous mineral deposits throughout the catchment. The Salmon River catchment also experienced the Bull Lake and Pinedale glaciations, which were the same glaciation events that shaped glacial landforms seen in the nearby national parks of Yellowstone and Grand Teton.
The geology of the Middle Salmon-Panther catchment reflects this pattern of underlying limestone formations, overlying granitic and volcanic minerals, and scattered glacial deposits. The majority of this catchment is limestone-based (Yellowjacket Formation and Lemhi Group), although the geology along the course of the river is more diverse. On the southern end of the catchment, the river flows through the Challis Volcanic group. Moving north, the river passes over alluvial deposits in the Lemhi Valley deposited by the Salmon River over time. Near North Fork, the river passes over the Yellowjacket Formation and Lemhi Group before turning westward into steep canyons composed of augen gneiss, a metamorphised granite, and gneissic metasedimentary rocks.
Ecoregions
Ecoregions
Level III ecoregions in the Middle Salmon-Panther catchment.
Level IV ecoregions in the Middle Salmon-Panther catchment.
The Salmon River is split almost evenly between the Idaho Batholith and Middle Rockies Level III ecoregions in this catchment (above left). Most of the catchment is part of the Southern Forested and Forested Mountains Level IV ecoregions (above right). Level IV ecoregions shift with proximity to the river, which is consistent with the geologic characteristics of this area. Ecoregions adjacent to the river in this catchment include Hot Dry Canyons, Dry Partly Wooded Mountains, Dry Schistose-Volcanic Hills, and Intermontane Sagebrush Valleys.
Land Cover
Land Cover
Land cover in the Middle Salmon-Panther catchment.
The Middle Salmon - Panther catchement is generally a remote, wild area. Highest intensity development and agriculture is concentrated near the city of Salmon, which is located in the Lemhi Valley. The rest of the catchment is split between coniferous forests, herbaceous vegetation, and shrub/scrub communities. Locations for the sites of interest are within shrub/scrub and herbaceous areas.
The remoteness of this catchment, in addition to the lack of damming, makes the Salmon River an ideal riverscape to study wild, minimally-developed gravel-bed river systems in the northwestern United States.
Site 1: Partially Confined
Site 1: Partially Confined
Tier 1 map of a partially-confined riverscape in the Middle Salmon-Panther catchment.
Location: 45.324346° N, -113.913262° W
Elevation: 1145 m
Annotated cross-sections at site 1 where a confining margin is present (top) and where a confining margin is absent (bottom).
Site 1 was partially confined with 15% confinement, making it planform-controlled. This result is consistent with the tier 1 map, where active floodplain percentage (37%) was relatively close to the inactive floodplain percentage (46%). A significant amount active floodplain area occurring in between sections of active channel rather than only occurring on the outside edges of the channel.
GUTs identified at site 1.
Analysis of GUTs at this site indicates that channel topography is highly variable at this reach. Bar development both on points and in-channel are frequent. Recently-used flood channels and dissections of larger bars are also common.
This reach has a strong pattern of riffle-pools with a few scattered rapids, likely caused by large boulders. Headcutting is also present at this reach, which is not surprising given the amount of energy required to transport sediment and create so many bars/bar dissections.
Site 2: Laterally Unconfined
Site 2: Laterally Unconfined
Tier 1 map of a laterally unconfined riverscape in the Middle Salmon-Panther catchment.
Location: 45.248834° N, -113.900521° W
Elevation: 1172 m
Annotated cross-section at site 2 demonstrating topography of a laterally unconfined riverscape.
Site 2 was laterally unconfined with no confining margins. The large majority of the valley bottom at this site was inactive floodplain (55%). The vegetation at this site made the separation between active and inactive floodplain very clear.
This site had the highest sinuosity of all three sites (1.05), which makes sense given the fact that the channel is laterally unconfined. The presence of paleochannels in inactive floodplain also indicates that the channel at this site has moved over time.
GUTs identified at site 2.
Although this site also contains bars and flood channels, the topography of this channel does not appear to change nearly as much as Site 1. This could be due to the differences in underlying geology between these two sites: this site is above alluvial deposits left behind in the floodplain of the ancient Salmon River; Site 1 is within an area of limestone formations, which may be easier to erode.
The riffle-pool flow pattern is also prominent at this site.
Site 3: Confined
Site 3: Confined
Tier 1 map of a confined riverscape in the Middle Salmon-Panther catchment.
Location: 45.392308° N, -114.179401° W
Elevation: 1055 m
Annotated cross-sections in site 3 where a confining margin is present on both sides (top) and present on one side only (bottom).
Site 3 was a confined site, which makes sense given that the geologic setting of the reach is a canyon of exposed augen gneiss.The site is confined on both sides - one side being the exposed canyon wall and the other side being the anthropogenically raised highway on the foot of the other canyon wall.
Overall, the ratio of valley bottom area to site length at this site was quite small compared to the other two sites. Stretched out, the valley bottom at this site would be long and thin as opposed to short and fat, like the valley bottoms at Sites 1 and 2. As a result, no inactive floodplain existed at this reach; any floodplain that existed at this reach appeared to be active floodplain.
Additionally, the slope at this site was the lowest of all three reaches (1.006). Although the river at this location is curving around a canyon wall, the sinuosity is still low because the length of the channel, which comprises most of the valley bottom, is very close to the length of the valley bottom centerline.
GUTs identified at site 3.
This site had a large riffle crest on the lower-elevation side of the reach. On the higher elevation side of the reach, multiple small rapids are present interspersed with pools. On the lower elevation side of the reach, the flow pattern shifted to a riffle-run pattern rather than the riffle-pool pattern observed at the other sites.
Aside from one small bar, site 3 did not have many floodplain features. This is to be expected considering the high degree of confinement at this reach, which would restrict the river from meandering or developing flood channels.
Comparison of Sites
Comparison of Sites
Intercomparison of sites and estimations of confinement patterns within the Middle Salmon-Panther catchment.
The Middle Salmon-Panther catchment has distinct areas of confinement styles throughout the watershed. Reaches around Sites 1, 2, and 3 were often very similar in terms of confinement and geomorphic units. I have driven up the highway that leads to Salmon from the south multiple times, which largely follows the Salmon River. South of this catchment, the river is mostly unconfined or planform-controlled. Large valleys like the Lemhi Valley are more likely to have laterally unconfined riverscapes that are often able to support networks of large beaver ponds.
The switch to margin-controlled and confined reaches appears to be related to catchment geology. Based on what I have learned from this catchment and what I have observed in my travels to Salmon, I would guess that geologic setting south of this catchment is either limestone formation or alluvial deposits from the ancient Salmon River. The road leading up to Salmon is quite open until the approach to Lemhi Valley, where the valley margins are closer together and shift to volcanic rock. Similarly, the shift from planform-controlled to margin-controlled and confinement in the downstream portion of the Middle-Fork Panther also corresponds with a shift in underlying geology from limestone to dry canyons/augen-gneiss. These materials take much longer to erode than limestone, which has likely resulted in higher confinement in these areas.
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