Natural history of the South Fork Snake River eastern Idaho emphasizing geomorphology hydrology and vegetation

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The geomorphology, hydrology, and vegetation of the upper Snake River, which is also known as the South Fork Snake River, was studied to assess the effects of the Palisades dam and other land uses on the river environment. These assessments were made using a variety of data sources including hydrologic data collected by the U.S. Geological Survey, aerial photography, plant collections, repeat photography of landscape scenes, channel material borings, plan and profile maps, and early explorer journals. Much of the data spans about 80 years. <br>

The South Fork Snake River is a proglacial, cobble-bedded stream that is braided over much if its length. Streamflow is dominated by snowmelt. Ninety two percent of the drainage basin is forested. Steppe, pasture, and cropland occupies most of the remaining area. <br>

The most important affects on the river results from Palisades reservoir management, which began in 1956. These affects are elimination of peak flows greater than the natural 3-year event and sediment trapping by the reservoir. Channel response to these affects are local channel degradation and widening in the first 0.5 river miles (RM) downstream from the dam. No changes in width or channel roughness were detected at a gaging stations 1.6 (RM) and 42 (RM) downstream from the dam. Reaches from 15 RM to 42 RM downstream from the dam had a 4% increase in width. For these same reaches, total sinuosity, which includes active anabranches, was 1.98 in 1941 and 2.02 in 1987. Lateral channel migration since dam closure is less than during periods with high floods. The at-a-station hydraulic geometry for five Snake River gaging stations, including one above the reservoir, was examined. Large shifts in the constants occurred at one station after passing a large flood. Shifts were statistically significant yet very slight at the stations with records spanning the pre- and post-dam periods. <br>

The most obvious vegetation change is an increase in mature cottonwood {Populus angustifolia) forest. This increase is due to a combination of natural flood history and human-induced flood control. Other important vegetation changes are an invasion of exotic grasses and forbs, and an increase in the native reed canary grass (Phalaris arundinacea) on young channel deposits. <br>

Methodology and interpretation for hydraulic geometry are also explored.

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Reference Code: U94MER01IDUS <br>

Full Citation: Merigliano, Michael F. 1994. Natural history of the South Fork Snake River eastern Idaho emphasizing geomorphology hydrology and vegetation [master’s thesis]. Graduate Student Theses, Dissertations, & Professional Papers. 8161. University of Montana, Missoula, MT. 278 p. [Accessed 2021 January 15]. https://scholarworks.umt.edu/etd/8161 <br>

Location: ELECTRONIC FILE - BOTANY: OTHER <br>

Keywords: dams, Idaho, geomorphology, hydrology, plant ecology <br>