Geologic Publications for Mount Rainier
Morphology and hydrology of a glacial stream - White River, Mount Rainier Washington
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Robert K. Fahnestock
Professional Paper 422-A
United States Geological Survey
This is a study of the processes by which a valley train is formed by a proglacial stream. The area investigated is the White River valley on the northeast flank of Mount Rainier, between the present terminus of Emmons Glacier and the moraine marking the terminal position in 1913. Five square miles of the 7.5-square-mile drainage basin above this moraine are presently covered by active ice.
Measurements of channel characteristics were made in 112 channels developed in noncohesive materials. Channel widths ranged from 0.7 to 60 feet, mean depths from about 0.03 foot to 2.08 feet, and mean velocities from 0.3 to 9 feet per second for discharges of about 0.01 to 430 cfs. The relations between these variables can be expressed by the equations: w=aQb
, and v = kQm
. The exponents for White River channels were found to be similar to the average of those for streams in the Southwestern States. In contrast, Brandywine Creek, Pa., with cohesive bank materials, had higher velocity exponents and extremely low width exponents. Width and depth of channels in noncohesive materials may change by scour and deposition as well as by flow at different depths in predetermined channels. White River channels, with steep slopes in coarse noncohesive materials, were narrower, slightly shallower, and had much higher flow velocities than the channels of Brandywine Creek in cohesive materials.
Slope of the valley train was related to particle size and discharge. Pebble counting demonstrated a systematic decrease of 60 mm in median diameter of the valley train deposits in a distance of 4,200 feet downstream from the source areas. Discharge was essentially constant through this reach, the stream received no major additions. Discharges of 200 to 500 cubic feet per second were capable of transporting almost all sizes of materials present and thus modified the form of the valley train.
Data on the velocities required to transport coarse materials in White River showed that a curve in which diameter is proportional to velocity to the 2.6 power approximates the relation better than the traditional sixth power law in which diameter is proportional to velocity to the 2.0 power. The few samples contained suspended-load concentrations up to 17,000 ppm.
The most graphic evidence of the large amount of material transported by the White River was the amount eroded and deposited on the valley train itself. Measurements indicated an average net increase in elevation of 1.2 feet during 1958 and a net decrease of 0.12 foot in 1959.
Description and analysis of the change in pattern of the White River were difficult at high flows because of the rapidity of the change. However, a marked change from a meandering pattern to a braided pattern took place with the onset of the high summer flows and the pattern returned to meanders with the low flows of fall.
Explanations offered in the literature for the cause of braided patterns include erodible banks, rapid and large variation in discharge, slope, and abundant load. The common element in all explanations seems to be a movement of bed load in such quantity or of such coarseness that there is deposition within the channel, causing the diversion of flow from one channel into other channels in a valley wide enough to provide freedom to braid. White River braiding took place most actively at large loads and discharges.
Although examples of braiding by an aggrading stream are common, the White River and the Sunwapta River, Alberta, have reaches in which degradation took place while the stream had a braided pattern. The conclusion is reached that both braided and meandering reaches can occur along the same stream, which may be aggrading, poised, or degrading. The pattern alone does not conclusively define the regimen of the stream.
The regimen of the glacier has long-term effects in providing debris to the stream; short-term effects of weather and runoff determine the current hydraulic characteristics, rate of deposition and erosion, and channel pattern.
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In Text Citation:
Fahnestock (1963) or (Fahnestock, 1963)
Fahnestock, R.K., 1963, Morphology and hydrology of a glacial stream - White River, Mount Rainier Washington: Professional Paper 422-A, United States Geological Survey, 75 p..