9 July, 1999
Today we met the "stream team". They consist of Christy Swindling, undergraduate student from University of California at Santa Cruz (UCSC), Erin Kraal, graduate student at UCSC, and Robert Anderson, professor of Earth Science at UCSC. Their task will be to monitor the discharge of the glacial stream (the Kennicott River) as it emerges from the base of the glacier at McCarthy. This will become parcticularly exciting for them when Hidden Creek Lake (located 12 miles up valley from the snout) breaks out and drains from beneath the glacier. When the lake drains, the discharge of the stream increases from a trickle to a raging torrent in a matter of minutes. They will be collecting discharge data by using a stream gauge which will be lowered from a bridge which spans the Kennicott River. Collecting this measurement will further enhance an understanding of the hydraulic connection between the subglacial and terminal stream channel(s?), and will help in understanding the geomorphic changes to the stream channel during the flood.
This morning we (the UCSC stream team, PSU Principal Investigator Andrew Fountain, PSU grad student Don Lindsay, and myself) picked up the stream gauge from the United States Geological Survey (USGS) field office in Anchorage. They will be loaning it to the project for the summer. We were also given a lesson on its use. The first step when using a stream gauge is to lower a water flow current meter to a position which is 60 percent of total stream depth from the surface of the stream. For example, a stream with a depth of 10 meters would need to have a current meter positioned at a depth of 6 meters. This depth provides the most characteristic "average" for the velocity at that cross sectional position of the stream. A current meter consists of a propeller-like device which spins in the stream at a rate which is dependant upon the velocity of the flow. The current meter is attached to a heavy, torpedo-shaped object with tail fins which stabilizes the position and orientation of the current meter. As the propeller spins in the water, it sends back an impulse every 5 revolutions via an electrical cable. These impulses are counted for a given period of time, from which the velocity of the stream at that point can be determined. In knowing the depth of the stream, and in taking a series of these measurements across the width of the stream, the discharge can be calculated. Of course, when the lake breaks out and the stream reaches flood stage, it is expected that ice chunks will be bobbing their way down the stream, and boulders will be moving along the bottom. Hopefully the stream gauge will survive the potential bombardment of unseen debris.
One of the chief interests of the stream team is to characterize how the stream channel will change during the flood. This is both scientifically interesting and will also provide for future hazard assessment of the stream. Any prediction of how the stream erodes during the glacial outburst flood will help minimize potential loss of life and property in the future.
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