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Channel Incision and Water-Table Decline Along a Recently Formed Proglacial Stream, Mendenhall Valley, Southeastern Alaska

Professional Paper 1760-E

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Abstract

Retreat of the Mendenhall Glacier, in southeastern Alaska, resulted in the formation of Mendenhall Lake, which has reduced the supply of coarse sediment to the proglacial Mendenhall River. Channel geometry surveys conducted in 1969 and 1998 over a 5.3 km reach of the Mendenhall River revealed reductions in mean bed elevations ranging from 0.4 to 1.5 meters based on cross sections replicated at 7 locations. Channel incision in the Mendenhall River is believed to be the result of a combination of factors resulting from localized and region-wide glacial retreat. In addition to a reduction of river stage due to channel incision, a decline in water-table elevations of about 0.6 m during a 17-year period from 1984 to 2001 was identified in an observation well located 250 m from the incising stream channel. Water-table elevations 600 m from the incising channel in the adjacent alluvial outwash aquifer respond in phase to changes in river stage, indicating water-levels in the adjacent aquifer are declining in response to river-channel incision. This study suggests channel incision can rapidly lower water-table elevations for large distances in the adjacent aquifer, potentially modifying the hydrology to a degree capable of influencing adjacent surface-water features, such as off-channel wetlands and flood-plain side channels.

Geospatial Extents

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Channel Incision and Water-Table Decline Along a Recently Formed Proglacial Stream, Mendenhall Valley, Southeastern Alaska
Series title:
Professional Paper
Series number:
1760
Chapter:
E
Edition:
-
Year Published:
2009
Language:
ENGLISH
Publisher:
U.S. Geological Survey
Contributing office(s):
Alaska Science Center
Description:
iv, 15 p.
Larger Work Type:
Report
Larger Work Subtype:
USGS Numbered Series
Larger Work Title:
Studies by the U.S. Geological Survey in Alaska, 2007
Online Only (Y/N):
Y