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Cory Miller
Student Watershed Research Award Recipient
Graduate Student
School of Forestry and Ecological Restoration Institute
cory.miller@nau.edu
c.miller@landterms.com
Advisor: Dr. Wallace Covington
Analysis of Current and Historical Surface Flows and
Hydrologic Response to Restoration Treatments in the Upper Lake Mary
Watershed, Arizona
Upper Lake Mary is the
sole surface water reservoir for Flagstaff, Arizona, and has
historically provided 40% of the city’s drinking water. The forested
watershed has grown dense with trees since large-scale logging,
livestock grazing, and fire suppression activities began approximately
135 years ago. Surface flows into the reservoir have declined over
time, even in years with similar precipitation. These factors suggest
that a likely cause is the increased transpiration and interception of
precipitation that accompanies increased overstory vegetation. In its
current condition, the watershed is at risk for severe wildfire that
could impede its ability to meet water quality standards for domestic
purposes. This study was undertaken to assess forest management
solutions to these problems. We calculated current and historic surface
flows based on forest inventory results. Four management alternatives
were analyzed: no action, thinning to 75% of current basal area,
thinning to 50% of current basal area, and restoration treatments based
on historic reference conditions. We modeled water yields,
sedimentation, and erosion resulting from these treatments. We also
determined the possible effects of severe wildfire on sedimentation,
erosion, and water quality. Water yield increases ranged from 3%-6.6%
for thinning to 75% of current basal area, 10.5%-19% for 50% reduction,
and 17%-28.9% for ecological restoration treatments. Restoration
treatment values are also the approximate amounts by which streamflows
have declined since about 1870. Erosion soil loss tolerances were
exceeded in the wildfire scenario, and for ecological restoration
treatments in some areas greater than 15% slope, but only in the first
few years following disturbance. Of the three thinning alternatives
modeled, only restoration treatments were self-sustaining in terms of
maintenance and renewal of streamflow response, because of
re-introduction of a frequent, low-intensity fire regime.
Cory Miller's Master's Project Professional Paper (6.5MB PDF)
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