Please Help! Evapotranspiration Question!

DASDLM dasdlm at
Wed Jul 5 14:43:46 EST 1995

I am conducting a literature search of the relationship between
evapotranspiration, fluctuating groundwater levels, and most importantly,
the impact of these fluctuations on slope stability.  The area of concern
is the Pacific Northwest, but information and references from any area are
welcome, including work done in an agricultural context.  I am primarily
concerned with deep-seated slope stability problems, i.e., earthflows.  I
am less concerned with shallow failures such as debris slides and debris
flows, but I am nonetheless interested in obtaining information about
these types of landslides, particularly where reference is made to root
strength.  The key issue is timber harvest and how it alters the local
groundwater regime and, thus, slope stability.  There are many unstable
areas and large earthflow complexes in the Cascade Mountains.  Many of
these areas have timber that private and federal agencies have harvested
or will soon harvest.  The concern is that removing this timber will
reduce evapotranspiration and cause higher seasonal groundwater levels,
which in turn will raise pore water pressures and result in unstable
conditions and, possibly, accelerated earthflow movement.  Since
earthflows are predominantly fine-grained and typically adjoin rivers,
resource specialists are concerned that increases in sediment delivery to
fish-bearing streams caused by accelerated or reactivated earthflows will
further degrade salmon spawning habitat.  Currently, most national forests
have guidelines for cutting timber in these circumstances.  However, some
of these guidelines will soon be revised, based in part on the information
found in this literature search.  If you have any references or
information on this broad topic, particularly those articles published
since 1990, please send them to me at "dasdlm at"  Thanks in advance.
 P.S.  Please pass this along to anyone who might be interested or have
some input.  Thanks.

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