Subject: Watershed Management #2
From: [email-masked] (Paul Cass)
Date: Sat, 26 Feb 1994 05:16:12 GMT
Newsgroups: sci.bio.ecology

The following article is part of a watershed seminar held at Oregon
State University in Spring, 1992.  The summary was written by Penny
Cass and approved by the speaker.  This article is part of a publication
that can be ordered from the Oregon Water Resources Research
Institute, OSU, Strand Ag Hall 210, Corvallis, OR 97331-2208 (503) 737-
4023.  The article may be reprinted without permission for educational
purposes.  If used, Please send 2 copies of your publication to OWRRI.

WATERSHED MANAGEMENT ON GRAZING LANDS
Hugh Barrett, Bureau of Land Management, Portland, OR

     "Wherever you are, you are in a watershed," explained Hugh
Barrett, emphasizing that rangelands should not be defined by the
presence of livestock.  "Grazing must also address watershed functions," 
     A rangeland watershed contains uplands, an aquatic zone, and a
transition area between these two ~ the riparian zone.  The rangeland
riparian zone is a broad flat, the potential floodplain, created as the
river meandered over the area.  These riparian zones can support a
complex vegetative community, yet much of this wetlands-type
community has lost its natural protection through beaver-trapping and
severe grazing.
     The fundamental functions of a watershed are: capture or
infiltration of moisture, storage of moisture, and the safe release of
moisture, through surface and subsurface flows.

CAPTURE OF MOISTURE
     The infiltration of moisture begins at the soil surface.  A major
problem in the West is the loss of vegetation and organic litter that
protects the soil surface.  Without the plants, which protect the soil, the
surface becomes a "puddled crust" that prevents water infiltration.  What
moisture is captured, evaporates more easily through the action of sun
and wind.
     Without infiltration, and with any slope, rain water will travel
overland, eroding topsoil and exposing subsurface soils that have very
low infiltration rates.  When overland flows concentrate, deep gullies are
formed, which then dry out even lower areas of the subsurface soils.

STORAGE OF MOISTURE
     Storage of moisture is important for plant growth and for
recharging groundwater as well as streams.  Yet, water that has
penetrated the surface is still vulnerable.  Some plants extract water
from the soil at excessive rates.  For instance, a western juniper with a
12' diameter crown can transpire 15 to 30 gallons of water per day from
the soil.  Such plants are one reason streams and springs no longer flow
and seeps have dried up.
     Junipers have long, shallow roots that compete with surrounding
vegetation for stored moisture.  Native evergreens, junipers used to be
controlled by fires that occurred about every forty years.  The grasses
between junipers used to carry fire from one tree to the next.  But with
fire suppression and severe grazing on the grasses, juniper has come to
dominate many of the West's rangeland watersheds.

SAFE RELEASE OF MOISTURE
     As watersheds lose their functions of moisture capture and
storage, overland flows break river channel banks causing further
erosion.  Destroyed by severe grazing, grasses along the rivers can no
longer trap sediments to protect the banks.
     When sediment isn't trapped and held by grasses, streams can
become entrenched.  Entrenched streams have narrow, deep defiles well
below the floodplain terrace.  The stream surface sets the top of the
water table.  When the stream is level with the floodplain, the entire
terrace is capable of storing moisture.  With stream entrenchment, water
that used to be stored for years is moved out of the system in weeks.
     Figure 1 shows the difference in water storage between an
entrenched and an intact rangeland watershed.  The entrenched system
is capable of storing approximately 135 acre feet, whereas the intact
system can potentially store 400 acre feet.

RANGELAND WATERSHED RESTORATION
     Entrenched riparian areas can be restored.  The sequence of
plant communities found in intact riparian zones frequently still exist in
entrenched areas.  Plant communities follow the water down an
entrenchment as they would down the drain of a basin.  So plants that
used to spread throughout a 1/4 mile zone may still exist in one foot
bands down the side of the entrenched bank.  As streams are
encouraged back to the level of the floodplain, plants usually refill the
valley.  With the return of grasses to trap sediments, one area protected
from grazing for 10 years, built up its stream bottom six feet.
     An important rangeland management task is changing the season
of use by livestock.  More effective than limiting the numbers of
animals, is limiting the seasons when grazing can occur.  Preventing
grazing before the seasons of high flow ~ early Spring and the mid-
summer season of thunderstorms ~ allows grasses to remain established
when they are most needed for trapping sediments.
     Grazing management that is sensitive to the water cycle of a
particular basin provides the foundation for restoring watershed
functions of capture, storage, and safe release.  Ranchers that have tried
moving cattle away from streams prior to high flows have found that
good watershed management practices can have economic benefits.  The
return of high quality grasses enhances both riparian systems and cattle
weight.
     Education about changing the seasonal use of cattle, the lopping
and spreading of juniper branches, and the additional erosion protection
required by south slopes where the sun strikes more harshly may provide
more benefits for rangeland watersheds than additional regulations.

REFERENCES:

Bedell, et al. 1991.  Watershed Management Guide for the Interior
Northwest. EM8436.  Oregon State University.

Elmore, D.W. 1987.  Personal communication.

Eddleman, L. 1992.  Personal communication.