Geology Reference
In-Depth Information
In this paper the focus will be on the application
of WEPP to management of a small agricultural
watershed, being a portion of a much larger water-
shed of great value because of the uses of the
streams and reservoirs for power generation, cool-
ing for power plants, water supply for municipali-
ties, and as a major recreation area in the state of
Missouri. The application to the small watershed
is one in which the Universal Soil Loss Equation
(USDA, 1961) or its derivatives (Williams, 1975)
or revisions (Wischmeier & Smith, 1978; Renard
et al
., 1997) might be applied to fields within the
small watershed.
Soil erosion modelling needs related to agri-
culture have dramatically increased in the half-
century since the release of the USLE in 1961.
Soil erosion modelling is used in evaluating fer-
tilizer application and manure management to
achieve environmental goals (Iowa NRCS, 2004).
Soil erosion models are a part of every large-scale
model dealing with land use and management
effects on sediment delivery to downstream loca-
tions. In the preface to the
User Requirements
for
WEPP (Foster & Lane, 1987), the need for enhanced
capabilities in erosion modelling was given as the
justification for its development.
OFE 1
OFE 1
1 OFE Hillslope
1 OFE Hillslope
OFE 1
OFE 2
OFE 3
OFE 2
OFE 1
2 OFE Hillslope
Flow direction
3 OFE Hillslope
Channel
Fig. 9.1
The WEPP Hillslope version models one
hillslope only, but a hillslope can have one or more
overland flow elements (OFEs) which are homogeneous
areas. Water flows downhill in a rill, passing from one
OFE to the next lower OFE, with the lowest OFE on
a hillslope discharging into a channel. The WEPP
Hillslope version models the processes on a hillslope.
The WEPP Watershed version models the processes that
occur in the channels and impoundments which receive
flow from hillslopes, other channels and impoundments.
components for the US nuclear weapons arsenal
using various radioactive and hazardous materials,
including plutonium and uranium and toxic metals
such as beryllium and other hazardous chemicals
(http://arq.lanl.gov/source/orgs/nmt/nmtdo/
AQarchive/06springsummer/index.shtml).
WEPP was used in closure of a problem landfill
near Las Vegas, Nevada (Smith
et al
., 2002), and
has been used in estimating the movement of
radioactive materials in an urban area (unpub-
lished work by Laflen). It is used to estimate daily
erosion for the state of Iowa (Cruse
et al
., 2006),
with results published each day on the Internet
(http://wepp.mesonet.agron.iastate.edu/).
The US has a total land area of nearly 9.4 bil-
lion km
2
. Major land uses are about 264 million
ha of forest, 238 million ha of grassland pasture
and range land, 199 million ha of cropland, 120
million ha of special use (mostly parks and wild-
life areas), 92.3 million ha of miscellaneous use,
and about 24.3 million ha of urban lands. WEPP
has been applied to all of these uses, perhaps
most extensively on forest and range lands.
9.1
Description of Problem Area
The example agricultural problem is the applica-
tion of WEPP to a small piece of land in southwest
Missouri, US (Fig. 9.2). The land is typical of much
of the area in western Missouri and eastern
Kansas. The area chosen is located about 5 km
south of the Marmaton river, a tributary to the
Little Osage river, which flows into the Osage
river, and, after receiving flow from several tribu-
taries, and passing through the Lake of the Ozarks
reservoir in Central Missouri, flows into the
Missouri river. The Osage river, its tributaries and
their reservoirs are major recreational areas. They
include several reservoirs that are important rec-
reational waters and that provide water to a
number of municipalities, generate power, supply
water for cooling power plants, and provide for
flood control. The last reservoir (and the first to be
