United States
Environmental Protection
Agency
Robert S. Kerr Environmental Research
Laboratory
Ada OK 74820
Research and Development
EPA-600/S2-83-025 June 1983
&EPA Project Summary
Nonpoint Sediment Production
in the Colusa Basin Drainage
Area, California
K. Tanji, M. Singer, J. Biggar, L Whittig, and D. Henderson
An investigation was conducted to
identify the nonpoint sources of
suspended matter in the California
Colusa Basin Drainage Area, to
interpret the factors contributing to or
affecting suspended solids loading, and
to develop recommendations for best
management practices. The 1977-
1979 project period (Phase I) focused
on an overview appraisal of sediment
production and transport. The 1979-81
project period (Phase II) involved
intensive quantitative investigations
into the causes of the turbidity problem
and the development of recommenda-
tions for sediment control.
The study area included the 70-mile-
long Colusa Basin Drain (CBD), the
164,000 ac Glenn-Colusa Irrigation
District (GCID), and selected
tributaries. This report contains data on
water flow and suspended and bedload
materials and their biological, chemical,
physical, and mineralogical properties,
rainfall simulation studies to extend the
usefulness of the Wischmeier Universal
Soil Loss Equation (USLE), a pesticide
survey for selected chemicals, and the
development and validation of a
computer simulation model for
sediment transport. This investigation
resulted in conclusions and the
development of guidelines for best
management practices and recommen-
dations for sediment control. These
findings, reported in Water Science and
Engineering Paper No. 4023, were
reviewed by project collaborators and
interested parties for feasibility and
implementation.
This Project Summary was developed
by EPA's Robert S. Kerr Environmental
Research Laboratory, Ada, OK, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Soil erosion and sediment production
can affect the productivity of lands
devoted to food and fiber production and
the quality of the receiving waters. Within
the context of these perspectives, this
project emphasizes drainage watersheds.
The objectives of this project are:
(1) to appraise soil erosion and
sediment production in the study
area;
(2) to conduct field investigations on
production and transport of sus-
pended matter;
(3) to ascertain factors contributing to
or influencing erosion and
sediment production and the
transport, deposition, and resus-
pension of sediment;
(4) to develop a sediment transport
model;
(5) to develop recommendations for
best management practices for
nonpoint source control on the
production of suspended matter in
the study area; and
(6) to consult and inform interested
parties and agencies on research
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findings and to review the
feasibility and implementation of
proposed management.
This project was coordinated with the
Soil Conservation Service (SCS) pilot
study in the Buckeye Creek-Dunnigan
Creek drainage area in northeastern Yolo
County, California. This project
contributed to the current Section 208 of
PL 92-500 planning efforts for developing
water quality management for non-
designated areas as well as meeting the
mandates of the State of California Porter-
Cologne Water Quality Act.
Conclusions
The conclusions generated from this
project are presented under five
headings: (1) sediment sources and yield,
(2) sediment component and sizes, (3)
factors (physical, chemical, mmeralogical,
and biological) controlling sediment
transport, (4) sediment as a pesticide
carrier, and (5) sediment transport
modeling.
Sediment Sources and Yield
The four potential sources of sediment-
yielding processes are sheet and rill,
channel, gully, and roadway erosion. In
the study area, sheet and rill erosion from
upland and dry-farmed areas are the
main sources of erosion; they are caused
by raindrop impact and the water flowing
on the soil surface. The Wischmeier and
Smith Universal Soil Loss equation
{LISLE) which underestimates the soil
loss by about 20%, was used to estimate
potential soil losses. In the western
portion of the basin, slope steepness was
a critical parameter for estimating poten-
tial soil losses. Rainfall-simulation
studies indicated that as slopes increased
beyond 40 percent, the effect of slope on
erosion decreased. The concentration of
suspended sediment in CBD indicated
that sediment was deposited at interme-
diate locations, wherever the entraining
runoff waters were inadequate for
sustaining transport. The deposited
sediment was transported to CBD by
stream-bed erosion during winter runoff.
Channel erosion is caused by sediment-
removal by shearing forces of water. This
sediment production comes from channel
banks and beds, and from channel over-
flow areas having no protective cover.
Gully erosion, viewed as a point source
of erosion, results from water accumula-
ting in narrow channels.
Erosion from roadways,especially
unpaved roads and shoulders of paved
roads, is also viewed as a point source
which causes sheet, rill, or gully erosion.
Sediment Component and Sizes
Analyses of water samples from CBD
and its tributaries indicate that the sus-
pended sediment composition, on the
average, was 60 percent minerals, 30
percent organics, and 10 percent
algae. Suspended organic matter
averaged 60 percent biodegradable
organic matter and 40 percent refractory
organic matter. Suspended mineral
sediments were mainly silt and clay, with
a small fraction of sand. The particle-size
analysis of the bedload sediment in CBD
was about 60 percent sand-size material,
10 to 30 percent organic matter, and
lesser amounts of silt, clay, and gravel.
Factors Controlling Sediment
Transport
The physical factors controlling
sediment production, transport, and
deposition are: flow pattern, flow rate,
bed configuration and roughness, current
velocities, fluid shear stress, critical
shear stress of the bed material, and
water depth.
The chemical factors affecting disper-
sion,flocculation, and sedimentation of
cohesive suspended particles in the drain
are the concentration of soluble ions:
total dissoved solids (TDS) or electrical
conductivity (EC), sodium adsorption ratio
(SAR), and pH of the water
The aquatic organisms contributed up
to 20 percent of the total suspended
sediments.
Clay-size (<2 fjm) particles constituted
over 50 percent of the suspended mineral
load in CBD. Chlorite and kaolin were the
dominant phyllosilicate species in coarse
clay (2 - 0.2 /urn) fractions. Smectite was
dominant in fine clay (<0.2/um)fractions
in suspended mineral matter. Adsorption
specificity exhibited by clays favored Ca
over Mg, and favored Ca and Mg over Na.
Sediment as a Pesticide Carrier
Emission of chemicals into the water
courses appeared to be site- and time-
specific. The degree of saturation of the
sediment with chemical was a function of
the concentration of chemical and
sediment in the aqueous phase. Spatial
and time surveys indicate complex
interaction of variations in timing of
application, sources of chemical and
water outflow, variations in drain flow
and probable biological and sedimenta-
tion processes that occur in the system.
Sediment Transport Modeling
A one-dimensional computer model
was developed and applied to a 20-mile-
long lower reach of CBD. Sensitivity
analysis indicated that the model was
sensitive to flow rate, current velocities,
settling velocities of particles, and the bed
shear stress.
Best Management Practices
(BMPs)
Practices designed to reduce erosion
and sediment delivery should not be an
impediment to continued agricultural
productivity, and they must be
economical. BMPs may stop or reduce
on-site soil erosion or prevent sediment
from reaching a body of water.
Livestock management can be the most
effective and least costly method of
erosion control. Practices to control soil
erosion and range productivity are
grouped into three broad management
types: vegetation management,
facilitating prastices, and accelerating
practices. A management program which
includes plant-growth acceleration and
appropriate animal management can
yield multiple positive benefits.
Conservation management practices
which increase animal yield are more
effective than sediment-retention
structures. The most productive BMP is
one designed specifically for a particular
area.
Soil loss on sloping cultivated areas
can be reduced by implementing contour
cropping, zero or minimum tillage
agriculture, conservation cropping
systems involving rotations of grasses
and legumes, or by allowing plants to
grow during critical erosion periods
Contour plowing of sloping land where
tillage is required helps prevent runoff
during storms, resulting in an increased
infiltration and reduced sediment.
Increased infiltration rates can be
maintained by reducing compaction
caused by excessive vehicular traffic and
equipment operation; by applying
chemicals, or incorporating organic
matter into the soil. The BMP for
controlling sediment production from
irrigated land consists of minimizing
surface runoff.
Unpaved roads are a major source of
sediment in the CBD. Road-management
practices can reduce sediment; e.g.,
closure of such roads in wet weather,
permanent closure of some nonessential
roads, and installation of water ba
culverts, and water spreaders. Chan
erosion can be controlled with vegetative
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stream bufferstrips alone, or in combina-
tion with grade stabilization and inlet
structures.
be applied to minimize contamination of
nontarget areas.
Recommendations
The first step for implementing BMPs is
education of landowners, farmers, and
ranchers to the long- and short-term
benefits possible with effective land
management. Once the land-use benefits
are understood, actual implementation of
practices should be facilitated.
Improved range management should
include vegetation management by
proper grazing pressure and planned
grazing levels, development of water
trails for livestock, and implementation of
practices to accelerate plant growth.
Conservation management practices
should be specific to the soil-slope-
vegetation-land-use problem.
Where erosion problems exist,
unpaved roads should be closed during
wet weather, permanently closed, or
rocked with water control structures.
Contour cropping, cultivation, and "no-
till" or "minimum-till" practices should
be implemented to reduce runoff in
cultivated areas. Equipment operation
and other vehicular traffic should be
regulated or reduced to lessen
compaction and to improve infiltration.
Chemicals or organic matter should be
used to improve water entry into the soil.
Catchment basins should be designed to
collect sediment discharge from culti-
vated fields.
Conservation cropping systems,
contour plowing on sloping lands, and
practices to reduce discharge of water
and sediment, e.g., reuse of tailwater
discharge from irrigated areas should be
practiced where appropriate to reduce
erosion and sediment yield. Careful plan-
ning and implementation of conservation
practices to reduce erosion should
precede development of range land or
dry-farmed land into cultivated and
irrigated land.
Control measures for channel erosion
should be implemented by reshaping the
channel, planting suitable ground covers,
erecting rock structures or riprap at
places where creeks bend, installing
large boulders with wire fences and
revetments to reduce land erosion,
and/or installation of sedimentation
basins.
To lessen the outflow of chemicals
from agricultural fields, the outflow of
water should be minimized during, and
''immediately after chemical application.
Optimum amounts of chemicals should
K. K. Tanji, the principal investigator, and the co-authors are with the Department
of Land, Air and Water Resources at the University of California, Davis, CA
95616.
Arthur G. Hornsby and James P. Law, Jr., are the EPA Project Officers (see
below).
The complete report, entitled "Nonpoint Sediment Production in the Colusa Basin
Drainage Area, California," (Order No. PB83-193 920; Cost: $14.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada, OK 74820
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