...From the pages of Agricultural Research magazine
Helping States Slow Sediment Movement: A High-Tech Approach to Clean Water Act Sediment Requirements
Hydrologist Mark Griffith
(left), hydraulic engineer
Carlos Alonso (center), and
technician Brian Bell analyze
photographs of the James
Creek (Mississippi) area.
When ARS's National Sediment
Laboratory scientists were asked by Mississippi officials to study James
Creek, in the northeastern part of the state, they saw more than a chance
to conduct a local field project.
They envisioned adding to a developing methodologyone aimed at
helping states comply with Clean Water Act sediment requirementsby
joining computer-modeling capabilities with river-related geologic studies.
During a 90-day analysis of the sediment-impaired creek, the scientists integrated for the first time large-scale geomorphologythe study of forms on Earth's surface and subsurface and the processes that create themwith two prominent ARS watershed and channel models to monitor sediment movement in water bodies.
The researchers work for the Oxford, Mississippi-based laboratory's Channel Watershed and Processes Research Unit (CWPRU).
An aerial view of a section of
James Creek, in Mississippi,
where channel incision has
led to rapid bank erosion
causing land loss and high
suspended sediment loads
within the water.
Hydraulic engineer Carlos Alonso, the unit's research leader, says
the union of these tools can enable state officials nationwide to meet
sediment pollution-control criteria for many watersheds by helping them
determine actual sediment loads and establish reference loadsall
the while sustaining a competitive agricultural economy.
"These detailed computer models help us determine how soil erosion
and sediment loading change over time," says Alonso. "In James
Creek, we laid a foundation and set standards for how this kind of research
might be done elsewhere."
The unit is already applying the integrated method to projects in Alabama, California, Kansas, Michigan, and elsewhere in Mississippi.
This focus on sediment pollution criteria is fueled by a renewed effort among states to comply with the Clean Water Act. The act calls for states to identify pollution-impaired water bodies and develop plans for meeting requirements for Total Maximum Daily Loads (TMDLs).
Hydrologist Mark Griffith
(top) uses a bore hole shear
device to determine the
cohesion of bank materials
while technician Brian Bell
prepares for a submerged-jet
test on fine-grained lower
bank materials. The data from
these tests will be used to
TMDLs specify the maximum amount of a pollutant a water body can receive and still meet quality standards set for its designated use by states, territories, and tribes. Compliance is monitored by each state in concurrence with the United States Environmental Protection Agency. Having a way to compare actual and reference loads assists greatly in creating sediment TMDLs for specific watersheds.
Sediment as a Pollutant
Of all pollutants requiring TMDLs, none is as prevalentor as
potentially damagingas sediment, says Alonso. "Physical,
chemical, and biological damage associated with sediment flow costs
about $16 billion annually in North America," he says. "Excessive
erosion and the transport and deposition of sediment in surface waters
are major water-quality problems."
While establishment of TMDLs was first prescribed in the Clean Water
Act of 1972, few have actually been developed, says unit geologist Andrew
Simon. But citizen concern and court challenges have propelled recent
action. The Mississippi Department of Environmental Quality responded
by requesting the James Creek study so that the state could develop
its federally mandated water-quality targets for sediment.
Alonso says one reason for delays in setting sediment TMDLs is that no proven methods existed for defining how much sediment constitutes a pollution hazard. "Procedures had to be developed for identifying streams that are especially vulnerable to erosion and sedimentation and for relating the sediment TMDLs to the designated uses of waterways in different regions," he says.
Watershed and channel
computer simulation models
help scientists identify
Here, agricultural engineer
Ron Bingner (left) and
hydraulic engineer Eddy
Langendoen study data
generated by a model.
Agricultural engineer Ronald Bingner says this task is complex, given the varied geography and management of land within watersheds. Eighty-four "ecoregions" have been identified in the continental United States based on similarities in climate, geology, topography, and ecology. "We hope our work at James Creek will make it easier to set target values in other ecoregions," he says.
In a two-pronged approach, the research team combined extensive field
measurements and their geomorphic analysis with simulations generated
by two computer models: the Annualized Agricultural Non-Point Source
Pollutant watershed model and the Conservational Channel Evolution and
Pollutant Transport System model.
The first model helps evaluate pollutant loadings within a watershed
and the effect farming and other activities have on pollution control.
It does this by continuously simulating runoff of sediment and chemical
pollutants. It was developed through a partnership between ARS and USDA's
Natural Resources Conservation Service.
The second model predicts how channel evolution and pollutant loadings will be affected by bank erosion and failures, streambed buildup and degradation, and streamside riparian vegetation. It was developed by Eddy Langendoen, a University of Mississippi scientist who collaborates with CWPRU on modeling channel processes.
Technology Complements Field Methods
Besides advancing computer-modeling capabilities, the James Creek research
also builds on significant, earlier sediment-related field methods.
For example, Simon and his colleagues used his expertise in geomorphology
to create new ways to identify reference sediment loadings for watersheds.
"It was during studies of watersheds in the Cascade Mountains
and along the Loess Bluff Line here in Mississippi that we first developed
the descriptive techniques used in James Creek," Simon says. "These
techniques, which include aerial reconnaissance, channel surveys, and
sampling and testing of stream boundary sediments, worked for those
very diverse regions, and we're expanding their use nationwide."
Simon says CWPRU is conducting reference research for 3,000 sites throughout the United States.
A Perfect Test Case
James Creek, which flows for 19.5 miles past uplands and fields and
through channels, was an ideal waterway on which to reinforce earlier
lessons. Its watershed is highly agricultural, mostly made up of cultivated
croplands, pastures, or fallow land. Like many Mississippi streams,
it is extensively channelized. Only the lower 4.1 miles retain a natural
As such, it illustrates a "Stages of Channel Evolution" theory
Simon and a colleague developed in 1986, when he worked for the U.S.
Geological Survey. The theory describes a stream's erosive evolution
in six stages, starting with a stable, undisturbed channel (stage I)
and ending with a refilled channel (stage VI). In between, the stream
is disturbed by some large-scale event, eroded, and then restabilized.
Through the two computer models described earlier and similar field
and modeling research studies, CWPRU scientists have concluded that
stages I and VI present the best conditions under which to determine
reference standards for sediment loadings. Another interesting finding
was that streambanksnot uplands and fields, as many believeare
the main contributors to sediment pollution in many disturbed stream
"Perhaps future decisions about reducing sediment loadings will
need to be based more on stream-channel processes and on stabilizing
eroding reaches and tributaries," says Alonso.
Each of the unit's scientists has been involved in this research. Bingner
and Alonso head the modeling aspects, while Simon and hydraulic engineer
Roger Kuhnle specialize in sediment yield and channel loadings. Former
ARS geologist Sean Bennett led studies on sediment loading effects on
reservoirs, lakes, and flood-control structures.
Simon says current and upcoming projects include in-depth studies of
each ecoregion. "We also want to identify at least two damaged
and two reference sites in each ecoregion for detailed analysis of sediment
transport," he says.
"Watershed-wide problems require an integrated approach to developing
sediment pollution standards that address all concerns," says Alonso.
"Combining field measurements, geomorphic analyses, and numerical
models has proven to be a powerful way for evaluating reference and
actual sediment-transport conditions. The James Creek research shows
how these techniques can be applied nationwide."By Luis
Pons, Agricultural Research Service Information Staff.
This research is part of Water Quality and Management, an ARS National
Program (#201) described on the World Wide Web at www.nps.ars.usda.gov.
Carlos V. Alonso and Andrew Simon are at the USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, 598 McElroy Dr., Oxford, MS 38655; phone (662) 232-2969 [Alonso], (662) 232-2918 [Simon], fax (662) 281-5706.
The six stages of Simon's Channel Evolution Model
are as follows:
Stage I: The waterway is a stable, undisturbed natural channel.
"Helping States Slow Sediment Movement: A High-Tech Approach to Clean Water Act Sediment Requirements" was published in the December 2003 issue of Agricultural Research magazine.