Publications—Open-File Report 00–497
By Gardner C. Bent, John R. Gray, Kirk P. Smith, and G. Douglas Glysson
U.S. Geological Survey Open-File Report 00–497
Prepared in cooperation with the Federal Highway Administration. A Contribution to the National Highway Runoff Data and Methodology Synthesis.
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This report is available in Portable Document Format (PDF):
OFR 00–497 (1,211 KB) – 62 pages
Accurate and representative sediment data
are critical for assessing the potential effects of
highway and urban runoff on receiving waters.
The U.S. Environmental Protection Agency identified
sediment as the most widespread pollutant in
the Nation's rivers and streams, affecting aquatic
habitat, drinking water treatment processes, and
recreational uses of rivers, lakes, and estuaries.
Representative sediment data are also necessary
for quantifying and interpreting concentrations,
loads, and effects of trace elements and organic
constituents associated with highway and urban
runoff. Many technical issues associated with the
collecting, processing, and analyzing of samples
must be addressed to produce valid (useful for
intended purposes), current, complete, and technically
defensible data for local, regional, and
national information needs. All aspects of sediment
data-collection programs need to be evaluated,
and adequate quality-control data must be
collected and documented so that the comparability
and representativeness of data obtained for
highway- and urban-runoff studies may be
assessed.
Collection of representative samples for the
measurement of sediment in highway and urban
runoff involves a number of interrelated issues.
Temporal and spatial variability in runoff result
from a combination of factors, including volume
and intensity of precipitation, rate of snowmelt,
and features of the drainage basin such as area,
slope, infiltration capacity, channel roughness, and
storage characteristics. In small drainage basins
such as those found in many highway and urban
settings, automatic samplers are often the most
suitable method for collecting samples of runoff
for a variety of reasons. Indirect sedimentmeasurement
methods are also useful as supplementary
and (or) surrogate means for monitoring
sediment in runoff. All of these methods have limitations
in addition to benefits, which must be
identified and quantified to produce representative
data. Methods for processing raw sediment samples
(including homogenization and subsampling)
for subsequent analysis for total suspended solids
or suspended-sediment concentration often
increase variance and may introduce bias. Processing
artifacts can be substantial if the methods used
are not appropriate for the concentrations and particle-
size distributions present in the samples
collected.
Analytical methods for determining sediment
concentrations include the suspendedsediment
concentration and the total suspended
solids methods. Although the terms suspendedsediment
concentration and total suspended solids
are often used interchangeably to describe the total
concentration of suspended solid-phase material,
the analytical methods differ and can produce substantially
different results. The total suspended
solids method, which commonly is used to produce
highway- and urban-runoff sediment data,
may not be valid for studies of runoff water quality.
Studies of fluvial and highway-runoff sediment
data indicate that analyses of samples by the total
suspended solids method tends to underrepresent
the true sediment concentration, and that relations
between total suspended solids and suspendedsediment
concentration are not transferable from site to site even when grain-size distribution information
is available. Total suspended solids data
used to calculate suspended-sediment loads in
highways and urban runoff may be fundamentally
unreliable. Consequently, use of total suspended
solids data may have adverse consequences for the
assessment, design, and maintenance of sedimentremoval
best management practices. Therefore, it
may be necessary to analyze water samples using
the suspended-sediment concentration method.
Data quality, comparability, and utility are
important considerations in collection, processing,
and analysis of sediment samples and interpretation
of sediment data for highway- and urbanrunoff
studies. Results from sediment studies must
be comparable and readily transferable to be
useful to resource managers and regulators. To
meet these objectives, supporting ancillary information
must be available to document the methods
and procedures that are used and to describe
quality-assurance and quality-control procedures
that are used in the studies. Valid, current, and
technically defensible protocols for collecting,
processing, and analyzing sediment data for the
determination of water quality in highway and
urban runoff therefore need to be documented with
study results.
Abstract
Introduction
Sediment Concepts Related to Highway Runoff
Sample-Collection Methods
Automatic Samplers
Pumping Samplers
Passive Samplers
Indirect Methods for Measuring Sediment
Bottom Material
Turbidity
Other Indirect Methods
Sample-Processing Methods
Homogenization
Subsampling Water-Sediment Mixtures
Sample-Analysis Methods
Measurement of Sediment Concentration
Particle-Size Distribution
Specific Gravity
Other Sediment Measurements
Data-Quality Considerations
Documentation of Methods
Quality Assurance/Quality Control
Summary
References
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Suggested Citation:
Bent, G.C., Gray, J.R., Smith, K.P., and Glysson, G.D., 2001, A synopsis of technical issues for monitoring sediment in highway and urban runoff: U.S. Geological Survey Open-File Report 00-497, 51 p.
For additional information write to:
Director,
USGS Massachusetts–Rhode Island Water Science Center
10 Bearfoot Road
Northborough, MA 01532or visit our Web site at:
http://ma.water.usgs.gov
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