ASTM D7512-09
(Guide)Standard Guide for Monitoring of Suspended-Sediment Concentration in Open Channel Flow Using Optical Instrumentation
Standard Guide for Monitoring of Suspended-Sediment Concentration in Open Channel Flow Using Optical Instrumentation
SIGNIFICANCE AND USE
This guide is general and intended as a planning guide. To satisfactorily monitor a specific site, an investigator must sometimes design specific installation structures or modify those given in this guide to meet the requirements of the site in question. Because of the dynamic nature of the sediment transport process, the extent to which characteristics such as mass concentration and particle-size distribution are accurately represented in the monitoring program depends on the type of equipment used and method of collection of the SSC samples used to calibrate the optical readings. Sediment concentration is highly variable in both time and space. Numerous samples must be collected and analyzed with proper equipment and standardized methods for the rating of the optical equipment at a particular site (see Guide D4411 and Practice D3977).
All optical equipment have an upper limit for valid readings, beyond which the meter will not read properly, commonly referred to as “blacking out.” If upper range of SSC are expected to cause optical instrument black out, then some other means should be devised, such as automatic pumping samplers, to collect samples during this period. See Edwards and Glysson (1) and Glysson (2) for information on collection of suspended sediment samples using pumping samplers. It should be noted that other technologies, such as lasers and acoustic dopplers, are also being used to monitor SSC continuously.
The user of this guide should realize that because different technologies and different models of the same technology of turbidity meters can produce significantly different outputs for the same environmental sample, only one manufacturer and model of the turbidity meter can be used to develop the relationship between the SSC and turbidity readings at a site. If a different manufacturer or a different model type of turbidity meter is used, a new relationship will need to be develop for the site.
SCOPE
1.1 This guide covers the equipment and basic procedures for installation, operation, and calibration of optical equipment as a surrogate for the continuous determination of suspended-sediment concentration (SSC) in open channel flow.
1.2 This guide emphasizes general principles for the application of optical measurements to be used to estimate suspended-sediment concentration (SSC) in water. Only in a few instances are step-by-step instructions given. Continuous monitoring is a field-based operation, methods and equipment are usually modified to suit local conditions. The modification process depends upon the operator skill and judgment.
1.3 This guide covers the use of the output from an optical instrument, such as turbidity and suspended-solids meters, to record data that can be correlated with suspended-sediment concentration. It does not cover the process of collecting data for continuous turbidity record, which would require additional calibration of the turbidity readings to the mean turbidity of the measurement cross section. For the purposes of this method it is assumed that the dependent variable will be mean cross-sectional suspended-sediment concentration data.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
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Designation: D7512 − 09
StandardGuide for
Monitoring of Suspended-Sediment Concentration in Open
Channel Flow Using Optical Instrumentation
This standard is issued under the fixed designation D7512; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D4410 Terminology for Fluvial Sediment
D4411 Guide for Sampling Fluvial Sediment in Motion
1.1 This guide covers the equipment and basic procedures
D6764 Guide for Collection of Water Temperature,
for installation, operation, and calibration of optical equipment
Dissolved-Oxygen Concentrations, Specific Electrical
as a surrogate for the continuous determination of suspended-
Conductance, and pH Data from Open Channels
sediment concentration (SSC) in open channel flow.
D7315 Test Method for Determination of Turbidity Above 1
1.2 This guide emphasizes general principles for the appli-
Turbidity Unit (TU) in Static Mode
cation of optical measurements to be used to estimate
suspended-sediment concentration (SSC) in water. Only in a
3. Terminology
few instances are step-by-step instructions given. Continuous
3.1 Definitions:
monitoring is a field-based operation, methods and equipment
3.1.1 calibration drift, n—the error that is the result of drift
are usually modified to suit local conditions. The modification
in the sensor reading from the last time the sensor was
process depends upon the operator skill and judgment.
calibrated, and is determined by the difference between
1.3 This guide covers the use of the output from an optical
cleaned-sensor readings in calibration standards and the true,
instrument, such as turbidity and suspended-solids meters, to
temperature-compensated value of the calibration standards.
record data that can be correlated with suspended-sediment
3.1.2 fouling, n—the error that can result from a variety of
concentration. It does not cover the process of collecting data
sources (such as biological growth on the sonde and covering
for continuous turbidity record, which would require additional
of the probe with sediment), and is determined by the differ-
calibration of the turbidity readings to the mean turbidity of the
ence between sensor measurements in the environment before
measurement cross section. For the purposes of this method it
and after the sensors are cleaned.
is assumed that the dependent variable will be mean cross-
3.1.3 continuous, adj—refers to a time series of unit values
sectional suspended-sediment concentration data.
that are close enough in time to simulate a continuous record.
1.4 This standard does not purport to address all of the
3.1.3.1 Discussion—Generally, in studies of open-channel
safety concerns, if any, associated with its use. It is the
flow, 15-minute intervals are used and are adequate to esti-
responsibility of the user of this standard to establish appro-
mated continuous record. However, the time interval maybe as
priate safety and health practices and to determine the
little as a minute or as great as an hour.
applicability of regulatory limitations prior to use.
3.1.4 sonde, n—part of the monitoring equipment that con-
tains the measurement sensors.
2. Referenced Documents
3.1.4.1 Discussion—A sonde may be either a single param-
2.1 ASTM Standards:
eter sensor or a combination of different sensors of different
D1129 Terminology Relating to Water
parameters.
D3977 Test Methods for Determining Sediment Concentra-
tion in Water Samples
4. Summary of Guide
4.1 This guide covers the equipment and basic procedures
for installation, operation, and calibration of optical equipment
This practice is under the jurisdiction of ASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,
as a surrogate for the continuous or near continuous determi-
and Open-Channel Flow.
nation of SSC in open channel flow.
Current edition approved Oct. 1, 2009. Published October 2009. DOI: 10.1520/
D7512-09.
4.2 This guide emphasizes general principles for one par-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ticular application of optical measurements in water. This
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
guide covers the use of nephelometers and backscatter type
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. turbidity meters to record data that can be correlated with SSC.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7512 − 09
5. Significance and Use ensure selection of the proper instrumentation. Things to
consider, but are not limited to, are: the instruments ability to
5.1 This guide is general and intended as a planning guide.
survive the study site environment, the degree of fouling that
To satisfactorily monitor a specific site, an investigator must
may take place, and the range of readings likely to be
sometimes design specific installation structures or modify
encountered at the site.
those given in this guide to meet the requirements of the site in
question. Because of the dynamic nature of the sediment 6.4 If a flow-through or in-situ monitoring device is used, a
transport process, the extent to which characteristics such as recording system must be installed. The recording system must
mass concentration and particle-size distribution are accurately have enough storage capacity to store all data recorded
represented in the monitoring program depends on the type of between site service visits. See manufacturer’s advice on
equipment used and method of collection of the SSC samples which recording devices will work best for the type of monitor
used to calibrate the optical readings. Sediment concentration being used.
is highly variable in both time and space. Numerous samples
6.5 Remote access and near real-time transmission of data
must be collected and analyzed with proper equipment and
from the site to the office can be very important in meeting the
standardized methods for the rating of the optical equipment at
objectives of the monitoring station. Remote access and the
a particular site (see Guide D4411 and Practice D3977).
near real-time transmittal of the recorded data take other
5.2 All optical equipment have an upper limit for valid
equipment (such as a data collection platform (DCP), and
readings, beyond which the meter will not read properly, transmittal antenna) in addition to the optical sensor. A DCP
commonly referred to as “blacking out.” If upper range of SSC
performs the same fundamental function as a basic data
are expected to cause optical instrument black out, then some recorder (BDR). They both collect data from attached sensors
other means should be devised, such as automatic pumping
on a timed interval and store the results. The difference is the
samplers, to collect samples during this period. See Edwards BDR retains the data until it is retrieved manually, while the
and Glysson (1) and Glysson (2) for information on collection DCP has the ability to transmit the collected data to another
of suspended sediment samples using pumping samplers. It location. Since data is transferred elsewhere for storage shortly
should be noted that other technologies, such as lasers and after collection, a DCP may have less memory than a BDR.
acoustic dopplers, are also being used to monitor SSC continu- The data may be transmitted via telephone modem, line-of-site
ously. radio link or satellite. It is beyond the scope of this guide to
discuss how to instrument a site for remote data transmission
5.3 The user of this guide should realize that because
and no single reference on how to do this is available for
different technologies and different models of the same tech-
reference here. The user is encouraged to visit the U.S.
nology of turbidity meters can produce significantly different
Geological Survey’s Hydrologic Instrumentation Facility web
outputs for the same environmental sample, only one manu-
site for information on equipment needs and used by the USGS
facturer and model of the turbidity meter can be used to
(http://wwwhif.er.usgs.gov/public/contacts.htm).
develop the relationship between the SSC and turbidity read-
ings at a site. If a different manufacturer or a different model 6.6 The installation of an automatic pumping sampler,
type of turbidity meter is used, a new relationship will need to especially in remote areas, will allow samples to be collected
be develop for the site.
that can be used to relate the optical reading to the suspended-
sediment concentration in the stream and also address the
6. Apparatus
blackout periods discussed in Section 5.2. Detailed information
6.1 In general, three types of configurations of installations concerning the installation and operation of pumping samplers
of monitors can be used: (1) the flow-through monitoring is beyond the scope of this guide. See Edwards and Glysson (1)
system, (2) the in-situ monitoring system, and (3) the self and Glysson (2) for more information on the use of automatic
contained, combined sensor and recording system. pumping samplers.
6.2 Optical instruments such as photoelectric nephelometer
7. Site Selection
(best used for lower levels of SSC) and backscatter sensors
(best used for higher levels of SSC) provide the basis for this
7.1 The procedure for establishing a sampling location
method. For more information concerning the advantages and
should emphasize the quest for a stream-data site. A stream-
disadvantages of each, see Test Method D7315. As they
data site is as a cross section displaying relatively stable
become available, other sensors may be used.
hydrologic characteristics and uniform depths over a wide
6.2.1 The Alliance for Coastal Techniologies (ACT) did an
range of stream discharges, from which representative sedi-
in-situ evaluation of different nephelometer technologist. Users
ment data can be obtained and related to a stage-discharge
of this Guide may be interested in the results of this study
rating and optical readings from the site. This is an idealized
which can be form on the web at http://www.act-us.info/
concept because the perfect site is rare at best. Therefore, it is
evaluation_reports.php. necessary to note the limitations of the most suitable site
available and build a program to minimize the disadvantages
6.3 Before selecting the type of meter to be used, the
and maximize the advantages.
operator needs to review the site requirements in order to
7.2 Sites that may be affected by backwater conditions
should be avoided whenever possible. Backwater condition is
The boldface numbers in parentheses refer to a list of references at the end of
this standard. a transient condition that occurs when water is backed up or
D7512 − 09
retarded in a stream by tides or from inflow from another given situation; if a reasonably stable relation between the
stream. Backwater affects both stage-discharge and velocity- sample-point reading and mean cross-section concentration
discharge relationships. Therefore, a given discharge may have cannot be attained by the following outlined steps, the meter
varying stage and mean stream velocity and thus have varying should not be installed and an alternate location considered.
sediment transport rates.
8.1.2 Consider only the part of the vertical that could be
sampled using a standard US depth- or point-integrating
7.3 A sediment-measuring site located downstream from the
suspended-sediment sampler, excluding the unsampled zone,
confluence of two streams may require extra sediment mea-
because data collected with a depth- or point-integrating
surements due to incomplete mixing of the flows from the
sampler will be used to calibrate the optical meter. See Guide
tributaries. Moving the sampling location far enough down-
D4411 and Edwards and Glysson (1) for information on the
stream to ensure adequate mixing of the tributary flows should
unsampled zone, proper procedures, and equipment to collect
be investigated.
samples for SSC analysis.
7.4 Because sediment samples must be obtained more
8.1.3 Determine, if possible, the depth of the point of mean
frequently during high flows, and it is imperative that a site be
sediment concentration in each vertical for each size class of
selected where obtaining data during these times are feasible.
particles finer than 0.250 mm, from a series of carefully
Particular attention should be given to the ease of access to the
collected point integrated samples. See Edwards and Glysson
water-stage recorder and to a usable bridge or cable during
(1) for information on the collection of point samples and Guy
high flows, many of which occur at night. Sites accessible only
(5) for procedures for determining particle size of sediment
by poorly maintained backroads or trails should be avoided.
samples.
7.5 The average monitoring site will consist of a shelter to
8.1.4 Determine, if possible, the mean depth of occurrence
house and protect the equipment and some means for either
of the mean sediment concentration in each vertical for all
bringing water to the meters or conduits that will allow the
particles finer than 0.250 mm.
meter to be placed in the flow zone of the channel. The shelter
8.1.5 Use the mean depth of occurrence of the mean
should be located to minimize the distance between the stream
sediment concentration in the cross section as a reference depth
and the meters, and at a high enough elevation to protect the
for placement of the sampling point.
equipment during flooding events. Some instruments may need
8.1.6 Adjust the depth location of the sampling point to
AC power and therefore the proximity to power lines is
avoid interference by dune migration (which may bury the
important.
probe) or contamination by bed material.
7.6 For additional information and discussion on the selec-
8.1.7 Adjust the depth location of the sampling point to
tion of a site for the collection of surface water and sediment
ensure submergence at all times.
data see Edwards and Glysson (1), Wagner and others (3), and
8.1.8 Locate the sampling point laterally in the flow at a
Rantz and others (4).
distance far enough from the bank to eliminate any possible
bank effects such as inflow of overland flow for the banks and
8. Installation of Equipment
localized increased SSC do to bank erosion.
8.1 Placement of sensor in cross section of the stream: The
8.1.9 Place the sampling point in a zone of high velocity and
primary consider when
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