1、Designation: D7512 09 (Reapproved 2015)Standard Guide forMonitoring of Suspended-Sediment Concentration in OpenChannel Flow Using Optical Instrumentation1This standard is issued under the fixed designation D7512; the number immediately following the designation indicates the year oforiginal adoption
2、 or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the equipment and basic proceduresfor installation, operat
3、ion, and calibration of optical equipmentas a surrogate for the continuous determination of suspended-sediment concentration (SSC) in open channel flow.1.2 This guide emphasizes general principles for the appli-cation of optical measurements to be used to estimatesuspended-sediment concentration (SS
4、C) in water. Only in afew instances are step-by-step instructions given. Continuousmonitoring is a field-based operation, methods and equipmentare usually modified to suit local conditions. The modificationprocess depends upon the operator skill and judgment.1.3 This guide covers the use of the outp
5、ut from an opticalinstrument, such as turbidity and suspended-solids meters, torecord data that can be correlated with suspended-sedimentconcentration. It does not cover the process of collecting datafor continuous turbidity record, which would require additionalcalibration of the turbidity readings
6、 to the mean turbidity of themeasurement cross section. For the purposes of this method itis assumed that the dependent variable will be mean cross-sectional suspended-sediment concentration data.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are inclu
7、ded in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to
8、 use.2. Referenced Documents2.1 ASTM Standards:2D3977 Test Methods for Determining Sediment Concentra-tion in Water SamplesD4411 Guide for Sampling Fluvial Sediment in MotionD7315 Test Method for Determination of Turbidity Above 1Turbidity Unit (TU) in Static Mode3. Terminology3.1 Definitions:3.1.1
9、calibration drift, nthe error that is the result of driftin the sensor reading from the last time the sensor wascalibrated, and is determined by the difference betweencleaned-sensor readings in calibration standards and the true,temperature-compensated value of the calibration standards.3.1.2 contin
10、uous, adjrefers to a time series of unit valuesthat are close enough in time to simulate a continuous record.3.1.2.1 DiscussionGenerally, in studies of open-channelflow, 15-minute intervals are used and are adequate to esti-mated continuous record. However, the time interval maybe aslittle as a minu
11、te or as great as an hour.3.1.3 fouling, nthe error that can result from a variety ofsources (such as biological growth on the sonde and coveringof the probe with sediment), and is determined by the differ-ence between sensor measurements in the environment beforeand after the sensors are cleaned.3.
12、1.4 sonde, npart of the monitoring equipment that con-tains the measurement sensors.3.1.4.1 DiscussionA sonde may be either a single param-eter sensor or a combination of different sensors of differentparameters.4. Summary of Guide4.1 This guide covers the equipment and basic proceduresfor installat
13、ion, operation, and calibration of optical equipmentas a surrogate for the continuous or near continuous determi-nation of SSC in open channel flow.1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.07 on Sediments, Geomorpholo
14、gy,and Open-Channel Flow.Current edition approved Jan. 15, 2015. Published February 2015. Originallyapproved in 2009. Last previous edition approved in 2009 as D7512 09. DOI:10.1520/D7512-09R15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at s
15、erviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.2 This guide emphasizes general principles for one
16、par-ticular application of optical measurements in water. Thisguide covers the use of nephelometers and backscatter typeturbidity meters to record data that can be correlated with SSC.5. Significance and Use5.1 This guide is general and intended as a planning guide.To satisfactorily monitor a specif
17、ic site, an investigator mustsometimes design specific installation structures or modifythose given in this guide to meet the requirements of the site inquestion. Because of the dynamic nature of the sedimenttransport process, the extent to which characteristics such asmass concentration and particl
18、e-size distribution are accuratelyrepresented in the monitoring program depends on the type ofequipment used and method of collection of the SSC samplesused to calibrate the optical readings. Sediment concentrationis highly variable in both time and space. Numerous samplesmust be collected and analy
19、zed with proper equipment andstandardized methods for the rating of the optical equipment ata particular site (see Guide D4411 and Practice D3977).5.2 All optical equipment have an upper limit for validreadings, beyond which the meter will not read properly,commonly referred to as “blacking out.” If
20、 upper range of SSCare expected to cause optical instrument black out, then someother means should be devised, such as automatic pumpingsamplers, to collect samples during this period. See Edwardsand Glysson (1)3and Glysson (2) for information on collectionof suspended sediment samples using pumping
21、 samplers. Itshould be noted that other technologies, such as lasers andacoustic dopplers, are also being used to monitor SSC continu-ously.5.3 The user of this guide should realize that becausedifferent technologies and different models of the same tech-nology of turbidity meters can produce signif
22、icantly differentoutputs for the same environmental sample, only one manu-facturer and model of the turbidity meter can be used todevelop the relationship between the SSC and turbidity read-ings at a site. If a different manufacturer or a different modeltype of turbidity meter is used, a new relatio
23、nship will need tobe develop for the site.6. Apparatus6.1 In general, three types of configurations of installationsof monitors can be used: (1) the flow-through monitoringsystem, (2) the in-situ monitoring system, and (3) the selfcontained, combined sensor and recording system.6.2 Optical instrumen
24、ts such as photoelectric nephelometer(best used for lower levels of SSC) and backscatter sensors(best used for higher levels of SSC) provide the basis for thismethod. For more information concerning the advantages anddisadvantages of each, see Test Method D7315. As theybecome available, other sensor
25、s may be used.6.2.1 The Alliance for Coastal Techniologies (ACT) did anin-situ evaluation of different nephelometer technologist. Usersof this guide may be interested in the results of this study whichcan be found online.46.3 Before selecting the type of meter to be used, theoperator needs to review
26、 the site requirements in order toensure selection of the proper instrumentation. Things toconsider, but are not limited to, are: the instruments ability tosurvive the study site environment, the degree of fouling thatmay take place, and the range of readings likely to beencountered at the site.6.4
27、If a flow-through or in-situ monitoring device is used, arecording system must be installed. The recording system musthave enough storage capacity to store all data recordedbetween site service visits. See manufacturers advice onwhich recording devices will work best for the type of monitorbeing use
28、d.6.5 Remote access and near real-time transmission of datafrom the site to the office can be very important in meeting theobjectives of the monitoring station. Remote access and thenear real-time transmittal of the recorded data take otherequipment (such as a data collection platform (DCP), andtran
29、smittal antenna) in addition to the optical sensor. A DCPperforms the same fundamental function as a basic datarecorder (BDR). They both collect data from attached sensorson a timed interval and store the results. The difference is theBDR retains the data until it is retrieved manually, while theDCP
30、 has the ability to transmit the collected data to anotherlocation. Since data is transferred elsewhere for storage shortlyafter collection, a DCP may have less memory than a BDR.The data may be transmitted via telephone modem, line-of-siteradio link or satellite. It is beyond the scope of this guid
31、e todiscuss how to instrument a site for remote data transmissionand no single reference on how to do this is available forreference here. The user is encouraged to visit the U.S.Geological Surveys Hydrologic Instrumentation Facility web-site5for information on equipment needs and used by theUSGS.6.
32、6 The installation of an automatic pumping sampler,especially in remote areas, will allow samples to be collectedthat can be used to relate the optical reading to the suspended-sediment concentration in the stream and also address theblackout periods discussed in 5.2. Detailed information con-cernin
33、g the installation and operation of pumping samplers isbeyond the scope of this guide. See Edwards and Glysson (1)and Glysson (2) for more information on the use of automaticpumping samplers.7. Site Selection7.1 The procedure for establishing a sampling locationshould emphasize the quest for a strea
34、m-data site. A stream-data site is as a cross section displaying relatively stablehydrologic characteristics and uniform depths over a wide3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.4Available from http:/www.act-us.info/evaluation.php.5Available fro
35、m http:/water.usgs.gov/hif.D7512 09 (2015)2range of stream discharges, from which representative sedi-ment data can be obtained and related to a stage-dischargerating and optical readings from the site. This is an idealizedconcept because the perfect site is rare at best. Therefore, it isnecessary t
36、o note the limitations of the most suitable siteavailable and build a program to minimize the disadvantagesand maximize the advantages.7.2 Sites that may be affected by backwater conditionsshould be avoided whenever possible. Backwater condition isa transient condition that occurs when water is back
37、ed up orretarded in a stream by tides or from inflow from anotherstream. Backwater affects both stage-discharge and velocity-discharge relationships. Therefore, a given discharge may havevarying stage and mean stream velocity and thus have varyingsediment transport rates.7.3 Asediment-measuring site
38、 located downstream from theconfluence of two streams may require extra sediment mea-surements due to incomplete mixing of the flows from thetributaries. Moving the sampling location far enough down-stream to ensure adequate mixing of the tributary flows shouldbe investigated.7.4 Because sediment sa
39、mples must be obtained morefrequently during high flows, and it is imperative that a site beselected where obtaining data during these times are feasible.Particular attention should be given to the ease of access to thewater-stage recorder and to a usable bridge or cable duringhigh flows, many of wh
40、ich occur at night. Sites accessible onlyby poorly maintained backroads or trails should be avoided.7.5 The average monitoring site will consist of a shelter tohouse and protect the equipment and some means for eitherbringing water to the meters or conduits that will allow themeter to be placed in t
41、he flow zone of the channel. The sheltershould be located to minimize the distance between the streamand the meters, and at a high enough elevation to protect theequipment during flooding events. Some instruments may needAC power and therefore the proximity to power lines isimportant.7.6 For additio
42、nal information and discussion on the selec-tion of a site for the collection of surface water and sedimentdata see Edwards and Glysson (1), Wagner et al. (3), and Rantzet al.(4).8. Installation of Equipment8.1 Placement of sensor in cross section of the stream: Theprimary consider when placing an o
43、ptical meter, sensor, orwater intake (collectively referred in this section as “samplingpoint.”) in the streamflow at a cross section is that only onepoint in the flow is being sampled. Therefore, to yield reliableand representative data, the sampling point should be placed atthe point where the con
44、centration approximates the mean SSCfor the cross section for the full range of flows. SSC data mayhave to be collected from several verticals in the cross sectionto help define where the mean SSC values is most likely toaccrue (see (1). This is an idealistic concept and the meancross-section concen
45、tration almost never exists at the samepoint under varying streamflow conditions. It is even less likelythat specific guidelines for locating a sampling point undergiven stream conditions at one stage would produce the samesampling point location relative to the flow conditions at adifferent stage.
46、Therefore, generalized guidelines (modifiedfrom (1) are outlined here and should be considered on acase-by-case basis when selecting a sampling point.8.1.1 Select a stable cross section of reasonably uniformdepth and width to maximize the stability of the relationshipbetween sediment concentration a
47、t a point and the meansediment concentration in the cross section. This guideline is ofprimary importance in the decision to use an optical meter in agiven situation; if a reasonably stable relation between thesample-point reading and mean cross-section concentrationcannot be attained by the followi
48、ng outlined steps, the metershould not be installed and an alternate location considered.8.1.2 Consider only the part of the vertical that could besampled using a standard U.S. depth- or point-integratingsuspended-sediment sampler, excluding the unsampled zone,because data collected with a depth- or
49、 point-integratingsampler will be used to calibrate the optical meter. See GuideD4411 and Edwards and Glysson (1) for information on theunsampled zone, proper procedures, and equipment to collectsamples for SSC analysis.8.1.3 Determine, if possible, the depth of the point of meansediment concentration in each vertical for each size class ofparticles finer than 0.250 mm, from a series of carefullycollected point integrated samples. See Edwards and Glysson(1) for information on the collection of point samples and Guy(5) for procedures for determining particle size of sedim
