1、Designation: D7512 09Standard 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 or, in the case o
2、f 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, operation, and calibrati
3、on 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 (SSC) in water. Only
4、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 output from an optical
5、instrument, 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 to the mean turbi
6、dity 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 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespons
7、ibility of the user of this standard to establish appro-priate safety and health practices and to determine theapplicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD3977 Test Methods for Determining Sediment Concentra-tion
8、 in Water SamplesD4410 Terminology for Fluvial SedimentD4411 Guide for Sampling Fluvial Sediment in MotionD6764 Guide for Collection of Water Temperature,Dissolved-Oxygen Concentrations, Specific ElectricalConductance, and pH Data from Open ChannelsD7315 Test Method for Determination of Turbidity Ab
9、ove 1Turbidity Unit (TU) in Static Mode3. Terminology3.1 Definitions:3.1.1 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 t
10、rue,temperature-compensated value of the calibration standards.3.1.2 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 befor
11、eand after the sensors are cleaned.3.1.3 continuous, adjrefers to a time series of unit valuesthat are close enough in time to simulate a continuous record.3.1.3.1 DiscussionGenerally, in studies of open-channelflow, 15-minute intervals are used and are adequate to esti-mated continuous record. Howe
12、ver, the time interval maybe aslittle as a minute or as great as an hour.3.1.4 sonde, npart of the monitoring equipment thatcontains 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 G
13、uide4.1 This guide covers the equipment and basic proceduresfor installation, 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 t
14、he direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,and Open-Channel Flow.Current edition approved Oct. 1, 2009. Published October 2009. DOI: 10.1520/D7512-09.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.
15、org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 This guide emphasizes general principles for one par-ticula
16、r 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 specific site, a
17、n 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 particle-size dis
18、tribution 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 analyzed with p
19、roper 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 upper ran
20、ge 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 samplers.
21、 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 significantly di
22、fferentoutputs 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 relationship will
23、 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 instruments such as
24、 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 sensors may be u
25、sed.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 studywhich can be form on the web at http:/www.act-us.info/evaluation_reports.php.6.3 Before selecting the type of meter
26、 to be used, theoperator needs to review 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
27、likely to beencountered at the site.6.4 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 wo
28、rk best for the type of monitorbeing used.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
29、 data collection platform (DCP), andtransmittal 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 unti
30、l it is retrieved manually, while theDCP 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 satell
31、ite. It is beyond the scope of this guide 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 website for information on
32、 equipment needs and used by the USGS(http:/wwwhif.er.usgs.gov/public/contacts.htm).6.6 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
33、and also address theblackout periods discussed in Section 5.2. Detailed informationconcerning the installation and operation of pumping samplersis beyond the scope of this guide. See Edwards and Glysson (1)and Glysson (2) for more information on the use of automaticpumping samplers.7. Site Selection
34、7.1 The procedure for establishing a sampling locationshould emphasize the quest for a stream-data site. A stream-data site is as a cross section displaying relatively stablehydrologic characteristics and uniform depths over a widerange of stream discharges, from which representative sedi-ment data
35、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 to note the limitations of the most suitable siteavailable and build a program to minimize the disadvantagesand m
36、aximize the advantages.3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.D7512 0927.2 Sites that may be affected by backwater conditionsshould be avoided whenever possible. Backwater condition isa transient condition that occurs when water is backed up orr
37、etarded 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 A sediment-measuring site located
38、 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 samples mu
39、st 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 which occu
40、r 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 the flow
41、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 additional info
42、rmation and discussion on the selec-tion of a site for the collection of surface water and sedimentdata see Edwards and Glysson (1), Wagner and others (3), andRantz and others (4).8. Installation of Equipment8.1 Placement of sensor in cross section of the stream: Theprimary consider when placing an
43、optical 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 co
44、ncentration 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 conce
45、ntration 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
47、at 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 follow
48、ing 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 US 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 sediment
