ASTM D4411-2003 Standard Guide for Sampling Fluvial Sediment in Motion《运动中河流泥沙抽样的标准指南》.pdf

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1、Designation: D 4411 03Standard Guide forSampling Fluvial Sediment in Motion1This standard is issued under the fixed designation D 4411; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parenthe

2、ses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This guide covers the equipment and basic proceduresfor sampling to determine discharge of sediment transported bymoving liquids. Equipment and procedu

3、res were originallydeveloped to sample mineral sediments transported by riversbut they are applicable to sampling a variety of sedimentstransported in open channels or closed conduits. Procedures donot apply to sediments transported by flotation.1.2 This guide does not pertain directly to sampling t

4、odetermine nondischarge-weighted concentrations, which inspecial instances are of interest. However, much of the descrip-tive information on sampler requirements and sediment trans-port phenomena is applicable in sampling for these concentra-tions, and 9.2.8 and 13.1.3 briefly specify suitable equip

5、ment.Additional information on this subject will be added in thefuture.1.3 The cited references are not compiled as standards;however they do contain information that helps ensure standarddesign of equipment and procedures.1.4 Information given in this guide on sampling to deter-mine bedload dischar

6、ge is solely descriptive because nospecific sampling equipment or procedures are presently ac-cepted as representative of the state-of-the-art.As this situationchanges, details will be added to this guide.1.5 This standard does not purport to address all of thesafety concerns, if any, associated wit

7、h 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 use. Specific precau-tionary statements are given in Section 12.2. Referenced Documents2.1 ASTM Standards:D 1129 T

8、erminology Relating to Water2D 3977 Practice for Determining Suspended-SedimentConcentration in Water Samples33. Terminology3.1 Definitions:3.1.1 isokinetica condition of sampling, whereby liquidmoves with no acceleration as it leaves the ambient flow andenters the sampler nozzle.3.1.2 sampling vert

9、icalan approximately vertical pathfrom water surface to the streambed. Along this path, samplesare taken to define various properties of the flow such assediment concentration or particle-size distribution.3.1.3 sediment dischargemass of sediment transportedper unit of time.3.1.4 suspended sediments

10、ediment that is carried in sus-pension in the flow of a stream for appreciable lengths of time,being kept in this state by the upward components of flowturbulence or by Brownian motion.3.1.5 For definitions of other terms used in this guide, seeTerminology D 1129.3.2 Definitions of Terms Specific to

11、 This Standard:3.2.1 concentration, sedimentthe ratio of the mass of drysediment in a water-sediment mixture to the volume of thewater-sediment mixture. Refer to Practice D 3977.3.2.2 depth-integrating suspended sediment sampleraninstrument capable of collecting a water-sediment mixtureisokineticall

12、y as the instrument is traversed across the flow;hence, a sampler suitable for performing depth integration.3.2.3 depth-integrationa method of sampling at everypoint throughout a sampled depth whereby the water-sedimentmixture is collected isokinetically to ensure the contributionfrom each point is

13、proportional to the stream velocity at thepoint. This method yields a sample that is discharge-weightedover the sampled depth. Ordinarily, depth integration is per-formed by traversing either a depth- or point-integratingsampler vertically at an acceptably slow and constant rate;however, depth integ

14、ration can also be accomplished withvertical slot samplers.3.2.4 point-integrating suspended-sediment sampleraninstrument capable of collecting water-sediment mixtures iso-kinetically. The sampling action can be turned on and off while1This guide is under the jurisdiction of ASTM Committee D19 on Wa

15、ter and isthe direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,and Open-Channel Flow.Current edition approved Aug. 10, 2003. Published September 2003. Originallyapproved in 1984. Last previous edition approved in 1998 as D 4411 98.2Annual Book of ASTM Standards, Vol 11.01.3Di

16、scontinued; see 1994 Annual Book of ASTM Standards, Vol 11.02.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the sampler intake is submerged so as to permit sampling

17、for aspecified period of time; hence, an instrument suitable forperforming point or depth integration.3.2.5 point-integrationa method of sampling at a fixedpoint whereby a water-sediment mixture is withdrawn isoki-netically for a specified period of time.3.2.6 stream dischargethe quantity of flow pa

18、ssing agiven cross section in a given time. The flow includes themixture of liquid (usually water), dissolved solids, and sedi-ment.4. Significance and Use4.1 This guide is general and is intended as a planningguide. To satisfactorily sample a specific site, an investigatormust sometimes design new

19、sampling equipment or modifyexisting equipment. Because of the dynamic nature of thetransport process, the extent to which characteristics such asmass concentration and particle-size distribution are accuratelyrepresented in samples depends upon the method of collection.Sediment discharge is highly

20、variable both in time and space sonumerous samples properly collected with correctly designedequipment are necessary to provide data for discharge calcu-lations. General properties of both temporal and spatial varia-tions are discussed.5. Design of the Sampling Program5.1 The design of a sampling pr

21、ogram requires an evalua-tion of several factors. The objectives of the program and thetolerable degree of measurement accuracy must be stated inconcise terms. To achieve the objectives with minimum cost,care must be exercised in selecting the site, the samplingfrequency, the spatial distribution of

22、 sampling, the samplingequipment, and the operating procedures.5.2 A suitable site must meet requirements for both streamdischarge measurements and sediment sampling (1).4Theaccuracy of sediment discharge measurements are directlydependent on the accuracy of stream discharge measurements.Stream disc

23、harge usually is obtained from correlations betweenstream discharge, computed from flow velocity measurements,the stream cross-section geometry, and the water-surface el-evation (stage). The correlation must span the entire range ofdischarges which, for a river, includes flood and low flows.Therefor

24、e, it is advantageous to select a site that affords astable stage-discharge relationship. In small rivers and man-made channels, artificial controls as weirs can be installed.These will produce exceptionally stable and well definedstage-discharge relationships. In large rivers, only naturalcontrols

25、ordinarily exist. Riffles and points where the bottomslope changes abruptly, such as immediately upstream from anatural fall, serve as excellent controls. A straight uniformreach is satisfactory, but the reach must be removed frombridge piers and other obstructions that create backwatereffects.5.3 A

26、 sampling site should not be located immediatelydownstream from a confluence because poor lateral mixing ofthe sediment will require an excessive number of samples.Gaging and sampling stations should not be located at siteswhere there is inflow or outflow. In rivers, sampling duringfloods is essenti

27、al so access to the site must be considered.Periods of high discharge may occur at night and duringinclement weather when visibility is poor. In many instances,bridges afford the only practical sampling site.5.4 Sampling frequency can be optimized after a review ofthe data collected during an initia

28、l period of intensive sam-pling. Continuous records of water discharge and gage height(stage) should be maintained in an effort to discover parametersthat correlate with sediment discharge, and, therefore, can beused to indirectly estimate sediment discharge. During periodsof low-water discharge in

29、rivers, the sampling frequency canusually be decreased without loss of essential data. If thesediment discharge originates with a periodic activity, such asmanufacturing, then periodic sampling may be very efficient.5.5 The location and number of sampling verticals requiredat a sampling site is depe

30、ndent primarily upon the degree ofmixing in the cross section. If mixing is nearly complete, thatis the sediment is evenly and uniformly distributed in the crosssection, a single sample collected at one vertical and the waterdischarge at the time of sampling will provide the necessarydata to compute

31、 instantaneous sediment-discharge. Completemixing rarely occurs and only if all sediment particles inmotion have low fall velocities. Initially, poor mixing shouldbe assumed and, as with sampling any heterogeneous popula-tion, the number of sampling verticals should be large.5.6 If used properly, th

32、e equipment and procedures de-scribed in the following sections will ensure samples with ahigh degree of accuracy. The procedures are laborious butmany samples should be collected initially. If acceptably stablecoefficients can be demonstrated for all anticipated flowconditions, then a simplified sa

33、mpling method, such as pump-ing, may be adopted for some or all subsequent sampling.6. Hydraulic Factors6.1 Modes of Sediment Movement:6.1.1 Sediment particles are subject to several forces thatdetermine their mode of movement. In most instances wheresediment is transported, flow is turbulent so eac

34、h sedimentparticle is acted upon by both steady and fluctuating forces.The steady force of gravity and the downward component ofturbulent currents accelerate a particle toward the bed. Theforce of buoyancy and the upward components of turbulentcurrents accelerate a particle toward the surface. Relat

35、ivemotion between the liquid and the particle is opposed by a dragforce related to the fluid properties and the shape and size ofthe particle.6.1.2 Electrical charges on the surface of particles createforces that may cause the particles to either disperse orflocculate. For particles in the submicron

36、 range, electricalforces may dominate over the forces of gravity and buoyancy.6.1.3 Transport mode is determined by the character of aparticles movement. Clay and silt-size particles are relativelyunaffected by gravity and buoyant forces; hence, once theparticles are entrained, they remain suspended

37、 within the bodyof the flow for long periods of time and are transported in thesuspended mode.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D44110326.1.4 Somewhat larger particles are affected more by grav-ity. They travel in suspension but their exc

38、ursions into the floware less protracted and they readily return to the bed where theybecome a part of the bed material until they are resuspended.6.1.5 Still larger particles remain in almost continuouscontact with the bed. These particles, termed bedload, travel ina series of alternating steps int

39、errupted by periods of no motionwhen the particles are part of the streambed. The movement ofbedload particles invariably deforms the bed and produces abed form (that is, ripples, dunes, plane bed, antidunes, etc.),that in turn affects the flow and the bedload movement. Abedload particle moves when

40、lift and drag forces or impact ofanother moving particle overcomes resisting forces and dis-lodges the particle from its resting place.The magnitudes of theforces vary according to the fluid properties, the mean motionand the turbulence of the flow, the physical character of theparticle, and the deg

41、ree of exposure of the particle. The degreeof exposure depends largely on the size and shape of theparticle relative to other particles in the bed-material mixtureand on the position of the particle relative to the bed form andother relief features on the bed. Because of these factors, evenin steady

42、 flow, the bedload discharge at a point fluctuatessignificantly with time. Also, the discharge varies substantiallyfrom one point to another.6.1.6 Within a river or channel, the sizes of the particles intransport span a wide range and the flow condition determinesthe mode by which individual particl

43、es travel.Achange in flowconditions may cause particles to shift from one mode to theother.6.1.7 For transport purposes, the size of a particle is bestcharacterized by its fall diameter because this describes theparticles response to the steady forces in the transport process.6.2 Dispersion of Suspe

44、nded Sediment:6.2.1 The various forces acting on suspended-sedimentparticles cause them to disperse vertically in the flow. Aparticles upward velocity is essentially equal to the differencebetween the mean velocity of the upward currents and theparticles fall velocity. A particles downward velocity

45、isessentially equal to the sum of the mean velocity of thedownward currents and the particles fall velocity. As a result,there is a tendency for the flux of sediment through anyhorizontal plane to be greater in the downward direction.However, this tendency is naturally counteracted by the estab-lish

46、ment of a vertical concentration gradient. Because of thegradient, the sediment concentration in a parcel of water-sediment mixture moving upward through the plane is higherthan the sediment concentration in a parcel moving downwardthrough the plane. This difference in concentration produces anet up

47、ward flux that balances the net downward flux caused bysettling. Because of their high fall velocities, large particleshave a steeper gradient than smaller particles. Fig. 1 (2) shows(for a particular flow condition) the gradients for severalparticle-size ranges. Usually, the concentration of partic

48、lessmaller than approximately 60 m will be uniform throughoutthe entire depth.6.2.2 Turbulent flow disperses particles laterally from onebank to the other. Within a long straight channel of uniformcross section, lateral concentration gradients will be nearlysymmetrical and vertical concentration gra

49、dients will be simi-lar across the section. However, within a channel of irregularcross section, lateral gradients will lack symmetry and verticalgradients may differ significantly. Fig. 2 (3) illustrates thevariability within one cross section of the Rio Grande.6.2.3 Sediment entering from the side of a channel slowlydisperses as it moves downstream and lateral gradients mayexist for several hundred channel widths downstream. In ornear a channel bend, secondary flow accentuates both horizon-tal and vertical gradients. Until data have been collected toprove the contrary