Distribution of Open-File Report "Field Methods for Measurement of Fluvial Sediment" and the Proposed Water Resources Division (WRD) Polisy on Bedload Data Collection and Publication In Reply Refer To: September 13, 1988 WGS-Mail Stop 415 OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 88.17 Subject: PROGRAMS AND PLANS--Distribution of Open-File Report "Field Methods for Measurement of Fluvial Sediment" and the Proposed Water Resources Division (WRD) Policy on Bedload Data Collection and Publication The purpose of this memorandum is to (1) announce the release of Open-File Report 86-531 "Field Methods for Measurement of Fluvial Sediment" by Thomas K. Edwards and G. Douglas Glysson, and (2) solicit comments on the proposed WRD policy on bedload sampler and sampling procedures (attachment 1). Attached is a copy of the subject report that is designed to replace Techniques of Water-Resources Investigations (TWRI), Book 3, Chapter C2, by Guy and Norman. Because there is much controversy concerning acceptable bedload sampling procedures and therefore concerning the attached report and the proposed policy statement, we are releasing the report to the open file for evaluation before publishing it as a TWRI. During the next 6 months, if you find any errors or wish to comment on anything contained in the attached report, please send your comments to the Chief, Office of Surface Water. We will review the comments and make any necessary changes prior to sending the report for publication as a TWRI and issuing the bedload sampler and sampling procedures policy. Ernest F. Hubbard Acting Chief, Office of Surface Water 2 Attachments WRD Distribution: A, FO-LS Proposed Water Resources Division (WRD) Policy on Collection and Publication of Bedload Data BACKGROUND In the late 1960's, the Helley-Smith bedload sampler was developed by the California District. Its original design was based on the Arnhem bedload sampler that was developed in the 1930's. These samplers are pressure- differential type samplers; that is, they have nozzles that have larger cross- section openings at the rear of the nozzle than they have at the entrance. This can cause the flow to accelerate as it passes into the nozzle (Helley and Smith, 1971). The Arnhem and Helley-Smith samplers have a flare (ratio of exit area to entrance area) of 3.22. During 1973-76, extensive comparison testing of the Helley-Smith sampler was conducted in the field. Results of these tests were published in Professional Paper 1139 (Emmett, 1980). Based on these results, the Quality of Water Branch (QWB), now the Office of Water Quality, distributed QWB Technical Memorandum Nos. 76.04, 77.07, 79.17, and 80.07 and WRD Memorandum No. 77.60. These memorandums set interim policy and guidelines for the use of the Helley-Smith sampler, methods for data collec- tion, and publication of the data in the annual data reports. The proposed policy statement will replace all of the above-mentioned memorandums. In the late 1970's, the Technical Committee of the Subcommittee on Sedimenta- tion of the Interagency Advisory Committee on Water Data asked the WRD to conduct flume tests on the Helley-Smith sampler. Extensive flume tests on several versions of Helley-Smith type samplers were conducted at the St. Anthony Falls Hydraulic Laboratory. As a result of these tests, the Technical Committee, on May 15, 1985, accepted a modification of the origi-nal Helley- Smith nozzle as the "tentative standard" to be recommended for use by all Federal agencies. The accepted nozzle had the same entrance area and length as the original Helley-Smith nozzle and a flare of 1.40 instead of the 3.22. This decision was reaffirmed at the April 1988 meeting of the same committee. During the 1970's and 1980's, considerable work has been done on investigating bedload transport. These investigations showed that there is considerable temporal and spatial variation to bed-load transport. Depending on the rela- tive magnitude of the temporal and spatial variability, different sampling methods are optimal when making a bedload discharge measurement. Although it is important, the selection of the proper nozzle flare is probably less criti- cal than the selection of the proper sampling method for obtaining an accurate bedload discharge measurement. The WRD has made a considerable investment of resources in studying the sampling characteristics of Helley-Smith type bedload samplers. The WRD is also aware that many other types of bedload samplers are available and are in use throughout the world. In the interest of continuity and consistency, all bedload sampling efforts undertaken by the WRD should use the Helley-Smith type samplers recommended in this memorandum. Alternative samplers may be considered for sampling in situations outside the range of the Helley-Smith type samplers or in situations where funding is available to construct an efficient bedload trap in the streambed. Please contact the Office of Surface Water regarding the use of alternative samplers and storage of the data collected. POLICY The following policy and guidelines for the collection, publication, and storage of bedload data supersede previous policy and guideline statements given in QWB Technical Memorandum Nos. 76.04, 77.07, 79.17, and 80.07, as well as WRD Memorandum No. 77.60. Sampler Selection a. Bed-material size: Previous guidelines stated that the Helley-Smith sampler should not be used when the median diameter of the bed material is smaller than 1.0 millimeters (mm) except where the content of material finer than 0.25 mm is no greater than 15 percent. Likewise, the policy stated that the sampler should not be used in streams in which large particles or irregular bed configurations are likely to interfere with a good fit of the sampler to the streambed. With the intent of expanding the range of conditions in which bedload samplers can be used, it is now the WRD policy that samples can be collected wherever physical conditions will permit sample collection. Physical conditions will permit sample collection: when the bed material is firm enough to physically support the sampler without it sinking into the bed; when the bed material is fine enough and the streambed even enough for the nozzle to lay flat on the streambed; and when the stream velocity is low enough to not allow the sampler to properly set on the streambed. Because samples will be collected under a wider range of conditions, it will be mandatory that particle-size analysis of the bed material, bedload, and suspended load is known. It will not be necessary to perform these analyses on every sample but enough analyses should be performed to accurately define these particle sizes when bedload samples are to be collected at the site. The particle sizes can vary with both flow and season of the year. b. Bag mesh size: Large quantities of fine material, particularly organics, and large organic material, such as leaves, can clog the sampler bag, thus invalidating the sample. Increasing the mesh size of the bag may decrease this clogging problem. However, field personnel will have to use their own judgment as to which mesh size to use. Mesh sizes normally used are 0.25, 0.5, 1.0, and 2.0 mm with the 0.25 mm size being the most common. The mesh size should be selected to minimize both the clogging and the loss of the fine bedload through the mesh. c. Nozzle flare: The WRD endorses the use of the 1.40 flare nozzle recom- mended by the Technical Committee of the Subcommittee on Sedimentation. However, it is realized that differences between the 1.40 and 3.22 flare have not yet been completely quantified but are likely to be small rela- tive to potential errors induced by suboptimal sampling procedures. It is therefore acceptable to use existing samplers with the 3.22 flare. A note of caution, however: if the bedload sampled is predominantly sand (>50 percent), significant errors in the measured transport rate, up to a factor of two, may be encountered when using the 3.22 flare nozzle (Hubbell and others, 1985). In such cases, it is recommended that the 1.40 flare nozzle be used. d. Nozzle size: At present (1988), no established criteria exists for the selection of size nozzle. However, the Chinese have done some work in this area. Based on their work, it is suggested that the diameter (D70) of the material being sampled not exceed one-twelfth of the nozzle size (Note: D70 is the diameter of the particles for which 70 percent of the sample is finer.) Sampling Procedure a. Staylines: A stayline is a line connected to the suspension hanger bar of a sediment sampler. This line is also connected to an upstream, cross- stream line and keeps the sampler from drifting downstream while being lowered through the sampling vertical. Staylines also help eliminate cross-stream "swimming" of the sampler. The use of staylines when collecting bedload samples using a cable suspension is believed to reduce scooping. Therefore, they are recommended for use then bedload samples are collected using a cable or handline. For more information on stay- lines, contact the Chief, Office of Surface Water. b. Cross-sectional procedures: Bedload transport is extremely variable both spatially and temporally. The sampling procedure is very important to the accuracy of the result, but the optimal sampling procedure is dependent on local conditions in the field. At one extreme the spatial variations may be much larger than the temporal variations and at the other extreme the temporal variations may be much larger than the spatial variations. The open-file report announced by the cover memorandum lists three procedures that can be used. They are the Single Equal Width Increment (SEWI) method, the Multiple Equal Width Increment (MEWI) method, and the Unequal Width Increment (UWI) method. It is the responsibility of the field personnel to select the procedure that is optimal for the local condi- tions. Ordinarily, excess samples will have to be collected at a site until enough experience is gained to select the appropriate procedure for the site. The SEWI procedure is essentially identical to the provisional procedure described in QWB Technical Memorandum No. 79.17. c. Sample compositing: As described in the report announced in the cover memorandum, individual bedload samples can be (1) analyzed individually, or (2) composited into one or more samples for analyses. Whichever method of compositing is selected for computing bedload discharge, an analysis of particle-size distribution must be made on enough samples so that the sizes of sediment being moved will be known. Remember that the more samples one composites, the less one learns about variability in space and time. DOCUMENTATION WRD Memorandum No. 77.60 restricts publication of bedload data obtained with the Helley-Smith sampler from being reported in the State annual data reports. It is now believed that enough is known about these samplers and sampling procedures to allow the data to be stored in WATSTORE and published in the annual data reports. The data will be qualified, however, by also storing with each sample data set at least: (1) type of sampler, (2) bag mesh size, and (3) method of collection. Parameter codes for these data are attached to this memorandum as well as a list of suggested data that should be recorded for each sample. Samples collected prior to the issuance of this memorandum for which the sampler type, mesh size, and method of collection are known should be entered and stored in WATSTORE also. Districts should review any bedload data stored in WATSTORE and either enter the required data or remove the data from the file. Questions and/or comments concerning this new policy should be directed to the Chief, Office of Surface Water, 415 National Center, Reston, Virginia 22092. Mandatory Data to be Stored with Bedload Samples Parameter Code Description --- Date --- Time 00061 Instantaneous stream discharge 80225 Bedload discharge * Type of sampler 82398 Sampling methodology * Bedload sampler bag mesh size 00063 Number of sampling points 80226-80238 --- **Bedload particle size distribution (.062-128 mm) 80154 **Suspended sediment concentration 70337-70341 **Suspended sediment particle-size distribution and (.002-2 mm) 70342-70347(1) or 70331-70336(2) --- **Bed material particle-size distribution 80157-80163(1) (.004-2 mm, fall diameter; .062-128 mm, sieve diameter) 80164-80175(2) 00010 Stream temperature * Thickness of nozzle wall OPTIONAL ADDITIONAL DATA 00009 Vertical location, feet from left bank looking downstream 00065 Gage height 00055 Stream velocity 00004 Stream width 00064 Depth of stream, mean *Codes for these parameters have been requested and will be obtained prior to issuing this policy. **It is not necessary to collect these data for every sample but enough analyses should be performed to accurately define these parameters for all seasons and flow conditions in which bedload samples are to be collected at the site. (1)Fall diameter (2)Sieve diameter Sampling Method Codes (partial list) Code Description ** SEWI ** MEWI ** UWI 30 Single vertical Type of Sampler Codes (partial list) Code Description ** 3" x 3", 3.22 flare, Helley-Smith type ** 6" x 6", 3.22 flare, Helley-Smith type ** 3" x 3", 1.40 flare, Helley-Smith type ** 6" x 6", 1.40 flare, Helley-Smith type ** 6" x 12", 1.40 flare, Helley-Smith type ** 3" x 3", 1.40 flare, FIASP type ** 6" x 12", 1.40 flare, Hubbell #5 type ** 6" x 12", 1.40 flare, Toutle River type 2 ** 6" x 6", 3.22 flare, Toutle River type 1 **Codes for these parameters have been requested and will be obtained prior to issuing this policy. References Druffel, L., Emmett, W. W., Schneider, V. R., and Skinner, J. V., 1976, Laboratory hydraulic calibration of the Helley-Smith bedload sediment sampler: U.S. Geological Survey Open-File Report 76-752, 63 p. Emmett, W. W., 1980, A field calibration of the sediment-trapping characteristics of the Helley-Smith bedload sampler: U.S. Geological Survey Professional Paper 1139, 44 p. Helley, E. J., and Smith, W., 1971, Development and calibration of a pressure- difference bedload sampler: U.S. Geological Survey Open-File Report, 18 p. Hubbell, D. W., 1964, Apparatus and techniques for measuring bedload: U.S. Geological Survey Water-Supply Paper 1748, 74 p. Hubbell, D. W., Stevens, H. H., Jr., Skinner, J. V., and Beverage, J. P., 1985, New approach to calibrating bedload samplers, Journal of Hydraulic Division, American Society of Civil Engineers, v. 111, no. 4, p. 677- 694. Guy, H. P., and Norman, V. W., 1970, Field methods for measurement of fluvial sediment: Techniques of Water-Resources Investigations of the U.S. Geological Survey, Book 3, Chapter C2, 59 p.