Call for collaboration in WMO project for the assessment of the performance of flow measurement instruments and techniques
[No abstract available]
Journal of Hydraulic Engineering↗
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Results for “Flow Measurement and Instrumentation”
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Discharge characteristics of triangular-notch thin-plate weirs
The triangular-notch, thin-plate weir is a convenient, inexpensive, and relatively precise flow-measuring instrument. It is frequently used to measure the flow of water in laboratories and in small, natural streams. The purpose of this report is to present a comprehensive analysis of the discharge characteristics of triangular-notch weirs. Previously-published data are analyzed in the light of the effective-head concept, and a new discharge formula is proposed. Coefficients are recommended, and requirements for precise measurements are described. Limits of applicability are discussed. The report includes an extensive review of the literature of triangular-notch weirs.
Open-File Report↗
Utility of an instantaneous salt dilution method for measuring streamflow in headwater streams
Streamflow records are biased toward large streams and rivers, yet small headwater streams are often the focus of ecological research in response to climate change. Conventional flow measurement instruments such as acoustic Doppler velocimeters (ADVs) do not perform well during low-flow conditions in small streams, truncating the development of rating curves during critical baseflow conditions dominated by groundwater inflow. We revisited an instantaneous solute tracer injection method as an alternative to ADVs based on paired measurements to compare their precision, efficiency, and feasibility within headwater streams across a range of flow conditions. We show that the precision of discharge measurements using salt dilution by slug injection and ADV methods were comparable overall, but salt dilution was more precise during the lowest flows and required less time to implement. Often, headwater streams were at or below the depth threshold where ADV measurements could even be attempted and transects were complicated by coarse bed material and cobbles. We discuss the methodological benefits and limitations of salt dilution by slug injection and conclude that the method could facilitate a proliferation of streamflow observation across headwater stream networks that are highly undersampled compared to larger streams.
Virginia↗
Errors in acoustic doppler profiler velocity measurements caused by flow disturbance
Acoustic Doppler current profilers (ADCPs) are commonly used to measure streamflow and water velocities in rivers and streams. This paper presents laboratory, field, and numerical model evidence of errors in ADCP measurements caused by flow disturbance. A state-of-the-art three-dimensional computational fluid dynamic model is validated with and used to complement field and laboratory observations of flow disturbance and its effect on measured velocities. Results show that near the instrument, flow velocities measured by the ADCP are neither the undisturbed stream velocity nor the velocity of the flow field around the ADCP. The velocities measured by the ADCP are biased low due to the downward flow near the upstream face of the ADCP and upward recovering flow in the path of downstream transducer, which violate the flow homogeneity assumption used to transform beam velocities into Cartesian velocity components. The magnitude of the bias is dependent on the deployment configuration, the diameter of the instrument, and the approach velocity, and was observed to range from more than 25% at 5cm from the transducers to less than 1% at about 50cm from the transducers for the scenarios simulated. ?? 2007 ASCE.
Journal of Hydraulic Engineering↗
Instrumentation for a dry-pond detention study
A 12.3-acre, fully urbanized, residential land-use catchment was instrumented by the U. S. Geological Survey in Topeka, Kansas. Hydraulic instrumentation for flow measurement includes two types of flumes, a pipe-insert flume and a culvert-inlet (manhole) flume. Samples of rainfall and runoff for water-quality analyses were collected by automatic, 3-liter, 24-sample capacity water samples controlled by multichannel data loggers. Ancillary equipment included a raingage and wet/dry atmospheric-deposition sampler. Nineteen stormwater runoff events were monitored at the site using the instrumentation system. The system has a high reliability of data capture and permits an accurate determination of storm-water loads.
Conference Paper↗
Broad-band acoustic Doppler current profiler
The broad-band acoustic Doppler current profiler is an instrument that determines velocity based on the Doppler principle by reflecting acoustic signals off sediment particles in the water. The instrument is capable of measuring velocity magnitude and direction throughout a water column and of measuring water depth. It is also capable of bottom tracking and can, therefore, keep track of its own relative position as it is moved across a channel. Discharge measurements can be made quickly and, based on limited tests, accurately with this instrument.
Flow Measurement and Instrumentation↗
Intercomparison of principal hydrometric instruments; Third phase, Evaluation of ultrasonic velocity meters for flow measurement in streams, canals, and estuaries
As part of the World Meteorological Organization ( WMO ) project Intercomparison of Principal Hydrometric Instruments , Third Phase , a questionnaire was prepared by the U.S. Geological Survey (USGS) on the application of Ultrasonic Velocity Meters (UVM's) for flow measurement in streams , canals , and estuaries . In 1996, this questionnaire was distributed internationally by the WMO and USGS, and distributed within the United States by the USGS. Completed questionnaires were returned by 26 agencies in 7 countries (Canada, France, Germany, The Netherlands, Switzerland, the United Kingdom, and the United States). The completed questionnaires described geometric and streamflow conditions, system configurations, and reasons for applying UVM systems for 260 sites, thus providing information on the applicability of UVM systems throughout the world. The completed questionnaires also provided information on operational issues such as (1) methods used to determine and verify UVM ratings, (2) methods used to determine the mean flow velocity for UVM systems, (3) operational reliability of UVM systems, (4) methods to estimate missing data, (5) common problems with UVM systems and guidelines to mitigate these problems, and (6) personnel training issues. The completed questionnaires also described a few unique or novel applications of UVM systems. In addition to summarizing the completed questionnaires, this report includes a brief overview of UVM application and operation, and a short summary of current (1998) information from UVM system manufacturers regarding system cost and capabilities. On the basis of the information from the completed questionnaires and provided by the manufacturers, the general applicability of UVM systems is discussed. In the finalisation of this report the financial support provided by the US National Committee for Scientific Hydrology is gratefully acknowledged.
Report↗
Development and testing of highway storm-sewer flow measurement and recording system
A comprehensive study and development of measuring instruments and techniques for measuring all components of flow in a storm-sewer drainage system was undertaken by the U.S. Geological Survey under the sponsorship of the Federal Highway Administration. The study involved laboratory and field calibration and testing of measuring flumes, pipe insert meters, weirs, electromagnetic velocity meters as well as the development and calibration of pneumatic-bubbler pressure transducer head measuring systems. Tracer-dilution and acoustic flow meter measurements were used in field verification tests. A single micrologger was used to record data from all the above instruments as well as from a tipping-bucket rain gage and also to activate on command the electromagnetic velocity meter and tracer-dilution systems. (Author 's abstract)
Water-Resources Investigations Report↗
STORM-SEWER FLOW MEASUREMENT AND RECORDING SYSTEM.
A comprehensive study and development of instruments and techniques for measuring all components of flow in a storm-sewer drainage system were undertaken by the U. S. Geological Survey under the sponsorship of FHWA. The study involved laboratory and field calibration and testing of measuring flumes, pipe insert meters, weirs, and electromagnetic velocity meters as well as the development and calibration of pneumatic bubbler and pressure transducer head-measuring systems. Tracer dilution and acoustic-flowmeter measurements were used in field verification tests. A single micrologger was used to record data from all the instruments and also to activate on command the electromagnetic velocity meter and tracer dilution systems.
Transportation Research Record↗
Improvements to estimate ADCP uncertainty sources for discharge measurements
The use of moving boat ADCPs (Acoustic Doppler Current Profilers) for discharge measurements requires identification of the sources and magnitude of uncertainty to ensure accurate measurements. Recently, a tool known as QUant was developed to estimate the contribution to the uncertainty estimates for each transect of moving-boat ADCP discharge measurements, by varying different sampling configurations parameters through the use of Monte Carlo simulations. QUant is not only useful for estimating ADCP discharge measurement uncertainty, but also for identifying contributions of the various sources of uncertainty. However, the software requires long computational times, and the method to estimate the uncertainty of multiple-transect measurements does not consider the correlation of the variables between transects. Therefore, improvements in QUant are needed to optimize its application for practical purposes by hydrographers immediately after discharge measurements. This work presents four approaches for optimizing the performance of QUant to estimate the contribution to the uncertainty of different selected variables on ADCP discharge measurements and describes a new method of estimating multi-transect uncertainty with the QUant model that considers the correlation of errors in selected variables between transects. The approaches for optimization and the new multi-transect uncertainty method are evaluated using a dataset of 38 field measurements from a variety of riverine settings.
Flow Measurement and Instrumentation↗
Field measurement of basal forces generated by erosive debris flows
It has been proposed that debris flows cut bedrock valleys in steeplands worldwide, but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows. Here we present and analyze measurements made using an automated sensor network, erosion bolts, and a 15.24 cm by 15.24 cm force plate installed in the bedrock channel floor of a steep catchment. These measurements allow us to quantify the distribution of basal forces from natural debris‒flow events that incised bedrock. Over the 4 year monitoring period, 11 debris‒flow events scoured the bedrock channel floor. No clear water flows were observed. Measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm. The basal force during these erosive debris‒flow events had a large‒magnitude (up to 21 kN, which was approximately 50 times larger than the concurrent time‒averaged mean force), high‒frequency (greater than 1 Hz) fluctuating component. We interpret these fluctuations as flow particles impacting the bed. The resulting variability in force magnitude increased linearly with the time‒averaged mean basal force. Probability density functions of basal normal forces were consistent with a generalized Pareto distribution, rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces. When the bed sediment thickness covering the force plate was greater than ~ 20 times the median bed sediment grain size, no significant fluctuations about the time‒averaged mean force were measured, indicating that a thin layer of sediment (~ 5 cm in the monitored cases) can effectively shield the subjacent bed from erosive impacts. Coarse‒grained granular surges and water‒rich, intersurge flow had very similar basal force distributions despite differences in appearance and bulk‒flow density. These results demonstrate that debris flows can have strong control on rates of steepland evolution and contribute to a foundation needed for modeling debris‒flow incision stochastically.
Journal of Geophysical Research F: Earth Surface↗
Feasibility study of the use of the acoustic velocity meter for measurement of net outflow from the Sacramento-San Joaquin Delta in California
A reliable measure of the fresh-water outflow from the Sacramento-San Joaquin delta is needed for the operation of the California Water Project and for the evaluation of the interrelated water problems of the delta and San Francisco Bay regions. The Chipps Island channel, immediately downstream from the confluence of the Sacramento and San Joaquin Rivers, is the most promising site for this flow measurement, but the conventional techniques used for evaluating steady flows cannot be employed there because the channel reach is in the tidal zone, and reversals of flow occur during each tidal cycle. Net outflows, which may be as little-as 2,000 cubic feet per second must necessarily be computed as the difference between the large ebbflow and floodflow volumes that move back and forth between the delta region and San Francisco Bay. Discharges during peak periods of the ebb and flood tidal cycles may exceed 300,000 cubic feet per second. In consequence, a very high degree of precision must be maintained in the gross flow measurements if meaningful computations of net outflow are to be made. This report evaluates the probable accuracies that might be achieved by use of an AVM (acoustic velocity meter), a device which measures the stream velocity along a diagonal line across the channel. The study indicates that this line velocity will provide a stable index of the mean velocity in the channel and that such an index could be used as a primary parameter for the computation of discharge. Therefore, net outflows probably could be computed with the required accuracy by the use of such a device. The significant factors controlling the precision of measurement would be the stability of the channel geometry and streamline orientation, the precision with which the current-meter measurements needed for calibration of the system could be made, the instrumental calibration stability of the AVM system, and the length of period over which net outflows were computed. The AVM system developed by the U.S. Geological Survey in cooperation with the California Department of Water Resources and the U.S. Army Corps of Engineers does not have the required instrumental stability for this precise flow measurement. However, other AVM systems now being produced commercially seem to have the desired error characteristics, and a system probably can be procured that will permit computation of the fresh-water outflow from the delta area.
Water Supply Paper↗
In search of earthquake-related hydrologic and chemical changes along Hayward Fault
Flow and chemical measurements have been made about once a month, and more frequently when required, since 1976 at two springs in Alum Rock Park in eastern San Jose, California, and since 1980 at two shallow wells in eastern Oakland in search of earthquake-related changes. All sites are on or near the Hayward Fault and are about 55 km apart. Temperature, electric conductivity, and water level or flow rate were measured in situ with portable instruments. Water samples were collected for later chemical and isotopic analyses in the laboratory. The measured flow rate at one of the springs showed a long-term decrease of about 40% since 1987, when a multi-year drought began in California. It also showed several increases that lasted a few days to a few months with amplitudes of 2.4 to 8.6 times the standard deviations above the background rate. Five of these increases were recorded shortly after nearby earthquakes of magnitude 5.0 or larger, and may have resulted from unclogging of the flow path and increase of permeability caused by strong seismic shaking. Two other flow increases were possibly induced by exceptionally heavy rainfalls. The water in both wells showed seasonal temperature and chemical variations, largely in response to rainfall. In 1980 the water also showed some clear chemical changes unrelated to rainfall that lasted a few months; these changes were followed by a magnitude 4 earthquake 37 km away. The chemical composition at one of the wells and at the springs also showed some longer-term variations that were not correlated with rainfall but possibly correlated with the five earthquakes mentioned above. These correlations suggest a common tectonic origin for the earthquakes and the anomalies. The last variation at the affected well occurred abruptly in 1989, shortly before a magnitude 5.0 earthquake 54 km away. ?? 1993.
California↗
Development of bridge-scour instrumentation for inspection and maintenance personnel
Inspecting bridges and monitoring scour during high flow can improve public transportation safety by providing early identification of scour and stream stability problems at bridges. Most bridge-inspection data are collected during low flow, when scour holes may have refilled. More than 25 percent of the States that responded to a questionnaire identified lack of adequate methodology and/or equipment as reasons for not collecting scour data during high-flow conditions. Therefore, the U.S. Geological Survey (USGS), in cooperation with the Federal Highway Administration, has begun to develop instrumentation for measuring scour that could be used by inspection and maintenance personnel during high-flow conditions. A variety of instruments and techniques for measuring scour were tested and evaluated in real-time bridge-scour data-collection studies by the USGS. In the National Scour study, fathometers were found to be superior to sounding weights and will be the primary bed-measuring instrument. The ability of low-cost fathometers and fish finders to locate the bed accurately is being evaluated. Simple and efficient methods for deploying the transducer during floods are also important for a successful measurement. The information and additional testing are being used to design new, portable scour-measuring systems.
Conference Paper↗
Instrumental lahar monitoring at Merapi Volcano, Central Java, Indonesia
More than 50 volcanic debris flows or lahars were generated around Mt Merapi during the first rainy season following the nuees ardentes of 22 November 1994. The rainfalls that triggered the lahars were analyzed, using such instruments as weather radar and telemetered rain gauges. Lahar dynamics were also monitored, using new non-contact detection instrumentation installed on the slopes of the volcano. These devices include real-time seismic amplitude measurement (RSAM), seismic spectral amplitude measurement (SSAM) and acoustic flow monitoring (AFM) systems. Calibration of the various systems was accomplished by field measurements of flow velocities and discharge, contemporaneously with instrumental monitoring. The 1994–1995 lahars were relatively short events, their duration in the Boyong river commonly ranging between 30 min and 1 h 30 min. The great majority (90%) of the lahars was recognized at Kaliurang village between 13:00 and 17:30 h, due to the predominance of afternoon rainfalls. The observed mean velocity of lahar fronts ranged between 1.1 and 3.4 m/s, whereas the peak velocity of the flows varied from 11 to 15 m/s, under the Gardu Pandang viewpoint location at Kaliurang, to 8–10 m/s at a section 500 m downstream from this site. River slopes vary from 28 to 22 m/km at the two sites. Peak discharges recorded in various events ranged from 33 to 360 m 3 /s, with the maximum value of peak discharge 360 m 3 /s, on 20 May 1995. To improve the lahar warning system along Boyong river, some instrumental thresholds were proposed: large and potentially hazardous lahars may be detected by RSAM units exceeding 400, SSAM units exceeding 80 on the highest frequency band, or AFM values greater than 1500 mV on the low-gain, broad-band setting.
Journal of Volcanology and Geothermal Research↗
Measurement of gas yields and flow rates using a custom flowmeter
A simple gas collection apparatus based on the principles of a Torricelli tube has been designed and built to measure gas volume yields and flow rates. This instrument is routinely used to monitor and collect methane gas released during methane hydrate dissociation experiments. It is easily and inexpensively built, operates at ambient pressures and temperatures, and measures gas volumes of up to 7 L to a precision of about 15 ml (about 0.0025 mol). It is capable of measuring gas flow rates varying from more than 103 to less than 10-1 ml/min during gas evolution events that span minutes to several days. We have obtained a highly reproducible hydrate number of n=5.891 with a propagated uncertainty of ??0.020 for synthetic methane hydrate. ?? 2001 American Institute of Physics.
Review of Scientific Instruments↗
Use of radars to monitor stream discharge by noncontact methods
Conventional measurements of river flows are costly, time‐consuming, and frequently dangerous. This report evaluates the use of a continuous wave microwave radar, a monostatic UHF Doppler radar, a pulsed Doppler microwave radar, and a ground‐penetrating radar to measure river flows continuously over long periods and without touching the water with any instruments. The experiments duplicate the flow records from conventional stream gauging stations on the San Joaquin River in California and the Cowlitz River in Washington. The purpose of the experiments was to directly measure the parameters necessary to compute flow: surface velocity (converted to mean velocity) and cross‐sectional area, thereby avoiding the uncertainty, complexity, and cost of maintaining rating curves. River channel cross sections were measured by ground‐penetrating radar suspended above the river. River surface water velocity was obtained by Bragg scattering of microwave and UHF Doppler radars, and the surface velocity data were converted to mean velocity on the basis of detailed velocity profiles measured by current meters and hydroacoustic instruments. Experiments using these radars to acquire a continuous record of flow were conducted for 4 weeks on the San Joaquin River and for 16 weeks on the Cowlitz River. At the San Joaquin River the radar noncontact measurements produced discharges more than 20% higher than the other independent measurements in the early part of the experiment. After the first 3 days, the noncontact radar discharge measurements were within 5% of the rating values. On the Cowlitz River at Castle Rock, correlation coefficients between the USGS stream gauging station rating curve discharge and discharge computed from three different Doppler radar systems and GPR data over the 16 week experiment were 0.883, 0.969, and 0.992. Noncontact radar results were within a few percent of discharge values obtained by gauging station, current meter, and hydroacoustic methods. Time series of surface velocity obtained by different radars in the Cowlitz River experiment also show small‐amplitude pulsations not found in stage records that reflect tidal energy at the gauging station. Noncontact discharge measurements made during a flood on 30 January 2004 agreed with the rated discharge to within 5%. Measurement at both field sites confirm that lognormal velocity profiles exist for a wide range of flows in these rivers, and mean velocity is approximately 0.85 times measured surface velocity. Noncontact methods of flow measurement appear to (1) be as accurate as conventional methods, (2) obtain data when standard contact methods are dangerous or cannot be obtained, and (3) provide insight into flow dynamics not available from detailed stage records alone.
Water Resources Research↗
Near bottom velocity measurements in San Francisco Bay, California
The ability to accurately measure long-term time-series of tidal currents in bays and estuaries is critical in estuarine hydrodynamic studies. Accurate measurements of tidal currents near the air-water interface and in the bottom boundary layer remain difficult in spite of the significant advances in technology for measuring tidal currents which have been achieved in recent years. One of the objectives of this study is to demonstrate that turbulent mean velocity distribution within the bottom boundary layer can be determined accurately by using a broad-band acoustic Doppler current profiler (BB-ADCP). A suite of instruments, including two BB-ADCPs and four electromagnetic (EM) current meters was deployed in San Francisco Bay, California in an investigation of resuspension and transport of sediment during March 1995. The velocity measurements obtained in the bottom boundary layer by BB-ADCP were highly coherent (r2>0.94) with the velocity measurements obtained by EM current meters. During early March 1995, both BB-ADCPs and EM current meters recorded a very unusual flow event. Agreement among independent measurements by these instruments in describing such an atypical hydrodynamic occurrence further validates the velocity measurements obtained by BB-ADCP in the bottom boundary layer.
Conference Paper↗