Determination of sediment concentration by the measurement of the difference in weight between a sample of sediment-laden water and an equal volume of clear water at the same temperature. [Based on 'displacement method' in Manual on Sediment Management and Measurement (WMO-No. 948). 2003.] Displacement method of sediments 372 A radar water level gauge transmits microwave energy to measure the distance between the sensor and the water surface. The time it takes for the energy to reflect off the water surface and return to the radar is used to calculate the distance between the sensor and the water surface. Water level can then be determined from the elevation of the radar sensor and the sensor's measured distance to the water surface [Based on Skolnik et al, Radar Handbook, 3rd edition, 2008; Fulford et al, Testing and use of radar water level sensors by the U.S. Geological Survey, Manual on sea level: Measurement and interpretation Volume V: Radar gauges, 2016 and Fulford et al, Laboratory and field tests of the Sutron RLR-0003-1 water level sensor: U.S. Geological Survey Open-File Report, 2015]. radar water level gauge 379 Computation of stream discharge based on a relation between stream index velocity and average velocity (index-velocity rating) and a relation between stage and cross-sectional area (stage-area rating). Given these ratings and concurrent observations of stream index velocity and stage, average velocity and area are computed and finally discharge as their product. [Based on Manual on Stream Gauging (WMO No. 1044), volume I] Stream index-velocity rating 377 Determination of the discharge of a stream by means of a man-made channel with clearly specified shape and dimensions. [Based on 'flume' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Flume 362 Determination of water velocity based on the principle that a conductor (water) moving through a magnetic field will produce an electrical current directly proportional to the speed of movement (Faraday’s law). By measuring this current and the resultant distortion in the magnetic field the instrument can be calibrated to determine point velocities of flowing water. [Based on Manual on Stream Gauging (WMO-No. 1044), Volume I. 2010] Electromagnetic current meter 376 Determination of water velocity by using the Doppler principle applied to sound transmitted under water, in which the instrument is mounted in a fixed position under the water, giving an index velocity for a significant part of the flowing stream. [Based on Manual on Stream Gauging (WMO No. 1044), volume I] Acoustic doppler velocity meter (ADVM) 378 Measurement of soil capacitance by means of radio frequency waves. The soil acts as the dielectric completing a capacitance circuit, which is part of a feedback loop of a high-frequency transistor oscillator. [Based on 'Frequency domain reflectometry' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Frequency domain reflectometry 419 Estimation of water content in unsaturated materials based on variations in their dielectric properties. [International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Time domain reflectometry (TDR) 203 Determination of stream velocity by means of an acoustic Doppler instrument, which measures the velocity of the water based on the Doppler shift experienced by an acoustic pulse of energy which is reflected off particles suspended in, and moving with, the water. [Based on 'Acoustic Doppler Velocimeter' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Acoustic doppler current meter 369 Determination of the elevation of the flood crest by the adherence of regranulated cork to a graduated staff held in a fixed position with relation to the datum. [Based on 'maximum-stage gauge' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Maximum-stage gauge 353 Determination of water stage by means of a gauge consisting of a float which rises and falls with changes in the water level; this movement being transmitted to a recording or indicating device. [Based on 'float gauge' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Wire-float recording gauge (hydrograph) 355 Level measurement gauge, the essential element of which is a pointed rod that is lowered until it touches the water surface. [International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Point gauge 352 Determination of water stage by means of a recording gauge, for example, a device that automatically records the water level as detected by a sensor, either continuously or at regular time intervals. Synonyms: limnigraph, stage recorder, water-level recorder. [Based on 'water-level recorder' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Recording gauge 354 49 Determination of the discharge of a stream by measuring the degree of dilution, caused by the flowing water, of an added tracer solution. Synonyms: chemical gauging, tracer dilution gauging. [Based on 'dilution gauging' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Dilution gauging 359 Manual measurement or observation made with a graduated fixed stake, a sturdy ruler, or an extendable graduated rod. Graduated device 261 Evaluation of the return time of acoustic waves emitted into a medium to determine the distance between source and target. This method is used in hydrology, for example, to determine the depth of a water body. [Based on 'echo sounder' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Echo sounding 345 An empirical relationship relating sediment discharge and streamflow based on correlation analysis of sediment samples and concurrent flow estimates and presented as a curve, table, or equation. [Based on 'sediment rating curve' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Water discharge-sediment discharge rating curve 373 Determination of electrical resistance between two electrodes embedded in blocks of a porous material buried in the ground and in equilibrium with the surrounding moist soil. [Based on 'porous blocks/electrical resistance blocks' in Guide to Hydrological Practices (WMO-No. 168), Volume II. 2009 edition.] Electrical resistance blocks (Porous blocks) 187 Measurement/observing method (terrestrial and hydrological) Determination of water stage by means of a graduated vertical scale, fixed to a staff or structure, on which the water level may be read. Synonym: vertical gauge. [Based on 'Staff gauge' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Staff gauge 349 Measurement of soil capacitance by means of radio frequency waves. The soil acts as the dielectric completing a capacitance circuit, which is part of a feedback loop of a high-frequency transistor oscillator. [Based on 'Frequency domain reflectometry' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Frequency domain reflectometry 346 Determination of the discharge of a stream by means of a relationship between water level and discharge for a given cross-section, which may be expressed as a curve, a table or an equation. [Based on 'stage-discharge relation' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Stage-discharge relation 363 Radar velocimetry or surface velocity radar (radar sensor) is an active remote sensing method which measures the surface velocity of moving water. The radar sensor transmits microwave energy of a known frequency at an incidence angle (from nadir) to the water surface, where small-scale surface features such as waves shift the frequency of the microwave energy that is returned to the sensor. The frequency shift is used to compute the surface velocity of the water using the Doppler effect. Note: Because radar sensors measure the velocity at the water surface a transfer function, such as the probability concept, is needed to translate the surface velocity to a mean channel velocity [Based on Chiu, Entropy and probability concepts in hydraulics: J. Hydraul. Eng. 113, 1987; Fulton et al, Near-field remote sensing of surface velocity and river discharge using radars and the probability concept at 10 U.S. Geological Survey Streamgages, Remote Sens. 12, 2020; Fulton e al, Measuring Real-Time Streamflow Using Emerging Technologies: Radar, Hydroacoustics, and the Probability Concept, Journal of Hydrology 357, 2008 and Khan et al, Uncertainty in remote sensing of streams using noncontact radars, Journal of Hydrology 603, 2021]. radar velocimetry 380 Determination of the discharge in a reach which is based on the surface slope, the reach roughness, the wetted perimeters and the flow areas of the various wetted cross-sections in the reach. [Based on 'slope-area method' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Slope-area method 360 Determination of water velocity by means of a current meter, for example, an instrument for measuring water velocity. Synonym: flowmeter. [Based on 'current meter' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Water current meter 364 Determination of water velocity by means of a current meter in which the rotor is a propeller rotating around an axis parallel to the flow. [Based on 'propeller-type current meter' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Propeller-type current meter 366 Soil heat flux plate 128 Measurement of the moisture content and hence the porosity of a geological formation by means of lowering a tool containing a radioactive element emitting neutrons and a neutron detector into a borehole. [Based on 'neutron logging' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Neutron probe 159 Determination of water stage by means of a non-vertical scale which is graduated to indicate vertical heights. [Based on 'inclined gauge' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Inclined gauge 350 Determination of gamma-ray attenuation at given depth of soil using a source and a detector placed at a given distance at the same depth. If the apparent dry bulk density of the soil is known the signal can be converted into a measure of the volumetric soil-moisture content. [Based on 'Gamma-ray attenuation' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Gamma-ray attenuation 420 Weighing of snow-cover mass per unit area. Snow pillows and snow scales 262 Method of determining the discharge of a stream by measuring the width, velocity, and depth of the flowing water at a number of elemental areas, over the cross-section, and summing the products. [Based on 'velocity-area method' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Velocity-area method 357 Recording gauge operating on the principle that static pressure at a fixed point in the stream is directly proportional to the head of liquid above the point, i.e. the water level is proportional to the pressure difference between a fixed spot in the water column and the atmospheric pressure. [Based on 'Recording gauges' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Pressure-actuated recording gauge 356 Soil thermometer 194 None of the codes in the table are applicable in the context of this particular observation. inapplicable inapplicable Determination of water stage by means of a non-recording gauge (e.g., graduated vertical or inclined staff gauge, wire-weight gauge, graduated rod, tape or point gauge and maximum-stage gauge). [Based on 'Non-recording gauges' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Non-recording gauge 421 Measurement of soil capillary tension by means of a porous cup, inserted in the soil, connected to a manometer by a water-filled tube. [Based on 'tensiometer' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Tensiometer 200 Estimation of the total sediment in a water sample by allowing the sediment to settle in a container, siphoning off the supernatant water, carefully transferring all the sediment from the container on to filter paper, then drying the sample and determining the mass of total sediment. [Based on 'gravimetric method' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Gravimetric sediment measurement 371 Determination of gamma-ray attenuation at given depth of soil using a source and a detector placed at a given distance at the same depth. If the apparent dry bulk density of the soil is known the signal can be converted into a measure of the volumetric soil-moisture content. [Based on 'Gamma-ray attenuation' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Gamma-ray attenuation 347 Determination of the decrease of intensity of a visible light or X-rays beam by means of a photoelectric or nuclear detector situated at constant distance from the source of the beam. This decrease, caused by the scattering and/or absorption by suspended-sediment particles, is proportional to the sediment concentration, if other relevant characteristics of water and sediment (chemical, mineral composition, etc.) remain unchanged. [Based on 'photoelectric or nuclear suspended-sediment gauges' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Optical or nuclear suspended-sediment gauge 370 Measurement/observing method (terrestrial and hydrological) A process for measuring the discharge of a well, spring, or stream by diverting its flow into a volumetric container and timing the fill. Volumetric method 375 An empirical relationship relating bed-material discharge and streamflow based on correlation analysis of sediment samples and concurrent flow estimates and presented as a curve, table, or equation. [Based on 'sediment rating curve' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Water discharge-bed material rating curve 374 The measurement of velocities at the free surface of a moving water body using PIV (Particle Image Velocimetry) or LSPIV (Large Scale Particle Image Velocimetry) operates on the principle of statistical estimation of the displacement of groups of particles in consecutive images. The estimation is most-often made using cross-correlations applied to the spatial distribution of the light intensity defining the patterns (i.e., the pattern image) enclosed in small interrogation areas covering the whole image. The results of image processing is a velocity vector field centered on the interrogation area grid determined by dividing the estimated displacement with the time between images in the pair. Note: Given that LSPIV images cover large areas usually recorded from an oblique angle to the flow surface, an additional step is customarily involved, i.e. image orthorectification [Based on Aberle et al., Experimental Hydraulics: Instrumentation and Measurement Techniques, 2017 and Muste et al., Large-Scale Particle Image Velocimetry for Measurements in Riverine Environments, Special Issue on Hydrologic Measurements, Water Resources Research 44, 2008]. image velocimetry 381 Determination of the discharge of a stream by means of a device or structure across the stream which causes a free or submerged fall. [Based on 'measuring weir' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Measuring weir 361 The measurement/observing method is unknown. unknown unknown Determination of water stage by means of a fine cable or wire attached to a weight which is lowered to the water surface in order to determine its position below a fixed above-surface point. [Based on 'wire weight gauge' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Wire-weight gauge 351 Determination of water velocity by means of a current meter whose rotor is composed of a wheel fitted with cups turning on a vertical axis. [Based on 'cup-type current meter' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Cup-type current meter 365 Measurement of the difference in travel time of acoustic (ultrasonic) pulses between transducers in a stream to determine the mean velocity on the signal path. [Based on 'acoustic (ultrasonic) velocity meter' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Acoustic (ultrasonic) velocity meter 367 2024-01-02T17:12:42.505Z An instrument that uses an acoustic doppler transducer to measure water velocity, depth and vessel path simultaneously and at various depths to compute discharge. The total discharge is computed from the profile information using matrix multiplication. [Based on 'Acoustic Doppler Current Profilers' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Acoustic doppler current profiler (ADCP) 368 Measurement of the amount of water in soil by weighing a sample before and after drying it in an oven at a temperature of 100-110 degrees Celsius. [Based on 'gravimetric method' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Gravimetric moisture determination 126 Determination of water stage by means of a non-recording gauge (e.g., graduated vertical or inclined staff gauge, wire-weight gauge, graduated rod, tape or point gauge and maximum-stage gauge). [Based on 'Non-recording gauges' in Guide to Hydrological Practices (WMO-No. 168), Volume I. 2008 edition, updated in 2020.] Non-recording gauge 348 Determination of water stage by means of a graduated vertical scale, fixed to a staff or structure, on which the water level may be read. Synonym: vertical gauge. [Based on 'Staff gauge' in International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Staff gauge 422 Emission of a modulated beam of light in the visible spectrum to determine the distance to a target by comparing the phase information from the reflected beam. Laser ranging 344 Measurement of the velocity of a stream by means of timing the downstream transit of a float or velocity rod. [International Glossary of Hydrology (WMO-No. 385). 2012 edition.] Float gauging 358 Transmission of an ultrasonic pulse towards the target and listening for a return echo from that target. Ultrasonic ranging 260