Prepared in cooperation with the University of Iowa IIHR – Hydroscience and Engineering

Evaluation of the Ott Hydromet Qliner for Measuring 

Discharge in Laboratory and Field Conditions

Open-File Report 2015–1052

U.S. Department of the Interior

U.S. Geological Survey
Cover. Left and right photographs: Ott Hydromet Qliner field comparison data collection on the Cedar River at Cedar Rapids, Iowa 

(USGS streamgage 05464500), March 19, 2007. Center photograph: USGS personnel collecting Ott Hydromet Qliner 

comparison data on the Cedar River at Cedar Rapids, Iowa (USGS streamgage 05464500), March 19, 2007. 

Background photograph: Ott Hydromet Qliner field comparison data collection on the Cedar River at Cedar Rapids, Iowa 

(USGS streamgage 05464500), March 19, 2007. 

All photographs by Clint VanSchepen, USGS.
Evaluation of the Ott Hydromet Qliner for 

Measuring Discharge in Laboratory and 

Field Conditions

By Jason C. McVay

Prepared in cooperation with the University of Iowa IIHR – Hydroscience and 

Engineering

Open-File Report 2015–1052

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

McVay, J.C., 2015, Evaluation of the Ott Hydromet Qliner for measuring discharge in laboratory and field conditions: 

U.S. Geological Survey Open-File Report 2015–1052, 13 p., http://dx.doi.org/10.3133/ofr20151052.

ISSN 2331-1258 (online)
iii

Acknowledgments

The author would like to acknowledge the collaborative effort that took place with the University 

of Iowa IIHR – Hydroscience and Engineering, specifically Andy Craig and Dr. Marian Muste. 

The author also is grateful to the staff of the U.S. Geological Survey Iowa Water Science Center 

who collected field data for this study. The author also thanks Dave Mueller and Mike Rehmel of 

the U.S. Geological Survey Office of Surface Water for the review of this report.
iv

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope .......................................................................................................................................2

Methods...........................................................................................................................................................2

Laboratory Methods.............................................................................................................................2

Field Methods........................................................................................................................................5

Laboratory Quality-Control and Quality-Assurance Procedures..................................................5

Field Comparison Measurements Quality-Control and Quality-Assurance Procedures..........7

Laboratory Results.........................................................................................................................................7

Field Results..................................................................................................................................................10

Summary and Conclusions.........................................................................................................................13

References Cited..........................................................................................................................................13

Figures

1. Plan view of in-beam test series measurement setup...........................................................2

2. Schematic of the University of Iowa IIHR – Hydroscience and Engineering

Environmental Flow Facility ........................................................................................................3

3. Schematic of in-axis test series setup......................................................................................4

4. Map showing location of U.S. Geological Survey streamgages where comparison

measurements were collected...................................................................................................6

Tables

1. Specifications for the Ott Hydromet 1.0 megahertz Qliner and the Sontek 

16 megahertz MicroADV..............................................................................................................5

2. Selected field sites for collection of Qliner comparison discharge measurement 

data .................................................................................................................................................7

3. Dispersion of different exposure time Qliner velocities around the 100-minute 

mean velocity results with flume water depth of 1.98 meters...............................................8

4. Qliner in-axis comparison results with a flume water depth of 1.98 meters, 

water speed of 0.47 meters per second, and a 40-second exposure time .........................9

5. Qliner in-axis comparison results with a flume water depth of 1.98 meters, 

water speed of 0.47 meters per second, meters and a 5-minute exposure time...............9

6. Qliner in-beam comparison results with a flume water depth of 1.98 meters, 

water speed of 0.47 meters per second, and a 40-second exposure time .........................9

7. Qliner in-beam comparison results with a flume water depth of 1.98 meters, 

water speed of 0.47 meters per second, and a 5-minute exposure time ............................9

8. Qliner field discharge measurement percent differences from comparison

discharge measurements..........................................................................................................11

9. Field Qliner mean velocity, and mean depth measurement percent differences from

field comparison methods.........................................................................................................12
v

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

meter (m) 3.280 foot (ft)

Area

square meter (m2) 10.763 square foot (ft2)

Volume

cubic meter (m3) 35.314 cubic foot (ft3) 

Flow rate

meter per second (m/s) 3.280 foot per second (ft/s)

cubic meter per second (m3/s) 35.314 cubic foot per second (ft3/s)

Abbreviations

EFF IIHR Environmental Flow Facility

IA WSC Iowa Water Science Center

IIHR University of Iowa IIHR – Hydroscience and Engineering

kHz kilohertz

MHz megahertz

MicroADV Micro Acoustic Doppler Velocimeter

s seconds

TRDI Teledyne RD Instruments

USGS U.S. Geological Survey

Evaluation of the Ott Hydromet Qliner for Measuring 

Discharge in Laboratory and Field Conditions

By Jason C. McVay

Abstract

The U.S. Geological Survey, in collaboration with the 

University of Iowa IIHR – Hydroscience and Engineering, 

evaluated the use of the Ott Hydromet Qliner using laboratory flume tests along with field validation tests. Analysis 

of the flume testing indicates the velocities measured by the 

Qliner at a 40-second exposure time results in higher dispersion of velocities from the mean velocity of data collected 

with a 5-minute exposure time. The percent data spread from 

the mean of a 100-minute mean of Qliner velocities for a 

40-second exposure time averaged 16.6 percent for the entire 

vertical, and a 5-minute mean produced a 6.2 percent data 

spread from the 100-minute mean. This 16.6 percent variation 

in measured velocity would result in a 3.32 percent variation 

in computed discharge assuming 25 verticals while averaging 

4 bins in each vertical. The flume testing also provided results 

that indicate the blanking distance of 0.20 meters is acceptable when using beams 1 and 2, however beam 3 is negatively biased near the transducer and the 0.20-meter blanking 

distance is not sufficient. Field testing included comparing the 

measured discharge by the Qliner to the discharge measured 

by a Price AA mechanical current meter and a Teledyne RDI 

Rio Grande 1200 kilohertz acoustic Doppler current profiler. 

The field tests indicated a difference between the discharges 

measured with the Qliner and the field reference discharge 

between -14.0 and 8.0 percent; however the average percent 

difference for all 22 field comparisons was 0.22, which was 

not statistically significant.

Introduction

The U.S. Geological Survey (USGS) has historically 

used mechanical rotational current meters such as Price AA 

and pygmy meters to measure discharge. Many alternatives to 

these meters have been developed over the past 20 years, especially in the area of hydroacoustic technology. The USGS has 

been using hydroacoustic devices, specifically acoustic Doppler current profilers (ADCPs) attached to manned or tethered 

boats since the mid-1990s to measure discharge in a variety 

of conditions (Gotvald and Oberg, 2008). Acoustic Doppler 

current profilers measure discharge by profiling a cross-section 

of a channel for water depth and water velocity. This method 

for measuring discharge can be biased when data are collected 

during moving bed conditions (Mueller and others, 2013). 

The use of differential global positioning systems (GPS) is a 

reliable alternative to ADCP bottom-tracking data for determining boat speed when measuring discharge under moving 

bed conditions; however, conditions may exist when GPS and 

ADCP bottom track methods are not reliable and therefore, 

other alternative devices have been researched. 

One such device is the Qliner manufactured by Ott 

Hydromet (Ott Hydromet, 2006). The Qliner measures velocities passing through the vertical axis of the instrument while it 

is maintained in a stationary location. The Qliner is capable of 

averaging velocities from three beams to calculate discharge. 

Beams 1 and 2 are the primary beams used to determine the 

mean velocity. Beams 1 and 2 are orientated at an angle of 

25 degrees from a vertical position: this angle limits their 

ability to measure velocity in water less than 0.76 meters (m) 

(fig. 1). Beam 3 is orientated horizontally at a 20-degree angle 

and is an optional beam used in data collection that was developed to collect velocity data in water less than 0.76 m. The 

Qliner uses the mid-section method as described in Rantz and 

others (1982). The mid-section method is not biased by moving bed conditions because the ADCP is held stationary for 

each velocity measurement and the velocity measured by the 

ADCP is only water velocity (Oberg and others, 2005). Using 

this stationary deployment approach eliminates the biases 

created from moving bed conditions, because bottom tracking 

is not required to obtain the correct water velocity. 

To evaluate the Qliner for use in measuring discharge, 

the USGS, in cooperation with the University of Iowa 

IIHR – Hydroscience and Engineering (IIHR), completed 

laboratory flume testing and field testing with the device. The 

flume testing was used to evaluate the measured velocities 

using beams 1, 2 and 3, as well as to evaluate the use of the 

manufacturer default 0.20-m blanking distance (Nortek-as, 

2005). A Sontek MicroADV (Sontek a Xylem Brand, 2015) 

was used in the flume as the velocity reference instrument 

(Craig and Muste, 2009). The USGS made discharge measurements in the field using the Qliner, comparing the results to 

other discharge measurement devices.
2 Evaluation of the Ott Hydromet Qliner for Measuring Discharge in Laboratory and Field Conditions

Purpose and Scope

The purpose of this report is to document the use of the 

Qliner for making field measurements of velocity and discharge. The first objective was to determine the minimum 

blanking distance needed to alleviate any bias in velocity 

measurements caused by signal interference, instrument ringing, and flow disturbance. The second objective addressed in 

this report was to determine the applicability and conditions of 

use for inclusion of beam-3 velocity data. The third objective 

was to determine the appropriate exposure time needed for 

an accurate measurement of velocity for the use in discharge 

measurements. Several studies have investigated the importance of exposure time and the effects on uncertainty related 

to discharge measurement data collection. Three such studies 

that were used to validate the need to change the USGS policy 

on discharge data collection methods are described in USGS 

Office of Surface Water memorandum 2011.08 (U.S. Geological Survey, 2011). Finally, this report provides information 

regarding the comparability of Qliner discharge measurements 

with other researched discharge measurement data collection 

devices. Flume testing and field comparisons were used to 

document the applicability of using the Qliner as an appropriate device for discharge measurements. A previous study 

completed by the U.S. Bureau of Reclamation examined the 

Qliner in laboratory and field settings (Frizell and Vermeyen, 

2007). This report adds to the Reclamation study in further, by 

examining individual cells of velocity data measured by the 

Qliner as well as evaluating the Qliner in the field in natural 

channels.

Methods

This study consists of two principle components: 

controlled laboratory tests of the Qliner and collection of 

field data to compare data collected using the Qliner to data 

collected concurrently using other discharge measurement 

devices. The IIHR provided the controlled environment flume 

testing of the Qliner instrumentation at their research facility 

with equipment and guidance provided by the USGS IA WSC. 

The USGS IA WSC completed the Qliner field evaluation 

tests.

Laboratory Methods

The laboratory tests of the Qliner were carried out in 

the IIHR Environmental Flow Facility (EFF). The EFF is a 

recirculating nontilting flume that is 19.81 m long, 3.05 m 

wide and 2.29 m deep. The maximum flume flow capacity is 

3.54 cubic meters per second (m3/s) re-circulated through two 

0.91-m pipe lines. Because of the requirement for a freeboard 

of 0.3 m, the maximum depth of flow available for this study 

was 1.98 m. Additional information regarding the EFF is 

described in Craig and Muste (2009). The experimental test 

area of this study was located 4.27 m downstream from the 

raised floor section of the flume. A schematic of the flume and 

experiment location is shown in figure 2.

The Qliner and Sontek MicroADV were mounted inplace on a traverse across the top of the flume and were stationary throughout the laboratory portion of this study (fig. 3). 

Figure 1. Plan view of in-beam test series measurement setup (Craig and Muste, 2009).

Beam 3

Water surface

Qliner measurement/cell location

Acoustic Doppler Velocimeter measurement

EXPLANATION

Flume bed

Flow

Beam 1 Beam 2
Methods 

3

Figure 2. Schematic of the University of Iowa IIHR – Hydroscience and Engineering Environmental Flow Facility (Craig and Muste, 2009).

Flow

Flow

Flow

Water surface

Test section

B. Longitudinal along the centerline

Ramp

0.91 m 1.52 m 0.91 m

3.05 m

1.98 m

Concrete

masonry

units 2.54 cm raised

floor section

begins

2.41 m

1.23 m

0.51 m

0.51 m

0.61 m0.61 m

1.23 m

2.56 m 4.27 m

0.51 m

0.51 m

typ

0.51 m

typ

1.37 m 1.98 m 7.87 m

A. Plan view

Flow

Flow

Flow

Flow

EXPLANATION

Direction of water flowMetersCentimetersTypical spacing

m

cmtyp

Flow

0.61 m

typ
4 Evaluation of the Ott Hydromet Qliner for Measuring Discharge in Laboratory and Field Conditions

The measurements included in-axis (vertical) and in-beam 

measurements with the Qliner and MicroADV. The Qliner 

velocity measurements were compared with the MicroADV 

velocity measurements (Craig and Muste, 2009). 

A Qliner with a frequency of 1 megahertz (MHz) was 

used in this study. The high-resolution, high-frequency reference instrument for the study was a Sontek MicroADV with a 

frequency of 16 MHz. Specifications of each instrument used 

in the study are presented in table 1. The velocity data collected by the Qliner and MicroADV are comparable because 

both instruments calculate velocity data based on the Doppler 

principle as described in Simpson and Oltmann (1993). 

The first test completed was an in-axis evaluation of 

the velocities measured by the Qliner. In this test series, 

the MicroADV and Qliner velocity profiles were measured 

nonconcurrently at the centerline of the test section in 0.91-m, 

1.52-m, and 1.98-m depths (Craig and Muste, 2009). For each 

flow depth, five 5-minute measurements were made with the 

Qliner mounted to a rigid aluminum frame suspended from a 

traverse (Craig and Muste, 2009). For all tests, the minimum 

manufacturer recommended blanking distance (0.2 m) and 

minimum cell size (0.3 m) were selected (Craig and Muste, 

2009). The maximum depth setting was set to the actual flow 

depth plus one cell (0.3 m) for each set of measurements 

(Craig and Muste, 2009). The immersion depth was measured 

at 0.06 m. Sets of consecutive 40-second measurements were 

extracted from the 5-minute measurements in post-processing 

of the data for analysis (Craig and Muste, 2009). 

The second test was carried out as an in-beam evaluation 

of the velocities measured by the Qliner. The MicroADV measurements were made concurrently and located in the centroid 

of the Qliner velocity measurement cells in beams 1, 2 and 3. 

The MicroADV measurements were made along the projected 

beams of the Qliner (fig. 1). To avoid potential interference 

of the velocity data by concurrently collecting data during 

the in-beam test, the MicroADV was placed in the beam 3 

projected line while recording beam 1 and 2 data, and then the 

MicroADV was placed in the projected line of beams 1 and 2 

while collecting beam 3 data (Craig and Muste, 2009). Thus 

the accuracy of the comparisons of the MicroADV data and 

Figure 3. Schematic of in-axis test series setup (Craig and Muste, 2009).

Qliner boat assembly

Qliner probe

Acoustic Doppler Velocimeter (ADV)

Centimeters

Meters

cm

m

EXPLANATION

1.524 m

z

x

3.048 m

Flume wall

Flume wall

5 cm

Flow

Q-Liner and ADV traverse
Methods 5

Table 1. Specifications for the Ott Hydromet 1.0 megahertz Qliner and the Sontek 16 megahertz MicroADV.

[MHz, megahertz; m, meters; cm3, cubic centimeters; m/s, meters per second; +/-, plus or minus]

Velocity 

instrument

Transducer 

frequency 

(MHz)

Maximum 

water depth 

(m)

Cell size 

(cm3)

Minumum blanking 

distance 

(m)

Velocity 

measurement range 

(m/s)

Manufacturer stated 

accuracy 

(m/s)

Qlinera 1 20 variable 0.1c +/- 10 0.05

MicroADVb 16 60 0.09 0.05 0.001 to 2.5 0.025

a

Specification for the Ott Qliner are from Ott Hydromet (2006).

b

Specifications for the Sontek 16 MHz MicroADV (2005).

c

At the time of the study a minumum blanking distance of 0.2 m was the recommended specification (Nortek-as, 2005).

the Qliner data is dependent on the assumption that the average flume velocities were uniform for the selected averaging 

period for the in-beam and in-axis tests (5 minutes, 40 seconds). Additional information on the determination of these 

MicroADV measurement locations is described in Craig and 

Muste (2009). A total of 15 MicroADV measurements were 

made corresponding to the 15 Qliner measurement cell locations: 4 measurements in beam 1, 4 measurements in beam 2, 

and 7 measurements in beam 3 (Craig and Muste, 2009). The 

same Qliner settings were used during the in-beam test as 

were used in the in-axis test. A schematic of the in-beam tests 

is shown in figure 1. 

The final laboratory test completed was to determine if 

incorporating beam 3 into the calculation of the mean velocity produces a bias into a computed discharge measurement. 

This test was set up to simulate a discharge measurement 

within the flume setting. Within the flume, there was a known 

cross-sectional area based on the width and the depth of the 

water during this test. The reference mean velocity was determined using the 1/6 power law (Craig and Muste, 2009) being 

applied to the point velocity measurements collected with 

the MicroADV. The discharge data collected with the Qliner 

were processed within the Ott Hydromet software QReview 

version 2.19 (Ott Hydromet, 2007) and compared with the 

data collected using the MicroADV. The MicroADV velocity data were recorded using the software package Sontek 

HorizonADV (Craig and Muste, 2009). The MicroADV discharge calculations were made using Microsoft Excel (Microsoft, 2007). 

Field Methods

The field sites were selected at USGS streamgages in 

Iowa that had stable controls and historically have discharge 

measurements that result in small deviations from the base 

stage-discharge relation for the site location. The objective 

for selecting sites was to minimize the effect of the channel 

conditions on the results of the discharge measurement data 

collected. A total of 11 different sites (fig. 4) having varying 

sizes of drainage areas within Iowa were used to collect the 

comparison measurement data (table 2). 

Field evaluation of the calculation of discharge was 

completed by USGS personnel following USGS discharge 

measurement policies that were in place during the time of 

data collection. Field methods used were based on guidance 

from the USGS Office of Surface Water Technical Memorandum and reports released before August 2008 (Rantz and 

others, 1982; U.S. Geological Survey, 2002; and U.S. Geological Survey, 2005). Field data collected using the Qliner 

followed USGS policy regarding mid-section measurements. 

This included an exposure time of 40 seconds per vertical as 

described in Rantz and others (1982).

There were 22 comparison measurements made between 

February 1, 2006, and August 13, 2008. The comparison 

discharge measurements were made with Price AA mechanical meters as described in Rantz and others (1982) or with a 

Teledyne RDI Rio Grande 1200 kilohertz (kHz) ADCP using 

the moving boat method described in USGS Office of Surface 

Water Technical Memorandum 2002.02 (U.S. Geological 

Survey, 2002) and in Oberg and others (2005).

Laboratory Quality-Control and QualityAssurance Procedures

Laboratory quality-control and quality-assurance procedures were created to provide a testing environment that would 

produce unbiased results. The IIHR personnel completed 

several quality-assurance and quality-control tests before and 

during the flume study. The initial quality-assurance test was 

to evaluate the reference instrument (MicroADV) velocity by 

comparison against a laser Doppler velocimeter before deploying the MicroADV as the reference velocity method for this 

study. The results for this test verified the velocity measurements collected with the MicroADV (Craig and Muste, 2009). 

Secondly to verify the flow in the flume within the area of the 
6 Evaluation of the Ott Hydromet Qliner for Measuring Discharge in Laboratory and Field Conditions

Qliner was free from pulsating and variable velocities, the 

flow was evaluated though a series of measurements made 

with the MicroADV and the Qliner. The results from this testing verified that the flow did not show pulsating or varying 

velocities throughout the footprint of the Qliner (Craig and 

Muste, 2009). 

The next quality-assurance test completed was to verify 

that the velocity measurements made by the Qliner were not 

affected by the flume environment. The test was created to 

compare similar velocity and depth measurements for a field 

environment to the same conditions in the flume. The Qliner 

data collected in the field were 10 consecutive 5-minute 

stationary measurements of velocity and depth. These field 

data were collected by USGS and IIHR staff at the USGS 

streamgage Iowa River at Iowa City, IA (05454500). The 

flume environment was then set up to reproduce the same 

velocity and depth observed during the field data collection. 

The computed errors and scattering were comparable for 

the field, and therefore indicated there was no interference 

between the Qliner and flume (Craig and Muste, 2009). 

Lastly, to eliminate any potential errors that may be 

attributed to an improperly functioning Qliner, a second Qliner 

was used to perform the same tests as the initial Qliner. The 

second Qliner in this test was a similar profiler with the same 

frequency as the initial Qliner. The two Qliners demonstrated 

comparable behavior in terms of deviations from the reference 

profile. The results of this test are reported in Craig and Muste 

(2009).

Figure 4. Location of U.S. Geological Survey streamgages where comparison measurements were collected.

0 50 100 MILES

0 50 100 KILOMETERS

IOWA

ILLINOIS

MISSOURI

NEBRASKA

WISCONSIN

MINNESOTA

SOUTH DAKOTA

96° 95° 94° 93° 92° 91° 90°

43°

42°

41°

06607500

05476750

05449500

05421740

05464500

05453100

05488110

05454500

05455700

05473450

Base from U.S. Geological Survey digital data,

2005–2012, various scales

Universal Transverse Mercator, Zone 15

North American Datum of 1983

05489500

Streamgage and station number

EXPLANATION

05489500
Laboratory Results 7

Field Comparison Measurements QualityControl and Quality-Assurance Procedures

The quality-control and quality-assurance methods used 

for the comparison testing of the Qliner field-computed discharge are similar to those used by the USGS for testing other 

acoustic instrumentation. These methods were developed from 

previously developed USGS test plans for acoustic instrumentation as discussed in the USGS Office of Surface Water Technical Memorandum 2005.05 (U.S. Geological Survey, 2005).

Two methods were used to compare the discharge measured by the Qliner. These methods were a comparison to a 

Price AA mechanical current meter measurement or a comparison with a Rio Grande 1200 kHz ADCP acoustic measurement device used by the USGS. The comparison method 

used was determined on the availability of equipment to 

collect data. When a mechanical meter was used, mid-section 

measurement techniques described in Rantz and others (1982) 

were followed. Measurements with a Rio Grande 1200 kHz 

ADCP followed methods described in USGS Office of Surface 

Water Technical Memorandum 2002.02 (U.S. Geological 

Survey, 2002) and in Oberg and others (2005). Measurements 

with either a mechanical current meter or an acoustic device 

were made as close as possible in time to the Qliner measurement at the same location.

Laboratory Results

The laboratory results used in this report document the 

comparability of the velocities collected by the Qliner to the 

reference velocity from the MicroADV. The dispersion of the 

velocities around the mean collected by the Qliner in the flume 

also was analyzed.

From the comparative analysis, several important 

objectives described in the Purpose and Scope section were 

addressed. The first of which was analyzing potential flow 

disturbance around the transducers to determine a minimum 

blanking distance for the Qliner. The results indicated that for 

beams 1 and 2, a blanking distance of 0.20 m was sufficient 

because the first cell reported (0.58 m) for the collection of 

velocity data was beyond the area of flow disturbance from 

the Qliner hull. Because of the bin size and angle of beam 1 

and 2, the first velocity cell is collected outside of the area 

affected by the hull. However, beam 3 collects data closer to 

the hull of the Qliner; with a 0.20 m blanking distance, beam 3 

reports the first cell at 0.26 m which is not sufficient resulting 

in a low bias in the near surface cells. If beam 3 is included 

in the collection of the velocity data, the overall velocity data 

would be negatively biased. This increased effect from the hull 

is attributed to the bin size and angle orientation of beam 3 on 

the transducer of the Qliner as beam 3 is collecting data closer 

to the hull. 

The raw velocity data from the Qliner also were analyzed 

to determine an optimum exposure time for reporting velocity in the use of discharge measurement calculations. Data 

collected for the flume velocity validation quality-assurance 

test were also used to analyze the dispersion of the velocities 

collected by the Qliner. Velocity data were collected for a total 

of 100 minutes and the mean velocity from this 100-minute 

average was used as the true velocity in the calculation of 

percent data spread, which is also known as coefficient of 

variation. The data were then separated into 5-minute and 

40-second exposure times. The standard deviation of the 

Qliner velocity data from each bin in the profile for each of 

Table 2. Selected field sites for collection of Qliner comparison discharge measurement data.

[USGS, U.S. Geological Survey; km2, square kilometers]

USGS streamgage number 

(fig. 4) USGS streamgage name Drainage area (km2)

Number of 

comparisons made

05489500 Des Moines River at Ottumwa, Iowa 8,739 1

05453100 Iowa River at Marengo, Iowa 7,236 1

05473450 Big Creek North of Mt. Pleasant, Iowa 150 1

05454500 Iowa River at Iowa City, Iowa 8,472 7

05464500 Cedar River at Cedar Rapids, Iowa 16,860 1

05421740 Wapsipinicon River near, Anamosa, Iowa 4,079 1

05476750 Des Moines River at Humbolt, Iowa 5,843 1

05449500 Iowa River near Rowan, Iowa 1,111 1

05488110 Des Moines River near Pella, Iowa 31,934 1

05455700 Iowa River near Lone Tree, Iowa 11,118 1

06607500 Little Sioux River near Turin, Iowa 9,132 6
8 Evaluation of the Ott Hydromet Qliner for Measuring Discharge in Laboratory and Field Conditions

these 5-minute and 40-second exposure times was determined 

(Helsel and Hirsch, 2002). This standard deviation was then 

divided by the 100-minute mean velocity to determine the 

percent data spread. The results presented in table 3 verify that 

the shorter exposure time results in a higher dispersion from 

the 100-minute mean velocity. The mean percent data spread 

of all of the bins collected in the profile for the 40-second data 

was 16.6 percent, as compared to the mean percent data spread 

of 6.2 percent for the 5-minute data. 

Furthermore, a random error was calculated from the 

mean percent data to associate the variation in velocity to the 

data collected during a mid-section discharge measurement. 

A typical USGS mid-section measurement would contain at 

least 25 verticals while collecting velocities for 40 seconds at 

each vertical (Rehmel, 2007). A random error associated with 

the velocities collected by the Qliner can be calculated by 

dividing the mean percent data spread by the square root of the 

number of verticals or samples. A random error or uncertainty 

of 3.32 percent from a 100-minute mean Qliner velocity can 

be expected when collecting 25 verticals with a 40-second 

exposure time for each vertical. 

The comparisons made between the Qliner and the 

MicroADV during the in-axis laboratory tests also indicated 

that a longer exposure time will result in Qliner mean velocities with less dispersion from the mean MicroADV velocity. 

The results from the in-axis tests were similar to the in-beam 

tests. The results from the in-axis test at a depth of 1.98 m 

and a velocity of 0.47 m/s are presented in tables 4 and 5. 

The results in table 4 indicate that when the Qliner velocity 

data are collected using a 40-second exposure time, the mean 

percent data spread from the mean MicroADV velocity is 

20.3 percent. The results in table 5 indicate that when exposure time is increased to 5 minutes, the mean percent data 

spread between the Qliner and the MicroADV decreases to 

6.6 percent.

The in-beam tests also indicate a longer exposure time 

would be needed for the collection of more precise velocity 

data with the Qliner. The in-beam testing results provided 

similar percent differences as the in-axis tests. The data show 

that a longer exposure time will decrease the variability in 

the velocity data and result in a more precise measurement 

of the velocity. The results of the 40-second exposure time 

resulted in a mean percent data spread from the MicroADV 

of 21.1 percent (table 6). The results of the 5-minute exposure 

time resulted in a mean percent data spread of 6.2 percent 

(table 7). 

The in-beam and in-axis tests revealed that a longer exposure time would result in less variation in velocity. Table 3 also 

shows a larger variation in velocity when collecting velocity 

data over a shorter averaging period. This increased variation 

associated with shorter averaging periods would indicate that 

there are fluctuations in flow caused by turbulence found in 

a natural flow environment over a period longer than 40 seconds. However, when averaged over the vertical and assuming 

that 25 verticals are collected during a typical mid-section 

discharge measurement, the variation in measured discharge 

would be on the order of plus or minus 3.32 percent. Despite 

the fact that there are large differences in the sample volume 

between the Qliner and the MicroADV, the results of a similar 

comparison indicated only slightly larger variation in the 

velocities when used in a mid-section discharge measurement.

Table 3. Dispersion of different exposure time Qliner velocities around the 100-minute mean velocity results with flume water depth of 

1.98 meters.

[m, meters; m/s, meters per second]

Bin depth 

(m)

Beams 

tested

Qliner 

100-minute 

mean velocity 

(m/s)

Qliner percent data 

spread from the 

100-minute mean 

velocity 

(5-minute 

exposure time)

Qliner percent data 

spread from the 

100-minute mean 

velocity 

(40-second 

exposure time)

Percent data spread 

random error when 

collecting 25 verticals 

(5-minute 

exposure time)

Percent data spread 

random error when 

collecting 25 verticals 

(40-second 

exposure time)

0.59 1, 2 0.451 5.9 13.6 1.17 2.72

0.89 1, 2 0.440 5.9 19.5 1.18 3.90

1.19 1, 2 0.415 7.5 20.4 1.49 4.08

1.49 1, 2 0.383 5.6 12.8 1.12 2.56

Mean 6.2 16.6 1.24 3.32
Laboratory Results 9

Table 4. Qliner in-axis comparison results with a flume water depth of 1.98 meters, water speed of 0.47 meters per second, and a 

40-second exposure time.

[m, meters; m/s, meters per second]

Bin depth 

(m)

Beams 

tested

MicroADV velocity 

(m/s) Depth cell Maximum percent difference from MicroADV

Qliner mean percent data spread from 

the MicroADV mean velocity

0.59 1, 2 0.473 1 24.9 18.5

0.89 1, 2 0.462 2 -18.2 12.8

1.19 1, 2 0.442 3 -47.2 25.4

1.49 1, 2 0.386 4 -28.0 24.4

Mean 20.3

Table 5. Qliner in-axis comparison results with a flume water depth of 1.98 meters, water speed of 0.47 meters per second, meters and 

a 5-minute exposure time.

[m, meters; m/s, meters per second]

Bin depth 

(m)

Beams 

tested

MicroADV velocity 

(m/s) Depth cell Maximum percent difference from MicroADV

Qliner mean percent data spread from 

the MicroADV mean velocity

0.59 1, 2 0.473 1 -16.5 7.1

0.89 1, 2 0.462 2 -13.6 6.0

1.19 1, 2 0.442 3 -17.5 7.3

1.49 1, 2 0.386 4 7.8 6.1

Mean 6.6

Table 6. Qliner in-beam comparison results with a flume water depth of 1.98 meters, water speed of 0.47 meters per second, and a 

40-second exposure time.

[m, meters; m/s, meters per second]

Bin depth 

(m)

Beams 

tested

MicroADV velocity 

(m/s) Depth cell Maximum percent difference from MicroADV

Qliner mean percent data spread from 

the MicroADV mean velocity

0.59 1, 2 0.440 1 -30.9 15.1

0.89 1, 2 0.431 2 28.2 19.8

1.19 1, 2 0.406 3 -40.4 27.9

1.49 1, 2 0.373 4 37.1 21.6

Mean 21.1

Table 7. Qliner in-beam comparison results with a flume water depth of 1.98 meters, water speed of 0.47 meters per second, and a 

5-minute exposure time.

[m, meters; m/s, meters per second]

Bin depth 

(m)

Beams 

tested

MicroADV velocity 

(m/s) Depth cell Maximum percent difference from MicroADV

Qliner mean percent data spread from 

the MicroADV mean velocity

0.59 1, 2 0.440 1 10.6 5.4

0.89 1, 2 0.431 2 11.8 5.8

1.19 1, 2 0.406 3 13.1 6.4

1.49 1, 2 0.373 4 22.1 7.3

Mean 6.2
10 Evaluation of the Ott Hydromet Qliner for Measuring Discharge in Laboratory and Field Conditions

Field Results

The comparison discharge measurements collected during the field testing period indicated a range in percent difference from the comparison method between -14.0 percent and 

8.0 percent (table 8), and the standard deviation was 5.15 percent. The mean percent difference was 0.22 percent from the 

comparison discharge measurements, and the median percent 

difference was 0.89 percent. Calculations were made using the 

data located in table 8. All of the comparison data collected 

during February 2006 to August 2008 were used in the comparison analysis. Two measurements made in January 2006 

and November 2006 with the Qliner were not used because of 

early software problems. Qliner software problems resulted in 

significant differences between the discharge computed by the 

data collection software used in the field and the software that 

is used in post-processing the data. Updated software versions 

were developed by the vendor (C. Meijer, written commun., 

2006), and these differences were not observed in any of the 

measurements collected from February 2006 to August 2008. 

Mean velocity and depth data also were used to 

evaluate the Qliner for the collection of discharge measurements (table 9). The range of percent differences from the 

comparison method of mean velocity was -10.22 percent to 

15.21 percent, with a standard deviation of 6.92. The velocity comparison data mean percent difference was 1.82, and 

the median was 1.29 percent different. The range of percent 

difference from the comparison method of mean depth was 

-11.69 percent to 16.81 percent, with a standard deviation of 

6.30. The Qliner mean depth data had a mean percent difference of 0.70 with a median percent difference of -0.04. 

A statistical analysis comparing the Qliner measured 

discharge with the comparison measured discharge was 

completed using a t-test to determine if the mean discharges 

from each device were statistically different. An f-test was 

computed to determine if the discharges from each device had 

equal variances. The f-test indicated the variances are equal. A 

two-sample t-test of equal variances was completed. A p-value 

threshold of 5 percent was used in this evaluation for the 

two-sample t-test. A p-value greater than 5 percent indicates 

the means of the two sample sets are not statistically different. 

The t-test results, p-value greater than 5 percent, indicated the 

mean discharge of the Qliner measurements was not statistically different than the comparison measurement, (Helsel and 

Hirsch, 2002). 
Field Results 11

Table 8. Qliner field discharge measurement percent differences from comparison discharge measurements.[USGS, U.S. Geological Survey; m3/s, meters per second; TRDI; Teledyne RD Instruments; kHz, kilohertz]

Date

USGS 

streamgage 

number 

(fig. 4)

USGS streamgage name Qliner discharge (m3/s) Comparison discharge (m3/s) Comparison method device Percent difference from comparison method

2/1/2006 05489500 Des Moines River at Ottumwa, Iowa 103 101 TRDI Rio Grande 1200 kHz 2.8

3/10/2006 05453100 Iowa River near Marengo, Iowa 33.1 38.5 TRDI Rio Grande 1200 kHz -14.03/13/2006 05473450 Big Creek North of Mt. Pleasant, Iowa 24.9 26.0 Price AA -4.29/26/2006 05454500 Iowa River at Iowa City, Iowa 28.6 29.0 Price AA -1.49/26/2006 05454500 Iowa River at Iowa City, Iowa 28.0 28.6 Price AA -2.09/26/2006 05454500 Iowa River at Iowa City, Iowa 28.6 29.2 TRDI Rio Grande 1200 kHz -1.99/26/2006 05454500 Iowa River at Iowa City, Iowa 28.0 29.2 TRDI Rio Grande 1200 kHz -3.99/26/2006 05454500 Iowa River at Iowa City, Iowa 28.6 29.4 TRDI Rio Grande 1200 kHz -2.99/26/2006 05454500 Iowa River at Iowa City, Iowa 28.0 29.4 TRDI Rio Grande 1200 kHz -4.83/19/2007 05464500 Cedar River at Cedar Rapids, Iowa 17.2 16.6 TRDI Rio Grande 1200 kHz 3.43/19/2007 05421740 Wapsipinicon River near Anamosa, Iowa 142 150 TRDI Rio Grande 1200 kHz -5.13/21/2007 05476750 Des Moines River at Humbolt, Iowa 182 169 TRDI Rio Grande 1200 kHz 7.93/21/2007 05449500 Iowa River at Rowan, Iowa 33.7 32.3 TRDI Rio Grande 1200 kHz 4.53/28/2007 05488110 Des Moines River near Pella, Iowa 651 660 TRDI Rio Grande 1200 kHz -1.3

4/9/2007 05454500 Iowa River at Iowa City, Iowa 215 207 TRDI Rio Grande 1200 kHz 3.74/9/2007 05455700 Iowa River at Lone Tree, Iowa 225 220 TRDI Rio Grande 1200 kHz 2.6

8/13/2008 06607500 Little Sioux River near Turin, Iowa 32.6 31.7 Price AA 2.78/13/2008 06607500 Little Sioux River near Turin, Iowa 31.1 31.7 Price AA -1.88/13/2008 06607500 Little Sioux River near Turin, Iowa 34.3 31.7 Price AA 8.08/13/2008 06607500 Little Sioux River near Turin, Iowa 34.0 31.7 Price AA 7.18/13/2008 06607500 Little Sioux River near Turin, Iowa 32.3 31.7 Price AA 1.88/13/2008 06607500 Little Sioux River near Turin, Iowa 32.8 31.7 Price AA 3.6

Mean 0.22
12 Evaluation of the Ott Hydromet Qliner for Measuring Discharge in Laboratory and Field Conditions Table 9. Field Qliner mean velocity, and mean depth measurement percent differences from field comparison methods. [USGS, U.S. Geological Survey; m, meters; m/s, meters per second; TRDI, Teledyne RD Instruments; kHz, kilohertz] Date USGS streamgage number (fig. 4) USGS streamgage name Comparison method device Qliner mean depth (m) Comparsion method mean depth (m) Percent difference of comparison method Qliner mean veloctiy (m/s) Comparsion method mean velocity (m/s) Percent dif- ference from comparison method 2/1/2006 05489500 Des Moines River at Ottumwa, Iowa TRDI Rio Grande 1200 kHz 0.83 0.88 -5.55 0.54 0.48 10.74 3/10/2006 05453100 Iowa River near Marengo, Iowa TRDI Rio Grande 1200 kHz 0.81 0.84 -4.03 0.51 0.57 -9.35 3/13/2006 05473450 Big Creek North of Mt. Pleasant, Iowa Price AA 1.52 1.72 -11.69 1.05 0.91 15.21 9/26/2006 05454500 Iowa River at Iowa City, Iowa Price AA 0.90 0.88 3.20 0.55 0.55 0.18 9/26/2006 05454500 Iowa River at Iowa City, Iowa Price AA 1.00 0.88 13.83 0.49 0.55 -10.22 9/26/2006 05454500 Iowa River at Iowa City, Iowa TRDI Rio Grande 1200 kHz 0.90 0.93 -2.90 0.55 0.54 1.29 9/26/2006 05454500 Iowa River at Iowa City, Iowa TRDI Rio Grande 1200 kHz 1.00 0.93 7.10 0.49 0.54 -9.23 9/26/2006 05454500 Iowa River at Iowa City, Iowa TRDI Rio Grande 1200 kHz 0.90 0.95 -5.35 0.55 0.53 3.58 9/26/2006 05454500 Iowa River at Iowa City, Iowa TRDI Rio Grande 1200 kHz 1.00 0.95 4.40 0.49 0.53 -7.17 3/19/2007 05464500 Cedar River at Cedar Rapids, Iowa TRDI Rio Grande 1200 kHz 3.11 2.95 5.42 1.20 1.19 0.50 3/19/2007 05421740 Wapsipinicon River near Anamosa, Iowa TRDI Rio Grande 1200 kHz 2.24 2.31 -3.07 1.02 0.89 14.22 3/21/2007 05476750 Des Moines River at Humbolt, Iowa TRDI Rio Grande 1200 kHz 2.35 2.29 2.75 1.28 1.17 9.06 3/21/2007 05449500 Iowa River at Rowan, Iowa TRDI Rio Grande 1200 kHz 1.68 1.64 2.13 0.44 0.43 2.09 3/28/2007 05488110 Des Moines River near Pella, Iowa TRDI Rio Grande 1200 kHz 4.45 4.45 -0.04 1.12 1.07 4.77 4/9/2007 05454500 Iowa River at Iowa City, Iowa TRDI Rio Grande 1200 kHz 3.19 2.73 16.81 0.95 0.90 4.87 4/9/2007 05455700 Iowa River at Lone Tree, Iowa TRDI Rio Grande 1200 kHz 1.94 1.94 0.15 0.86 0.83 3.25

8/13/2008 06607500 Little Sioux River near Turin, Iowa Price AA 1.17 1.17 0.00 0.60 0.61 -0.508/13/2008 06607500 Little Sioux River near Turin, Iowa Price AA 1.16 1.17 -0.85 0.59 0.61 -3.478/13/2008 06607500 Little Sioux River near Turin, Iowa Price AA 1.16 1.17 -0.85 0.65 0.61 7.108/13/2008 06607500 Little Sioux River near Turin, Iowa Price AA 1.12 1.17 -4.27 0.60 0.61 -0.508/13/2008 06607500 Little Sioux River near Turin, Iowa Price AA 1.16 1.17 -0.85 0.60 0.61 -0.508/13/2008 06607500 Little Sioux River near Turin, Iowa Price AA 1.16 1.17 -0.85 0.63 0.61 4.13

Mean depth (percent difference) 0.70 Mean velocity (percent difference) 1.82
References Cited 13

Summary and Conclusions

The U.S. Geological Survey, in cooperation with the 

University of Iowa IIHR – Hydroscience and Engineering, 

evaluated the use of the Ott Hydromet Qliner in laboratory 

and field conditions. The laboratory testing determined that 

a 0.20-m blanking distance is sufficient when using beams 1 

and 2; when including beam 3, a 0.20-m blanking distance can 

produce a negatively biased discharge as beam 3 is measuring 

unnatural flow disturbance caused by the hull directly in the 

data collection zone. At the time of this study, the ability for 

the user to set a blanking distance for beam 3 separate from 

beams 1 and 2 was not available. 

Another important result of this study was the determination of the variability and uncertainty in the Qliner velocity data. The laboratory testing indicated that the velocities 

measured by the Qliner at a 40-second exposure time results 

in a higher dispersion from the mean velocity of data collected with a 5-minute exposure time. The Qliner velocity 

data resulted in a mean percent data spread from a 100-minute mean Qliner velocity of 16.6 percent. This 16.6 percent 

variation in measured velocity would result in a 3.32 percent 

variation in computed discharge assuming 25 verticals while 

averaging 4 bins in each vertical.

The Qliner discharge field data collected during this study 

did not display any biases or significant deviations from the 

field comparison measurements. The mean percent difference 

between the Qliner measured discharge and the comparison 

discharge was 0.22, with a range of percent differences from 

-14.0 and 8.0. Field discharge measurement comparisons verified that the variability in the Qliner velocities for a typical 25 

vertical mid-section measurement is less than a single vertical 

measurement of velocity. 

References Cited

Craig, A., and Muste, M., 2009, Experimental evaluation 

of the Qliner measurement performance: IIHR Technical 

Report Series no. 485. [Also available at http://www.iihr.

uiowa.edu/wp-content/uploads/2014/05/TR485.pdf.]

Frizell, K.W., and Vermeyen, T.B., 2007, Comparing apples 

and oranges—Teledyne/RDI StreamPro ADCP and the Ott 

Qliner river discharge measurement system: U.S Bureau of 

Reclamation PAP-0965, 5 p., at http://www.usbr.gov/pmts/

hydraulics_lab/pubs/PAP/PAP-0965.pdf.

Gotvald, A.J., and Oberg, K.A., 2008, Acoustic Doppler current profiler applications used in river and estuaries by the 

U.S Geological Survey: U.S. Geological Survey Fact Sheet 

2008–3096, 4 p.

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 3, chap. A3, 522 p.

Microsoft, 2007, Microsoft Excel for Windows 2007.

Mueller, D.S., Wagner, C.R., Rehmel, M.S., Oberg, K.A, 

and Rainville, Francois, 2013, Measuring discharge with 

acoustic Doppler current profilers from a moving boat 

(ver. 2.0, December 2013): U.S. Geological Survey Techniques and Methods, book 3, chap. A22, 95 p., http://dx.doi.

org/10.3133/tm3A22.

Nortek-as, 2005, Aquadopp Profiler specifications brochure, 

2 p. 

Oberg, K.A., Morlock, S.E., and Caldwell, W.S., 2005, Quality 

assurance plan for discharge measurements using acoustic 

Doppler current profilers: U.S. Geological Survey Scientific 

Investigations Report 2005–5183, 35 p.

Ott Hydromet, 2006, Operating instruction mobile river 

discharge measurement system Ott Qliner, 70 p.

Ott Hydromet, 2007, Q-Review for Windows user manual 

v2.1, 11 p.

Rantz, S.E., and others, 1982, Measurement and computation of streamflow, volume 1, Measurement of discharge: 

U.S. Geological Survey Water-Supply Paper 2175, 631 p. 

Rehmel, M., 2007, Application of acoustic doppler velocimeters for streamflow measurements: Journal of Hydraulic 

Engineering, v. 133, no. 12, p. 1433–1438.

Simpson, M.R., Oltmann, R.N., 1993, Discharge measurement system using an acoustic Doppler current profiler with 

applications to large rivers and estuaries: U.S. Geological 

Survey Water-Supply Paper 2395, 32 p. [Also available at 

http://pubs.usgs.gov/wsp/wsp2395/.]

Sontek a Xylem Brand (2015), 16-MHZ MicroADV specifications Web page: accessed February 9, 2015, at http://www.

sontek.com/productsdetail.php?16-MHz-MicroADV-3.

U.S. Geological Survey, 2002, Policy and technical guidance 

on discharge measurements using acoustic Doppler current 

profilers: Office of Surface Water Technical Memorandum 

2002.02.

U.S. Geological Survey, 2005, Guidance on the use of RD 

Instruments StreamPro Acoustic Doppler Profiler: Office of 

Surface Water Technical Memorandum 2005.05.

U.S. Geological Survey, 2011, Exposure time for ADCP 

moving-boat discharge measurements made during steady 

flow conditions: Office of Surface Water Technical Memorandum 2011.08.
Publishing support provided by: 

Rolla Publishing Service Center

For more information concerning this publication, contact: 

Director, USGS Iowa Water Science Center 

P.O. Box 1230 

Iowa City, IA 52244 

(319) 337–4191

Or visit the Iowa Water Science Center Web site at: 

http://ia.water.usgs.gov/

McVay—Evaluation of the Ott Hydromet Qliner for Measuring Discharge in Laboratory and Field Conditions—Open-File Report 2015–1052

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20151052