Hydrometry: Field Manual, Field Application of ADCP Volume-4 Part V 2003

Government of India & Government of The Netherlands
DHV CONSULTANTS &
DELFT HYDRAULICS with
HALCROW, TAHAL, CES,
ORG & JPS
VOLUME 4
HYDROMETRY
FIELD MANUAL - PART V
FIELD APPLICATION OF ADCP

Field Manual – Hydrometry (SW) Volume 4 – Part V
Table of Contents
GENERAL 1
1 INTRODUCTION 2
2 OPERATING MODES AND SITE CONDITIONS 2
3 DEPLOYMENT 5
4 OPERATING SET-UP 5
5 MEASUREMENT RUNS 7
6 DATA HANDLING AND RECORDING 8
Hydrometry January 2003 Page i

GENERAL
The Field Manual on Hydrometry, comprises the procedures to be carried out to ensure proper
execution of design of the hydrometric network, and operation and maintenance of water level and
streamflow gauging stations. The operational procedures are tuned to the task descriptions prepared
for each Hydrological Information System (HIS) function. The task description for each HIS-function is
presented in Volume 1 of the Field Manual.
It is essential, that the procedures, described in the Manual, are closely followed to create uniformity
in the field operations, which is the first step to arrive at comparable hydrological data of high quality.
Further, reference is made to the other volumes of the manual where hydro-meteorology, sediment
transport measurements and water quality sampling and analysis is described. It is stressed that
hydrometry cannot be seen in isolation; in the HIS integration of networks and of activities is a must.
This Volume of the Field Manual consists of 8 parts:
• Part I deals with the steps to be taken for network design and optimisation. Furthermore, site
selection procedures are included, tuned to the suitability of a site for specific measurement
procedures.
• Part II comprises operation of water level gauging stations equipped with staff gauges,
autographic chart recorders or digital water level recorders.
• Part III comprises the preparatory activities and execution of float measurements, including
selection of float type, reach preparation, observation practice and discharge computation
• Part IV comprises the preparatory activities and execution of current meter measurements by
wading, and from cableways, bridges and boats. The procedure for discharge computation is
included.
• Part V deals with the field application of the Acoustic Doppler Current Profiler (ADCP). It covers
operating modes and site conditions, deployment, operating set-up and measurement runs as
well as the data handling and recording.
• Part VI presents the required activities for the execution of the Slope-Area Method and the
procedure to be applied to arrive at a discharge.
• Part VII comprises Field Inspections and Audits, with required check lists and standard forms.
• Part VIII, finally, deals with routine maintenance of gauging stations and calibration of equipment.
The procedures as listed out in this manual are in concurrence with the ISO standards as far as
available for the various techniques and applicable to the conditions in peninsular India.
Hydrometry January 2003 Page 1

1 INTRODUCTION
The principles of operation of the Acoustic Doppler Current Profiler (ADCP) are described in Chapter
6 of Volume 4, Design Manual, Hydrometry. Though several systems are on the market now, the
majority of operating experience in river flow applications has been obtained with RDI Broadband and
Workhorse systems. The RDI Workhorse is the successor of the Broadband models. The RDI Rio
Grande is a model of the Workhorse series specifically developed for flow measurements on rivers.
Recently also ADP instruments - manufactured SonTek - became available for flow measurement in
rivers. The ADP 1000 has been purchased by the Central Water Commission. Therefore the
suggested observation practices laid out in this section of the manual are in some instances specific
to the SonTek system.
The ADCP is a high tech, sophisticated and rather costly flow measurement device. This has the following
implications:
1. Staff with a high level of technical ability and computer literacy are required to operate the
equipment;
2. Even though the ADCP itself is fairly rugged, the transducers can be seriously damaged if they
are struck by a submerged, hard object such as a rock or tree trunk. Also, the associated laptop
PC required to download the data is often not really suitable for use in harsh operating
environments. Therefore the ADCP and its associated equipment has to be handled with care;
3. In view of the specialist nature of the equipment and its high capital cost, the technique is only
suitable for special sites where the value of the collected data is extremely high e.g. major rivers
at inter-State boundary or larger tidal reaches; when results are required quickly and for special
studies where the vector averaging and / or high detail is of importance.
4. If there are several important sites in close proximity of each other consideration should be given
to having a mobile team which can move from site to site with the ADCP.
2 OPERATING MODES AND SITE CONDITIONS
RDI ADCP
The RDI ADCP has several operating modes, which can be selected via the lap-top. The selection of
the most appropriate operating mode is dependent on site conditions. The selection of operating
modes is referred to briefly in the following sections of the manual. However, for detail the potential
user should refer to the manufacturer’s user manual.
Example:
The 600 kHz and 1200 kHz, 200 RDI Broadband systems have four operating modes i.e. modes 1, 4,
5 and 8.
A comparison of these different operating modes which has been taken from the manufacturers user
manual is contained in Table 1:
The major site constraint on the use of the ADCP is the channel depth
• Operating mode 1 only functions in depths greater than 1.0 m;
• Operating mode 4 only functions in depths greater than 3 m;
• Operating mode 5 only functions in depths greater than 1.25 m;

• Operating mode 8 only operates in depths greater than 0.8 m.
Channels are usually shallower nearer the banks than in the main part of the channel. To avoid losing
too much of the flow the following rules have been applied in practice:
• When using mode 8 the gauging section should be at least 0.8 m deep;
• When using mode 5 the gauging section should be at least .5 m deep;
• When using mode 4 the gauging section should be at least 3 m deep.
Mode 1 Mode 4 Mode 5 Mode 8
Minimum
recommended cell
size
0.10 m
0.20 m
0.25 m
0.50 m
0.10 m
0.20 m
0.10 m
0.20 m
Single ping standard
deviation (min. cell
size)
0.6 m/s
0.50 m/s
0.13 m/s
0.13 m/s
0.01 m/s
0.01 m/s
(at 0.50 m/s flow
velocity)
0.15 m/s
0.10 m/s
(at 1.0 m/s flow
velocity)
Minimum depth of
water
1.0 m
1.2 m
2.5 m
3.0 m
2.0 m
2.0 m
1.0 m
1.0 m
Maximum range
(Mode 5 & 8 for < 50
cm/s flow velocity)
20 m
50 m
20 m
60 m
4 m
8 m
4 m
8 m
Maximum relative
velocity
10 m/s
10 m/s
10 m/s
10 m/s
1 m/s
1 m/s
2 m/s
2 m/s
Typical application Very fast water of all
depths. Rough and
dynamic situations.
Good in streams too
fast or deep for
modes 5 & 8, and
not deep enough or
too rough for mode
4.
General purpose for
most streams more
than 3 m deep
Slow, shallow water
with low shear and
turbulence
conditions
Shallow streams
with velocities < 2
m/s and with high
shear (rough bed
and/or turbulence.
Works in shallow
water where mode 5
does not work well.
NOTES:
1 .Maximum range depends on water temperature and depth cell size. Use BBSETUP to compute the maximum
range for a particular ADCP set-up and water temperature. The standard deviation of modes 5 & 8 varies with water
velocity, boat speed, bedform roughness, channel depth and turbulence. Reference should be made to the ADCP for
further discussion on these modes
2 The figures in normal type are for the 1200 kHz system and those in italics for the 600 kHz system
Table 1: Comparison of performance of RDI 1200 kHz 20 0 and 600 kHz 200 ADCPs, both with
transducers at 0.25 m deep & blank set to 0.30 m
However, it is recommended that the effective depth should be greater than 1.5 m for at least
95% of the cross-section.
NOTE: The depth is actually the effective depth i.e. the position from the transducers to the bed of the
river. Therefore if the transducers are positioned 0.3 m below the surface, then an actual depth of 1.5
+ 0.3 m = 1.8 m is required.
Another major site consideration is flow velocity:
• Mode 4 is not suitable for gauging velocities less than 0.5 m/s;
• Mode 5 can accurately measure flow velocities a slow as 0.01 m/s;

• Mode 8 can accurately measure flow velocities greater than 0.06 m/s.
• Modes 1 & 4 can measure velocities up to 10 m/s;
• Modes 5 and 8 can only measure velocities up to 1 and 2 m/s respectively;
• The uncertainties in Mode 1 velocity readings are significantly higher than other modes.
The velocity and depth constraints can be combined together as follows in Table 2:
Velocity - v (m/s)
Depth (m) v < 0.04 0.06 >v>0.04 0.5 > v > 0.06 1.0 > v > 0.5 2.0 > v > 1.0 10 > v > 2.0
< 1.0 none none none none none none
1 < d < 1.5 none none mode 8 mode 8 mode 1 (?) mode 1
1.5 < d < 3.0 * mode 5 mode 5 mode 5 mode 1 (?) mode 1
3.0 < d < 4.0 * mode 5 mode 5 mode 4 mode 4 mode 4
d > 4.0 none none none mode 4 mode 4 mode 4
* - Minimum water velocity in mode 5 at these depths has not been ascertained.
Table 2: Guidance Table for Selecting RDI ADCP Operating Mode
It should be noted that the information provided above is based on current operating experience and
the manufacturer’s guidelines. It is possible that this table can be further developed and refined once
the appropriate operating experience under Indian conditions has been obtained and the make and
models of ADCPs purchased are known.
SonTek ADP
The major site constraint on the use of the ADCP is the channel depth. Channels are usually
shallower nearer the banks than in the main part of the channel.
To limit the size of unmeasured fraction of the cross section, the following guidelines have been
applied in practice:
Minimum cell size 0.25 m
Minimum depth of water 1 m
Maximum practical depth range (flow velocity) 20 m
Single ping standard deviation (min. cell size) 0.94 m/s
Maximum velocity relative to instrument 10 m/s
Table 3: Some limitations of the SonTek ADP 1000 kHz
However, it is recommended that the effective depth should be greater than 1.6 m for at least
95% of the cross-section.
NOTE: The minimum depth is based on the assumption that the blanking range is 0.5 m and that the
ADCP transducers are not deeper that 0.25 m below the surface. A water depth of 1.65 m would allow
for 3 cells and 0.15 margin for side lobe interference. The primary set-up could be based upon the
suggestions of SonTek’s SetUp Assistant. However, the Assistant does not anticipate shoals in the
cross section (it assumes a canal type of river) and might suggest a large cell size (to reduce the
single ping standard deviation). If shoals have to be crossed, the operator should decrease the cell
size to a useful value.

ADCPs are still under development and new models are introduced in rapid succession. Some of the
improvements are: smaller cells, higher accuracy and operation in shallower water as a result of
smaller cells and reduced blanking range.
3 DEPLOYMENT
The ADCP should be deployed from an outboard motor propelled boat, which has been specially
adapted for the task. The boat should be of a shallow draft type, preferably not greater than 0.5 m
when laden with the equipment and the required number of operatives. The crew should preferably
consist of no more than the Hydrologist, Assistant and boat driver. Also, the boat should be relatively
flat bottomed, stable and easily manoeuvred.
The ADCP should be fixed to the ADCP by means of a mounting arrangement. It should be possible
to fit the mounting arrangement to any boat. This arrangement should be such that the ADCP
transducers can be raised and lowered to different positions below the water surface in 0.1 m
increments from 0.1 to 1.0 m. A rigging facility is required to prevent the ADCP to lean back during
(fast) sailing. The rigging should be such that when the ADCP impacts with anything solid it can give
way and swivel to the surface. On some boats, like the survey boats as obtained under the Hydrology
Project for Integrated Bathymetric Surveying, it is possible to install the ADCP in a moon pool / well /
trunk pipe in the hull of a boat. This type of arrangement is normally found on boats for bathymetric
surveying. An adequate shelter should be provided on the boat to protect the operator and laptop PC
from sun and rain. A rigid working table should be provided on which to place the laptop PC and field
data forms.
The X-direction of the ADCP should be parallel with the longitudinal access of the boat. The three-beam
configuration of the SonTek ADPs prevents the installation with the beams in parallel with the
boat.
ADCPs can be deployed in self-contained and real-time mode. The latter is preferred since anomalies
and problems with the data being collected can be spotted immediately by means of the laptop PC.
However, to run the ADCP in real-time mode an external power (battery) source is required to
connect to the PC. Most of the current generation of laptop PCs will rarely run on their internal
batteries for more than two hours. Hence, a reliable and sturdy power adapter should be included with
the laptop PC to run both the laptop PC and the ADCP on a car battery. In some situations it might be
necessary to operate the equipment in self-contained mode, i.e. without a laptop PC connected but
recording data in internal memory. The ADCP should be fitted with such memory then. A PC is
required anyway to set-up the ADCP before and to retrieve the collected data after the deployment.
Presently, the CWC ADCPs are not equipped with internal memory for data storage.
4 OPERATING SET-UP
RDI ADCP
Prior to commencing a measurement various set up parameters must entered into the ADCP via the
PC lap top and deck box. The appropriate operating mode must be selected. This is discussed in
Chapter 2. For most rivers greater than 3.0 m deep, RDI Instruments (600kHz & 1200 kHz) Mode 4
will probably be appropriate. Certain deployment parameters can be set within each operating mode:
1. Bin size (size of each depth cell measured);
2. Blanking distance (parameter indicating which signals to ignore);
3. ADCP depth (depth of transducers below the surface).

4. The time between ‘pings’ can also be set-up. Experience has shown that if the time is set to
continuous (the default setting) interference can possibly occur between consecutive sets of
pings. The manufacturers have therefore recommended that the time be set to a small amount,
say 0.025 milli-seconds .
Even though the third point above is set when the ADCP is bolted onto the floats, not within the
operating mode, the information must be included in the deployment command file.
These values are set in whole decimetres. The bin, blanking and transducer depth depend on the
water depth and channel conditions. No data is collected less than 1 bin from the bottom. No data is
collected less than the sum of all three parameters from the water surface. Water velocities in these
upper and lower regions of the profile are estimated. The literature on the ADCP states that a
minimum of two depth cells must produce good velocity data to give accurate flow measurements.
There are certain rules to note:
1. Always ensure that the depth specified in the deployment file is the depth at which the
transducers are set;
2. Never use a blank of less than 0.2 m. It has shown that this will result in erroneous velocities
being recorded in the top bin;
3. In turbulent or high velocities ensure that the transducer depth is sufficient to be below the level of
aeration (at least 0.3 m);
4. When reading the data make sure the configuration file has the same parameter values as the
deployment file;
5. Make a note of the width of the channel between the end of the ADCP traverse and the bank. If
this distance is significantly large relative to the overall width it can be used to adjust the
calculated flow. This should not be a problem if the site is carefully selected i.e. avoid shallow
water.
The settings appropriate for an RDI, 600 kHz ADCP are contained in Table 3 below are provided as a
general guide:
Channel conditions Mode Bin (m) Blank (m) Transducer depth
(m)
Low velocity,
shallow channels
5 0.1 0.2 0.1
Shallow channels 8 0.1 0.2 0.1
Shallow channels,
high velocities
1 0.1 0.2 0.3
Channels 1.5 - 3.0
deep
5 (v < 2.0 m/s)
1 (v > 2.0 m/s)
0.1
0.1
0.2
0.2
0.2
0.3
Channels > 3.0 m
deep
4 0.5 (< 10 m)
1.0 (> 10 m)
0.5
0.5
0.5
0.5
Table 4: General guide to ADCP set-up settings
SonTek ADP
Prior to commencing a measurement various set-up parameters must be entered into the ADCP via
the laptop PC. Certain deployment parameters can be set within each operating mode:

1. Cell size (size of each depth cell measured)
2. Blanking distance (parameter indicating which signals to ignore);
3. ADCP draft (depth of transducers below the surface).
4. Ping rate (for real time application should be set to highest rate to reduce the velocity standard
deviation by averaging)
The cell, blanking distance and transducer depth depend on the water depth and channel conditions.
No data is collected less than 1 cell from the bottom. No data is collected at a depth less than the sum
of draft + blanking distance + cell size from the water surface. Water velocities in these upper and
lower regions of the profile are estimated. The literature on the ADCP states that a minimum of two
depth cells must produce good velocity data to give accurate flow measurements.
There are certain rules to note:
1. Always ensure that the depth specified in the set-up file is the actual depth at which the
transducers are mounted. That depth is measured from the water surface to the centre of the
transducer faces. The transducers are assumed to be in a horizontal plane;
2. Never use a blanking distance of less than 0.5 m.
3. In turbulent flow or high velocities ensure that the transducer depth is sufficient to be below the
level of aeration (at least 0.3 m) because trapped air is virtually blocking the passage of the
acoustic signals;
4. Make a note of the width of the channel between the departure point of the ADCP traverse and
the starting bank and the end point of the ADCP traverse and the ending bank. If this distance is
significantly large relative to the overall width it can be used to adjust the calculated flow. This
should not be a problem if the site is carefully selected i.e. avoid shallow water.
5 MEASUREMENT RUNS
Once the ADCP has been set-up the measurement of traverses can be commenced. When in real-time
mode the run can start immediately. However, operating the ADCP in self-contained (remote)
mode the cable from the laptop PC to the ADCP has to be disconnected prior to starting. A dummy
connector has to be placed on the ADCP plug socket to avoid damage of the electrical contacts by
water and dirt.
Even though the boat can traverse the river following an irregular path it is recommended that as
much as possible the boat traverses the river at right angles to the flow / banks. The boat speed
should be as slow as reasonably possible while at the same time being sufficient to maintain a steady,
smooth on-line course. The coarse should be kept stable, if needed, only gradual changes are
permitted. The same applies to the traversing speed over the ground. This speed should be low
enough to take at least several minutes to complete a full traverse. On wide channels the speed over
the ground may be increased to about the average flow velocity.
It is recommended that at least four traverses are made i.e. across and back twice and the calculated
discharges compared for consistency and repeatability for each run. If bottom-tracking errors occurred
in any calculated discharge or the calculated discharge deviates by more than 5% from the average of
the calculated discharges, the traverse should be set apart and another 2 traverses should be made.
For the estimation of the discharge, the unmeasured flow should be estimated by the RiverSurveyor
software (SonTek), the observer should enter his estimates for the distance to the start and end
banks. Both the top and bottom layers should be automatically extrapolated by RiverSurveyor
applying the standard power fit method.

It is recommended that the boat pauses (remains stationary while collecting data) in a fixed position at
the start and end of each traverse for a period of 30 - 60 seconds since this can assist with the final
interpretation and processing of the data. The start and stop of movement should be extremely
gradual to avoid bottom-tracking failure.
6 DATA HANDLING AND RECORDING
On completion of the runs an initial analysis of the collected data should be undertaken. In real- time
mode the data will be automatically loaded onto the PC. In self-contained mode it is necessary to re-connect
the ADCP to the laptop PC to download the data. As a rule of thumb the time taken to
download the data from the ADCP will be roughly the same as the time taken traversing the river.
Once the data has been downloaded a preliminary flow estimate can be obtained to see if the
calculated discharges are reasonable. A final flow estimate can be made when convenient.
A standard field sheet should be prepared which records relevant information for each traverse run.
This sheet should include fields or columns for the following information, which should be duly entered
during each traverse run:
1. date
2. site and river name
3. name(s) of observer(s)
4. ADCP Serial or Reference No.
5. method of deployment e.g. boat - real time or self contained
6. traverse number
7. name of data file
8. set-up parameters - cell size, draft of ADCP, blanking distance, ping rate
9. time of start of each traverse run
10. distance of traverse departure to start bank
11. gauge post reading at start of each traverse run
12. time of finish of each traverse run
13. distance of traverse finish to end bank
14. gauge post reading at finish of each traverse run
15. remarks

Hydrometry: Field Manual, Field Application of ADCP Volume-4 Part V 2003

More Related Content

What's hot (20)

Similar to Hydrometry: Field Manual, Field Application of ADCP Volume-4 Part V 2003 (20)

More from indiawrm (20)

Recently uploaded (20)

Hydrometry: Field Manual, Field Application of ADCP Volume-4 Part V 2003