1. HP IIIndian Hydrology Project
Technical Assistance
(Implementation Support) and
Management Consultancy
ADCP – How to specify an ADCP System and what components are required
1. Introduction
An Acoustic Doppler Current Profiler (ADCP) system offers users a new approach to measuring
discharge in rivers in India using high-frequency sound waves (ultrasound). Under HP-I a small
number of ADCP systems were procured by CWC and have been applied fairly successfully over the
past 8-10 years. However, the technology behind ADCPs has moved on significantly over the past 5
years or so, particularly as far as the electronics and software are concerned and such equipment is now
very widely used in the USA, China and Europe.
ADCP technology can be applied to large or small rivers, but is recommended for use under HP-II on
large wide rivers in India, where sediment loads are often high. For small rivers, TAMC suggests that
conventional current meter gauging by either wading or from boats offers the most appropriate means of
measuring discharge.
This note does not attempt to describe the principals behind the ADCP method of river discharge
gauging, but is intended to help IAs under HP-II to understand what components are required for an
operational system and how to produce a suitable specification of a system under World Bank
Procurement rules. However, useful reviews of how ADCPs work are available in a number of US
Geological Survey (USGS) publications many of which can be accessed through their website:
http://hydroacoustics.usgs.gov/movingboat/index.shtml and a good reference report is available at:
http://pubs.usgs.gov/tm/3a22/ . However, some of the reports on instrument performance which exist on
the USGS website refer to older versions of instrument or software and technical improvements in both
may now invalidate any accuracy or comparison data quoted.
2. ADCP components
An ADCP system consists of a series of components that together make up an operational direct river
discharge measuring package. A full system for use in India should consist of:
i. An ADCP instrument unit containing all of the required electronics, batteries, compass and tilt
sensors etc;
ii. A small (1 – 1.2m long) flotation platform for deployment of the ADCP unit (normally a plastic
or fibreglass trimaran or boat);
iii. A data transmission system to transmit data from the ADCP to a receiver on the river bank. This
may be a Bluetooth system (cheap but has a limited range of 100m or perhaps up to 200m) or a
radio modem system (more expensive but with a range of several kms);
iv. A robust laptop PC to receive and process the data on the riverbank;
v. A Differential Global Positioning System (DGPS) instrument to monitor the position of the
ADCP on the river (needed in situations where the river bed is unstable and where bed material is
moving, which is probably the normal situation in Indian rivers during the monsoon);
vi. Necessary connection cables and spare batteries etc plus manuals.
For Indian use, where ADCPs are probably going to be deployed on wide (>150 -200m) rivers with
high sediment loads and mobile beds, it is suggested that:
i. A radio telemetry system is required rather than the Bluetooth option;
HP II
Created on 10/06/2014
Filename: adcpprocurementnote-140609234741-
phpapp01.doc
1

2. ii. A 600 kHz transducer system might be better able to cope with high sediment loads than a 1200
kHz or 1.0 MHz system (see comments on transducer frequencies in following section);
iii. Because it is likely that rivers will have moving beds during periods of high flows, systems should
be equipped with a DGPS function.
3. Comments on available commercial ADCPs
ADCPs were first developed only some 20-25 years ago, but development has been rapid and the
technique is now widely used as stated in Sect 1 above. Original development was primarily by a
company called Teledyne RDI in California in the USA (http://www.rdinstruments.com/rio.aspx or
http://www.rdinstruments.com/riverray.aspx), for marine use but the company worked closely with the
USGS in adapting the technology for use in river flow gauging. However, a second US company,
Sontek/YSI (http://www.sontek.com/riversurveyor-s5-m9.php), has also been producing a similar
product for the past 15 years or so, and their product is widely used in the USA and China for example.
The term ‘ADCP’ is in fact copyrighted by RDI, and Sontek refer to their equipment as ADPs
(Acoustic Doppler Profilers), however an RDI ‘ADCP’ is in exactly the same type of streamflow
measuring instrument as a Sontek ‘ADP’.
Until recently RDI produced two instruments, a small one (StreamPro) for small rivers (up to 2.5-3m
deep) and a larger version (Rio Grande, or ‘large river’ in Spanish) for rivers up to 30-100m deep.
However, the Rio Grande is being replaced at the moment by a newer version called a RiverRay, which
is supposed to be much easier to use and which requires less specialised knowledge by users. All RDI
instruments use a 4 transducer array set at a 20o
beam angle, with river depth being measured using this
transducer array.
Sontek also have two instruments, an S5 for smaller streams (up to 5 m deep), and a larger M9 for large
streams up to 40 to 50 m deep. The M9 is interesting as it contains two separate transducer ranges, one
of 3.0 MHz for ‘small to medium depth rivers’ with limited sediment, and another of 1.0 MHz for large
rivers with a higher sediment load, and is thus effectively two systems in one unit. The S5 has a similar
array of 4 velocity measuring transducers as the RDI setup (although with a 25o
degree beam angle) but
includes a fifth vertical transducer to measure depth directly. The M9 has nine transducers, two sets of
4 with different frequencies for different modes plus a single vertical depth measuring transducer. This
approach differs from the current RDI range where two Rio Grande options are available, one with a
1200 kHz frequency for medium rivers and one of 600 kHz for large, sediment laden rivers. There is no
real advantage in Sontek over RDI in my opinion, as the 3.0 MHz option within the M9 would be of
little use in deep, sediment laden rivers where it is to be used in India; the 3.0 MHz frequency is not
suitable for rivers with a high sediment load.
Recently the German company, Ott, has produced a Qliner ADCP, for use in small to medium rivers
(maximum 20m depth) (http://www.ott-hydrometry.de/web/ott_de.nsf/id/pa_produkte_qliner_e.html).
This instrument does not yet have much of a ‘track record’ and has only been available for two years,
and it is suggested that it is not ideally suited to Indian conditions and hence should not be considered
for HP-II.
HP II
Created on 10/06/2014
Filename: adcpprocurementnote-140609234741-
phpapp01.doc
2

3. ADCP – Summary of differences between different models
Frequency Instrument Good Points Bad Points
High - >2 MHz
(> 2000 kHz)
1. RDI StreamPro
2000kHz
2. Sontek RiverSurveyor
M9 3.0 MHz mode
* Small bins (but
high noise error)
* Better accuracy for
same bin size
* Most susceptible to
moving bed
* Not good for high
sediment load
rivers
Medium – 1-2 MHz
(1000 – 2000 kHz)
1. RDI Rio Grande 1200
kHz
2. Sontek RiverSurveyor
M9 1.0 MHz mode
* Versatile and
suitable for most
conditions (can be
used on small and
larger rivers)
* Not suitable for
very shallow rivers
(< 1m)
* May be problems
in floods & high
sediment loads
Low - < 1 MHz
(< 1000 kHz)
1. RDI Rio Grande 600
kHz
2. Sontek RiverSurveyor
M9 1.0 MHz mode
* Robust
measurements
* More ‘energy’ to
get through
sediment laden
rivers (600 kHz
probably better
than 1.0 MHz)
* Big bins (low noise
error)
* Suitable for large
rivers (>3m depth)
and high sediment
loads
Note: 1 MHz = 1000 kHz
Tests were carried out on a number of different RDI and Sontek instruments in a current meter test tank
some years ago in the USA (see http://hydroacoustics.usgs.gov/publications/HHShih.pdf). However,
these tests were carried out more than 7 or 8 years ago and results may not be applicable to current
equipment sold by these manufacturers. Nevertheless, the paper demonstrated that the 1200 kHz RDI
instrument was most accurate over a range of velocities but followed closely by the 600 kHz RDI. A
Sontek 1500 kHz ADCP was somewhat less accurate overall, and their 500 kHz instrument showed
considerable scatter in velocity measurement. A recent comparison of ADCP products by the national
hydrometric authority in the UK (the Environment Agency) found that the RDI Rio Grande was
superior to the Sontek RiverSurveyor for a number of reasons. However, Sontek products have a good
reputation worldwide and have a proven track record. For HP-II, either a Rio Grande 600 kHz model
(or the new RiverRay model), or a Sontek M9 RiverSurveyor would be suitable.
Frank Farquharson
6th
November 2009
HP II
Created on 10/06/2014
Filename: adcpprocurementnote-140609234741-
phpapp01.doc
3