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Hydrological forecasting - Prévisions hydrologiques (Proceedings of the Oxford Symposium,
April 1980; Actes du Colloque d'Oxford, avril 1980): IAHS-AISH Publ. no. 1 29.
A flood forecasting data acquisition system
G. P. B R U N S D O N and M. T U R N E R Institute of Hydrology, Wallingford, UK
Abstract. This paper describes a low cost data acquisition system for use in flood forecasting.
The system consists of a base station (made up of a microcomputer with printer and magnetic tape
peripherals) communicating with outstations using standard telemetry techniques. The base station
controls the complete system, analysing and displaying all data; the unit hydrograph is adopted as
the flood forecasting model within the computer. There are two types of outstations, (1 ) for the
measurement of rainfall and (2) for the measurement of river level. Both types include valuable data
storage capacity so that in the event of a communications failure, data can be retained until the
link is re-established.
Système d'acquisition des données en vue de la prévision des crues
Résumé. Cette communication présente un système peu coûteux d'acquisition de données en
vue de la prévision des crues. Le système consiste en une station de base (constituée d'un mini-
ordinateur avec imprimante et périphériques pour bandes magnétiques) mise en rapport avec des
stations extérieures utilisant les techniques classiques de la télémesure. La station de base contrôle
l'ensemble du système, analyse et présente toutes les données sous une forme convenable: l'hydro-
gramme unitaire est adopté comme modèle de prévision de crue dans l'ordinateur. Il y a deux types
de stations extérieures, (1) pour la mesure des précipitations et (2) pour le relevé du niveau de la
rivière. Ces deux types comportent une capacité d'emmagasinement de données suffisante de façon
à pouvoir conserver les données en cas de rupture des communications jusqu'à leur rétablissement.
INTRODUCTION
The data acquisition system described in this paper is designed to forecast floods and
to operate in remote areas. The instrumentation is compact, simple to operate and
exploits modern technological development. Low cost, reliability and minimal main-
tenance requirements were the factors which determined its design.
GENERAL DESIGN
The system consists of a base station and two outstations measuring rainfall and river
level respectively. At present, the latter is used mainly as a measurement check but will
be incorporated within a later version of the device to improve forecasts. The system
uses a single raingauge sited appropriately and feeding data via a telemetry line to the
base station. Flood forecasts are calculated by a unit hydrograph procedure and give
warnings of imminent flooding together with data displayed on a visual display screen.
The telemetry system uses a coded command word which is suitable for future expan-
sion of the system if required and any telemetry system such as a radio, wire link or
public telephone network may be used with the necessary terminal equipment and
approval, where necessary. The base station uses a microcomputer with a tape cassette
and output printer as suitable peripherals. Control, together with full data analysis
including display control, is accomplished using a single microprocessor.
The outstations use a rain and river level recorder developed by the Institute of
Hydrology but modified to accept full two-way control of telemetry signals. Each
station is called separately and a chosen command is issued indicating whether to send
either all the stored data or the last recorded data word. As explained later, this gives
11
12 G. P. Brunsdon and M. Turner
the advantage that full recovery of data is possible should the communication link fail
for a period not exceeding two days. Three attempts are made to establish contact
with each gauge before failure is pronounced. However, further attempts are always
made at the beginning of each period. Resetting and synchronization of all field gauges
respond to a particular code allowing the clocks and address counters of all gauges to
be set to zero simultaneously. Each gauge has its own crystal timing source. For each
gauge, priority is given to entering the current reading into store.
The base unit takes the form of a small desk top microcomputer. It is operated
from a mains power supply and is used in an office environment. A visual display unit
(VDU) shows the time and date of the last recorded data, the last 24-h total of rainfall
and river level. The predicted river flow is displayed with the expected time at which
an alarm condition is likely to be encountered. Failure of either or both gauges will be
displayed if this should occur. A printer peripheral is provided for listing a 24-h record
of events from the actual time it is requested. The provision of an audio cassette
recorder for recording daily blocks of data is being considered. All of these functions
are commanded from a keyboard.
SYSTEM DESCRIPTION: OUTSTATION
Raingauge
A modified form of the solid state rainfall recorder, as used by the Institute (Turner
and Brunsdon, 1978), was chosen for measuring rainfall. Briefly, the recorder uses a
tipping bucket whose tips are recorded in a buffer counter. After a set period, such as
10 min, these counts are transferred to a location in store pointed to by the address
counter. This counter is then incremented by one and the buffer counter reset to zero,
ready for the next period. The previous operation is then repeated. When the storage
capacity is full the store then recycles, starting from zero, and overwriting into the
zero address position. The store accommodates 256 words which when using a 10-min
period has a storage capacity of about 1.75 days. For the flood forecasting system
described in this paper, the buffer counter was changed to a BCD 3lA digit counter, to
be compatible with the river level gauge described in the next section. The store has
also been re-arranged to accommodate 256 BCD words of four digit capacity. Additions
have included a Cmos universal asynchronous receive and transmit integrated circuit
for transmission and receiving purposes, together with the decoding circuit necessary
to identify command codes and particular field stations. A complete block diagram is
shown in Fig. 1.
River level gauge
Figure 2 shows a block diagram of the river level gauge. Here the particular sensor
involved is a pressure transducer with low output, the signal being measured in milli-
volts. This signal is first amplified before being passed to a dual slope integrator analog
to digital convertor; its output is presented as a 3]6 digit display. The method of
recording into store is similar to that of the raingauge, whilst control, decoding and
RAIN STORE
BUFFER
GAUGE
COUNTER 256X4 X4
\ ^ '
DECODE
I CLK \_.
CONT ROL
W^
FIGURE 1. Block diagram of raingauge.
A flood forecasting data acquisition system 13
\ LEVEL STORE
\GAUGE /
\A M ^ p ^
P 256 x4 x4
«^ 1 t
I 1
DECODE
& RX
TX
CONTROL
FIGURE 2. Block diagram of river level gauge,
transmission circuits are also similar. Tri-state line drivers are provided for transmission
and reception circuits. Using balanced 600 lines, distances of 3000 m can be accom-
modated. If other types of telemetry are preferred, i.e. radio or public telephone lines,
then standard RS232.V24 interfaces would be specified.
Decoding
The decoding relies on an eight-bit transmitted word. Starting with the most significant
two bits the code is broken down into four and is used to identify the type of station.
The next two bits again break down into a four function command. Finally, the lower
four significant bits are used as address locations. Figure 3 shows the code structure.
MSB
1
/
^ ^ V
OUTSTATION FUNCTION ADDRESS
OO CALL R G OO RESET
0 1 CALL LG 0 1 LAST DATA
16 L O C A T I O N S
1 O CALL WS 1 0 ALL DATA
1 1 CALL ALL 1 1 SPARE 1111 -*"
FIGURE 3. Structure of command word decoding.
SYSTEM DESCRIPTION: BASE STATION
Hardware
The base station is built up around a microcomputer of type M6800 produced by
Motorola. Here advantages are taken of the Motorola micro module concepts; modules
consist of developed printed circuit boards already assembled and tested. The modules
used in this system include a central processor, input/output, display, memory and
Eprom modules. The complete design basically follows similar lines to the autonomous
development system developed by Motorola but with some modification and additions
which result in a small compact unit suitable for office use. A photograph of a typical
base station is shown in Fig. 4, and Fig. 5 shows a block diagram of the base station
system. The central processor provides the heart of the unit, handling control of the
total system together with all data input and output. A clock system providing a
minute pulse is used for timing requirements. This is crystal controlled with an accuracy
of 3 s per month. Real time is always displayed in the left hand bottom corner of the
display. The central processor unit handles its own VDU via a display module. The
telemetry line is connected to a suitable modem via the processor's serial input module
14 G. P. Brunsdon and M. Turner
"ï&,"*msm
FIGURE 4. Typical base station (top) with enlargement of display (bottom).
A flood forecasting data acquisition system 15
8K
E.P.R.O.M '
6850
ACI A
6820
P I A
AUDIO
CASSETTE
FIGURE 5. Block diagram of base station hardware.
(6850). Output is available from the (6820) parallel output module for hard copy
records. Input to the microcomputer is always through the keyboard. An audio
cassette interface is available for recorded data to be stored on C60 type cassettes.
Storage requirements allocate 8K of Read Only Memory to be used for the system
program and a further 4K for Random Access Memory requirements. The total system
will run operationally in approximately 12K of memory.
Software
Software is illustrated by the flow diagrams of Figs 6 and 7. All software has been
written in assembly language with the exception of the unit hydrograph program
which was written in Fortran. This latter program is a subroutine linked to the main
assembly program. Software within the computer is illustrated by Fig. 6 which shows
software grouped into various blocks. These blocks can be further reduced to three
UNIT NTERUPT PROGRAM
HYDROGRAF
"
SUBROUTINE
*1
1 '
N.M.I DISPLAY
Tf M Ë
PROGRAM COt' T R O L TIME
I
MAIN PROGRAM
»Lr GRAPH PLOT J
V.D. U •r
L
&ISPLAY
> 1r PRINT RECORDER J
1
FIGURE 6. Flow diagram of base station software within the computer.
Z
16
- €L
^
/^~\
L OAD
STACK
rn
SET
N Mi
VECTOR
*
j CLK, HOL
1
SET
STORE
1
G. P. Brunsdon and M. Turner
LOCATiO
& FLAGS
INZ.
UNIT
X
HYDHOG
o
\
| PRINT
PRiNT
I RAIN
16 SPACES
j RESULT
Hill
A flood forecasting data acquisition system 17
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18 G. P. Brunsdon and M, Turner
distinct programs, namely executive, main program and interrupt. The main program
is always entered from the executive and initializes, sets and displays the correct titling
time and date requirements. The clock is normally held until released from a keyboard
command. The interrupt program is actuated by grounding the non-maskable interrupt
line of the processor which immediately exercises control on the system, displays new
information on the VDU and thus returns to the main program. After an initialization
routine, this main program finally displays a prompt sign (+) at the end of the real
time display and waits for instructions to be entered by the operator from the key-
board. These instructions include such requests for the printing of data, displaying
rainfall total and river level averages. Commands will reset the complete system,
produce new displays and hold the clock for resynchronization. A command to enter
the executive program for debugging is also provided. Facilities for a command to
produce a unit hy drograph plot are available ; the addition of an XY plotter could be
included as extra peripheral equipment if required. The flow diagrams are shown in
Fig. 7.
System design
The present system has been designed for minimal instrumentation using only one
raingauge and one river level gauge. Drainage basins may require additional instrumen-
tation and each area will provide its own unit hydrograph parameters for inclusion in
the model. This will be accommodated by providing individual software packages for
each scheme. Naturally, restrictions will be imposed by the computer hardware but
additional memory can always be incorporated to satisfy the needs of individual
schemes.
FUTURE DEVELOPMENTS
The complete simulation system has been built up for testing purposes and encourag-
ing results have been obtained. Prototype units are now being built to obtain practical
experience in field conditions. A base station will be similar to that shown in Fig. 4.
A new forecasting model is also being evaluated using river level to produce a more
accurate forecast. The system developed so far is of relatively low cost and satisfies the
design requirements; further trials are necessary, however, before its performance can
be fully assessed.
REFERENCE
Turner, M. and Brunsdon, G. P. (1978) Solid state event recorder for rainfall measurement. Hydrol.
Set Bull. 23, no. 1, 143-149.
