| In The Field - Other GIS Applications |
| Catchment Analysis Using GIS: An Engineer's
Perspective |
| By Alan Knott, Manchester, England 44-(0)1612-286-282,
knott@pbworld.com, Robert
Holt, holtro@pbworld.com
and Phillip Lucy, lucyp@pbworld.com |
| GIS proved to be extremely useful in providing information
that was critical to developing flow forecasting models for catchment
blocks, including the distribution of engineering sites, rivers, floodplains
and population areas. It also helped us to provide our client with
a detailed procurement and planning tool. |
|
For the last decade, our group has provided consultancy services
for the Environment Agency for England & Wales' (and its predecessor's)
real-time operational systems and, in particular, its telemetry
and flow forecasting modelling systems. As part of the regional
telemetry scheme for the agency's Anglian Region, we designed and
are implementing the Anglian Flow Forecasting Modelling System (AFFMS),
a distributed, resilient computer system capable of running flow
forecasting models in "real-time" and producing predictions
of the future state of rivers in the region. [Ed. note: See
also another article by Alan, "Telemetry
and Forecasting Systems for Managing Rivers and the Environment,"
PB Network Issue No. 45, September '99, pp. 50-52.]
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| Figure 1: 12 Anglian Catchments with
Subcatchment Boundaries |
The Anglian Region, one of eight regions within the Environment Agency
for England & Wales, has been divided into 12 "catchment
blocks," (Figure 1) and forecasting models are needed for each.
They will enable users from a variety of departments to look ahead
and use the forecasts to help to operate river control structures
or manage a pollution incident, advise on abstraction and discharges,
or warn of impending flooding.
Before the agency's hydrologists could scope and scale the models
for each catchment and prioritise their implementation, however, they
needed to:
- Review the characteristics of each catchment
- Define the extent and complexity of the required
model
- Judge the availability and quality of the data for building
and calibrating the models.
Geographical presentation of the catchment characteristics and the
associated data was a logical and highly effective way of representing
the information in a format that was easy to understand.
Characteristics of the Anglian Region
The Anglian Region has an area of 26 740 km2 (10,700 square
miles), a coastline of 485 km (291 miles) and fluvial flood defences,
such as embankments, dams, gates, sluices, locks, barriers and land
drainage pumps, of 6195 km (3,717 miles). It has a population of 6
million with the major conurbations (aggregation of urban communities)
in Lincoln, Peterborough and Ipswich. The region has huge areas of
low-lying land with extensive land reclamation demanding attention
for flood risk management. Shoreline defences and management are an
important aspect of the region.
Catchment models for the Witham, and the Welland and Glen catchment
blocks have been developed within the AFFMS project. The development
of the models for the other 10 catchment blocks form the basis of
a regionwide modelling project. We have applied the GIS application
to assist in planning the modelling implementation and developing
the procurement strategy to be employed.
GIS Selection and Data Validation
The GIS package we decided to purchase was ArcView, developed by the
Environmental Systems Research Institute (ESRI) of the U.S. Initially
we had little experience with GIS products and had to develop a lot
of the detailed requirements for the project by investigation. We
were provided with a basic set of data from the client in a variety
of formats, including Microsoft Excel and DBII, together with a GIS
Shape File for the whole of the Anglian Region. We needed to rationalise
duplicated data, which we did by transforming the data and the formats
into GIS formats. By presenting the transformed data within GIS, it
soon became clear that some elements of data were invalid-for example,
land instrumentation lying within the sea-and that we had embarked
on a major GIS development.
One issue engineers found difficult was the lack of readily available
good quality mapping data. Investigations into the possibility of
purchasing mapping data from Ordnance Survey within the UK revealed
high licensing costs that were prohibitive for this relatively small,
single project.
GIS Development
Determining Basic Maps. The project
fitted naturally into two map project structures within the ArcView
GIS package. First, we determined the need to present a map of each
catchment's river systems overlaid with the engineering facilities
within a catchment, including river gauging stations, tidal stations,
climate stations, rain gauge stations, pumping stations and sluices.
The extent and type of the existing hydrodynamic modelling within
a catchment was displayed on the engineering facilities map also.
We also needed to present a map of each catchment's river system overlaid
with the population distribution and flood risk zones (Figure 2).
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| Figure 2: Ancholme Catchment's River
System Overlaid with its Population Distribution and Flood Risk
Zones |
Setting up Themes. The basis of flow modelling is to determine
the forecast flow and levels at various locations within each catchment.
It was decided to show these overlaid on each of the two GIS maps
required for each catchment. We found the ability to set up themes
(which are effectively layers or overlays similar in fashion to CAD
package layers) on a map and set the graphical and textual properties
of the theme to be very useful for presenting a wide range of data
on one map.
ArcView requires decisions to be made for the presentation and appearance
for each theme on each map, so we established a set of defined rules
for the size, colour, type and location of each (these are shown on
the keys for Figure 2).
Managing File Structure and
Disk Space. The need to display such a wide variety of themes
on one map together with the need to build separate maps for each
catchment meant we needed to pay particular attention to the disk
file structure and disk space for the ArcView project, data, shape
and theme files. At the end of the project, the 24 catchment maps
(two for every catchment block) were derived from some 2000 data files
that take up approximately 80 Mb of disk space.
Reaping
the Benefits. The decision-making ability available to us from
producing the catchments in a graphical form was immense. We were
able to determine the extent of the floodplains, visualise the size
of the catchments and analyse the extent and distribution of the engineering
installations. From this information we were able to quantify and
prioritise the schedule of model development required for each catchment
block.
Lessons and Suggestions
As stated above, one of the major difficulties we had was being unable
to obtain suitable mapping reference data because of budgetary constraints.
With such data, however, we could have shown many additional features
on our maps. For example, a theme of the major road and rail networks
(with associated river bridges) would have been of interest, particularly
those lying within the flood risk areas. We did attempt to use commercially
available travel route software but the formats were not compatible.
The use of GIS has been analysed within the context of our core engineering
activities. We can see that we could make great use of this technology
for the analysis of such things as communication routes to remote
telemetry site installations. We could also present the location and
distribution of telemetry outstations throughout an area and, say,
link this to scanning radio masts or telephone exchanges. Furthermore,
there is the potential for connecting GIS to real-time Supervisory
Control and Data Acquisition (SCADA) systems and legacy database systems
to provide extra insight and visualisation of the data they contain.
This could be undertaken without incurring the full costs of having
to re-engineer their databases.
We have found that extended facilities are available to present a
range of data for a theme including the display of images, which could
be related to site surveys. In our view, we could extend the use of
this package extensively if mapping data were available.
Conclusion
We found the ArcView GIS to be an extremely useful and beneficial
project tool and are very keen to develop and extend our use of such
technology. We are certain that there are many applications for which
GIS is the natural and best method of representing data and we see
this technology as one that can be used across the broad spectrum
of PB's activities. Indeed, GIS may well be one of the technologies
that enables some of the synergies within the PB family to be fully
realised. |
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Alan Knott is a chartered electrical engineer
specialising in computer systems applications, including communications
technology and software engineering. After a career that included
the delivery of large telemetry systems to the defence industry
and wide area networks for the academic and scientific communities,
he has played a leading role in large operational information system
projects, including the development of strategies and the design
and implementation of multi-million pound systems for the water
industry throughout the UK and in the Middle East and Australia.
Alan is the Technology Manager for PB Technologies.
Bob Holt, a chartered engineer and member of the British Computer
Society, specialises in the implementation of real-time systems
and has worked on a number of high-profile projects in the gas and
water sectors. Recently, he has taken a leading role in the development
of real-time operational systems for the environment sector.
Phillip Lucy is a Senior Systems Engineer with extensive experience
in using computer technology to solve complex engineering problems.
He has applied his knowledge and skills across many industries including
water, transport and power with applications ranging from plant
automation to management information systems.
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