Geographic Information Systems and Spatial Data in the
Service of Flood Management: A Report on an Initiative of
the State Emergency Service
Peter Crowe (Planning and Research Officer), Peter Cinque (Controller Sydney Western Division) and Belinda K. Davies (Hawkesbury-Nepean GIS Officer),
New South Wales State Emergency Service Abstract
This paper explores the uses and potential of Geographic Information Systems (GIS) in improving the management of flood response operations. For the past four years the State Emergency Service has been active in the development of a GIS capability for the valley of the Hawkesbury-Nepean River, but there is great promise for its application on a statewide basis. The GIS tool is a vital one in the contexts of planning for floods, educating the populations at risk and managing floods as they actually rise. GIS will help the SES to make sense of the complex and detailed hydrological, demographic, cadastral and other information which is available to today’s flood managers. In particular it will be valuable in the visualisation, to an extent not previously possible, of the likely impacts of developing floods. By using GIS in both the planning and the operational contexts, flood managers will be able to see in advance, and in considerable detail, what a coming flood will mean to communities in its path and will be able to make more informed and timely decisions about response actions and the allocation of resources. GIS, in short, carries the potential to revolutionise the SES’s handling of flood intelligence. Access to spatial data held by councils and other government agencies will be critical to the full realisation of this potential. The paper reports on progress to date in the implementation of GIS and discusses its future development as a tool in flood management activities.
Introduction
The State Emergency Service (SES), as the legislated combat agency for flooding in New South Wales, is always looking for ways to improve its ability to understand floods and their effects on the community. For nearly a decade, the SES has recognised the potential of GIS to assist in its management of floods and storms. However it was not until the report to the state government of the Hawkesbury-Nepean Flood Management Advisory Committee (1997) that a viable vehicle for the development of GIS within the SES could be forseen. The Hawkesbury-Nepean Floodplain Management Strategy project, which emanated from this report, is a five-year, multi-agency project aimed at making the communities in the Hawkesbury-Nepean valley better able to prepare for, respond to and withstand the effects of severe flooding. As part of the strategy the SES is responsible for, among other things, the development of:
“…a flood intelligence system based upon Geographical Information System (GIS) technology … that will display, on a real-time basis, the same flood intelligence in all agencies monitoring or combating the flood.” (Hawkesbury-Nepean Floodplain Management Advisory Committee, 1997, Appendix D, p13)
As a result of this recommendation the SES has introduced and begun to explore GIS technology. GIS was recommended because of its capability to combine, analyse and display spatial data and because of the flexibility of its output. GIS products range from printed hardcopy paper maps and interactive web-based maps to images that can be emailed or incorporated in text documents or PowerPoint presentations.
Arguably the most critical component of any GIS system is the spatial data used in analysis and visualisation. The agencies of the NSW and Federal governments are
important sources of spatial information, but of critical importance to the SES flood information system is the data held by councils of local government, whose unique need for detailed spatial information provides probably the most important repository of spatial data available.
This paper uses examples from the Hawkesbury-Nepean project to show how GIS is being used as a tool to better plan for and manage floods on the Hawkesbury Nepean River system. It also explores the development of a GIS-based flood intelligence system.
Flood Intelligence
In NSW, information about the effects of flooding on a community is gathered, interpreted and recorded by the SES. This progression is referred to as the flood intelligence process, which involves the interpretation of flood data that describes the effects on the environment at risk - that is, communities, people and infrastructure. Such information is vital to flood managers since it gives them insights into likely flood impacts before they are felt and allows them to make decisions which will contribute to the lessening of, or at least the management of, their consequences.
Historically information was recorded on cards, each of which was related to the reference area of a flood gauge. Today this intelligence is held in an online database where the advantages of such a system are available to SES planners and emergency managers. Information is stored as ‘heights’ of flood water on the flood gauge with text narratives describing the effects on the community at those heights. This information can be extracted from the database as graphs or as formatted MS Word documents that are termed Flood Intelligence Cards. Because of the vital role of flood intelligence, the SES has placed considerable emphasis on augmenting its flood intelligence system in recent times (Pfister and Rutledge, 2002).
One strategy for augmenting the flood intelligence system involves GIS. The SES has used GIS to represent flood intelligence geographically as well as to identify additional flood effects. Rather than completely relying on information about past floods, or waiting for the next one to occur, flood intelligence can be generated synthetically in the GIS by overlaying information about the floodplain environment with flood boundaries based on different flood scenarios. Intelligence developed during this process can be stored in the database as spatial objects enabling flood intelligence to be extracted and displayed in a variety of formats, including the traditional graphs and cards but also as dynamic maps.
To enable this process the SES is developing a prototype geo-database schema, based on the current flood intelligence database. As a first step, a copy of the existing flood intelligence database was modified to accommodate coordinate fields, so that X and Y values for point data could be entered for existing and new flood intelligence records. Further work is also being done to incorporate into the database relevant polygon and region data, for example flood extents and Local Environment Plans.
This development involves the use of spatial data management middleware that sits on top of a relational database management system. This middleware allows the creation and storage of complex spatial data types as well as more sophisticated data management and distribution. Using this strategy, spatial information and flood intelligence can be more easily kept up-to-date at various headquarters using database replication methods.
In recent years the SES has also benefited from a number of technological advances designed to hasten the gathering and delivery of data about rainfall volumes and river heights. These have been developed by a number of organisations. Services include telemetered rain and river gauges and Internet services such as the Manly Hydraulics Laboratory’s Flood-to-Fax service and the Commonwealth Bureau of Meteorology's EnviroMon monitoring system and flood data web site. This real-time data is fed into
operational software and displayed in the GIS environment along with existing spatial data and flood intelligence.
Flood Mapping
Flood mapping is not a new practice. The former Public Works Department and Water Resources Commission each produced a series of inundation maps for towns in NSW (Water Resources Commission, 1980) from 1977 until the program was discontinued because of adverse community and political reaction in 1985. These inundation maps were based on design floods, usually floods with an Annual Exceedance Probability (AEP) of 1%, 2% and 5%. Councils, government agencies and their consultants have continued to conduct flood and other hydrological studies. Those conducting these studies often use GIS-based flood modelling software to produce maps depicting flood boundaries, for less cost and of a greater range of design floods, than was the case previously. The resulting flood maps are now more likely of (for example) 0.2%, 0.4%, 1%, 2%, 5%, 10% AEP and the Probable Maximum Flood (PMF).
Whilst design floods are useful in local government urban planning and risk management studies they are less than perfect in the emergency management context because they have several idealised assumptions, such as uniform rainfall distribution over the catchment, resulting in a flood of a given AEP. Emergency management is concerned with not only the extent of flooding for different AEP events but also with other issues such as the range of rates of rise that may be encountered in real floods, the development of different types of flood-affected areas and the heights at which evacuation routes are cut.
Essentially, design floods do not model real floods. A perfect illustration is the 1867 flood of record on the Hawkesbury-Nepean River, a complex river system fed by five major tributaries and several large creeks that contribute, in varying degrees, to the development and severity of flooding in a particular episode. At Camden this flood is estimated to have been a 7% AEP (1 in 15 year Annual Recurrence Interval) event, at Penrith it is estimated as being a 0.6% AEP (1 in 170 year ARI) event while at Windsor it is thought to have been roughly a 0.4% AEP (1 in 250 year ARI) event. At Wisemans Ferry it did not reach the 1% AEP level (Sydney Water, 1995). As a result of this variability no single design flood map or even a combination of design flood maps could have illustrated this flood.
Emergency managers are almost always faced with floods very different from idealised design floods, so the existing design flood maps have many shortcomings for emergency management from this standpoint. Flood maps produced from design floods are often paper based so the information presented on the printed map is necessarily limited to the elements included by the map maker. Typically there is no capability to add other data or query the underlying data for further information such as at-risk addresses, the number of people who are likely to be affected or the appropriate evacuation routes.
The inadequacies of design floods and associated paper based maps in an emergency management context leads to a need to be able to produce a flood boundary that more closely represents a real flood. The simulation or capture of near-to-real flood boundaries, therefore, is critical to the success of using GIS as an aid in managing flood emergencies. There are several strategies that the SES has proposed, or is trialing, in order to produce a useable emergency flood management product.
The first method involves ‘pausing’ the production of design floods in GIS, mid-process, to produce flood polygons at 1 metre increments up to the design level. These flood boundaries are then stored in a library and can be matched to the predicted flood height during flood response operations so as to illustrate a coming flood. This method has been used previously, notably for the town of Benalla on the Broken River in Victoria (Hazel, 1999).
A variant of this approach being trialed by the SES involves defining a series of gauge reference areas (assumed to be relatively flat) for the key gauges on the Hawkesbury Nepean River system. For each gauge reference area flood boundaries are produced based on increments of one or two metres up to the PMF design flood, using contour data (surveyed or interpolated). To date this has been done for the Windsor gauge reference area. Whilst this method is rudimentary and does not take into account flood gradients between gauges, it allows a more flexible approach than the use of a design flood. It allows an emergency manager to visualise the approximate flood extent for current gauge heights as well as for predicted heights and to produce map products which are less course than those which were previously available.
A second, more ambitious and detailed method, is being developed by Webb McKeown, a floodplain management consultancy retained by the SES. It involves using predicted flood heights at key gauges on the Hawkesbury Nepean river to generate an approximate 3D flood surface profile, which can then be intersected with the Digital Terrain Model (DTM) of the area to produce an estimated flood boundary to within an accuracy of ±0.5 metres. This will allow approximate flood extents to be created ‘on the fly’ using current or predicted gauge heights. This approach differs from using a design flood in that it can produce an equal time flood display rather than an equal AEP display. If successful this will be an important development to enhancing the use of GIS in flood management within the SES.
A third method, yet to be fully investigated, involves the use of an air-borne multi-spectral scanner to capture images of flood waters at regular intervals and as the flood peaks at critical points along the river. The Daedalus Multi-Spectral Scanner can be flown to anywhere in NSW within a few hours and can deliver, via electronic means, a geo-rectified flood polygon within two hours of the image being captured. This process will not have a predictive ability but, depending on the time from capture to display, will be an excellent record of the flood and possibly the most accurate ‘near-to-real-time’ flood boundaries able to be obtained on the day.
Sources ofSpatial Data
Spatial data is at the core of a GIS and therefore at the core of its application to flood emergency management. The SES’s primary source of spatial data has been Land and Property Information (LPI), MapInfo Corporation and local Councils.
In the management of flood scenarios, the quality of decisions made with assistance from a GIS will depend completely on the timeliness, relevance, accuracy and currency of the data available. The data themes most relevant to flood management include demographic data, LEP zones, cadastral parcels, transport layers (roads and railway lines), address data, elevation data (contour, Digital Terrain Models (DTM) and Digital Elevation Models (DEM)), aerial photos and flood boundaries. This list is not exhaustive, as other data sets may be available from councils and other producers of local spatial data.
Many of the core data sets listed above are available to the SES, through a licence agreement from LPI. However, LPI are currently not able to provide some essential data in the format that is required, such as road centre lines with street address attributes, and therefore the need arises to look at alternate sources for this required data.
An obvious source of current and well maintained spatial data are local councils whose own requirements for detailed spatial information provides one of the most important repositories of spatial data available. Councils spend time and effort checking, correcting and maintaining spatial data for their respective areas, so it seems logical to extend the well-established relationship between councils and their local SES units to the supply of this digital spatial data. Some councils, notably Gunnedah and Maitland, have already made available their digital spatial data to their local SES units.
The SES encourages all councils that maintain spatial data to be open to sharing the data and, where appropriate, assistance in its use with their SES flood managers. Such a cooperation will ultimately benefit not only the SES and the Council but also the local community.
Further to the supply of local digital spatial data, the SES would benefit greatly from the willingness of councils to extend the specification of flood studies carried out in their areas. The inclusion of such items as the output of one metre increment flood boundaries, identification of heights of possible evacuation routes and the range of rates of rise up to when evacuation routes are cut would greatly benefit the flood planning process.
Flood Emergency Management
The emergency management of floods begins with the data gathering or flood intelligence phase, continues through the planning phase and the conduct of community education about the problem and its management and, when necessary, culminates in the combat or operational phase. These phases should not be viewed as separate entities, as each informs and complements the others in a continuous process. Information about the effects of a flood event is added to the flood intelligence database and then used to update the Local Flood Plan and so on. While the role of GIS in each of the phases is described separately below, the phases themselves should be thought of as part of an ongoing process.
Using GIS in Flood Planning
The Hawkesbury Nepean project has provided a unique opportunity to test and demonstrate the benefits to all levels of the organisation - Unit, Division and State - of using GIS in flood planning.
Using the GIS to display a combination of aerial photography, road centre lines, rivers, creeks, contours, cadastral and administrative boundaries has been particularly useful in the initial stages of planning. This combination provides a discussion focus and helps to illustrate local knowledge. Being able to create, enlarge and print a map has been a boon in familiarising emergency managers with an area prone to flooding.
As previously stated, design floods are a not a true representation of real flood behaviour but they have proven to be an aid during the planning process when used in conjunction with other flood intelligence. Using the tools available in GIS, flood extents at 2 metre intervals were overlayed on a 3 dimensional Digital Terrain Model (DTM) of the Lowlands area of Richmond and Agnes Banks, and used to create an animation of potential inundation. Being able to present a growing flood enables SES planners and local SES members, some of whom may not have seen a flood in their area, to better visualise and contextualise their local flood knowledge.
Projecting a map, with a rich set of underlying data, onto a wall screen and having the ability to manipulate aspects of the map during flood planning meetings has greatly improved communication between emergency managers and has led to a more detailed understanding of the problems to be addressed. During flood planning sessions for Hawkesbury City, a need was identified for accurate height data at specific locations in the floodplain. SES Unit members with experience of previous flooding in the area explained that the residents in the Lowlands become isolated in the early stages of a flood, and many refuse to leave their homes until it is too late for safe evacuation to be undertaken.
To fully understand the implications for evacuation in this area a surveying technique called a Real-Time Kinematic Global Positioning System (RTK GPS) was used to capture very accurate Australian Height Datum (AHD) levels and locations and other
characteristics of residences, road low points and intersections. This data was then incorporated into the planning process and flood simulations. This method of data collection shows great promise for use in all parts of the state confirming, or in many cases identifying, the height of levees (of which there are none in the Hawkesbury Nepean river system), roads and other points of interest during the flood planning stage. The SES is now able to use existing spatial data as well as generate new spatial data. Further to this, the Hawkesbury SES Unit has successfully used GIS to create street segments for use in doorknocking operations in Windsor and McGraths Hill. By displaying the cadastral boundaries and overlaying incremental flood extents with the road network, priorities for doorknocking effort were easily identified. Segment boundaries were drawn to contain a manageable number of properties for the purpose (usually 15-20) with the objective that one doorknocking team would be able to complete its block in an appropriate amount of time. In the process, areas of early inundation and road closures were given a higher priority for doorknocking. Work is currently under way to segment other ‘flood-threat’ areas in the Hawkesbury LGA for doorknock purposes. GIS has also contributed to the Flood Plan document as well, by providing customised sector and evacuation route maps of the area being planned for. These maps are exported in various image formats and inserted into the plan. These and other documents have been enhanced by the flexible output of maps from GIS.
Using GIS for Community Education
Maps and imagery created in the GIS have been used at community information meetings to help describe the complexity of issues surrounding the Hawkesbury Nepean River system. Three-dimensional models showing progressive inundation have been compiled into slide shows to demonstrate and explain the possible effects of flooding. Factors such as population increase, population turnover and the time which has passed since the last major flood have meant that there are segments of the community with little or no knowledge or experience of flooding and its effects in the area. Hence ‘‘there is a need to be able to translate information on river heights into area flooded and the effects…’’ (Opper, 2002). Simply providing the general public with information on river gauge heights is not enough. This information needs to be supported by a description of the known and possible consequences, and by what actions should be taken.
Issues such as which major tributaries feed the Hawkesbury-Nepean River system, when evacuation routes are cut and how islands are created by rising flood waters are more easily explained using these illustrations and visual aids.
These slide shows have been very effective in demonstrating the possible behaviour and extent of a major flood over the terrain. In showing the ‘where’ of a flood, community members are also able to gain an appreciation of the ‘why’ of various aspects of the planning process such as locations of road evacuation routes and why it is necessary to evacuate early. These animations and 3D displays make the concept of a flood come alive and quickly break down barriers to acceptance of the idea that floods ‘can happen here’ and of a greater magnitude than can easily be believed.
Figure 1. This image, created using GIS 3D technology, is one of a series used in a slide show to help describe to the community when and where flooding will cut evacuation routes in the event of a Hawkesbury Nepean flood.
To date customised flood simulations, based on GIS output, have been shown at community information meetings in Windsor, Penrith, Blacktown, Mount Druitt, Emu Plains, McGraths Hill, Pitt Town, Riverstone and Shanes Park.
Using GIS in Flood Emergency Response Operations
The SES has also developed GIS as an operational tool but, as the last flood on the Hawkesbury-Nepean River took place in 1992, this capability has not yet been applied to a real flood event. By integrating data from external sources, such as EnviroMon and the Flood Intelligence database, GIS is being used to provide a rich and dynamic information display.
There are four key gauges on the Hawkesbury Nepean river for which the Bureau of Meteorology provide flood warnings - Penrith, Richmond, Windsor and Webbs Creek. Also, there are a number of additional gauges, both manual and electronic, which are sources of current river heights. Data from these electronic gauges is delivered to SES headquarters using EnviroMon from which regular data snapshots are extracted. The previously mentioned prototype flood intelligence database has been incorporated into the GIS and integrates the flood gauge height data from EnviroMon with flood intelligence and other data such as flood extent polygons (design and calculated), evacuation routes and sector boundaries. The GIS interface provides a mechanism for emergency managers to view these relationships almost instantly and in context on a map. These displays are useful despite possible discrepancies between actual gauge heights and their recorded and extrapolated effects in the gauge reference area.
The SES has created operational workspaces in advance that can be used by flood emergency managers to view operationally related data. An evacuation route status map has been designed to show the status of road points such as restricted access, reported
closure due to local flooding and where mainstream flooding has cut roads. For instance, it is known that the Windsor evacuation route is cut at a flood height of 15 metres by mainstream flooding. The map symbol allocated to the relevant low point can be programmed to automatically change to a ‘road closed’ symbol when the gauge height provided by EnviroMon reaches 15 metres. These events will also be supported by field observations. Where there is a discrepancy the map can be manually changed to the correct status.
Another useful display is sector status maps showing when emergency management sectors have been doorknocked, evacuated, and/or when the last evacuation route is cut resulting in isolation.
GIS and its outputs, including maps and animated displays, have an important role to play in informing the public, briefing the media, Government and the managers of other agencies about the developing flood.
Summary
The SES has accomplished a great deal in the development of GIS technology to aid its flood management role. GIS has already proved its worth in informing the flood planning process, enhancing public education about flooding in the Hawkesbury Nepean valley and providing rich operational displays that integrate disparate data about floods. The SES has gone a significant way to achieving the Hawkesbury-Nepean strategy goal of a real time flood intelligence system across agencies.
There is still work to do in the area of creating flood intelligence from spatial data in a GIS format. The existing flood intelligence data does not readily lend itself to storage as spatial objects, and the process of gathering new data in a format easily incorporated into a geo-database is still to be fully explored and developed.
The roll-out of the GIS to SES Divisions and Units beyond the Hawkesbury-Nepean project has not yet begun. The development of more sophisticated tools specific to the SES’s roles will be an ongoing task, as will the sourcing and management of spatial data relating to all flood prone communities in NSW.
Given that funding for GIS resources in the SES has been limited to the Hawkesbury-Nepean project it is anticipated that the use of GIS in the SES for flood management throughout the State will be dependant, at least in part, on future funding arrangements. The SES is committed to developing this technology as an aid in its flood management role. The speed with which we can further develop and deploy GIS, and the effectiveness with which it can fulfil its potential, will depend on assistance and partnerships with organisations such as DLWC and LPI, and very importantly with local councils.
References
Hazel, V. 1999, Flood Mapping: GIS Creates Benalla Flood Inundation Maps, GIS User, Issue 31, December January 1999, pp. 40-42
Hawkesbury-Nepean Flood Management Advisory Committee 1997, Achieving a Hawkesbury-Nepean Floodplain Management Strategy, New South Wales Government.
Water Resources Commission 1980, The Flood Inundation Mapping Programme,
New South Wales Government.
Opper, S. 2002, Flood Warnings: Status and Latest Trends, EMA Occasional Workshop Series.
Pfister, N. and Rutledge, A. 2002, The Role of the New South Wales State Emergency Service in Flood Management, paper presented at the 42nd Annual Conference of the
Floodplain Management Authorities, Kempsey.
Sydney Water Corporation 1995, Proposed Warragamba Flood Mitigation Dam EIS, New South Wales Government.
Personal Profile of the Presenter
Peter Crowe has had ten years experience as a specialist in the use of GIS and a longer period of involvement in land systems work as a surveyor and survey draftsman. For the last four years he has been responsible for developing the SES's GIS capability so that GIS can be used in planning for and responding to floods and storms This is his first presentation to the Floodplain Management Authority Conference.
The Other Authors
Peter Cinque is a senior regional manager in the SES and has prime responsibility for ensuring that the SES is ready for flooding in the Hawkesbury-Nepean River valley. This valley has possibly Australia's most serious flood threat in terms of the potential numbers of people having to evacuate and the volume of damage which severe flooding can generate.
Belinda Davies is a volunteer member of the SES and has a background in environmental science. She is presently working on the SES GIS program.
Author's Contact Details
State Emergency Service State Headquarters, PO Box MC6126, Wollongong, NSW 2521.
Peter.Crowe@ses.nsw.gov.au
Peter.Cinque@ses.nsw.gov.au Belinda.Davies@bigpond.com
Presented at the 43rd Annual Conference of the Floodplain Management Authorities of NSW, Forbes, 2003.
