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Flood Warning in Southland
This page describes the flood warning system operated by Environment Southland throughout the region. It assists individuals and agencies responsible for managing and responding to flood disasters to understand the flood warning system. More details are given in specific information brochures describing the warning system for each river system.
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Information on this page was last updated: September 2005
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Download this page in PDF format here. |
History
The history of flood warning in Southland dates back to the 11th July 1947 when the then Southland Catchment Board issued its first flood warning on radio broadcast. The procedure adopted then has remained largely unchanged since. Flood warning messages broadcast to the general public contain only rainfall and river level situation at the time the broadcast was prepared. The interpretation of this information is left to the user of the information.
Early in the Southland Catchment Board's history it was accepted that the issuing of river level reports during flood events was a service the Board should supply and therefore flood warning, although not a statutory obligation, is a service this Council freely provides to the general public.
Because of the need for the Council to act quickly and decisively in a number of diverse operations during a flood event, it is essential for the Duty Flood Warning Officer to be provided with a clear, uncluttered picture of the important existing situations and the forecast trends. Only then will he be free to make decisions, to allocate manpower and direct and authorise actions in critical areas with minimum delay.
The Council is ever mindful of the problems that are associated with floods particularly a major event when residential areas are in danger of becoming inundated by flood water and to this end the Council's general policy is to keep organisations such as Civil Defence, City and District Councils advised well in advance of likely problems which may arise during a given event.
Flood Warning
Flood warning is an integral component of counter disaster arrangements for a community at risk from flooding.
The aim of the warning system is to minimize loss of life and property damage by warning people of the likelihood and size of a flood so that they may evacuate, shift property or stock to higher ground, or implement other temporary flood loss reduction measures.
Warnings are of limited value unless they are delivered in a timely and effective manner and property owners and residents in the flood-threatened area believe the warning and take appropriate action in advance of being flooded.
Roles & Responsibilities
The responsibility for flood forecasting and warning services in Southland rests with Environment Southland.
In the Southland region, the effectiveness of the flood warning system depends on the cooperative involvement of Environment Southland, Civil Defence and Local Government agencies working with flood-threatened communities.
Environment Southland coordinates the development and operation of flood warning services in Southland.
The roles of the primary agencies involved in the flood warning system, are outlined to the right. |
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Flood Classifications
At each flood warning river height station, the severity of flooding is described as minor, moderate or major according to the effects caused in the local area or on the downstream flood plains.
Major Flooding : This causes inundation of large areas, isolating urban areas. Major disruptions occur to road and rail links. Evacuation of many houses and business premises may be required. In rural areas widespread flooding of farmland will most likely occur. Flood protection systems (stopbanks) running at near 100% capacity.
Moderate Flooding : This causes the inundation of low lying rural areas requiring the removal of stock and/or the evacuation of some houses. Main traffic bridges may be closed by floodwaters. Flood protection systems contain flood water.
Minor Flooding : This causes inconvenience such as closing of minor roads, flooding of low lying rural areas close to main rivers. The zero level of a river gauge ("gauge zero") is typically set at the low flow level of the river or stream, i.e. the water level of the stream after a long dry spell. River heights are measured in metres above the gaugeboard zero with normal river level at or close to 1.00 metres. For example, a river level height reading of 5 metres means that the water level has risen 4 metres above its normal level. In tidal areas, the gaugeboard zero may be set at the mean sea level.
Flood Warning Operations
The development and provision of flood warning services in Southland is the role of Environment Southland’s Flood Warning Operations Centre in Invercargill.
Environment Southland provides flood warnings in the Southland region, predominantly within the Waiau, Aparima, Oreti, Waihopai and Mataura catchments. The aim of the warning system is to minimise loss of life and property damage by warning people of the likelihood and size of a flood so that they may evacuate, shift property or stock to higher ground, or implement other temporary flood loss reduction measures.
Flood Warning Watch service operates on a 24 hour 7 day basis.
Flood Warning Watch staff have two broad responsibilities:
- To monitor and/or receive notice of weather and/or hydrological events that may lead to flooding, and respond accordingly.
- To ensure that the flood warning system is fully operational at all times, and effect repairs where appropriate.
The Flood Warning Operations Centre operates up to 24 hours per day depending on the severity and extent of a flood event. The Duty Watch Officer or Flood Warning Officer can be contacted via Environment Southland’s 24 Hours Emergency Service phone numbers; (03) 211 5225 or Southland Area Call Free (0800) 768 845.
The basic components of the flood forecasting system are shown in the diagram below.
Data Collection & Transmission
Rainfall and river level data is collected from over 55 sites throughout Southland via radio and telephone telemetry from automatic stations.
Meteorological & Hydrological Data
The collated data is analysed using a range of techniques and software to produce reports and graphs and make the data available through Environment Southland’s web site. Complex computer simulation models for the Mataura and Oreti Rivers developed by NIWA for ES is utilized to predict the likely timing and severity of flooding at specific sites. This forecast information is assessed and passed on to emergency organistaions
Flood Warning Services
- River Level Bulletins.
These contain the latest observed above normal heights at flood warning sites within a river system and are issued regularly, usually 2 hourly during daylight hours.
- Flood Information
During a flood event those persons affected, can ring the flood warning office and received up to date river level and rainfall information, and forecast river levels.
- Flood Forecasts
Forecast peak flood levels and discharge is available for 8 sites on Southlands main rivers. The Flowroute software produces forecast flood peak data at these sites from upstream information.
- Professional Advice
Environment Southland staff provides direct assessments of flood conditions and forecasts to Civil Defence, emergency agencies and Local Government officers.
Flood Warning and River Height Bulletins
Environment Southland issues flood warnings and river level bulletins regularly during floods for the Mataura River and its main tributaries, the Makarewa River, Oreti River and Winton Detention Dam, Aparima River and Otautau Stream, Waiau River and three Invercargill Flood Schemes. These bulletins are issued normally at 2 hourly intervals during daylight hours, but on a 24 hour basis during the crucial stages of major flood events.
These bulletins are sent to radio stations for broadcast, and to the local Councils, Civil Defence, Emergency Services and a number of other agencies involved in managing flood response activities
Radio
The Environment Southland issues flood warning messages to all the radio news media in Southland, Foveaux Radio, Radio Network, Radio Southland, Hokonui Gold and Southland Television. These flood warnings in the form of river level situation bulletins and are issued at 2 hourly intervals (1 hourly during the crucial stages of a major flood event) and are normally broadcast immediately following national link commitments on the hour.
Local response organisations
These include City and District Councils, Civil Defence organizations and the NZ Police.
Internet/World Wide Web
Flood Warnings, River Situation Bulletins, river level and other weather related data is available on Environment Southland’s Web page at http://www.es.govt.nz . River level, river flow, rainfall and ait temperature data is updated hourly automatically
Telephone River Levels
A part of the instrumentation at a number of river level sites in the region is telephone answering units which permits the instrument to be interrogated by telephone to obtain the current river level at a given site. Environment Southland makes available to those persons or organisations who are directly affected by flooding within the Southland, the unlisted telephone numbers of each instrument.
River Catchment Information Brochures
Environment Southland produces Catchment brochures for the main river systems in Southland which contain detailed information such as flood warning information for the particular catchment, telephone interrogation of flood warning sites, flood peak travel times, historic peak flood heights and maps showing catchment river level stations and rainfall sites.
Futher Information
For further information please contact:
The Flood Warning Officer, Environment Southland, Private Bag 90116, Invercargill. Phone; 03 211 5115 or Southland Area Call Free 0800768 845 during office hours.
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