Map Notes Flood depth zones

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Map Notes Flood depth zones Powered By Docstoc
					Map Notes
Flood behaviour                                     This map does not show flooding from local                The flood extents shown are a prediction of land
A flood occurs when a pipe, channel or creek         stormwater drains that can occur as a result             affected for the specific level of risk. They do not
cannot carry the volume of water in the system.     of localised heavy rainfall. Nor does it show            necessarily indicate the threat to buildings located
When this occurs, floodwaters travel across the      flooding that may occur as a result of interaction        on that land. Flood assessment for particular sites
land and can damage property and threaten safety.   with adjoining catchments. In particular, flood extents   requires more detailed interpretation, survey and
Flooding is a natural event.                        in the area between Mile End and the northern side       hydraulic analysis.
                                                    of the Airport are possibly greater than shown
The extent of flooding shown on this map is based    due to the effect of runoff from those areas.            The limit of flooding shown is not a boundary
on predictions of flood behaviour of the             Similarly this map does not show flooding from either     between flood prone and flood free land.
watercourses (channels and creeks).                 the Sturt River or the River Torrens, both of which      Larger floods could inundate areas outside the
                                                    have a very low probability.                             areas shown.
Localised flooding from street drainage is not
shown on this map and it can occur in severe        The data on this map is based on survey, hydraulic       Watercourses
storms in most areas of the catchment.              and hydrological modelling in 2002 of accuracy           Properties directly adjacent natural watercourses
                                                    sufficient for broad-scale flood risk management and       are flood-prone irrespective of their status on
This map is intended to help promote public         planning. The modelling reflects current practice but     this map. Actual flood extents will vary from one
awareness of the flood hazard from the Brown Hill    there are uncertainties associated with the data on      flood to another because they are affected by
and Keswick Creek systems and assist people who     which the models are based and, therefore, on the        earthworks, debris blockages, further development
undertake development in the area.                  flood extents shown on this map.                          within the catchments and other factors.

Limitations and other important                     The predicted flood extents are not based on              Disclaimer
notes about this map                                historical floods. Actual flood extents will vary from
                                                    one flood to another because of earthworks, debris        This map is provided on the basis that those
This map delineates areas south and west of         blockages, further development within the                responsible for its preparation and publication
Adelaide assessed as subject to floods from Brown    catchments and other factors.                            do not accept any responsibility for any loss or
Hill Creek, Keswick Creek, Park Lands Creek and                                                              damage alleged to be suffered by anyone as a
Glen Osmond Creek.                                                                                           result of the publication of the map and the
                                                                                                             notations on it, or a result of the use or misuse
                                                                                                             of the information provided herein.

                         Flood depth
                         zones                      Light blue (Depth less than 0.1metre)                    Dark blue (Depth 0.1metre to 0.25metre)
                                                    During a 1 in 100 year flood it is expected               During a 1 in 100 year flood it is
                         Coloured bars relate       that water will be less than 100 millimetres             expected that water will be between
                         to map above               (4 inches) above the ground level. In most               100 and 250 millimetres (4 to 10 inches)
                                                    cases houses will not be affected.                       above the ground level and some houses
                                                                                                             may be affected.
   Brown Hill and Keswick Creeks
   floodplain inundation map
   1 in 100 year flood

Purple (Depth 0.25metre to 0.5metre)            Light pink (Depth 0.5metre to 1.0metre)         Dark pink (Depth greater than 1metre)
During a 1 in 100 year flood it is expected      During a 1 in 100 year flood it is expected      Flooding will reach a depth of greater than
that water will be between 250 and              that water will be between 500 millimetres      one metre (about 3 feet). Property damage
500 millimetres (10 to 20 inches) above         and one metre (20 inches to about 3 feet)       is likely and these areas have a hazard rating
ground level. Property damage is possible and   above ground level. Property damage is likely   of high to extreme.
these areas have a medium hazard rating.        and these areas have a high hazard rating.
1 in 100 year floodplain                              The benefits of floodplain mapping                      Areas where water depth is greater or areas near
                                                                                                           watercourses where the velocity of water is high
A floodplain is an area of land subject to            The floodplain study and map will help Councils
                                                                                                           are more hazardous and evacuation to higher
inundation by water from a watercourse.              make planning decisions for safe and orderly
                                                                                                           ground may be required. Residents in these areas
Over a very long period of time a floodplain will     development.
                                                                                                           should have a plan in the event of rising
be inundated to various degrees on different
occasions. The map identifies those areas             The map will also help the Board and Councils
vulnerable to flooding in a 1 in 100-year flood        with the development of appropriate planning
                                                                                                           Important things to consider in the event of
from the watercourses. A flood of such a              policies and flood management, prevention
                                                                                                           a flood are:
magnitude would be expected to occur on              and mitigation initiatives. These may take
average about once every 100 years and               some time to develop, assess and then fund.
                                                                                                           • Avoid fast flowing water. Remember that at
consequently there is a 1 percent chance             Considerable State and Local Government
                                                                                                             stormwater inlets in the street there may be
(1 in 100) of a flood of this magnitude in any        negotiations will be involved.
                                                                                                             eddies that could be dangerous.
one year. Of course floods do not occur on a
regular basis and a 1 in 100 year flood need not      Impact on development in the                          • Avoid wading, even in shallow water, and if
occur in every 100 year period. Conversely there     floodplain                                               you must enter shallow floodwater, wear solid
could be several floods that exceed the 1 in 100                                                              shoes and check depth with a stick.
                                                     Councils will take the flood mapping into
year flood within any period of 100 years.
                                                     account when they make decisions on                   • If you have time, elevate valuable possessions
                                                     development applications. This might, for               in your home (personal papers, photo albums,
It is important to note that greater floods
                                                     example, require ground floor levels for new             family mementos, electronic equipment etc as
than that shown on the map are possible.
                                                     structures to be raised to ensure that they are         high as possible.
The 1 in 100 year flood is chosen as it is
                                                     above the likely flood level.
internationally recognised for urban planning and                                                          • Turn off electricity, gas and water.
development purposes.
                                                     In due course each Council’s Development Plan         • Listen to the radio for information
                                                     will be changed to ensure that development is           and updates.
Why the map was made
                                                     planned in a way that recognises the location
The first step in flood management is to have up-      of flood prone areas                                   Insurance
to-date information about the extent of flooding.
                                                                                                           Questions about insurance should be directed to
The area was last mapped in 1984 and with            In the meantime developers should discuss their
                                                                                                           your insurance company.
development occurring over the last 20 years and     specific situation with their local Council before
the very considerable advances in flood modelling     committing to a project.
                                                                                                           Property values
and mapping techniques, it was considered
prudent to improve the level of knowledge and        Flood warnings                                        It is important to note that the floodplain
understanding of flood potential.                                                                           mapping study has not changed the likelihood
                                                     A flood monitoring system known as ALERT has
                                                                                                           of a severe storm occurring. The existence
                                                     been installed by Councils and the Bureau of
This up-to-date floodplain mapping study will                                                               of the floodplain map does not increase the risk
                                                     Meteorology. It consists of a network of rainfall
inform residents, Councils and the State                                                                   of being flooded.
                                                     and water level stations connected to computers
Government and help better prepare mitigation
                                                     at the Bureau’s offices at Kent Town and the SES
strategies for floods. It will assist Councils with                                                         A recent report prepared by the Natural Hazards
                                                     at Mitcham. When heavy rain falls, the rainfall
planning decisions to ensure development takes                                                             Research Centre based at Macquarie University
                                                     alarms are triggered, and emergency response
place in a safe and orderly manner.                                                                        indicates that experience in Australia and overseas
                                                     staff are alerted to the potential for floods.
                                                                                                           is that there should be no long-term impact on
How the map was made                                 However floods are generated so quickly                property values as a result of the release of the
                                                     along Glen Osmond Creek and Park Lands                floodplain maps.
The mapping was produced by specialist water
                                                     Creek in the Unley area that it is not realistic
resource consultants Hydro Tasmania using
                                                     to expect any prior warning of floods.                 Further information
state of the art survey and computer modelling
                                                     The situation with Brown Hill Creek and areas
technologies that provide the best possible                                                                If you require further information contact your
                                                     further downstream along Keswick Creek
estimation of flood behaviour. The study was one                                                            local Council or the Patawalonga Catchment
                                                     is a little better as a major flood will take longer
of the most advanced and complex floodplain                                                                 Water Management Board.
                                                     to rise and it is possible some flood warnings
studies undertaken in Australia.
                                                     can be issued via the media.
                                                                                                           City of Adelaide 8203 7203
                                                     What to do in a flood                                  City of Burnside 8366 4200
                                                     Personal safety is the most important                 City of Mitcham 8372 8888
                                                     consideration during a flood. Although floods
                                                     greater than the 1 in 100 year flood are possible,     City of Unley 8372 5111
                                                     it is important to remember that the vast majority    City of West Torrens 8416 6333
                                                     of the floodplain shown on the map is very
                                                     shallow and consequently of low to medium risk.       Patawalonga Catchment
                                                     In areas of shallow flooding, driving or walking       Water Management Board 8271 9190
                                                     from your home could be more hazardous than
                                                     staying at home.

 Patawalonga Catchment
Water Management Board
Brown Hill and Keswick Creeks
Floodplain Mapping Study
                   Floodplain mapping is being progressively undertaken across
                   metropolitan Adelaide. Assessments and flood management
                   strategies have already been put in place for the River Torrens
                   and the Sturt River. In conjunction with local Councils, the
                   Patawalonga and Torrens Catchment Water Management Boards
                   are now assessing other watercourses including Brown Hill and
                   Keswick Creeks in the Patawalonga Catchment and First,
                   Second, Third and Fourth Creeks and other areas in the Torrens
                   Catchment. The mapping for Brown Hill and Keswick Creeks
                   is now completed.

                   The map on this fact sheet results from a detailed two-year
                   study for the Brown Hill and Keswick Creeks Flood Management
                   Group. The Group is made up of the Patawalonga Catchment
                   Water Management Board, the City Councils of Adelaide,
                   Burnside, Mitcham, Unley and West Torrens and State
                   Government representatives. The study was undertaken for
                   the Group by water resources consultants Hydro Tasmania.

                   Since European settlement, thousands of residential, commercial
      Fact Sheet

                   and industrial properties have been developed on the Brown
                   Hill and Keswick Creeks floodplains across an area of some
                   60 square kilometres.

                   The Patawalonga Catchment Water Management Board
                   convened the Brown Hill and Keswick Creeks Flood Management
                   Group to provide a forum to focus on matters of flooding and
                   watercourse management in and along the Brown Hill and
                   Keswick Creeks system.

                   Just over 5,000 residential and commercial properties are
                   within the 1in100 year floodplain (see back page for definition).
                   About 3,700 properties (74%) are in very low hazard areas
                   with less than 100 millimetres (4 inches) of flood depth.
                   The flood damage bill from the 1 in 100 year flood is estimated
                   to be between $100 and $200 million.

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Description: Map Notes Flood depth zones