Home Our environment Stormwater/Flood Management

Printer friendly version

Flooding at Smiths Lake

Flooding

How does flooding occur?

Flooding occurs when there is too much water coming from the contributing catchment area into a downstream location that is unable to move this water efficiently away. Simply there is more water coming in than going out. Flooding can be looked at in two ways. The first is as a result of an inefficient stormwater network (localised flooding) and the second is because of a water body (lake, dam, river) being supercharged with incoming water (mainstream flooding).
Whilst Council endeavours to minimise the effects localised flooding through adequate sizing of pipes/channels, Council cannot guarantee that every property will be dry 100% of the time, ie during extreme weather events.

Great Lakes Council is more so concerned with the implications of mainstream flooding and devising mitigation measures that are both feasible and cost effective. Throughout the floodplain investigation process aspects for minimalisation of over floor flooding include levee banks, voluntary house raising, setting minimum floor levels and purchase of land and the maintenance of a flood level warning system.

Flood Study Process

Great Lakes Council conducts flood studies for all mainstream flooding areas (lakes and rivers) and conducts this in accordance with the Floodplain Development Manual. This manual dictates a three step process whereby a flood study is conducted on the designated water body to ascertain the height as to which water will rise in a specific rain event. From this rain event a contour corresponding to the modelled flood height is mapped and the number of houses and properties/houses numbered. The second step in this process is conducting a study investigating all of the mitigation options for the area and ascertains how effective they will be. The third step is the development of a management plan that reviews all of the options and recommends the most feasible. Typical recommendations may include erection of a flood warning device, voluntary house raising, levee banks etc.

How is a flood measured?

Flood heights are measured in relation to a common datum (AHD, Australian Height Datum) or base point. The datum to which all flood heights are measured is mean sea level. Mean Sea Level is 0m AHD.
Floods are modelled for certain rainfall events and are listed in statistical terms. The common flood frequencies measured are 1:20yr, 1:50yr and 1:100yr. The notation should be read as follows: there will be a storm with a given intensity 1yr out of every 20, 50 or 100 years. Or relating that to a yearly percentage 1:100 is a 1% percent chance.

Where can I obtain flood information?

The majority of Flood Studies, Management Studies and Management Plans are available for download, they are also available for viewing at Council's Office or a copy can be purchased by contacting Council on (02) 6591 7222.

Written information relating to flooding can be purchased from Council by applying for the following Certificates:-

Flood Level Certificate

This certificate will provide confirmation as to whether the land subject to the application is flood effected, and if it is it will provide a level.  It is limited to providing flood information that Council has in its pocession in relation to flood studies or historical information and does not take into consideration Council's planning controls or policies. Should you require this information a copy of Council's Flood Management Policy can be provided or an application can be made for Planning Certificates 149(2) or 149(5).

Prior to making an application for the Flood Level Certificate please contact Council's Engineering Services Division to confirm Council has information available given Council does not hold this information for every property.

A fee of $35 is to be be paid at time of application. Please allow approximately 5 working days for this information to be sent to you. See below to download an application.

Section 149 Certificate

Section 149 of the Environmental Planning and Assessment (EP&A) Act 1979, requires that local councils, upon application, must issue a Planning Certificate providing information on the planning controls relating to any piece of land within the Council Area, this information includes the hazard of flooding, for further information regarding Section 149 Certificate.

Flood Management Studies, Plans and Policies

Council has prepared a number of Flood Management Studies, Plans and Policies; 

Contact details
Drainage Engineer
02 6591 7273 (ph)
02 6591 7242 (fax)
council@greatlakes.nsw.gov.au

© 2008 Great Lakes Council
This page: http://www.greatlakes.local-e.nsw.gov.au/environment/6867/6875.html