@article {bnh-5210, title = {Urbanisation pressures and flood risk: Gawler River catchment and regional development}, year = {2018}, month = {12/2018}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Adelaide is built on a natural floodplain and as such is at constant threat of\ inundation from flood waters. The risk from flooding is a significant threat to\ South Australia, with it being the State{\textquoteright}s most costly natural hazard. In 2017 the\ State{\textquoteright}s average annual damages from flooding were approximated at $32\ million (Burns et al., 2017). It is also estimated that 8,500 properties are\ vulnerable to a 1-in-100-year event (as of 2010).

Flood risk is a complex interaction between many dynamic and interrelated\ processes, and can be considered as the combination of the flood hazard itself\ (its depth, extent, and velocity can all be considered), along with the assets\ and values exposed to the hazard and the vulnerabilities of these. This can be\ considered as the {\textquoteleft}risk triangle{\textquoteright} (Crichton, 1999).\ Each of these factors is also subject to change with time. Flood hazard is\ impacted by climate change via various mechanisms including changing\ intensity and frequency of rainfall events, along with impacts on vegetation\ and antecedent moisture (van Aalst, 2006; Alfieri et al., 2015). The exposure and\ vulnerability of the region is also changing with increased economic\ productivity and residential demands for land, along with different building\ codes and personal resilience (Koks et al., 2015; Mazzorana et al., 2012).

There are also interactions between the components of flood risk such as the\ impact of urbanisation in a floodplain {\textendash} increasing the number of exposed\ assets and increasing runoff, along with new developments and changing\ building codes influencing the vulnerability of buildings in a floodplain. This\ report will specifically highlight the interaction between new development in a\ region and its flood risk in the Gawler River floodplain.

As exposure increases driven by the need to meet economic and population\ demands for land, catchments become increasingly urbanised and hence\ impermeable. This reduces the ability for the landscape to manage the risk of\ pluvial flooding, as natural surfaces are replaced with more impermeable\ surfaces (like concrete or asphalt) leading to increased runoff.

This report will look at the probability of urbanisation in the Gawler River\ floodplain in comparison to areas subject to inundation and of high flood\ hazard.

To achieve this the Metronamica land use model (www.metronamica.nl) was\ applied to the region and calibrated to incorporate the local context and\ conditions appropriately. This model was then used to consider scenarios for the
region{\textquoteright}s growth (economic and population) to 2050 to consider the location\ and likelihood of urbanisation and its relationship to flood hazard.

This is done to highlight the value of considering changes in urbanisation and flood risk, however it should be noted this modelling is performed as proof-of-concept and should not be used for any planning or investment decision.

}, issn = {434}, author = {Graeme Riddell and Hedwig van Delden and Holger Maier} }