EVALUATING FLOOD MITIGATION OPTIONS USING GIS AUTOMATION
Ferguson, R.,1 Reddish, J.2
1
Morphum Environmental
2
Opus International Consultants
Aims
Flood mitigation design can involve a large number of hydraulic simulations to compare the
effects of different storm return periods and mitigation options on water levels. Identifying
structures affected by flooding under each model scenario, so that mitigation performance can be
evaluated, can therefore be a slow and inconsistent process. This project aimed to improve the
efficiency of flood mitigation planning by automating this process within a GIS environment.
Method
A series of flood mitigation options were modelled in an intensively developed suburb in Auckland
to identify the most effective way to protect residential properties from chronic flooding. An
automated procedure was developed in GIS to relate predicted water levels from the hydraulic
models to surveyed building floor levels so that the severity of flooding could be quantified over a
range of rainfall and mitigation scenarios. The procedure assigned a flood hazard rating to each
property and summarised this information in graphical and tabular forms so that the efficacy of
different mitigation options could be directly compared.
Results
Automation enabled the merits of different mitigation designs to be compared more efficiently by
speeding up and enforcing the consistency of data processing. This allowed the effect of different
design parameters on flood impacts to be tested without a serious time penalty and consequent
cost. The most appropriate mitigation option – a high-flow bypass pipeline and a stone wall flood
defence – was then selected for further development. The automated approach explicitly
documents the analysis workflow to clearly communicate methods and assumptions, and is
widely applicable to other forms of hydrological and hydraulic analysis that have a repetitive
element.