Development and application of a decision support methodology for flood risk management planning in a Scottish context
Coupled hydraulic model-GIS-decision framework computer simulations have been used
to analyse the risk of urban river flooding to both built environment and residents. Hec-
RAS software was used to simulate flooding in the existing channel system using a range
of flood return intervals from 1 in 5yr to 1 in 1000yr events, and then repeated for two
design options of the river channel that were developed as possible river rehabilitation
schemes.Using ArcView GIS software, census data and property data, assessments were
made of the performance of each channel with regard to both the social and the economic
impacts on the surrounding community in times of flood. Social impacts represented the
residents affected classified by area into degrees of risk. Economic impacts involved the
per-property calculation of potential buildings and contents damage felt by both
residential and commercial properties from flood inundation.
Results from the three channels modelled have shown that the impacts on the surrounding
community have to be assessed in tandem with the hydraulic performance as these will
affect its acceptability. The nature of these impacts could mean a different outcome in
terms of channel design selection as illustrated by the fact that the hydraulic performance
of the two proposed designs is similar, while the socio-economic impacts vary by up to
90%. Despite this, both of the design options result in significant improvements over the
existing scheme, highlighting the need for an improved channel system in this locale.
The results produced by this investigation point towards the assessment criteria that
should be applied to any river channel engineering works such that the fitness-for-purpose
assessment is transparent and accounts for all significant factors. The framework for an
analysis tool is presented that can be used by planners in the context of assessing the
viability of river design schemes in the urban environment.