Dear Jonathan (and the List),

Many thanks for the information.  I have updated "Fact Sheet 1:  Mitigation 
Saves" with a new case study of Australian flood mitigation.

I have a question relating to the fifth case study quoted in the Executive 
Summary of the BTRE report:
"A levee proposed for the Tamworth industrial area would significantly 
reduce flood damage (the cost of the November 2000 flood is estimated at 
close to half a million dollars). It is also estimated that the existing CBD 
levee would avoid at least $5.36 million potential direct damage in a 
100-year average recurrence interval (ARI) flood."

The Executive Summary also describes the levee paradox as "the increase in 
potential damage resulting from floods greater than the design level (for 
example, if development behind levees increases or residents’ flood 
awareness diminishes)".  This tendency of structural flood defences to 
increase long-term vulnerability is well-established in the flood management 
literature, although often not established enough in flood management 
practice.

Similarly, when I first suggested to this list the idea of the "Mitigation 
Saves" Fact Sheet, a list member provided this intriguing example from the 
U.K.:
"National Appraisal of Assets at Risk from Flooding and Coastal Erosion, 
including the potential impact of climate change. published by the English 
Department for Environment, Food and Rural Affairs (DEFRA) in July 2001 
concluded that:
  a. "The capital works and maintenance investment needed to continue to 
provide and maintain present defence standards is in excess of £0.3 
billion/year;
  b. "Current standards of defence reduce annual average damages to 
approximately £0.8 billion/year;
  c. "Continuing to invest at present levels of approximately £0.24 billion 
per year will result in increasing annual average damage possibly at the 
rate of some £10-15 million per year."
The phrase "capital works and maintenance" leads me to assume that the 
"defence standards" are achieved by mainly structural defences.

During the 1997 Red River floods, the media reported that in Manitoba, the 
Winnipeg Floodway also called the Red River Floodway saved Winnipeg from a 
flood disaster.

I have so far been reluctant to include these examples because they might 
provide ammunition for policy-makers who wish to rely on structural defences 
to the detriment of truly long-term mitigation strategies.  My perception, 
possibly incorrect yet backed up by many studies, has been that the 
dominance of structural solutions has been a major drawback in flood 
management in the U.K. and the U.S.A. amongst other countries, although a 
shift towards more comprehensive solutions has been occurring over the past 
few years.  In contrast, Ontario has had successes with non-structural 
solutions for several decades and the benefits are as clear as the other 
four Australian case studies in the BTRE report.

My question to the list is whether or not I am being unduly biased against 
structural defences in the case of flood management.  Or am I misreading or 
not fully understanding what these examples of structural defence mitigation 
represent?

Naturally, exceptions will always exist.  But can a general tendency exist 
for structural flood defences to be a viable, long-term flood mitigation 
strategy?  For example, could the Winnipeg Floodway or a similar solution 
"fail", particularly if the floodway were built through an uninhabited area 
which might be an immense floodplain.

Thank you for any thoughts,
Ilan

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