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NWRM: evenmoreattractive solutions than theyappearat first sight
MMSD (2011) considered the financial cost-effectiveness of a deep-storage tunnel for urban
stormwatermanagement, andcompared it toother storagepossibilities. The illustrationbelow
shows that some of the alternative approaches to urban stormwatermanagement aremore
(financially) cost-effective than deep-water storage. However themost cost-effective are not
the kind ofmeasures that couldbe extensively applied in the artificial soils that are prevalent
in urban landscapes (e.g. native landscaping, soil amendments and rain gardens). On purely
financial grounds, NWRM would then be concluded to play only a marginal role in cost-
effectiveurban stormwatermanagement.
However, the comparison in the figure is incomplete and misleading because traditional
cost-effectiveness analysis only considers one effect (captured stormwater run-off), one
benefit (reduced infrastructure cost) andfinancial costs. Thus, the cost of the infrastructure is
underestimated (as theexternalitiesof thedeep tunnel storagearenotaccounted for), thecosts
avoidedby thegreen infrastructureoptionsare ignored (savings inwater treatment, reductions
inenergy consumption inhouseholds, etc.), as are the co-benefits (increase inpropertyvalues,
reducedpollutantloads,groundwaterrecharge,improvedairquality,etc.).Withinthiscomparison
acompletelydifferentresultwouldariseiftheexternalcostsofthedeeptunnelstorageweretaken
intoaccount,with thehorizontal line in thefiguremovingupwards. If theavoidedexternalities
implied by the direct and ancillary benefits, or positive externalities other than storingwater
were considered,
all the net costs of
theNWRMwould
thenbe lowered.
Illustration9
X = % of increased storage capacity as compared to target capacity (Milwaukee's Regional Green Infrastructure Plan: MMSD, 2011).
Y = Incremental cost (€/m3 of storage capacity). [Note: An Exchange rate of 1 €= 1.35 US$ was applied]
Source: IMDEA calculations based on MMSD (2013)
Enhancingpolicycoordination tomake themostoutofNWRM inyourplanningprocess
