b'terDetentionAssembly(SDA),The stormwater is shown asThere is now a growing interest from municipalities, building known as a blue roof. Claims area climatic load hydrograph. The being made that NBSCR, whensystemhydrographshowstheowners, insurers and other stakeholders to use the vast unused properly designed, constructed anddischargerate.Thereduction maintained, have the potential toin the peak discharge seen in the mitigatestormwaterimpactsbyclimatic load hydrograph is re- surface of commercial roofs in the dense urban canopy to 25to75percentandmoderateferred to as retention or deten-urban overheating by up to 1.5C.tioncapacity.Theincreaseinmitigate the adverse impacts of urban flooding.These technologies can effectivelythe time to peak is referred to as reduce stormwater runoff by usingthe lag, the time that the water advanced drain technologies and op- will be discharged/released. The erational strategies to store and releaseshaded area between the climat-stormwater during and after extremeic load and system hydrographs storm events. shows the detained volume.Inspiteoftheseperceivedben- When designing NBSCR, efits,thegrowthofNBSCRinthe detained volume is required Canada is limited due to the lack ofto achieve a desired detention science-basedvalidationandregula- effect. The maximum detained tory requirements. National Researchvolumeoccurswhenthetwo Council Canada (NRCC) is forminghydrographsintersect.For a consortium with industry partnersVRAapplications,themaxi-and policy makers to develop a com- mum detention depends on the prehensive guideline and best man- soilcomposition(organicvs. agementpracticesfortheeffectiveinorganic rate) and the level of and practical implementation of thesaturation before the rain event, NBSCR. whereasthemaximumdeten-Hereareseveralquestionswithtion for the SDA depends on their answers outlining the concept ofthe volume of the tray only. The this research activity. objective is to enhance and in-What Are the NBSCRcrease the water detention and Technologies? stormwater capture to mitigate urban flooding.TheVRAandSDA,inspired and supported by nature, offer op- What Are the tionsforurbanenvironmentsinBenefits of NBSCR mitigating storm flooding (Figure 1). The VRA can retain water: theTechnologies?stormwater is captured on the as- TheNBSCRtechnolo-sembly, where it is reduced due togies have the potential to pro-vaporization and its release to thevide multiple benefits related to sewerage system is delayed, lower- stormwater management:ing the runoff volume. The SDA1.Reducing the peak flow candetainwater:stormwatercanfromstormevents, betemporarilyheldontheroof,mitigatingfloodrisk andbyimplementingadvancedandreducingthepos-drainagesystems,stormwaterissibleseweroverflows released in a controlled manner toand erosion in receiving thesewerageinfrastructure.Thestreams.VRA naturally delays and reduces2.Reusingstormwater stormwater runoff from the roof,(e.g.,flushingtoilets, whereastheSDAprovidescon- irrigatinglawnsand trolled conditions for the roofs dis- gardens)orallowing charge rate, allowing large volumesittoevaporatefroma of water to be detained. rooftop(lesseningthe What Is the Stormwatereffectsofurbanheat island).Asaresult, Detention Concept in NBSlesswaterreachestheCR Design? municipal system than Localclimatepatterns(i.e.,would from a tradition-storm intensity, wind, vapour pres- al roof system. This can sure,airtemperatureandincom- extend the life span of ing radiation) influence the designmunicipalinfrastruc-of the NBSCR. The magnitudeture and maintain wa-of the stormwater dictates the pro- ter cycle balance.portion of rainfall that is detained,3.Utilizing the vast spaces andthetimebetweenstormsde- of the unused surfaces terminesthedischargerates.Ac- of commercial roofs in cordingly,ahydrographcurveisdense urban areas that requiredtoassessthestormwaterlack adequate stormwa-detention capacity (Figure 2). ter infrastructure.ORN THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ONTARIO ROOFING NEWSISSUE 4 2022/239'