Green roofs have emerged as effective stormwater management systems, but understanding the contribution of their various components to hydrological performance is crucial for optimizing their design and implementation. More empirically measured data on the hydrological function of green roof vegetation is needed, especially under realistic low-maintenance, non-irrigated scenarios. Further, targeted, evidence-based plant selection based on ecological theories may improve green roof hydrological performance. Previous research has suggested that, in contrast to monocultures, mixtures of species with complementary traits could optimize provisioning of various ecosystem services. Thus, species mixtures based on their adaptive life strategy using the CSR theory (Competitor, Stress tolerator, and Ruderal) were hypothesized to have better hydrological performance than a Sedum monoculture or bare substrate under natural conditions over multiple seasons. To test this hypothesis, the runoff from thirty 2 m2 green roof modules was measured. The retention and detention performance of different green roof treatments were evaluated for 84 precipitation events of varying rain depth and intensity during snow-free periods. Differences in retention as well as detention between the vegetation treatments varied, but generally increased with increasing rain event volume and the Stress-tolerant treatment generally performed better than bare substrate. On a mean event basis, the mixture of stress-tolerator species demonstrated a 74 % retention rate, while the Bare substrate retained 72 % of the rainfalls. Overall, the green roofs, including bare substrate and vegetated treatments, effectively retained >50 % of the cumulative precipitation depth. In line with previous studies, the Sedum monoculture generally showed worse hydrological performance than other non-succulent vegetation mixtures, despite its relatively high cover and survival. The vegetated treatment with the highest species richness and diversity in life strategies (Mix) did not provide the best vegetation cover, or hydrological performance. Instead, the Stress-tolerant treatment, characterized by the high survival rate of a single graminoid species, consistently demonstrated superior event-based stormwater retention and peak attenuation capabilities.

Blue green infrastructure (BGI), in recent decades, have been increasingly recognized as robust stormwater control measures to reduce urbanflooding, promote infiltration, and restore a catchment’s flow to its pre-development stage. However, studies comparing the hydrologicalbenefits of BGI alternatives at catchment scale are often limited to single catchment or single/few BGI options scaled over a catchment.This study designed a set of BGI alternatives as a combination of different BGI facilities in terms of the following: (a) spatial distributionscale (end-of-pipe vs. decentralized) and (b) naturalness scale (less engineered vs. more engineered), in three different urban catchmentsrepresenting an inner city, a residential suburb, and a new urban housing. In addition, their hydrological performances were compared.A 10-year return period design rain and a continuous rain series of 11 years were modelled for each BGI alternative using the computermodel stormwater management model (SWMM). It was observed that in most catchments, decentralized alternatives (both engineeredand natural) showed better potential to reduce the magnitude and frequency of flooding than centralized measures. Similarly, the testeddecentralized natural, less engineered alternatives showed higher potential to increase infiltration than the decentralized engineered alternativesin all three catchments. Meanwhile, infiltration-based BGI alternatives showed similar potential to mimic pre-development flow as otherdecentralized BGI alternatives.

Klimatanpassning är en stor utmaning för samhällsbyggandet och det krävs ny kunskap om hur detta ska göras.I artikeln ges ett axplock av intressanta internationella forskningsresultat som rör klimatanpassning av dagvatten-system. Förändringar i nederbörd går redan att urskilja i observerade data, och dessutom kan de vara starkare ibebyggda områden. Osäkerhet i prognoser av framtida regn gör att erforderlig dimensionering av dagvattensys-tem kan vara oklar. Dimensionering baserad på långtidssimulering kan ge bättre statistik angående systemetsfunktion än dimensionering baserad på ett enskilt regntillfälle. Blå-grön infrastruktur kan bidra med minskningav avrinningsvolymer och -flöden, men deras funktion är inte garanterad samtidigt som de kräver underhåll ochatt de byggs på rätt sätt. På avrinningsområdesnivå kan blå-grön infrastruktur tydligt minska flöden, men atthitta tillräckligt med utrymme i befintlig bebyggelse kan vara svårt.

Climate change adaptation of urban areas is a major challenge and new knowledge is needed on how to do this.This article provides an overview of interesting international research results related to climate change adapta-tion of stormwater systems. Changes in precipitation are already discernible in observed data and may be strong-er in built-up areas. Uncertainty in forecasts of future rainfall means that the required sizing of stormwatersystems can be uncertain. Sizing based on long-term simulations can provide a better statistical description ofsystem performance. Blue-green infrastructure can contribute to the reduction of runoff volumes and flows, buttheir functioning is not guaranteed, and they require maintenance and proper construction. At the catchmentlevel, blue-green infrastructure can clearly reduce flows, but finding sufficient space in existing urban develop-ment can be difficult.

Reduction of runoff flow peaks and volumes is one of the performance objectives of grass swales in the context of Green Stormwater Infrastructure (GSI). Towards this end, a study of the feasibility of using a retrofitted swale outlet control weir (SOCW) to reduce runoff volume and peak flow, by enhancing swale runoff storage and infiltration into swale soils, was conducted in Luleå, Northern Sweden. Experimental field work consisted of 43 irrigation-driven runoff experiments, mimicking rainfall events with return periods between 1- to 50-years, with a constant intensity and duration of 30 min, in a 30-m long grass swale section. Experimental results confirmed that, under the tested conditions, swales with the retrofitted outflow control, reduced runoff volumes and peak flows. Such reductions ranged from 32 percentage points (for 2-year) to 1 and 4 percentage points (for 50-year return period) for runoff volumes and peak flows, respectively. Outcomes of scenarios with outflow controls clearly indicated a decreasing performance with increasing flow rates (and irrigation event return periods). Furthermore, the retrofitted swale controlled the outflow release during less frequent 20 to 50-year events, which would contribute to reducing flood risks in downstream urban areas.

Biofilter används idag mest i syfte att förbättra vattenkvalitet, men med tanke på framtida klimatförändringar är det intressant att se om de även kan bidra till minskade översvämningsrisker. Att öka lagringskapaciteten kan göras genom att öka lagringsvolymen på ytan eller att öka dräneringslagrets tjocklek. Denna skrift visar vilka effekter detta har på filtrets hydrologiska prestanda.

Due to large spatial and temporal variations of soil properties that govern swale infiltration capacities, traditional methods for estimating saturated hydraulic conductivity (ksat) values could potentially lead to erroneous estimation of the total system infiltration capacity. To increase the knowledge of grassed swale infiltration performance and the relationship between hydraulic properties related to the spatial variation within the swale, two methods were applied to estimate ksat values: 1) point measurements using the Modified Philip Dunne (MPD) Infiltrometer, and 2) a full-scale infiltration test (FSIT). A large variation in calculated ksat values was found, ranging from 22 to 1382 mm/hr, with lower/higher values at the swale bottom, and right swale slope respectively. Infiltration point measurements, with a geometric mean of 81 mm/hr, showed higher infiltration rates than those obtained from FSIT, which yielded 34 and 22 mm/hr (for test 1 and 2 respectively). Moreover, FSIT results showed an agreement with ksat values obtained from MPD infiltrometer at the swale bottom. In addition, infiltration rates are significantly reduced as the groundwater mound gets closer to the bottom of the grassed swale.

En raison des grandes variations spatiales et temporelles des propriétés du sol qui régissent les capacités d'infiltration des noues, les méthodes traditionnelles d'estimation des valeurs de conductivité hydraulique saturée (ksat) pourraient potentiellement conduire à une estimation erronée de la capacité d'infiltration totale du système. Afin d'accroître la connaissance des capacités d'infiltration des noues enherbées et de la relation entre les propriétés hydrauliques liées aux classes de texture du sol, deux méthodes ont été appliquées pour estimer les valeurs de ksat : 1) des mesures ponctuelles à l'aide de l'infiltromètre Philip Dunne modifié (MPD), et 2) un test d’infiltration à pleine échelle (FSIT). Une grande variation dans les valeurs calculées de ksat a été trouvée, allant de 22 à 1382 mm/h, avec des valeurs inférieures/élevées au fond de la noue et à droite de la pente de la noue respectivement. Les mesures des points d'infiltration, avec une moyenne géométrique de 81 mm/h, ont montré des taux d'infiltration plus élevés que ceux obtenus à partir du FSIT, avec 34 et 22 mm/h (pour les tests 1 et 2 respectivement). De plus, les résultats du FSIT ont montré un accord avec les valeurs de ksat obtenues au fond de la noue. De plus, les taux d'infiltration diminuent considérablement à mesure que le niveau de la nappe phréatique se rapproche du fond de la noue enherbée.

Klimatförändring och urbanisering leder till allt större översvämningsrisker i våra städer. Därför finns det ett behov av yteffektiva åtgärder för att hålla riskerna begränsade. En sådan lösning kan vara att strypa utflödet från svackdiken för att tillfälligt lagra mer vatten och öka andelen som kan infiltrera i marken. I denna studie har fältförsök genomförts för att kvantifiera effekten av en sådan lösning för regn med återkomsttider mellan 1 och 50 år. Resultaten visar att såväl flödesvolym som maxflöde kan minskas med upp till 32% för mindre regntillfällen. Effekten av flödesstrypningen blir dock mindre för större regntillfällen, och ytterliggare designalternativ bör utredas.

The effects of green areas on design flow (Qdim) and required flow detention volume (Vd) were studied for differenttransport times, rain durations and rain intensities. The StormTac Web model was used for the calculations on a36 ha urban catchment with green areas. Simulated runoff coefficients from different rain intensities and raindurations were used as input data, as well as new functions from literature data. The effects of 9 calculation caseswere studied, where the following factors resulted in greater to smaller impact: (1) Return time; (2) Green areas,generally; (3) Average runoff coefficient, general uncertainty; (4) Functions impermeability-runoff coefficient; (5)Climate factor; (6) Linear function for green areas, rain intensity; (7) The Curve number method; (8) Rural andurban function, rain intensity and (9) Rain intensity. The same order of impact was valid for Vd except for theCurve number method which gives the 3rd largest and Rural and urban function the 5th largest impact. Thevariation of different specific assumptions regarding green areas and runoff coefficients gave Qdim = 1 600–2 700l/s and Vd = 530–3 600 m3, so the assumptions made in the calculations have a clear impact. The new functionsfor which the runoff coefficients are not static but varying with rain intensity and rain durations are recommendedfor further studies.

Gröna ytors påverkan på dimensionerande flöden (Qdim) och erforderlig fördröjningsvolym (Vd) studeradesvid olika rinntider, regnvaraktigheter och regnintensiteter. Dagvatten- och recipientmodellen StormTac Webanvändes för beräkningarna på ett 36 ha stort urbant avrinningsområde med grönytor. Modellerade avrinningskoefficienter från olika regnintensiteter och regnvaraktigheter användes som indata, liksom nya samband baseradepå data från litteraturstudier. Påverkan av 9 beräkningsfall med olika antaganden simulerades, där följande i stor-leksordning gav störst till minst påverkan på Qdim:(1) Återkomsttid; (2) Grönytor, generellt; (3) Genomsnittligavrinningskoefficient, generell osäkerhet; (4) Samband impermeabilitet-avrinningskoefficient; (5) Klimatfaktor;(6) Linjär funktion för grönytor, regnintensitet; (7) Kurvnummer-metoden, (8) Rural och urban funktion,regnintensitet och (9) Regnintensitet. Samma påverkansordning gällde för Vd utom för Kurvnummer-metodenmed 3e största och Rural och urban funktion med 5e största påverkan. Variationen av olika specifika antagandenkring gröna ytor och avrinningskoefficienter gav Qdim = 1 600–2 700 l/s och Vd = 530–3 600 m3, så det spelar storroll vilka antaganden som görs. De nya sambanden för vilka avrinningskoefficienterna inte är statiska utan varie-rande med regnintensitet och regnvaraktighet rekommenderas att utredas vidare.