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Hydrologic processes of vegetated swales in controlling urban stormwater
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.ORCID-id: 0000-0002-2321-164X
2024 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Vegetated swales are an integral component of Green Stormwater Infrastructure (GSI), designed to manage urban stormwater at its source by reducing volumes and peaks, retaining water within the urban landscape, and providing high-capacity runoff pathways. They facilitate the integration of vegetation-based stormwater solutions with traditional grey infrastructure, creating synergies and enhancing urban drainage. In light of contemporary urban drainage challenges, swales are now assigned multiple functions beyond stormwater conveyance, necessitating enhanced predictability and reduced uncertainties in their hydrologic performance.

This thesis investigates the hydrologic functions of vegetated swales in controlling urban stormwater. Vegetated swales are shallow, vegetated channels that manage runoff through infiltration, conveyance, storage, dissipation, and filtration, leading to reduced runoff volumes and attenuated peak flows. The study aims to advance the understanding of swale functions by examining their hydrologic and hydraulic performance under varying conditions. Key objectives include exploring the relationship between hydraulic and hydrological factors and swale hydrographs, such as soil moisture dynamics and swale characteristics, representing swale processes and spatial variability, and evaluating long-term hydrological behavior concerning soil water content (SWC).

The methodology involved field experiments and long-term monitoring at two swales in Luleå and a combined stormwater control measure (SCM) in Skellefteå, Northern Sweden. These swales, with differing topographies and vegetative covers, were subjected to controlled irrigation experiments to mimic runoff inflows. The combined SCM, consisting of a rocky slope, vegetated slope, and vegetated collector swale arranged in series, was monitored to assess hydrologic parameters and responses based on natural rainfall inflows. Data collection included rainfall events, inflow and outflow hydrographs, soil infiltration, and SWC using Time Domain Reflectometry (TDR).

The study highlights the influence of initial soil moisture conditions only on vegetated swale function. Low SWC leads to high runoff attenuation (up to 74%), whereas high SWC results in predominant conveyance function (attenuation as low as 17%). Runoff peaks were proportionally reduced, with outflow hydrograph lag times ranging from 5 to 15 minutes. Variability in soil properties, hydraulic conductivity, and topography significantly affected swale performance, with bottom slope irregularities impacting runoff dissipation. Double-ring infiltrometer measurements showed infiltration rates varying from 1.78 to 9.41 cm/hr across the swales.

For the example of a vegetated swale in combination with additional drainage features upstream, runoff volume reductions frequently exceeded those in studies on grassed swales or filter strips, attributed to large pervious areas and abundant depression storage. Hydrological reductions varied with site-specific conditions, such as soil properties and shallow groundwater interactions, resulting in a median runoff coefficient of 0.03 over 60 storm events. Groundwater interactions and soil moisture fluctuations influenced unsaturated zone dynamics, causing water exfiltration even during dry periods, leading to variable runoff travel times and delayed peak lag times.

Eight years of monitoring revealed high spatial variability in SWC, attributed to soil mixing during development. Vegetated slopes showed greater SWC variability than the downstream swale, influenced by lateral stormwater inflows. Seasonal trends indicated increasing site moisture, driven by vegetation maturation, which improved stormwater retention and site resilience.

Overall, this dissertation enhances the understanding of influential processes and environmental conditions impacting the function and effectiveness of vegetated swales, providing valuable information to reduce uncertainties in designing and predicting swale hydrological responses.

sted, utgiver, år, opplag, sider
Luleå: Luleå University of Technology, 2024.
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Emneord [en]
Green Stormwater Infrastructure, grass swales, stormwater mitigation, urban drainage
Emneord [sv]
svackdiken, dagvattenhantering, grön infrastruktur, öppen dagvattenhantering
HSV kategori
Forskningsprogram
VA-teknik; Centrumbildning - Centrum för dagvattenhantering (DRIZZLE)
Identifikatorer
URN: urn:nbn:se:ltu:diva-105583ISBN: 978-91-8048-587-6 (tryckt)ISBN: 978-91-8048-588-3 (digital)OAI: oai:DiVA.org:ltu-105583DiVA, id: diva2:1860725
Disputas
2024-09-27, E632, Luleå University of Technology, Luleå, 09:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2024-05-27 Laget: 2024-05-24 Sist oppdatert: 2024-07-11bibliografisk kontrollert
Delarbeid
1. The effects of initial soil moisture conditions on swale flow hydrographs
Åpne denne publikasjonen i ny fane eller vindu >>The effects of initial soil moisture conditions on swale flow hydrographs
Vise andre…
2018 (engelsk)Inngår i: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 32, nr 5, s. 644-654Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The effects of soil water content (SWC) on the formation of run‐off in grass swales draining into astorm sewer system were studied in two 30‐m test swales with trapezoidal cross sections. Swale1 was built in a loamy fine‐sand soil, on a slope of 1.5%, and Swale 2 was built in a sandy loam soil,on a slope of 0.7%. In experimental runs, the swales were irrigated with 2 flow rates reproducing run‐off from block rainfalls with intensities approximately corresponding to 2‐month and 3‐year events. Run‐off experiments were conducted for initial SWC (SWCini) ranging from 0.18 to 0.43 m3/m3. For low SWCini, the run‐off volume was greatly reduced by up to 82%, but at highSWCini, the volume reduction was as low as 15%. The relative swale flow volume reductions decreased with increasing SWCini and, for the conditions studied, indicated a transition of the dominating swale functions from run‐off dissipation to conveyance. Run‐off flow peaks were reduced proportionally to the flow volume reductions, in the range from 4% to 55%. The swale outflow hydrograph lag times varied from 5 to 15 min, with the high values corresponding tolow SWCini. Analysis of swale inflow/outflow hydrographs for high SWCini allowed estimations of the saturated hydraulic conductivities as 3.27 and 4.84 cm/hr in Swales 1 and 2, respectively. Such estimates differed from averages (N = 9) of double‐ring infiltrometer measurements (9.41 and 1.78 cm/hr). Irregularities in swale bottom slopes created bottom surface depression storage of 0.35 and 0.61 m3 for Swales 1 and 2, respectively, and functioned similarly as check bermscontributing to run‐off attenuation. The experimental findings offer implications for drainage swale planning and design: (a) SWCini strongly affect swale functioning in run‐off dissipation and conveyance during the early phase of run‐off, which is particularly important for design storms and their antecedent moisture conditions, and (b) concerning the longevity of swale operation, Swale 1 remains fully functional even after almost 60 years of operation, as judged from its attractive appearance, good infiltration rates (3.27 cm/hr), and high flow capacity.

sted, utgiver, år, opplag, sider
John Wiley & Sons, 2018
Emneord
field study, flow attenuation and conveyance, grass swales, Green Infrastructure, soil moisture, water balance
HSV kategori
Forskningsprogram
VA-teknik; Centrumbildning - Centrum för dagvattenhantering (DRIZZLE)
Identifikatorer
urn:nbn:se:ltu:diva-67686 (URN)10.1002/hyp.11446 (DOI)000426510600005 ()2-s2.0-85041918889 (Scopus ID)
Forskningsfinansiär
Swedish Research Council Formas, 2015-121
Merknad

Validerad;2018;Nivå 2;2018-02-28 (svasva)

Tilgjengelig fra: 2018-02-19 Laget: 2018-02-19 Sist oppdatert: 2024-05-24bibliografisk kontrollert
2. High-resolution modelling of the grass swale response to runoff inflows with Mike SHE
Åpne denne publikasjonen i ny fane eller vindu >>High-resolution modelling of the grass swale response to runoff inflows with Mike SHE
2018 (engelsk)Inngår i: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 562, s. 411-422Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The feasibility of simulating the hydrological response of a grass swale to runoff inflows was examined using the hydrological model Mike SHE and the available input data from 12 irrigation events mimicking runoff from block rainfalls. The test swale channel had a trapezoidal cross-section, bottom slope of 1.5%, length of 30 m, and was built in loamy fine sand. The irrigation events consisted in releasing two equal constant inflows to the swale: a concentrated longitudinal flow at the upstream end and a distributed lateral inflow along the swale side slope adjacent to the contributing drainage area. The total inflows approximated runoff from two events with return periods of 2 months and 3 years, respectively, for durations of 30 min. Irrigation experiments were done for two states of the initial soil moisture, dry or wet antecedent moisture conditions (AMC). Mike SHE has been extensively used on catchments of various sizes, but rarely for small stormwater management facilities and their detailed topography investigated in this study. The latter application required high spatial and temporal resolutions, with computational cells of 0.2 × 0.2 m and time steps as short as 0.6 s to avoid computational instabilities. For dominant hydrological processes, the following computational options in Mike SHE were chosen: Soil infiltration – the van Genuchten equation, unsaturated zone flow – the one-dimensional Richards equation, and overland flow – the diffusive wave approximation of the St. Venant equations. For study purposes, the model was calibrated for single events representing one of four combinations of low and high inflows, and dry and wet AMC, and then applied to the remaining 11 events. This was complemented by calibration for two events, representing high inflow on wet AMC and low inflow in dry AMC. The goodness of fit was statistically assessed for observed and simulated peak flows, hydrograph volumes, Nash-Sutcliffe model efficiencies (NSE), and soil water content (SWC) in swale soil layers. The best fit (NSE > 0.8) was obtained for high inflows and wet AMC (i.e., when the primary swale function is flow conveyance); the least fit was noted for low inflows and dry AMC, when the primary swale function is flow attenuation. Furthermore, this observation indicates the overall importance of correct modelling of the soil infiltration. The effects of spatial variation of SWC on the swale discharge hydrograph could not be confirmed from simulation results, but high topographical accuracy was beneficial for reproducing well the locations of the observed water ponding. No significant increases in simulated SWC at 0.3 m or greater depths were noted, which agreed with field observations. Overall, the results indicated that Mike SHE was effective in process-oriented small-scale modelling of grass swale flow hydrographs.

sted, utgiver, år, opplag, sider
Elsevier, 2018
Emneord
Grass swale, Distributed modelling, Mike SHE, Soil water content, Stormwater management
HSV kategori
Forskningsprogram
VA-teknik; Centrumbildning - Centrum för dagvattenhantering (DRIZZLE)
Identifikatorer
urn:nbn:se:ltu:diva-68751 (URN)10.1016/j.jhydrol.2018.05.024 (DOI)000438003000031 ()2-s2.0-85046868673 (Scopus ID)
Prosjekter
GrönNano
Forskningsfinansiär
Swedish Research Council Formas, 2015-778
Merknad

Validerad;2018;Nivå 2;2018-05-16 (andbra)

Tilgjengelig fra: 2018-05-16 Laget: 2018-05-16 Sist oppdatert: 2024-05-24bibliografisk kontrollert
3. Next generation swale design for stormwater runoff treatment: A comprehensive approach
Åpne denne publikasjonen i ny fane eller vindu >>Next generation swale design for stormwater runoff treatment: A comprehensive approach
Vise andre…
2021 (engelsk)Inngår i: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 279, artikkel-id 111756Artikkel, forskningsoversikt (Fagfellevurdert) Published
Abstract [en]

Swales are the oldest and most common stormwater control measure for conveying and treating roadway runoff worldwide. Swales are also gaining popularity as part of stormwater treatment trains and as crucial elements in green infrastructure to build more resilient cities. To achieve higher pollutant reductions, swale alternatives with engineered media (bioswales) and wetland conditions (wet swales) are being tested. However, the available swale design guidance is primarily focused on hydraulic conveyance, overlooking their function as an important water quality treatment tool. The objective of this article is to provide science-based swale design guidance for treating targeted pollutants in stormwater runoff. This guidance is underpinned by a literature review.

The results of this review suggest that well-maintained grass swales with check dams or infiltration swales are the best options for runoff volume reduction and removal of sediment and heavy metals. For nitrogen removal, wet swales are the most effective swale alternative. Bioswales are best for phosphorus and bacteria removal; both wet swales and bioswales can also treat heavy metals. Selection of a swale type depends on the site constraints, local climate, and available funding for design, construction, and operation. Appropriate siting, pre-design site investigations, and consideration of future maintenance during design are critical to successful long-term swale performance. Swale design recommendations based on a synthesis of the available research are provided, but actual design standards should be developed using local empirical data. Future research is necessary to identify optimal design parameters for all swale types, especially for wet swales.

sted, utgiver, år, opplag, sider
Elsevier, 2021
Emneord
Stormwater, Grass swales, Bioswale, Wet swale, Green infrastructure, Water quality
HSV kategori
Forskningsprogram
VA-teknik; Centrumbildning - Centrum för dagvattenhantering (DRIZZLE)
Identifikatorer
urn:nbn:se:ltu:diva-82208 (URN)10.1016/j.jenvman.2020.111756 (DOI)000608234500002 ()33360437 (PubMedID)2-s2.0-85098470668 (Scopus ID)
Forskningsfinansiär
Vinnova, 2016-05176
Merknad

Validerad;2021;Nivå 2;2021-01-08 (alebob)

Tilgjengelig fra: 2021-01-08 Laget: 2021-01-08 Sist oppdatert: 2024-05-24bibliografisk kontrollert
4. Green infrastructure drainage of a commercial plaza without directly connected impervious areas: a case study
Åpne denne publikasjonen i ny fane eller vindu >>Green infrastructure drainage of a commercial plaza without directly connected impervious areas: a case study
Vise andre…
2022 (engelsk)Inngår i: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 86, nr 11, s. 2777-2793Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

A paired-catchment study of two adjacent commercial areas in northern Sweden, one with Green Infrastructure (GI) storm drainage and the other with a conventional storm sewer system, served to evaluate the hydrological performance of both drainage systems and demonstrate advantages of GI. The GI catchment avoided directly-connected impervious areas by diverting runoff from a parking lot to a cascade of three infiltration features, a fractured rock strip draining onto a sloping infiltration area, followed by a collector swale. Both catchments were monitored over 4 years by measuring rainfall, runoff and, in the vicinity of the swale, soil water content and groundwater levels. For frequent storms, the median GI efficiencies in reducing runoff volumes and peak flows, and extending peak flow lags, were 96, 99 and 60%, respectively, compared to conventional drainage The storm rainfall depth, initial soil water content, increases in intra-event soil water storage and groundwater levels, had statistically significant effects on either runoff volume or peak flow reductions. No effects were found for storm rainfall intensity and duration, antecedent dry days, and initial groundwater levels. The study demonstrated that GI drainage can be successfully applied even in the challenging environment of a subarctic climate.

sted, utgiver, år, opplag, sider
IWA Publishing, 2022
Emneord
commercial runoff, directly connected impervious area (DCIA), green infrastructure (GI), low impact development (LID) monitoring, Semi-natural stormwater control
HSV kategori
Forskningsprogram
VA-teknik; Centrumbildning - Centrum för dagvattenhantering (DRIZZLE)
Identifikatorer
urn:nbn:se:ltu:diva-94326 (URN)10.2166/wst.2022.381 (DOI)000888985800001 ()36515188 (PubMedID)2-s2.0-85144015491 (Scopus ID)
Forskningsfinansiär
Swedish Research Council Formas, 2015-778Vinnova, 2016-05176
Merknad

Validerad;2023;Nivå 2;2023-02-10 (joosat);

Licens fulltext: CC BY License

Tilgjengelig fra: 2022-11-29 Laget: 2022-11-29 Sist oppdatert: 2024-05-24bibliografisk kontrollert
5. Comparison of spatial interpolation methods for soil moisture in Green Stormwater Infrastructure
Åpne denne publikasjonen i ny fane eller vindu >>Comparison of spatial interpolation methods for soil moisture in Green Stormwater Infrastructure
2021 (engelsk)Inngår i: 15th International Conference on Urban Drainage 2021 Delegates Handbook / [ed] David McCarthy, 2021, s. 598-600, artikkel-id 188Konferansepaper, Oral presentation with published abstract (Fagfellevurdert)
Abstract [en]

Knowledge about soil-physical variables of Green Stormwater Infrastructure (GSI) like soil moisture (θ) is essential to understanding their hydrologic and treatment performance. θ depends on many local factors and is subject to high spatial and temporal variability (Takagi and Lin, 2012; Yao et al. 2013; Nasta et al. 2018). Information about the spatially continuous data of θ can help to understand the hydrologic response and provide an input for initial conditions to improve hydrologic modelling results. A number of deterministic and probabilistic interpolation methods and tools are available today to model the spatial distribution of environmental parameters such as θ (Li and Heap 2011; Yao et al. 2013). The quality of the spatial interpolation, however, depends on sample size, sample distribution and correlation to various other factors, for example terrain profile or vegetation coverage and makes the selection of the appropriate method difficult. Six methods commonly applied to soil characteristics have been selected to interpolate data that has been retrieved from 16 time-domain reflectometers measuring θ in the upper 30 cm of a GSI-site ́s surface. As θ changes at each sampling point also vary over time and therefore change the coefficients of some interpolation methods, estimates were compared for each hour of a 24-hour rainfall event. This is especially relevant as GSI soils are not only subjected to rainfall but also to distinct lateral inflows from impervious areas. Cross-validation and common error calculations were used to assess the statistical performance of the results and identify a method with least errors.

Emneord
Green Stormwater Infrastructure, Soil moisture, spatial interpolation
HSV kategori
Forskningsprogram
VA-teknik; Centrumbildning - Centrum för dagvattenhantering (DRIZZLE)
Identifikatorer
urn:nbn:se:ltu:diva-89444 (URN)
Konferanse
15th International Conference on Urban Drainage (ICUD 2021), October 25-28, 2021, Online/Melbourne, Australia
Tilgjengelig fra: 2022-03-04 Laget: 2022-03-04 Sist oppdatert: 2024-05-24bibliografisk kontrollert
6. Variability and trends in soil moisture of a maturing Green Stormwater Facility
Åpne denne publikasjonen i ny fane eller vindu >>Variability and trends in soil moisture of a maturing Green Stormwater Facility
Vise andre…
(engelsk)Manuskript (preprint) (Annet vitenskapelig)
HSV kategori
Forskningsprogram
VA-teknik
Identifikatorer
urn:nbn:se:ltu:diva-105580 (URN)
Forskningsfinansiär
Swedish Research Council Formas, 2015-778Vinnova, 2022-03092
Tilgjengelig fra: 2024-05-23 Laget: 2024-05-23 Sist oppdatert: 2024-05-24

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