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High-resolution modelling of the grass swale response to runoff inflows with Mike SHE
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.ORCID iD: 0000-0002-2321-164x
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.ORCID iD: 0000-0003-0367-3449
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.ORCID iD: 0000-0001-9938-8217
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.ORCID iD: 0000-0003-1725-6478
2018 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 562, p. 411-422Article in journal (Refereed) 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.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 562, p. 411-422
Keywords [en]
Grass swale, Distributed modelling, Mike SHE, Soil water content, Stormwater management
National Category
Oceanography, Hydrology and Water Resources Water Engineering
Research subject
Urban Water Engineering; Centre - Centre for Stormwater Management (DRIZZLE)
Identifiers
URN: urn:nbn:se:ltu:diva-68751DOI: 10.1016/j.jhydrol.2018.05.024ISI: 000438003000031Scopus ID: 2-s2.0-85046868673OAI: oai:DiVA.org:ltu-68751DiVA, id: diva2:1206292
Projects
GrönNano
Funder
Swedish Research Council Formas, 2015-778
Note

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

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2024-05-24Bibliographically approved
In thesis
1. Hydrologic processes of vegetated swales in controlling urban stormwater
Open this publication in new window or tab >>Hydrologic processes of vegetated swales in controlling urban stormwater
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Green Stormwater Infrastructure, grass swales, stormwater mitigation, urban drainage, svackdiken, dagvattenhantering, grön infrastruktur, öppen dagvattenhantering
National Category
Other Environmental Engineering
Research subject
Urban Water Engineering; Centre - Centre for Stormwater Management (DRIZZLE)
Identifiers
urn:nbn:se:ltu:diva-105583 (URN)978-91-8048-587-6 (ISBN)978-91-8048-588-3 (ISBN)
Public defence
2024-09-27, E632, Luleå University of Technology, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2024-05-27 Created: 2024-05-24 Last updated: 2024-09-06Bibliographically approved

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