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Next generation swale design for stormwater runoff treatment: A comprehensive approach
Department of Biological and Agricultural Engineering, North Carolina State University, Box 7625, Raleigh, NC, 27695, USA. Department of Environment-Water Resources, AECOM, 1600 Perimeter Park Dr, Suite 400, Morrisville, NC, 27560, USA.
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: 0000-0001-5548-4397
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2021 (English)In: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 279, article id 111756Article, review/survey (Refereed) 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.

Place, publisher, year, edition, pages
Elsevier, 2021. Vol. 279, article id 111756
Keywords [en]
Stormwater, Grass swales, Bioswale, Wet swale, Green infrastructure, Water quality
National Category
Water Engineering
Research subject
Urban Water Engineering; Centre - Centre for Stormwater Management (DRIZZLE)
Identifiers
URN: urn:nbn:se:ltu:diva-82208DOI: 10.1016/j.jenvman.2020.111756ISI: 000608234500002PubMedID: 33360437Scopus ID: 2-s2.0-85098470668OAI: oai:DiVA.org:ltu-82208DiVA, id: diva2:1515314
Funder
Vinnova, 2016-05176
Note

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

Available from: 2021-01-08 Created: 2021-01-08 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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Rujner, HendrikLeonhardt, GüntherBlecken, Godecke-TobiasViklander, Maria

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