| 1. |
- Broekhuizen, Ico, et al.
(författare)
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Improving hydrological modelling of urban drainage swales through use of soil water content observations
- 2020
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Ingår i: Journal of Hydrology X. - 2589-9155.
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Tidskriftsartikel (refereegranskat)abstract
- Flow observations alone may not provide sufficient information for calibration of detailed hydrological models of urban drainage swales. Therefore this study investigated the added value of using soil water content (SWC) observations made throughout the swale. This can be done by (1) including SWC in the likelihood function that is used to quantify model performance or (2) by using the SWC observations to set initial conditions in the model. The results show that combining outflow and SWC in the likelihood function is necessary to obtain reliable and precise predictions for both variables, and that this increases the number of parameters that are identifiable from the data. Using SWC observations to set initial model conditions improves model performance and affects the degree to which soil hydraulic parameters are identifiable. Overall, it is concluded that SWC observations may be a valuable complement to outflow observations in the modelling of urbanswales.
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| 2. |
- Broekhuizen, Ico, et al.
(författare)
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Towards using soil water content observations for calibration of distributed urban drainage models : [Vers l’utilisation d'observations de teneur en eau du sol pour le calage de modèles distribués d’assainissement urbain]
- 2019
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Ingår i: 10e Conférence internationale L'eau dans la ville. - : GRAIE. ; , s. 124-124
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Konferensbidrag (refereegranskat)abstract
- Fully distributed urban drainage models can be used to analyse and predict the behaviour of green urban drainage infrastructure such as swales, but they need to be calibrated for specific study sites. Using only drainage outflow measurements may not provide enough information to do this in an optimal way, so additional types of measurements have to be considered. This study identifies different approaches to including soil water content (SWC) observations in the calibration process and investigates how they affect parameter identifiability and the predictive uncertainty of the calibrated model. This is done using the Generalized Likelihood Uncertainty Estimation methodology applied to a model of a large urban swale. It was found that setting initial conditions based on the SWC measurements improved the fit between observed and simulated SWC, but also reduced the accuracy of the simulated amount of infiltration. Including SWC observations allowed to identify one parameter (saturated moisture content of the swale bottom) that was not identifiable from outflow measurements alone. Including SWC observations in the derivation of predictive uncertainty bounds made those bounds narrower (more precise), but where SWC had been used to set initial conditions the uncertainty bound failed to capture the observations. It is concluded that SWC observations can provide useful information for the calibration of distributed urban drainage models.
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| 3. |
- Ekka, Sujit A., et al.
(författare)
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Next generation swale design for stormwater runoff treatment : A comprehensive approach
- 2021
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Ingår i: Journal of Environmental Management. - : Elsevier. - 0301-4797 .- 1095-8630. ; 279
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Forskningsöversikt (refereegranskat)abstract
- 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.
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| 4. |
- Rujner, Hendrik, 1983-, et al.
(författare)
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Advancing green infrastructure design : Field evaluation of grassed urban drainage swales
- 2016
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Ingår i: Novatech proceedings 2016.
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Konferensbidrag (refereegranskat)abstract
- Grassed drainage swales, which represent common elements of urban green infrastructures, are designed for different soils, flow capacities, dimensions, slopes and vegetation. Their design is often based on local experience rather than technical guidelines, and consequently, the design and performance of grassed swales, with respect to flow capacity and stormwater management objectives may significantly vary from one jurisdiction to another. To improve this situation and reduce design uncertainties, a field study of grassed swales was conducted by assessing their hydrologic performance. A 30-m section of an urban grassed swale in sandy soils, located in the City of Luleå (Northern Sweden), was equipped with a mobile water supply system and instrumented for measuring swale flow characteristics. The water supply system comprised five containers (~ 1 m3 each) providing controlled longitudinal and lateral inflows into the tested swale section. These inflows were selected to mimic stormwater runoff from a typical drainage area. At the first test site, 14 rainfall events of 30- minute duration were simulated and the resulting swale flows and soil moisture conditions were measured. The experimental variables addressed included wet and dry antecedent conditions, and three inflow rates. The preliminary results indicate that the degree of swale inflow attenuation depended on the magnitude of runoff inflow, on the initial soil moisture conditions and that significant volumes of water can be stored and transmitted during the stormwater drainage process.
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| 5. |
- Rujner, Hendrik, 1983-, et al.
(författare)
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Comparison of spatial interpolation methods for soil moisture in Green Stormwater Infrastructure
- 2021
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Ingår i: 15th International Conference on Urban Drainage 2021 Delegates Handbook. ; , s. 598-600
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 6. |
- Rujner, Hendrik, 1983-, et al.
(författare)
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Green infrastructure drainage of a commercial plaza without directly connected impervious areas: a case study
- 2022
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 86:11, s. 2777-2793
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Rujner, Hendrik, 1983-
(författare)
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Green Urban Drainage Infrastructure : Hydrology and Modelling of Grass Swales
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The management of urban runoff has evolved along with the advancement of understanding of runoff environmental impacts. Besides the impacts on water quality in the receiving waters, the impacts on the urban hydrologic regime include reduced infiltration by the sealing of pervious land, reduced evapotranspiration by removal of vegetation, and the resulting increase of stormwater runoff peaks and volumes causing flooding, and ultimately degradation of receiving waters. In such considerations, urban stormwater management benefits from the implementation of Green Infrastructure which includes decentralized vegetative controls that capture and infiltrates rain where it falls and thus reduces and improves stormwater runoff. An example of small scale elements of Green Infrastructure are traditional grass swales. Through shallow depressions with mild side slopes grass swales collect and infiltrate stormwater from parking lots and roads, while runoff flows are attenuated and further conveyed depending on the hydraulic loading. Grass swales usually operate reliably and their maintenance needs are well understood. Their hydrological performance is, beside their dimensions and the contributing area, determined mainly by hydraulic and soil-related hydrological parameters that change with the intensity of the storm. Yet, because swales discharge to downstream drainage elements, either to the conventional sewer system or to other stormwater management facilities, the knowledge of the underlying inter-related processes and influential factors that govern the hydraulic and hydrological performance of grass swales is required.Against this background, this thesis is devoted to such questions as (i) what are the differences in the hydraulic and hydrological performance of the studied swales, (ii) how do soil characteristics, including the antecedent soil moisture, influence the swale water balance for various hydraulic loadings; and (iii) how can the related hydrological processes be simulated in high-resolution and reliably predicted using a grid-based, distributed model. For this purpose, full-scale studies were performed in three 30-m grass swale sections in Luleå, Northern Sweden, by collecting hydraulic and hydrological data based on routine storm events mimicking block-rainfall storm events of 2 months and 3 years recurrence. The resulting runoff and soil moisture data were used to calculate the swale water balance, to derive event hydrographs and to obtain calibration and validation data for model simulations. The experimental results showed that the relative swale flow volume reduction decreased with an increasing soil moisture and indicated the transition in dominating swale functions: at low initial SWC, runoff was highly attenuated (up to 74%), but for high SWC, the conveyance function dominated (with attenuation as low as 17%). Runoff flow peaks were reduced, proportionally to the volume reductions. Swale outflow hydrograph lag times varied between 5 to 15 minutes and decreased with increasing soil moisture. The swale wetness affected runoff formation, attenuation and subsequent outlet discharge and, for the short-duration events tested, only the top soil layer contributed to these findings. In the three swales tested, soils, initial soil water content, saturated hydraulic conductivity and topography varied spatially significantly. Double-ring infiltrometer measurements resulted in values of 1.78, 4.04 and 9.41 cm/hr (n=9) in the three swales tested and deviated from estimates from averages of spatially integrated infiltration rates. However, with regard to spatial variability, only the topography, described as irregularities in the swale bottom slopes affected the swale runoff dissipation and conveyance in the early phase of the events. Together with estimates of the water stored in the top soil layer, 4-32% of runoff volumes from the mimicked 2-month storm were temporarily stored. The distributed model Mike SHE was found capable of simulating swale drainage processes, when properly calibrated. Close agreement (NSE>0.8) was found not only for the measured and simulated swale outlet hydrographs, but also for the changes of the soil moisture in the top soil layer, which shows rapid increase up to the saturated soil water content, but minor or no progression in depths of 0.2 m. The model output was little sensitive to the initial soil water content, especially for low inflow which resulted in larger residuals in simulated runoff peak flows and volumes. As in field measurements, spatial variability of the initial soil water content had no effect on the swale outflow, but the accuracy of the topographical representation. The thesis findings include several implications regarding effects of the assessed parameters in the application of the model for swale flow simulation and eventually the design of grass swales.
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| 8. |
- Rujner, Hendrik, 1983-, et al.
(författare)
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High-resolution modelling of the grass swale response to runoff inflows with Mike SHE
- 2018
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Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 562, s. 411-422
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Rujner, Hendrik, 1983-
(författare)
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Hydrologic processes of vegetated swales in controlling urban stormwater
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 10. |
- Rujner, Hendrik, et al.
(författare)
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The effects of initial soil moisture conditions on swale flow hydrographs
- 2018
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Ingår i: Hydrological Processes. - : John Wiley & Sons. - 0885-6087 .- 1099-1085. ; 32:5, s. 644-654
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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