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- Hallberg, Magnus, 1963-
(författare)
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Treatment conditions for the removal of contaminants from road runoff
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The pollutant load in road runoff is related to traffic densities and road maintenance activities. Inurbanised areas treatment of road runoff is common and often considered necessary. The pollutantsare partitioned between the particulate and dissolved matter. However, the contaminantstend to have an affinity to the particulate material. Sedimentation, the predominant treatmentmethod for road runoff uses various types of ponds. Design tools used for stormwater treatmentsystems are based on extensive data from existing treatment systems. The variations in the empiricaldata make it difficult when attempting to evaluate precise conditions for pollutant removaland thereby minimising the land use for a treatment facility. This is a concern in highly urbanisedareas where land use often is restricted.In this work, field studies were conducted in three separate watersheds along the same motorwaywith an annual average daily traffic exceeding 120,000 vehicles. The aim was to assess treatmentconditions for the removal of contaminants from road runoff.The study of mass transport of total suspended solids used the EU Directive (1991/271/EEC)discharge requirement for urban wastewater treatment: 60 mg/l during winter and summer. Theresults showed that a capture of the total runoff volume was necessary during both seasons. Tenmetals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn), as dissolved and particulate bound, werestudied in the road runoff during a winter season and the following summer period. The dissolvedpart of Al, Cd, Co, Cr, Mn, and Ni was significantly higher in winter. The mass concentration(mg/kg) for all metals was significantly higher over the summer except for Al and Co, whichshowed a higher mass concentration during the winter. The total metal concentration showed agood correlation to total suspended solids (TSS) during winter with exception for Cd. Good correlationto TSS was also found for the summer period for Al, Cu, Fe, Mn, Ni, and Zn. A simplemodel could describe sedimentation by the initial concentration of TSS, albeit road salt (NaCl)had a significant impact on the sedimentation process during winter. Removal of dissolved metalswas studied by column experiments using water granulated blast furnace slag. The result showedgood removal for Cd, Cu, Ni, and Zn independent of NaCl concentrations. Sediment accumulation(mg sediment/mm precipitation) was relatively consistent for the studied summer seasons asopposed to winter. The sediment differed in metal mass concentrations (mg/kg) between theseasons. Concentrations of Cu and Zn were high in regard to the guidelines for sensitivity ofsediment dwelling organisms and Swedish guidelines for contaminated soils.The findings suggest that the entire runoff volume must be captured for treatment. The reductionof TSS concentration could be estimated for a specific surface load (m/h). This would alsoapply for majority of the studied metals that correlated well to the particulate material. Reactivefilter technology using water granulated blast furnace slag could be applied for treatment of runofffor the reduction of dissolved metals. However, long-term studies are necessary for its practicalimplementation. Furthermore; the work shows that on-line turbidity measurements could beused for expedient process control for treatment facilities in similar watersheds dominated byroads. The work could be used together with existing design methods and models to evaluate andoptimise road runoff treatment.
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| 2. |
- 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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