Appropriately constructed pollutant export models can help set management priorities for catchments, identify critical pollutant source areas, and are important tools for developing and evaluating economically viable ways of minimising surface water pollution.¶ This thesis presents a comparison, an evaluation and an integration of models for predicting the export of environmental pollutants, in particular sediment, through river systems. A review of the capabilities and limitations of current water quality modelling approaches is made. Several water quality and quantity modelling approaches are applied and evaluated in the catchment of the upper Murrumbidgee River.¶ The IHACRES rainfall-runoff model and a simple hydrologic routing model are applied with the aim of developing a capacity to predict streamflow at various catchment scales and to enable integration with other pollutant load estimation techniques. Methods for calculating pollutant loads from observed pollutant concentration and modelled streamflow data are also investigated. Sediment export is estimated using these methods over a 10-year period for two case study subcatchments. Approaches for water quality sampling are discussed and a novel monitoring program using rising stage siphon samplers is presented. Results from a refinement of the Sediment River Network model in the upper Murrumbidgee catchment (SedNet-UM) are presented. The model provides a capacity to quantify sediment source, transport and to simulate the effects of management change in the catchment. The investigation of the model includes rigorous examination of the behaviour of the model through sensitivity assessment and comparison with other sediment modelling studies. The major conclusion reached through sensitivity assessment was that the outputs of the model are most sensitive to perturbation of the hydrologic parameters of the model.¶ The SedNet-UM application demonstrates that it is possible to construct stream pollutant models that assist in prioritising management across catchment scales. It can be concluded that SedNet and similar variants have much potential to address common resource management issues requiring the identification of the source, propagation and fate of environmental pollutants. In addition, incorporating the strengths of a conceptual rainfall-runoff model and the semi-distributed SedNet model has been identified as very useful for the future prediction of environmental pollutant export.

Pollutants follow various subsurface and surface water pathways from sources within a catchment to its outlet and may cause detrimental effects on downstream water quality and ecosystems. Along their different transport pathways through a catchment, pollutants may be attenuated subject to different physical and biogeochemical processes. In this thesis, physical process effects on such catchment-scale pollutant transport and attenuation, resulting coastal pollutant loading and its efficient abatement are investigated. For this purpose, pollutant transport-attenuation is modeled both generically using a Lagrangian Stochastic Advective-Reactive (LaSAR) approach and site specifically for the Swedish Norrström basin using the GIS-based dynamic nitrogen transport-attenuation model POLFLOW. Furthermore, the role of such modeling for catchment-scale pollutant abatement is also investigated by use of economic optimization modeling. Results indicate that appropriate characterization of catchment-scale solute transport and attenuation processes requires accurate quantification of the specific solute pathways from different sources in a catchment, through the subsurface and surface water systems of the catchment, to the catchment outlet. The various physical processes that act on solute transported along these pathways may be quantified appropriately by use of relevant solute travel time distributions for each water subsystem that the pathways cross through the catchment. Such distributions capture the physical solute travel time variability from source to catchment outlet and its effects on reactive pollutant transport. Results of this thesis show specifically that neglect of such physical solute travel time variability in large-scale models of nitrogen transport and attenuation in catchments may yield misleading model estimates of nitrogen attenuation rates. Results for nitrogen abatement optimization in catchments further indicate that inefficient solutions for coastal nitrogen load reduction may result from simplifying physical transport assumptions made in different catchment-scale nitrogen transport-attenuation models. Modeling of possible future nitrogen management scenarios show also that slow nitrogen transport and reversible mass transfer processes in the subsurface water systems of catchments may greatly delay and temporally redistribute coastal nitrogen load effects of inland nitrogen source abatement over decades or much longer. Achievement of the national Swedish environmental objective to reduce the anthropogenic coastal nitrogen loading by 30% may therefore require up to a 40% reduction of both point sources, for achieving a fast coastal load response, and diffuse sources, for maintaining the coastal load reduction also in the long term. / QC 20100908

Watershed monitoring programs generally do not have perfect data collection success rates due to a variety of field and laboratory factors. A major source of error in many stream-gaging records is lost or missing data caused by malfunctioning stream-side equipment. Studies estimate that between 5 and 20 percent of stream-gaging data may be marked as missing for one reason or another. Reconstructing or infilling missing data methods generate larger sets of data. These larger data sets generally generate better estimates of the sampled parameter and permit practical applications of the data in hydrologic or water quality calculations. This study utilizes data from a watershed monitoring program operating in the Northern Virginia area to: (1) identify and summarize the major reasons for the occurrence of missing data; (2) provide recommendations for reducing the occurrence of missing data; (3) describe methods for infilling missing chemical data; (4) develop and evaluate methods for infilling values to replace missing chemical data; and (5) recommend different infilling methods for various conditions. An evaluation of different infilling methods for chemical data over a variety of factors (e.g., amount of annual rainfall, whether the missing chemical parameter is strongly correlated with flow, amount of missing data) is performed using Monte Carlo modeling. Using the results of the Monte Carlo modeling, a Decision Support System (DSS) is developed for easy application of the most appropriate infilling method. / Master of Science

Hamrebäcken rinner genom östra delen av Västerås och har Mälaren som recipient. Under bäckens flödesväg tillkommer dagvatten och föroreningar i form av näringsämnen och tungmetaller från dess avrinningsområde. Bäcken utgör ett av de mest prioriterade vattendragen i Västerås gällande utsläpp av dagvatten. Detta examensarbete har utförts med syftet att utreda föroreningssituationen för Hamrebäcken och hur dess recipient Mälaren påverkas. Examensarbetet syftade även till att undersöka reningseffekten för en befintlig dagvattendamm samt att utifrån ett kostnads- och reningsperspektiv beskriva ett antal åtgärdsförslag för att uppnå en förbättring av bäckens ekologiska och kemiska status. Utvärdering av Hamrebäckens föroreningsbelastning samt reningseffekt för befintlig dagvattendamm och åtgärdsförslag utfördes med hjälp av den Excelbaserade dagvatten- och recipientmodellen StormTac.   Resultatet från studien visade att den modellerade belastningen från flera av bäckens delavrinningsområden överskrider föreslagna riktvärden för mindre vattendrag. Den totala belastningen från Hamrebäckens avrinningsområde överskrider i fallet för föroreningarna bly och suspenderat material även föreslagna riktvärden för Mälaren. Modellering av den befintliga dammen indikerar att anläggningen är underdimensionerad i förhållande till dess belastningsyta. Dammens reningseffekt uppnår inte heller effektmålen i Västerås stads handlingsplan för dagvatten. Ett förslag om utbyggnation av dammen har tagits fram utifrån litteraturstudie och tillgänglig yta för åtgärden. Den simulerade ombyggnationen uppnådde inte uppsatta effektmål men gav en betydande ökning i reningseffekt. Åtgärder som syftar till att öka dammens avskiljningsförmåga bör därför utredas ytterligare.   Fyra ytterligare åtgärdsförslag togs fram och reningseffekten av dessa modellerades i StormTac. Detta inkluderade två olika placeringar av dagvattendammar, en skärmbassäng med flytande våtmark, samt en konstruerad våtmark. Från genomförd modellering rekommenderas vidare utredning av åtgärdsförslagen inkluderande ett anläggande av en skärmbassäng med flytande våtmark, alternativt en konstruerad våtmark. Detta då dessa åtgärdsförslag uppnådde effektmålen för rening enligt Västerås stads handlingsplan för dagvatten. Åtgärdsförslagen skilde sig något åt gällande kostnadseffektivitet. Detta ansågs dock inte ensamt vara argument nog för att motivera anläggning av något åtgärdsförslag till följd av osäkerheter i det beräknade resultatet. Att en skärmbassäng kan utföras i närtid och inte kräver några ingrepp i avrinningsområdet kan anses som ytterligare argument för installation av anläggningen. En konstruerad våtmark kan i sin tur motiveras med att anläggningen bidrar till att höja det estetiska och ekologiska värdet av området. Dessa argument bör beaktas i valet av metod och det fortsatta arbetet med att minska områdets föroreningsbelastning och förbättra bäckens ekologiska och kemiska status. / Hamrebäcken is a small stream in Västerås, which flows through the eastern part of the city. Along it’s course to Lake Mälaren, the stream receives polluted stormwater containing such as heavy metals and nutrients. The primary objective of this master thesis was to investigate the level of pollutants in Hamrebäcken. A secondary objective was to study the reduction efficiency of an existing wet stormwater treatment pond in the area, and propose ways in which to achieve a higher ecological and chemical status for the stream. The stormwater and recipient software model StormTac was used to estimate the level of pollutants and to investigate the reduction efficiencies of different stormwater treatment facilities.   The study revealed that pollutant levels were too high for several of the subwatersheds, based on the recommended guidance for small streams. The pollutant load for the total watershed exceeded the guidance levels for Lake Mälaren for lead and suspended solids. Modelling the reduction efficiency of the existing wet pond indicated that the pond’s size was inadequate to cater for the quantity of incoming stormwater in need of treatment. Subsequently, the pollution reduction efficiency of the pond was not meeting those objectives set out in the Stormwater Action Plan developed by Västerås municipality. A proposal for rebuilding the pond was therefore developed, taking into account the existing conditions of the area and using recommendations from literature. When modeled in StormTac, the modified pond showed a substantial increase in reduction efficiency compared to that of the existing pond. Despite not reaching the objectives of the Action Plan, this suggested that it would be beneficial to investigate measures that increase the reduction efficiency of the existing wet pond further. As a result, an additional four alternatives for reducing the pollutant load of Hamrebäcken were developed using StormTac. These consisted of two wet stormwater treatment ponds at different locations within the watershed, a screen basin with floating treatment wetlands, and a constructed wetland.   The modeling revealed that the most feasible of the investigated measures was an installation of either a screen basin with floating treatment wetlands or a constructed wetland, both measures adjacent to the outlet of Hamrebäcken. This was mainly due to the modeled reduction capacity of these measures where the reduction objectives of the Action Plan were reached. A difference in cost effectiveness was found between the different measures. This was however not considered to solely be argument to justify the implementation of a certain measure due to uncertainties in the modelled result. The fact that a screen basin can be installed in the near future and without occupying space in the watershed are additional arguments for the use of this measure. A constructed wetland can in return be motivated by a potential increase in esthetic and ecological value of the area. These arguments should be considered in the continued investigation of choosing a measure for reducing the pollutant load of Hamrebäcken and to achieve a higher ecological and chemical status for the stream.