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  • 101.
    Zmijewski, Nicholas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Effects of Watershed Dynamics on Water Reservoir Operation Planning: Considering the Dynamic Effects of Streamflow in Hydropower Operation2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Water reservoirs are used to regulate river discharge for a variety of reasons, such as flood mitigation, water availability for irrigation, municipal consumption and power production purposes. Recent efforts to increase the amount of renewable power production have seen an increase in intermittent climate-variable power production due to wind and solar power production. The additional variable energy production has increased the need for regulating the capacity of the electrical system, to which hydropower production is a significant contributor. The hydraulic impact on the time lags of flows between production stations have often largely been ignored in optimization planning models in favor of computational efficiency and simplicity. In this thesis, the hydrodynamics in the stream network connecting managed reservoirs were described using the kinematic-diffusive wave (KD) equation, which was implemented in optimization schemes to illustrate the effects of wave diffusion in flow stretches on the resulting production schedule. The effect of wave diffusion within a watershed on the variance of the discharge hydrograph within a river network was also analyzed using a spectral approach, illustrating that wave diffusion increases the variance of the hydrograph while the regulation of reservoirs generally increases the variance of the hydrograph over primarily short periods. Although stream hydrodynamics can increase the potential regulation capacity, the total capacity for power regulation in the Swedish reservoir system also depends significantly on the variability in climatic variables. Alternative formulations of the environmental objectives, which are often imposed as hard constraints on discharge, were further examined. The trade-off between the objectives of hydropower production and improvement of water quality in downstream areas was examined to potentially improve the ecological and aquatic environments and the regulation capacity of the network of reservoirs.

  • 102.
    Zmijewski, Nicholas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Bottacin-Busolin, Andrea
    University of Manchester, UK.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Incorporating Hydrologic Routing into Reservoir Operation Models: Implications for Hydropower Production Planning2016Inngår i: Water resources management, ISSN 0920-4741, E-ISSN 1573-1650, Vol. 30, nr 2, s. 623-640Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Increased reliance on variable and intermittent energy sources is likely to lead to a change in the production strategies of hydropower, thereby increasing the importance of accurate forecasting of production. For optimization models applied to water reservoirs, the computational cost increases with the number of reservoirs and future time-steps considered, often requiring simplification of the physical description of the flow dynamics. Here it is demonstrated that deficiency of the model of the flow dynamics on stream-reaches gives rise to errors in short-term planning, which leads to sub-optimal production. Here a simplified hydraulic model based on the kinematic-diffusion wave model was incorporated in the optimization of reservoir production planning. The time-lag distributions of the streams were evaluated for River Dalälven and implemented in a computationally efficient form of the kinematic-diffusion wave equation incorporated in a production optimization algorithm for a series of reservoirs. Compared to using a single time-lag for the water transfer on flow reaches between hydropower stations, the wave diffusion was found to affect the management as a deviation between the actual production and the planned production. The deviation was found to increase with increasing short-term regulation and decreasing Peclet number below about 10. For a sufficiently high Peclet number and long wavelength characterizing individual stream reaches, the distribution of time-lags become sufficiently narrow to motivate being replaced by a simpler description such as the constant time-lag.

  • 103.
    Zmijewski, Nicholas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Coupled geomorphologic dispersion and reservoir managementManuskript (preprint) (Annet vitenskapelig)
  • 104.
    Zmijewski, Nicholas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Hydrograph variances over different timescales in hydropower production networks2016Inngår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, nr 8, s. 5829-5846Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The operation of water reservoirs involves a spectrum of timescales based on the distribution of stream flow travel times between reservoirs, as well as the technical, environmental, and social constraints imposed on the operation. In this research, a hydrodynamically based description of the flow between hydropower stations was implemented to study the relative importance of wave diffusion on the spectrum of hydrograph variance in a regulated watershed. Using spectral decomposition of the effluence hydrograph of a watershed, an exact expression of the variance in the outflow response was derived, as a function of the trends of hydraulic and geomorphologic dispersion and management of production and reservoirs. We show that the power spectra of involved time-series follow nearly fractal patterns, which facilitates examination of the relative importance of wave diffusion and possible changes in production demand on the outflow spectrum. The exact spectral solution can also identify statistical bounds of future demand patterns due to limitations in storage capacity. The impact of the hydraulic description of the stream flow on the reservoir discharge was examined for a given power demand in River Dalälven, Sweden, as function of a stream flow Peclet number. The regulation of hydropower production on the River Dalälven generally increased the short-term variance in the effluence hydrograph, whereas wave diffusion decreased the short-term variance over periods of <1 week, depending on the Peclet number (Pe) of the stream reach. This implies that flow variance becomes more erratic (closer to white noise) as a result of current production objectives.

  • 105.
    Zmijewski, Nicholas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Trade-Offs between phosphorous discharge and hydropower production using reservoir regulation2017Inngår i: Journal of water resources planning and management, ISSN 0733-9496, E-ISSN 1943-5452, Vol. 143, nr 9, artikkel-id 04017052Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The management of water flow using reservoirs for the purpose of hydropower production can have significant impacts on solute transport. Reducing the phosphorous load to downstream areas can be of great importance for aquatic habitats associated with recipient waters, as well as for the overall health of coastal and estuary areas. This study demonstrates a combined operation of a network of reservoirs with the objectives of hydropower production and improvement of water quality in downstream areas using a multiobjective approach and incorporating the transport of phosphorous in the watershed. A genetic optimization method was used to determine the trade-off between power production and mitigation of phosphorous discharge in the reservoir network of the Dalälven River, Sweden. The phosphorous export can be reduced (-5%) with a limited loss of power production (-4.3%), but further reduction is associated with a significant loss in total power production. The trade-off between the two objectives is determined using Pareto diagrams and examined for varying particulate conditions.

  • 106.
    Åkesson, Anna
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Peakflow response of stream networks: implications of physical descriptions of streams and temporal change2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Through distributed stream network routing, it has quantitatively been shown that the relationship between flow travel time and discharge varies strongly nonlinearly with stream stage and with catchment-specific properties.

    Physically derived distributions of water travel times through a stream network were successfully used to parameterise the streamflow response function of a compartmental hydrological model. Predictions were found to improve compared to conventional statistically based parameterisation schemes, for most of the modelled scenarios, particularly for peakflow conditions.

    A Fourier spectral analysis of 55-110 years of daily discharge time series from 79 unregulated catchments in Sweden revealed that the discharge power spectral slope has gradually increased over time, with significant increases for 58 catchments. The results indicated that the catchment scaling function power spectrum had steepened in most of the catchments for which historical precipitation series were available. These results suggest that (local) land-use changes within the catchments may affect the discharge power spectra more significantly than changes in precipitation (climate change).

    A case study from an agriculturally intense catchment using historical (from the 1880s) and modern stream network maps revealed that the average stream network flow distance as well as average water levels were substantially diminished over the past century, while average bottom slopes increased. The study verifies the hypothesis that anthropogenic changes (determined through scenario modelling using a 1D distributed routing model) of stream network properties can have a substantial influence on the travel times through the stream networks and thus on the discharge hydrographs.

    The findings stress the need for a more hydrodynamically based approach to adequately describe the variation of streamflow response, especially for predictions of higher discharges. An increased physical basis of response functions can be beneficial in improving discharge predictions during conditions in which conventional parameterisation based on historical flow patterns may not be possible - for example, for extreme peak flows and during periods of nonstationary conditions, such as during periods of climate and/or land use change.

  • 107.
    Åkesson, Anna
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Stadler, Charlotte
    KTH, Skolan för bioteknologi (BIO), Proteomik och nanobioteknologi.
    Sullivan, D. P.
    Wiking, Mikaela
    KTH, Skolan för bioteknologi (BIO), Proteomik och nanobioteknologi.
    Krijgsveld, J.
    Uhlen, M.
    Lundberg, Emma
    KTH, Skolan för bioteknologi (BIO), Proteomik och nanobioteknologi.
    Large-scale spatial mapping of the nuclear human proteome.2016Inngår i: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 27Artikkel i tidsskrift (Fagfellevurdert)
  • 108.
    Åkesson, Anna
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Bottacin-Busolin, Andrea
    Hydraulic response in flooded stream networks2015Inngår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, nr 1, s. 213-240Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Average water travel times through a stream network were determined as a function of stage (discharge) and stream network properties. Contrary to most previous studies on the topic, the present work allowed for streamflow velocities to vary spatially (for most of the analyses) as well as temporally. The results show that different stream network mechanisms and properties interact in a complex and stage-dependent manner, implying that the relative importance of the different hydraulic properties varies in space and over time. Theoretical reasoning, based on the central temporal moments derived from the kinematic-diffusive wave equation in a semi-2-D formulation including the effects of flooded cross sections, shows that the hydraulic properties in contrast to the geomorphological properties will become increasingly important as the discharge increases, stressing the importance of accurately describing the hydraulic mechanisms within stream networks. Using the physically based, stage-dependent response function as a parameterization basis for the streamflow routing routine (a linear reservoir) of a hydrological model, discharge predictions were shown to improve in two Swedish catchments, compared with a conventional, statistically based parameterization scheme. Predictions improved for a wide range of modeled scenarios, for the entire discharge series as well as for peak flow conditions. The foremost novelty of the study lies in that the physically based response function for a streamflow routing routine has successfully been determined independent of calibration, i.e., entirely through process-based hydraulic stream network modeling.

  • 109.
    Åkesson, Anna
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Riml, Joakim
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Seibert, Jan
    Change in streamflow response in unregulated catchments in Sweden over the last century2016Inngår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Fourier spectral analysis of 55-110 years of daily discharge time series in 79 unregulated catchments in Sweden reveals that the discharge power spectrum slope in most of the studied catchments has gradually steepened over time. This statistically significant drift in the periodicity of dominant hydrologic response processes can be attributed to a change in either climatic forcing factors or anthropogenic effects on the land surface, e.g., land-use changes. For those locations for which historical meteorological observations are available (the 41 southernmost catchments), the results of our analyses of changes in precipitation power spectra indicate that local land-use changes within the catchments may affect discharge power spectra more significantly than precipitation pattern changes (resulting from climate change).

    By using 1D distributed hydraulic routing, we quantitatively analyze how travel time distributions within stream networks can vary because of anthropogenic impacts, such as changes in stream network spatial coordinates (these stream networks are derived from three maps: two from the present and one from the 1880s), river width modifications, stream channel excavation, and the elimination of thresholds in stream bottom topography that cause exceedingly low local bottom slopes.

    The findings that the discharge power spectrum may change significantly over time, implies that conventional, statistically-based parameterization of hydrological models that rely on assumptions of stationarity may be less suited than more physically based parameterization alternatives. This essential information must be considered when performing tasks that involve (peak) flow predictions, such as those for dimensioning and flood risk management purposes.

     

123 101 - 109 of 109
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