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Torabi Haghighi, A., Ashraf, F. B., Riml, J., Koskela, J., Kløve, B. & Marttila, H. (2019). A power market-based operation support model for sub-daily hydropower regulation practices. Applied Energy, 255, Article ID 113905.
Open this publication in new window or tab >>A power market-based operation support model for sub-daily hydropower regulation practices
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2019 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 255, article id 113905Article in journal (Refereed) Published
Abstract [en]

With increasing power production from renewable energy sources, sub-daily variations in energy demand need to be balanced. Today, hydropower is commonly used as balancing power. In this study, we quantified the impact of capacity constraints, in terms of reservoir volume and hydropower capacity, on the potential to comply with instant energy demand. To evaluate the impact, we developed two new metrics, power market impact and system efficiency ratio, which are based on two threshold flow regimes derived from natural flow as lower threshold release and regulated flow (based on hourly energy prices) as upper threshold release. The operation support model comprises 96 different regulation scenarios based on varying combinations of hydropower and reservoir capacities. For each scenario, an hourly water balance was simulated, to obtain the highest complying with upper threshold release based on actual energy demand. We tested the framework on the Kemijoki river with defined thresholds based on the natural flow regime (tributary river Ounasjoki) and the hourly energy price in Finland in 2017, and estimated the impact of regulation on hourly flow regime at the Taivalkoski hydropower station. The annual flow regime impact in 2013, 2014 and 2015 was estimated to be 74%, 84% and 61%, respectively, while the monthly impact varied from 27% to 100%. Our framework for evaluating interactions between the power market and sub-daily regulation practices is a useful novel tool for sustainable river management and can be easily applied to different rivers and regions and evaluated for different timescales.

Place, publisher, year, edition, pages
Elsevier Ltd, 2019
Keywords
Flow regime alteration, Hydropeaking, Power market, Renewable energy, River regulation, Sub-daily variation, Commerce, Energy management, Hydroelectric power, Reservoirs (water), Rivers, Daily variations, Flow regimes, Renewable energies, Power markets, alternative energy, demand analysis, energy market, flow regulation, hydrological regime, power generation, regulatory framework, river management, threshold, water budget, Finland, Kemijoki River, Lappi [Finland]
National Category
Water Engineering Infrastructure Engineering Energy Systems
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-263474 (URN)10.1016/j.apenergy.2019.113905 (DOI)000497978100121 ()2-s2.0-85072215037 (Scopus ID)
Note

QC 20191206

Available from: 2019-12-06 Created: 2019-12-06 Last updated: 2020-01-13Bibliographically approved
Wörman, A., Mojarrad, B. B. & Riml, J. (2019). Fragmentation of the Hyporheic Zone Due to Regional Groundwater Circulation. Water resources research, 55(2), 1-21
Open this publication in new window or tab >>Fragmentation of the Hyporheic Zone Due to Regional Groundwater Circulation
2019 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 55, no 2, p. 1-21Article in journal (Refereed) Published
Abstract [en]

By use of numerical modeling and field observations, this work quantified the effects of catchment-scale upwelling groundwater on the hyporheic (below stream) fluxes over a wide range of spatial scales. A groundwater flow model was developed that specifically accounted for the hydrostatic and dynamic head fluctuations induced by the streambed topography. Although the magnitudes and relative importance of these streambed-induced fluxes were found to be highly sensitive to site-specific hydromorphological properties, we showed that streambed topographic structures exert a predominant control on the magnitude of hyporheic exchange fluxes in a Swedish boreal catchment. The magnitude of the exchange intensity evaluated at the streambed interface was found to be dominated by the streambed-induced hydraulic head across stream order. However, the catchment-scale groundwater flow field substantially affected the distribution of groundwater discharge points and thus decreased the fragmentation of the hyporheic zone, specifically by shifting the cumulative density function toward larger areas of coherent upwelling at the streambed interface. This work highlights the spectrum of spatial scales affecting the surface water-groundwater exchange patterns and resolves the roles of key mechanisms in controlling the fragmentation of the hyporheic zone.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-244783 (URN)10.1029/2018WR024609 (DOI)000461858900020 ()2-s2.0-85061595295 (Scopus ID)
Note

QC 20190304

Available from: 2019-02-25 Created: 2019-02-25 Last updated: 2020-03-09Bibliographically approved
Riml, J., Campeau, A., Bishop, K. & Wallin, M. B. (2019). Spectral Decomposition Reveals New Perspectives on CO2 Concentration Patterns and Soil-Stream Linkages. Journal of Geophysical Research - Biogeosciences, 124(10), 3039-3056
Open this publication in new window or tab >>Spectral Decomposition Reveals New Perspectives on CO2 Concentration Patterns and Soil-Stream Linkages
2019 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 124, no 10, p. 3039-3056Article in journal (Refereed) Published
Abstract [en]

The rapid development of novel technologies to obtain high-frequency observations has provided new possibilities to observe and understand carbon cycling in inland waters. This study investigates carbon dioxide (CO2) dynamics along a boreal soil-stream transect using a state-of-the-art data set in combination with a spectral methodology to identify controls on stream CO2. The spectral decomposition of hourly observations revealed intermediate (multiday) to long-term (monthly) patterns across the upslope-riparian-stream continuum, with similar power law increases in CO2 concentration fluctuations with increasing period. High-frequency CO2 variabilities, specifically diel CO2 concentration fluctuations, were also identified at all locations but were substantially amplified in the stream compared to in the riparian groundwater. Moreover, the spectral coherence between soil and stream CO2 fluctuations was inconsistent and restricted to episodic events. In contrast, we found a strong and consistent spectral coherence between the riparian groundwater level and stream CO2 concentration, indicating a hydrological control on stream CO2 dynamics. However, during some time spans even these patterns were obscured, suggesting that additional processes, such as CO2 evasion and in-stream metabolism, modulated the influence from riparian sources. The scales and patterns of temporal coherences (or lack thereof) between CO2 at different points in the catchment, as well as with other factors, for example, groundwater levels and Photosynthetically Active Radiation, provide new perspectives on the range of processes governing stream CO2 dynamics. Thus, this study highlights the potential of using spectral decomposition of high-resolution, spatially distributed data of different types to investigate biogeochemical transformations and pathways linking terrestrial and aquatic systems.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
Keywords
time series analyses, spectral decomposition, wavelet analyses, soil-stream linkage, hydrochemical connectivity, aquatic CO2
National Category
Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-263665 (URN)10.1029/2018JG004981 (DOI)000491915000001 ()2-s2.0-85074565427 (Scopus ID)
Note

QC 20191108

Available from: 2019-11-08 Created: 2019-11-08 Last updated: 2020-01-02Bibliographically approved
Bin Ashraf, F., Haghighi, A. T., Riml, J., Alfredsen, K., Koskela, J. J., Klove, B. & Marttila, H. (2018). Changes in short term river flow regulation and hydropeaking in Nordic rivers. Scientific Reports, 8, Article ID 17232.
Open this publication in new window or tab >>Changes in short term river flow regulation and hydropeaking in Nordic rivers
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2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 17232Article in journal (Refereed) Published
Abstract [en]

Quantifying short-term changes in river flow is important in understanding the environmental impacts of hydropower generation. Energy markets can change rapidly and energy demand fluctuates at sub-daily scales, which may cause corresponding changes in regulated river flow (hydropeaking). Due to increasing use of renewable energy, in future hydropower will play a greater role as a load balancing power source. This may increase current hydropeaking levels in Nordic river systems, creating challenges in maintaining a healthy ecological status. This study examined driving forces for hydropeaking in Nordic rivers using extensive datasets from 150 sites with hourly time step river discharge data. It also investigated the influence of increased wind power production on hydropeaking. The data revealed that hydropeaking is at high levels in the Nordic rivers and have seen an increase over the last decade and especially over the past few years. These results indicate that increased building for renewable energy may increase hydropeaking in Nordic rivers.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-239994 (URN)10.1038/s41598-018-35406-3 (DOI)000450911800003 ()30467316 (PubMedID)2-s2.0-85057108172 (Scopus ID)
Note

QC 20181211

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-11Bibliographically approved
Morén, I., Wörman, A. & Riml, J. (2017). Design of Remediation Actions for Nutrient Mitigation in the Hyporheic Zone. Water resources research, 53(11), 8872-8899
Open this publication in new window or tab >>Design of Remediation Actions for Nutrient Mitigation in the Hyporheic Zone
2017 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, no 11, p. 8872-8899Article in journal (Refereed) Published
Abstract [en]

Although hyporheic exchange has been shown to be of great importance for the overall water quality of streams, it is rarely considered quantitatively in stream remediation projects. A main driver of hyporheic exchange is the hydraulic head fluctuation along the streambed, which can be enhanced by modifications of the streambed topography. Here we present an analytical 2-D spectral subsurface flow model to estimate the hyporheic exchange associated with streambed topographies over a wide range of spatial scales; a model that was validated using tracer-test-results and measurements of hydraulic conductivity. Specifically, engineered steps in the stream were shown to induce a larger hyporheic exchange velocity and shorter hyporheic residence times compared to the observed topography in Tullstorps Brook, Sweden. Hyporheic properties were used to parameterize a longitudinal transport model that accounted for reactions in terms of first-order decay and instantaneous adsorption. Theoretical analyses of the mitigation effect for nitrate due to denitrification in the hyporheic zone show that there is a Damkohler number of the hyporheic zone, associated with several different stream geomorphologies, that optimizes nitrate mass removal on stream reach scale. This optimum can be limited by the available hydraulic head gradient given by the slope of the stream and the geological constraints of the streambed. The model illustrates the complex interactions between design strategies for nutrient mitigation, hyporheic flow patterns, and stream biogeochemistry and highlights the importance to diagnose a stream prior remediation, specifically to evaluate if remediation targets are transport or reaction controlled.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-221034 (URN)10.1002/2016WR020127 (DOI)000418736700013 ()2-s2.0-85033605629 (Scopus ID)
Funder
EU, FP7, Seventh Framework ProgrammeSwedish Research Council FormasSwedish Environmental Protection Agency
Note

QC 20180112

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-01-12Bibliographically approved
Wörman, A., Bottacin-Busolin, A., Zmijewski, N. & Riml, J. (2017). Spectral decomposition of regulatory thresholds for climate-driven fluctuations in hydro- and wind power availability. Water resources research, 53(8), 7296-7315
Open this publication in new window or tab >>Spectral decomposition of regulatory thresholds for climate-driven fluctuations in hydro- and wind power availability
2017 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, no 8, p. 7296-7315Article in journal (Refereed) Published
Abstract [en]

Climate-driven fluctuations in the runoff and potential energy of surface water are generally large in comparison to the capacity of hydropower regulation, particularly when hydropower is used to balance the electricity production from covarying renewable energy sources such as wind power. To define the bounds of reservoir storage capacity, we introduce a dedicated reservoir volume that aggregates the storage capacity of several reservoirs to handle runoff from specific watersheds. We show how the storage bounds can be related to a spectrum of the climate-driven modes of variability in water availability and to the covariation between water and wind availability. A regional case study of the entire hydropower system in Sweden indicates that the longest regulation period possible to consider spans from a few days of individual subwatersheds up to several years, with an average limit of a couple of months. Watershed damping of the runoff substantially increases the longest considered regulation period and capacity. The high covariance found between the potential energy of the surface water and wind energy significantly reduces the longest considered regulation period when hydropower is used to balance the fluctuating wind power. Plain Language Summary The availability of renewable energy fluctuates significantly with climate and needs to be regulated to be sufficient at all times. This regulation can be achieved by storing hydropower in water reservoirs, but is complicated by the vast spatial distribution of storage locations, size variations in reservoirs, the covariation of renewable energy, and the range of frequencies that need to be considered in climate variations. This study provides a new method of analysis that can provide estimates of the most effective use of hydropower reservoirs and the limits of their use for regulating renewable energy. Based on data from entire Sweden we show how the storage bounds can be related to a spectrum of the climate-driven modes of variability in water availability and to the covariation between water and wind availability. The high covariance found between the potential energy of the surface water and wind energy significantly reduces the longest considered regulation period when hydropower is used to balance the fluctuating wind power.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:kth:diva-215476 (URN)10.1002/2017WR020460 (DOI)000411202000050 ()2-s2.0-85029710517 (Scopus ID)
Note

QC 20171016

Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2017-10-16Bibliographically approved
Wörman, A., Lindstrom, G. & Riml, J. (2017). The power of runoff. Journal of Hydrology, 548, 784-793
Open this publication in new window or tab >>The power of runoff
2017 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 548, p. 784-793Article in journal (Refereed) Published
Abstract [en]

Although the potential energy of surface water is a small part of Earth's energy budget, this highly variable physical property is a key component in the terrestrial hydrologic cycle empowering geomorphological and hydrological processes throughout the hydrosphere. By downscaling of the daily hydrometeorological data acquired in Sweden over the last half-century this study quantifies the spatial and temporal distribution of the dominating energy components in terrestrial hydrology, including the frictional resistance in surface water and groundwater as well as hydropower. The energy consumed in groundwater circulation was found to be 34.6 TWh/fy or a heat production of approximately 13% of the geothermal heat flux. Significant climate driven, periodic fluctuations in the power of runoff, stream flows and groundwater circulation were revealed that have not previously been documented. We found that the runoff power ranged from 173 to 260 TWh/y even when averaged over the entire surface of Sweden in a five-year moving window. We separated short-term fluctuations in runoff due to precipitation filtered through the watershed from longer-term seasonal and climate driven modes. Strong climate driven correlations between the power of runoff and climate indices, wind and solar intensity were found over periods of 3.6 and 8 years. The high covariance that we found between the potential energy of surface water and wind energy implies significant challenges for the combination of these renewable energy sources.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2017
Keywords
Energy components of terrestrial hydrology, Climate driven fluctuations in the power of runoff, Groundwater energy, Surface water energy, Hydropower
National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:kth:diva-210938 (URN)10.1016/j.jhydrol.2017.03.041 (DOI)000403739000059 ()2-s2.0-85018523561 (Scopus ID)
Note

QC 20170714

Available from: 2017-07-14 Created: 2017-07-14 Last updated: 2017-07-14Bibliographically approved
Åkesson, A., Wörman, A., Riml, J. & Seibert, J. (2016). Change in streamflow response in unregulated catchments in Sweden over the last century. Water resources research
Open this publication in new window or tab >>Change in streamflow response in unregulated catchments in Sweden over the last century
2016 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973Article in journal (Refereed) Published
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.

 

Place, publisher, year, edition, pages
Blackwell Publishing, 2016
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:kth:diva-172935 (URN)10.1002/2015WR018116 (DOI)000383684400008 ()2-s2.0-84980327282 (Scopus ID)
Funder
StandUp
Note

QC 20160823

Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2019-10-17Bibliographically approved
Riml, J. & Wörman, A. (2015). Spatiotemporal decomposition of solute dispersion in watersheds. Water resources research, 51(4), 2377-2392
Open this publication in new window or tab >>Spatiotemporal decomposition of solute dispersion in watersheds
2015 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 4, p. 2377-2392Article in journal (Refereed) Published
Abstract [en]

Information about the effect of different dispersion mechanisms on the solute response in watersheds is crucial for understanding the temporal dynamics of many water quality problems. However, to quantify these processes from stream water quality time series may be difficult because the governing mechanisms responsible for the concentration fluctuations span a wide range of temporal and spatial scales. In an attempt to address the quantification problem, we propose a novel methodology that includes a spectral decomposition of the watershed solute response using a distributed solute transport model for the network of transport pathways in surface and subsurface water. Closed form solutions of the transport problem in both the Laplace and Fourier domains are used to derive formal expressions of (i) the central temporal moments of a solute pulse response and (ii) the power spectral response of a solute concentration time series. By evaluating high-frequency hydrochemical data from the Upper Hafren Watershed, Wales, we linked the watershed dispersion mechanisms to the damping of the concentration fluctuations in different frequency intervals reflecting various environments responsible for the damping. The evaluation of the frequency-dependent model parameters indicate that the contribution of the different environments to the concentration fluctuations at the watershed effluent varies with period. For the longest periods (predominantly groundwater transport pathways) we found that the frequency typical transport time of chloride was 100 times longer and that sodium had a 2.5 times greater retardation factor compared with the shortest periods (predominantly shallow groundwater and surface water transport pathways).

Keywords
solute transport, watershed dispersion, transport network, modeling, spectral analysis, central temporal moments
National Category
Oceanography, Hydrology and Water Resources
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-149531 (URN)10.1002/2014WR016385 (DOI)000354733500029 ()2-s2.0-84929624256 (Scopus ID)
Note

QC 20150615. Updated from manuscript to article in journal.

Available from: 2014-08-22 Created: 2014-08-22 Last updated: 2018-01-11Bibliographically approved
Riml, J. (2014). Solute Transport Across Scales: Time Series Analyses of Water Quality Responses to Quantify Retention and Attenuation Mechanisms in Watersheds. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Solute Transport Across Scales: Time Series Analyses of Water Quality Responses to Quantify Retention and Attenuation Mechanisms in Watersheds
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The intra-continental movement of waterborne contaminants is governed by the distribution of solute load in the landscape along with the characteristics and distribution of the hydrological pathways that transport the solutes. An understanding of the processes affecting the transport and fate of the contaminants is crucial for assessments of solute concentrations and their environmental effect on downstream recipients. Elevated concentration of nutrients and the presence of anthropogenic substances, such as pharmaceutical residues, are two examples of the current problems related to hydrological transport. The overall objective of this thesis is to increase the mechanistic understanding of the governing hydrological transport processes and their links to geomorphological and biogeochemical retention and attenuation processes. Specifically, this study aims to quantify the processes governing the transport and fate of waterborne contaminants on the point, stream reach, and watershed scales by evaluating time series obtained from stream tracer tests and water quality monitoring data. The process quantification was achieved by deriving formal expressions for the key transport characteristics, such as the central temporal moments of a unit solute response function and the spectral scaling function for time series of solute responses, which attributes the solute response in the Laplace and Fourier domains to the governing processes and spatial regions within the watershed. The results demonstrate that in addition to the hydrological and biogeochemical processes, the distribution of the load in the landscape and the geomorphological properties in terms of the distribution of transport pathway distances have defined effects on the solute response. Furthermore, the spatial variability between and along the transport pathways significantly affect the solute response. The results indicate that environments with high retention and attenuation intensity, such as stream-reaches with pronounced hyporheic zones, may often dominate the solute flux in the watershed effluent, especially for reactive solutes. The mechanistic-based framework along with the evaluation methodologies presented within this study describes how the results can be generalized in terms of model parameters that reflect the hydrology, geomorphology and biogeochemistry in the studied area. This procedure is demonstrated by the parameterization of a compartment-in-series model for phosphorous transport.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. p. x, 62
Series
TRITA-LWR. PHD, ISSN 1650-8602 ; 2014:05
Keywords
Solute transport modeling; Transient storage; Tracer test; Central temporal moments; Spectral analysis; Parameterization
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:kth:diva-149528 (URN)978-91-7595-232-1 (ISBN)
Public defence
2014-09-12, F3, Lindstedtvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140826

Available from: 2014-08-26 Created: 2014-08-22 Last updated: 2018-01-11Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2716-4446

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