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| 2. |
- Bishop, Kevin, et al.
(författare)
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Water storage in a till catchment. II : Implications of transmissivity feedback for flow paths and turnover times
- 2011
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 25:25, s. 3950-3959
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores the flow paths and turnover times within a catchment characterized by the transmissivity feedback mechanism where there is a strong increase in the saturated hydraulic conductivity towards the soil surface and precipitation inputs saturate progressively more superficial layers of the soil profile. The analysis is facilitated by the correlation between catchment water storage and groundwater levels, which made it possible to model the daily spatial distribution of water storage, both vertically in different soil horizons and horizontally across a 6300-m2 till catchment. Soil properties and episodic precipitation input dynamics, combined with the influence of topographic features, concentrate flow in the horizontal, vertical, and temporal dimensions. Within the soil profile, there was a vertical concentration of lateral flow to superficial soil horizons (upper 30?cm of the soil), where much of the annual flow occurred during runoff episodes. Overland flow from a limited portion of the catchment can contribute to peak flows but is not a necessary condition for runoff episodes. The spatial concentration of flow, and the episodic nature of runoff events, resulted in a strong and spatially structured differentiation of local flow velocities within the catchment. There were large differences in the time spent by the laterally flowing water at different depths, with turnover times of lateral flow across a 1-m-wide soil pedon ranging from under 1?h at 10- to 20-cm depth to a month at 70- to 80-cm depth. In many regards, the hydrology of this catchment appears typical of the hydrology in till soils, which are widespread in Fenno-Scandia. Copyright (c) 2011 John Wiley & Sons, Ltd.
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| 3. |
- Davies, J., et al.
(författare)
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Integrated modeling of flow and residence times at the catchment scale with multiple interacting pathways
- 2013
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49:8, s. 4738-4750
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Tidskriftsartikel (refereegranskat)abstract
- There is still a need for catchment hydrological and transport models that properly integrate the effects of preferential flows while accounting for differences in velocities and celerities. A modeling methodology is presented here which uses particle tracking methods to simulate both flow and transport in multiple pathways in a single consistent solution. Water fluxes and storages are determined by the volume and density of particles and transport is attained by labeling the particles with information that may be tracked throughout the lifetime of that particle in the catchment. The methodology allows representation of preferential flows through the use of particle velocity distributions, and mixing between pathways can be achieved with pathway transition probabilities. A transferable 3-D modeling methodology is presented for the first time and applied to a unique step-shift isotope experiment that was carried out at the 0.63 ha G1 catchment in Gardsjon, Sweden. This application highlights the importance of combining flow and transport in hydrological representations, and the importance of pathway velocity distributions and interactions in obtaining a satisfactory representation of the observations.
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| 4. |
- Gebrehiwot, Solomon Gebreyohannis, et al.
(författare)
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Is observation uncertainty masking the signal of land use change impacts on hydrology?
- 2019
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Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 570, s. 393-400
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of hydrological impacts of land use change raises questions about whether, and how much, such impacts are misrepresented because of errors in river flow observations. In this paper, land use change impacts (represented by changes in watershed storage) and different ranges of discharge measurement error are compared to assess how errors in discharge measurement can potentially mask a land use change impact. Using a watershed from the Ethiopian highlands to exemplify this, we simulated five different levels of land use change impacts with five levels of watershed storage reductions (from 10% to 50% change) and the associated time series of runoff. Different levels of observation error were then introduced into these artificial time series. Comparison was made between every pair, i.e. a time series derived from a certain level of land use change (storage reduction) versus a time series corresponding to a given level of observation error, using a step-change t-test. Significant step-changes between pairs define the detectability of land use change impact. The analysis was made for the entire 30-year time series as well as for the most extreme annual weather conditions. The results showed that for the average year and wettest year, 75% or more error in observed discharge masks the maximum simulated land use change impact on hydrology. In dry years, a 50% error in discharge is enough to mask the same impact. Knowing (and improving) the level of data quality contributes to a better understanding of hydrological uncertainties and improves the precision in assessing land use change impacts. Both of these are essential elements in water resources development planning.
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| 5. |
- Norén, Viveca, 1972-, et al.
(författare)
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Drinking water risk assessment in practice : the case of Swedish drinking water producers at risk from floods
- 2016
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Ingår i: Environment Systems and Decisions. - : Springer. - 2194-5403 .- 2194-5411. ; 36:3, s. 239-252
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Tidskriftsartikel (refereegranskat)abstract
- To achieve a safe and reliable drinking water supply, water producers need to manage a large range of risks regarding both water quality and quantity. A risk management approach where risks are systematically identified and handled in a preventive manner is promoted by the World Health Organization and supported by researchers and drinking water experts worldwide. Risk assessment is an important part of such a management approach, and a variety of tools for risk assessment are described in the literature. There is, however, little knowledge of how drinking water risk assessment is performed in practice, including which tools that are actually used. This study investigates the use of risk assessment tools, and the approach to risk management, on a local level in the Swedish water sector. It is based on interviews with key persons from a targeted selection of water producers. We find that the application of tools as well as the approach to risk assessment and management differs considerably between the water producers. The tools most frequently used are mainly the ones promoted or required by Swedish national organizations. Although many of the water producers have done some kind of risk assessment, most have not implemented a risk management approach. Furthermore, their knowledge of the concepts of risk and risk management is often limited. The largest challenge identified is to prioritize risk assessment, so that it is actually performed and then used as a basis for managing risk in a systematic way.
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| 6. |
- Norén, Viveca, 1972-, et al.
(författare)
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Flood riskassessment – Practices in flood prone Swedish municipalities
- 2016
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Ingår i: International Journal of Disaster Risk Reduction. - Uppsala Univ, Dept Earth Sci, Villavagen, SE-75236 Uppsala, Sweden. [Noren, Viveca; Bishop, Kevin] Uppsala Univ, Dept Earth Sci, Villavagen 16, SE-75236 Uppsala, Sweden. [Noren, Viveca; Nyberg, Lars; Bishop, Kevin] Uppsala Univ, Ctr Nat Disaster Sci, Villavagen 16, SE-75236 Uppsala, Sweden. [Hedelin, Beatrice; Nyberg, Lars] Karlstad Univ, Dept Environm & Life Sci, Ctr Climate & Safety, SE-65188 Karlstad, Sweden. [Bishop, Kevin] Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, POB 7050, SE-75007 Uppsala, Sweden. : Elsevier. - 2212-4209. ; 18, s. 206-217
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Tidskriftsartikel (refereegranskat)abstract
- Risk assessments are important to ensure efficient and effective flood risk management. Methods and strategies for flood risk assessment are described in the literature, but less is known about how assessments are actually performed. We have studied local flood risk assessments in Sweden by interviewing flood risk managers in municipalities and analyzing documentation of flood risk assessment efforts.There is a large variation between municipalities in how flood risk assessment has been done. The efforts made in association with the EU Floods Directive together with a Government Commission about a flood in Lake Mälaren are the most advanced assessments. Only a few of the municipalities have done comparable assessments. Generally, however, there is a lack of experience and theoretical knowledge about concepts and methods of flood risk assessment in the municipalities. In the assessments studied, the flood it self had been rather well defined in hazard maps. The consequences of a flood had been studied in the larger projects but only by half of the municipalities. It is mainly direct, tangible consequences that have been included. It is mainly the exposure of assets that has been investigated while little attention has been paid to vulnerability. To improve flood risk assessment in Sweden there is a need for knowledge and resources in the municipalities. Prioritization and motivation are needed to actually perform the assessments. National guidelines for may be helpful to guide municipalities in this work and to have more uniform risk assessment.
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| 7. |
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| 8. |
- Seibert, J., 1968-, et al.
(författare)
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Water storage in a till catchment. I : Distributed modelling and relationship to runoff
- 2011
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 25:25, s. 3937-3949
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Tidskriftsartikel (refereegranskat)abstract
- Although water storage is an important variable to understand the hydrological functioning of a catchment, it is challenging to estimate the total water storage in a catchment. Catchment water storage can be estimated on the basis of water balance, but this approach is prone to errors in the different water balance terms. Here, an approach is presented to estimate the daily dynamics of catchment-wide soil water and groundwater storage on the basis of groundwater-level observations, soil properties and an assumption of hydrological equilibrium above the water table. This approach was applied to a 6300-m2 till catchment in Southwest Sweden. The predicted mean catchment water storage between April 1991 and June 1992 was 210mm and ranged from 190 to 260mm. The estimated water storage followed runoff rates closely especially during recession periods. On average, 79% of the water storage was held in the unsaturated zone, and the remaining 21% was groundwater, but this proportion varied strongly with runoff and total storage. During dry conditions, unsaturated storage accounted for at maximum 95% of the water storage; during wet conditions, this number dropped to 40%. Copyright (c) 2011 John Wiley & Sons, Ltd.
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| 9. |
- Temnerud, Johan, et al.
(författare)
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Map-based prediction of organic carbon in headwater streams improved by downstream observations from the river outlet
- 2016
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 13:2, s. 399-413
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Tidskriftsartikel (refereegranskat)abstract
- In spite of the great abundance and ecological importance of headwater streams, managers are usually limited by a lack of information about water chemistry in these headwaters. In this study we test whether river outlet chemistry can be used as an additional source of information to improve the prediction of the chemistry of upstream headwaters (size < 2 km(2)), relative to models based on map information alone. We use the concentration of total organic carbon (TOC), an important stream ecosystem parameter, as the target for our study. Between 2000 and 2008, we carried out 17 synoptic surveys in 9 mesoscale catchments (size 32-235 km(2)). Over 900 water samples were collected in total, primarily from headwater streams but also including each catchment's river outlet during every survey. First we used partial least square regression (PLS) to model the distribution (median, interquartile range (IQR)) of headwater stream TOC for a given catchment, based on a large number of candidate variables including sub-catchment characteristics from GIS, and measured river chemistry at the catchment outlet. The best candidate variables from the PLS models were then used in hierarchical linear mixed models (MM) to model TOC in individual headwater streams. Three predictor variables were consistently selected for the MM calibration sets: (1) proportion of forested wetlands in the sub-catchment (positively correlated with headwater stream TOC), (2) proportion of lake surface cover in the sub-catchment (negatively correlated with headwater stream TOC), and (3) river outlet TOC (positively correlated with headwater stream TOC). Including river outlet TOC improved predictions, with 5-15% lower prediction errors than when using map information alone. Thus, data on water chemistry measured at river outlets offer information which can complement GIS-based modelling of headwater stream chemistry.
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| 10. |
- van der Velde, Ype, et al.
(författare)
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Consequences of mixing assumptions for time-variable travel time distributions
- 2015
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 29:16, s. 3460-3474
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Tidskriftsartikel (refereegranskat)abstract
- The current generation of catchment travel time distribution (TTD) research, integrating nearly three decades of work since publication of Water's Journey from Rain to Stream, seeks to represent the full distribution in catchment travel times and its temporal variability. Here, we compare conceptualizations of increasing complexity with regards to mixing of water storages and evaluate how these assumptions influence time-variable TTD estimates for two catchments with contrasting climates: the Gardsjon catchment in Sweden and the Marshall Gulch catchment in Arizona, USA. Our results highlight that, as long as catchment TTDs cannot be measured directly but need to be inferred from input-output signals of catchments, the inferred catchment TTDs depend strongly on the underlying assumptions of mixing within a catchment. Furthermore, we found that the conceptualization of the evapotranspiration flux strongly influences the inferred travel times of stream discharge. For the wet and forested Gardsjon catchment in Sweden, we inferred that evapotranspiration most likely resembles a completely mixed sample of the water stored in the catchment; however, for the drier Marshall Gulch catchment in Arizona, evapotranspiration predominantly contained the younger water stored in the catchment. For the Marshall Gulch catchment, this higher probability for young water in evapotranspiration resulted in older water in the stream compared to travel times inferred with assumptions of complete mixing. New observations that focus on the TTD of the evapotranspiration flux and the actual travel time of water through a catchment are necessary to improve identification of mixing and consequently travel times of stream water. Copyright (c) 2014 John Wiley & Sons, Ltd.
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