| 1. |
- Larsen, F, et al.
(författare)
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A preliminary analysis of the groundwater recharge to the Karoo formations, mid-Zambezi basin, Zimbabwe
- 2002
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Ingår i: Physics and Chemistry of the Earth. - 1474-7065. ; 27:11-22, s. 765-772
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Tidskriftsartikel (refereegranskat)abstract
- A multi-disciplinary study is being carried out on recharge to the Karoo sandstone aquifer in the western part of Zimbabwe, where recharge is controlled by the presence of a thick, confining basalt layer. The aquifer is geographically extensive, and has been identified throughout the southern part of the mid-Zambezi basin (Fig. 1). The potential for groundwater abstraction seems to be huge. The key issues in this part of the study are the extent of the recharge area and the recharge rates. The direct recharge area has previously been considered to be the area of outcrop of Karoo Forest sandstone, before it dips below an impervious basalt cover. However,, resistivity profiling shows that the basalt at the basin margin is weathered and fractured, and probably permeable, while the basalt deeper into the basin is fresh, solid and impermeable. Field and laboratory analysis of 22 groundwater samples support this extension of the recharge area to include a large area below the fractured basalt. CO2 gas pressures, calculated with the code PHREEQC using field measurements of pH and alkalinity, show that below the fractured basalt the groundwater is an open system in contact with atmospheric CO2. The C-14 and nitrate concentrations in this groundwater also indicate that recent infiltration takes place. The chloride contents of the rainfall and the groundwater in the recharge area have been measured to calculate direct recharge from rainfall. These data indicate that the direct recharge is in the range of 10-130 mm/yr, with an average value of 25 mm/yr. Preliminary results of recharge estimate using Cl-36 data suggests lower direct infiltration rates, but further studies are needed. The combination of hydro-chemical, isotopic and geophysical investigations show that the recharge area extends well beyond the sandstone outcrop area, northwards beneath the basalt some 20 km beyond the basalt margin.
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| 2. |
- Forsman, Åsa, 1972-, et al.
(författare)
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Generic structures of decision support systems for evaluation of policy measures to reduce catchment-scale nitrogen fluxes
- 2003
-
Ingår i: Physics and Chemistry of the Earth. - 1474-7065 .- 1873-5193. ; 28:14-15, s. 589-598
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Tidskriftsartikel (refereegranskat)abstract
- Decision support systems (DSSs) for evaluation of different policy measures have two important functions: To assess how considered policy measures may influence the behavior of actors, and to predict the effects of a given set of actions generated from the anticipated behavior. So far, almost all attempts to construct DSSs for environmental management have focused on assessing the impact of a set of actions on the environment. Here, we describe the generic structure of a DSS that enables more complete evaluation of regional or national policies to reduce nitrogen inputs to water. In particular, we expound the principles for linking models of farm economic behavior to catchment-scale models of the transport and transformation of nitrogen in soil and water. First, we define system boundaries for nitrogen fluxes through the agricultural sector and the ambient environment to create a basis for model integration. Thereafter, we show how different modules operating on different temporal and spatial scales can be interlinked. Finally, we demonstrate how statistical emulators or meta-models can be derived to reduce the computational burden and increase the transparency of the DSS. In particular, we show when and how the temporal or spatial resolution of model inputs can be reduced without significantly influencing the estimates of annual nitrogen fluxes on a catchment scale.
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| 3. |
- Achite, Mohammed, et al.
(författare)
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An improved adaptive neuro-fuzzy inference system for hydrological drought prediction in Algeria
- 2023
-
Ingår i: Physics and Chemistry of the Earth. - 1474-7065. ; 131
-
Tidskriftsartikel (refereegranskat)abstract
- Drought has negative impacts on water resources, food security, soil degradation, desertification and agricultural productivity. The meteorological and hydrological droughts prediction using standardized precipitation/runoff indices (SPI/SRI) is crucial for effective water resource management. In this study, we suggest ANFISWCA, an adaptive neuro-fuzzy inference system (ANFIS) optimized by the water cycle algorithm (WCA), for hydrological drought forecasting in semi-arid regions of Algeria. The new model was used to predict SRI at 3-, 6-, 9-, and 12-month accumulation periods in the Wadi Mina basin, Algeria. The results of the model were assessed using four criteria; determination coefficient, mean absolute error, variance accounted for, and root mean square error, and compared with those of the standalone ANFIS model. The findings suggested that throughout the testing phase at all the sub-basins, the proposed hybrid model outperformed the conventional model for estimating drought. This study indicated that the WCA algorithm enhanced the ANFIS model's drought forecasting accuracy. The proposed model could be employed for forecasting drought at multi-timescales, deciding on remedial strategies for dealing with drought at study stations, and aiding in sustainable water resources management.
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| 4. |
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| 5. |
- Arvidsson, Kristina, et al.
(författare)
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A hydrogeological study of the Nhandugue River, Mozambique – A major groundwater recharge zone
- 2011
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 36:14-15, s. 789-797
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Tidskriftsartikel (refereegranskat)abstract
- The Nhandugue River flows over the western margin of the Urema Rift, the southernmost extension of the East African Rift System, and marks the north-western border of Gorongosa National Park, Mozambique. It constitutes one of the major indispensable water resources for the ecosystem that the park protects. Our study focused on the hydrogeological conditions at the western rift margin by resistivity measurements, soil sampling and discharge measurements. The resistivity results suggest that the area is heavily faulted and constitutes a major groundwater recharge zone. East of the rift margin the resistivity indicate that solid gneiss is fractured and weathered, and is overlain by sandstone and alluvial sediments. The top 10-15 m of the alluvial sequence is interpreted as sand. The sand layer extends back to the rift margin thus also covering the gneiss. The sandstone outcrops a few kilometers from the rift margin and dips towards east/south-east. Further into the rift valley, the sand is underlain by lenses of silt and clay on top of sand mixed with finer matter. In the lower end of the investigated area the lenses of silt and clay appears as a more or less continuous layer between the two sand units. The topmost alluvial sand constitutes an unconfined aquifer under which the solid gneiss forms a hydraulic boundary and the fractured gneiss an unconfined aquifer. The sandstone is an unconfined aquifer in the west, becoming semi-confined down dip. The lenses of silt and clay forms an aquitard and the underlying sand mixed with finer matter a semi-confined aquifer. The surface runoff decreases downstream and it is therefore concluded that surface water infiltrates as recharge to the aquifers and moves as groundwater in an east/south-eastward direction.
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| 6. |
- Baresel, Christian, et al.
(författare)
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Estimating subsurface nitrogen accumulation–depletion in catchments by input–output flow analysis
- 2006
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 31:17, s. 1030-1037
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Tidskriftsartikel (refereegranskat)abstract
- We use input-output analysis of nitrogen flows between various sources-sectors and natural waters in the Swedish Norrstrom drainage basin for investigating and bounding the implication range of some uncertainty sources for results of subsurface nitrogen accumulation-depletion in this basin. We quantify different possible base and extreme assumptions of nitrogen discharges and transport pathways from agriculture to surface and groundwater in the basin. The results are robust in showing considerable nitrogen accumulation-depletion flow interactions taking place between the basin's mobile water and accumulated nitrogen pools in soils, sediments and/or relatively immobile subsurface water zones for all different scenario assumptions. Similar scenario robustness is also found in resulting relative contributions of different active nitrogen source-sectors to nitrogen flows in natural water systems. In the Norrstrom basin, and possibly more generally, nitrogen accumulation-depletion flows to and from accumulated legacies for the future or from the past appear therefore to be more important for water quality than current nitrogen discharges from active source-sectors.
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| 7. |
- Barthel, Roland, 1967, et al.
(författare)
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Aspects of choosing appropriate concepts for modelling groundwater resources in regional integrated water resources management - Examples from the Neckar (Germany) and Ouémé catchment (Benin)
- 2008
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 33:1-2, s. 92-114
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Tidskriftsartikel (refereegranskat)abstract
- Two regional groundwater flow models (Neckar catchment, Germany, 14,000 km2, and Southern Ouémé Basin, Benin, 11,000 km2) were developed within the framework of the integrated management project 'RIVERTWIN' (www.rivertwin.org). Both models were evaluated with respect to the question if the chosen modelling approaches (multi-layered finite difference numerical flow modelling, steady state and transient) are appropriate in view of the existing management problems in the catchments, the data availability and the hydrogeological and hydrological conditions in the basins. It is shown that neither the model in the well-investigated, data-rich basin in Western Europe with its highly developed water related infrastructure, nor the model in the hydrogeologically less well-known and less developed basin in Western Africa provide results that are fully applicable to the main regional management tasks. In the case of the Ouémé, the groundwater related problems are foremost of local character and therefore cannot be addressed by regional models in a meaningful way. Data scarcity and complex, unfavourable geological conditions (crystalline rocks, discontinuous aquifers) support the conclusion that numerical 3D groundwater flow models are currently not helpful to manage groundwater related management problems in the Ouémé basin. A better understanding of regional hydrological surface and subsurface processes is required first. Methods for a reliable estimation of groundwater recharge and subsequently groundwater availability were identified as the most urgently needed tool for meaningful groundwater management in view of climatic, demographic and land use change. In the Neckar catchment the results of the analysis are less pronounced; here regional groundwater problems could clearly benefit from a physically based 3D model since the hydrogeological system is strictly stratified with several important aquifers in the vertical sequence. As a general conclusion it can be stated that regional scale groundwater flow modelling concepts seem to be difficult to integrate in management systems and difficult to transfer from one basin to another. This means the question of how to represent the groundwater resources appropriately has to be discussed very thoroughly for any new integrated water resources management problem. It is not possible to give a final recommendation on which modelling concept is the most appropriate one in regional integrated modelling and management. Hence, this article is only intended to provide an in depth discussion of the aspects that need to be considered in the process of choosing appropriate modelling concepts. © 2007 Elsevier Ltd. All rights reserved.
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| 8. |
- Barthel, Roland, 1967, et al.
(författare)
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Large-scale water resources management within the framework of GLOWA-Danube. Part A: The groundwater model
- 2005
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 30:6-7, s. 372-382
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Tidskriftsartikel (refereegranskat)abstract
- The research project GLOWA-Danube, financed by the German Federal Government, is investigating long-term changes in the water cycle of the upper Danube river basin (77,000 km(2)) in light of global climatic change. Its aim is to build a fully integrated decision-support tool "DANUBIA" that combines the competence of 11 different research institutes in domains covering all major aspects governing the water cycle-from the formation of clouds, to groundwater flow patterns, to the behaviour of the water consumer. Both the influence of natural changes in the ecosystem, such as climate change, and changes in human behaviour, such as changes in land use or water consumption, are considered. DANUBIA is comprised of 15 individual disciplinary models that are connected via customized interfaces that facilitate network-based parallel calculations. The strictly object-oriented DANUBIA architecture was developed using the graphical notation tool UML (Unified Modeling Language) and has been implemented in Java code. All models use the same spatial discretisation for the exchange of data (1 x 1 km grid cells) but are using different time steps. The representation of a vast number of relevant physical and social processes that occur at different spatial and temporal scales is a very demanding task. Newly developed up- and downscaling procedures [Rojanschi, V., 2001. Effects of upscaling for a finite-difference flow model. Master's Thesis, Institut fur Wasserbau, Universitat Stuttgart, Stuttgart, Germany] and a sophisticated time controller developed by the computer sciences group [Hennicker, R., Barth, M., Kraus, A., Ludwig, M., 2002. DANUBIA: A Web-based modelling and decision support system for integrative global change research in the upper Danube basin. In: GSF (Ed.), GLOWA, German Program on Global Change in the Hydrological Cycle Status Report 2002. GSF, Munich, pp. 35-38; Kraus, A., Ludwig, M., 2003. GLOWA-Danube Papers Technical Release No. 002 (Danubia Framework), Software-Release No.: 0.9.2, Documentation Version: 0.10, Release Date: 27 March 2003] are required to solve the emerging problems. After a first successful public demonstration of the DANUBIA package (nine models) in May 2002 [Mauser, W., Stolz, R., Colgan, A., 2002. GLOWA-Danube: integrative techniques, scenarios and strategies regarding global change of the water cycle. In: GSF (Ed.), GLOWA, German Program on Global Change in the Hydrological Cycle (Phase I, 2000-2003) Status Report 2002. GSF, Munich, pp. 31-34], the research consortium is now preparing a first validation run of DANUBIA for the period 1995-1999 with all 15 models. After successful completion of the validation, a scenario run based on IPCC climate scenarios [IPCC, 2001. Climate Change 2001: Synthesis Report. In: Watson, R.T., Core Writing Team (Eds.), A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, NY, USA, 398pp] for a five year period between 2025 and 2040 will follow at the end of 2003. The research group "Groundwater and Water Resources Management" at the Institute of Hydraulic Engineering, Universitat Stuttgart, is contributing both a three-dimensional groundwater flow model of the catchment and an agent-based model for simulating water supply and distribution. This paper gives a general overview of the GLOWA-Danube project and describes the groundwater modeling segment. Nickel et al. deal with the water supply model in a second contribution to this special issue. A three-dimensional numerical groundwater flow model consisting of four main layers has been developed and is in a continual state of refinement (MODFLOW, [McDonald, M.G., Harbaugh, AW., 1988. A modular three-dimensional finite-difference ground-water flow model: US Geological Survey Techniques of Water-Resources Investigations, Washington, USA (book 6, Chapter A1)]). One main research focus has been on the investigation of upscaling techniques to meet the requirement of a fixed 1 x 1 km cell size. This cell size is compulsory for all models in DANUBIA in order to facilitate a one to one parameter exchange. In a second stage, a transport model (nitrogen) will be added (MT3D): [Zheng, C., Hathaway, D-L., 1991. MT3D: a new modular three-dimensional transport model and its application in predicting the persistence and transport of dissolved compounds from a gasoline spill, with implications for remediation. Association of Ground Water Scientists and Engineers Annual Meeting on Innovative Ground Water Technologies for the '90s, National Ground Water Association, Westerville, Ohio, USA. Ground Water 29 (5)]. (c) 2005 Elsevier Ltd. All rights reserved.
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| 9. |
- Barthel, Roland, 1967, et al.
(författare)
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Linking the physical and the socio-economic compartments of an integrated water and land use management model on a river basin scale using an object-oriented water supply model
- 2005
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 30:6-7, s. 389-397
-
Tidskriftsartikel (refereegranskat)abstract
- Within the framework of the research project 'GLOWA-Danube', a model of the water supply sector has been developed. GLOWA-Danube investigates long-term changes in the water cycle of the Upper Danube river basin in light of global change. For this purpose, the decision support system DANUBIA, comprising 15 fully coupled models, has been developed. Within DANUBIA the water supply model ('WaterSupply') forms the link between various physical models determining water quality and availability and several socio-economic models determining water consumption and demand. Having a central focus on public drinking water supply, its purpose is to correctly simulate the present day system of water extraction and distribution and the related costs, but also to allow meaningful response to possible future changes of boundary conditions, first and foremost changes in water demand or water availability and quality. Response mechanisms are also envisioned for changes in political and economic boundary conditions, and advances in technology. The model will be used locate critical regions which could experience water stress in the future, but does not aim to find the appropriate solutions or to predict the optimal organisation of water supply in the Danube Basin under such changing conditions. In the object-oriented model structure, both water supply companies (WSC) and communities are represented by main classes. Both classes have a limited view and knowledge of their environment. A community knows where and how much water is consumed and from which WSC it is served. A WSC possesses information regarding extraction sites and water rights, raw water quality and potential collaborating WSC. The WSC can perform actions that are different from 'business as usual'. These deviations from their usual behaviour can be interpreted by decision makers but should not be regarded as a replacement for the decision-making process itself. The model is conceptualised using object-oriented concepts of the Unified Modelling Language (UML) and is implemented in JAVA. This short overview is meant to answer key questions such as why and how WaterSupply was implemented, what is unique and new about the model and what are the general lessons learned and the added value with regard to integrated modelling on a river basin scale. It is obvious that in the attempt to answer these questions it is not possible to satisfy experts from all the relevant related fields, which include computer sciences, economy, behavioural science and not least water supply engineering and hydrology. (c) 2005 Elsevier Ltd. All rights reserved.
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| 10. |
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| 11. |
- Cattin, Rodolphe, et al.
(författare)
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Joint inversion of ground gravity data and satellite gravity gradients between Nepal and Bhutan : New insights on structural and seismic segmentation of the Himalayan arc
- 2021
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier. - 1474-7065 .- 1873-5193. ; 123
-
Tidskriftsartikel (refereegranskat)abstract
- Along-strike variation in the geometry of lithospheric structures is a key control parameter for the occurrence and propagation of major interplate earthquakes in subduction and collision zones. The lateral segmentation of the Himalayan arc is now well-established from various observations, including topography, gravity anomalies, exhumation rates, and present-day seismic activity. Good knowledge of the main geometric features of these segments and their boundaries is thus the next step to improve seismic hazard assessment in this area. Following recent studies, we focus our approach on the transition zone between Nepal and Bhutan where both M > 8 earthquakes and changes in the geometry of the Indian plate have been documented. Ground gravity data sets are combined with satellite gravity gradients provided by the GOCE mission (Gravity Field and Steady-State Ocean Circulation Explorer) in a joint inversion to assess the location and the geometry of this transition. We obtain a ca. 10 km wide transition zone located at the western border of Bhutan that is aligned with the Madhupur fault in the foreland and coincides with the Dhubri-Chungthang fault zone and the Yadong-Gulu rift in Himalaya and southern Tibet, respectively. This sharp segment boundary at depth can act as a barrier to earthquake rupture propagation. It can possibly restrict the size of large earthquakes and thus reduce the occurrence probability of M > 9 earthquakes along the Main Himalayan Thrust.
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| 12. |
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| 13. |
- Di Baldassarre, Giuliano, et al.
(författare)
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Effect of observation errors on the uncertainty of design floods
- 2012
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 42-44, s. 85-90
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the uncertainty in the estimation of the design flood induced by errors in flood data. We initially describe and critically discuss the main sources of uncertainty affecting river discharge data, when they are derived using stage-discharge rating curves. Then, different error structures are used to investigate the effects of flood data errors on design flood estimation. Annual maxima values of river discharge observed on the Po River (Italy) at Pontelagoscuro are used as an example. The study demonstrates that observation errors may have a significant impact on the uncertainty of design floods, especially when the rating curve is affected by systematic errors.
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| 14. |
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| 15. |
- Di Donna, Alice, et al.
(författare)
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The contribution of swelling to self-sealing of claystone studied through x-ray tomography
- 2022
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 127
-
Tidskriftsartikel (refereegranskat)abstract
- Many countries, as among others France, Belgium and Switzerland, are facing the issue of finding a proper solution to store radioactive waste coming from nuclear power plants. The possibility to store them in underground tunnels is largely considered and investigated. In France, Andra (Agence Nationale pour la gestion des Déchets RAdioactifs) selected the Callovo-Oxfordian clay rock situated in the Meuse/Haute Marne site between 400 and 600 m depth as possible host rock deposit. The excavation of the storage tunnels is expected to create a fractured zone around galleries. The factures will be then gradually re-saturated by the underground water coming from the surrounding rock and they are expected to self-seal in contact with water, thanks to the swelling potential of COx. The capacity of self-sealing, i.e. closing of fractures after water contact and possibly restoring of permeability, is thus of primary interest for the safety of the storage system with respect to water, gas and solutes transport. The physical mechanisms driving this phenomenon are mainly the swelling and de-structuration of the clay matrix present in the claystone. In this work, the self-sealing response of COx was investigated through x-ray tomography at multi-micrometre and sub-micrometre voxel size. The objective was to study the influence of mineralogy, size of the discontinuity, hydraulic paths, mutual orientation of the bedding plane and fractures. The size of the discontinuity is of primary importance in determining the percentage of closure. Fractures parallel to the bedding plane are more likely to seal as swelling is anisotropic and occurs mainly perpendicular to the bedding plane. The main novelty is represented by the direct and local observation of the physical process of self-sealing down to a scale lower than 1 μm.
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| 16. |
- Gallart, Francesc, et al.
(författare)
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Upscaling discrete internal observations for obtaining catchment-averaged TOPMODEL parameters in a small Mediterranean mountain basin
- 2008
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 33:17-18, s. 1090-1094
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Tidskriftsartikel (refereegranskat)abstract
- Discrete observations on recession flows, local depth to the water table and the extent of saturated areas were used in the Vallcebre small research basin for obtaining the distribution functions of the TOPMODEL catchment parameters that drive the behaviour of the saturated store. Using this parameter information within GLUE framework, the robustness of discharge simulations was improved and the uncertainty of flow separation between two components was significantly reduced when compared with the results obtained with customary calibration with flow data at the outlet. Nevertheless, the analysis of the uncertainty in the determination of the local value of the topographic index at the piezometer location demonstrated that this may be a relevant limitation of the approach, particularly for high values of the topographic index, and a careful selection of the piezometer is recommended. The use of the extent of saturated areas provided the best and more representative results, although the simulated patterns of saturated areas did not match well the observed ones, because the role of local controls beyond the topographic index.
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| 17. |
- Ghorbanpour, Ali Karbalaye, et al.
(författare)
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Water and productivity accounting using WA+ framework for sustainable water resources management : Case study of northwestern Iran
- 2022
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 128
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Tidskriftsartikel (refereegranskat)abstract
- An exhaustive evaluation of water resources is a prerequisite for evidence-informed planning and implementing sustainable management strategies. However, the lack of sufficient information on water supply and consumption, alongside the technical limitations on comprehensive accounting for inter-relations and interactions between the subsystems, has resulted in decisions with often long-lasting outcomes and undesirable consequences. Water accounting is a tool for systematic acquisition, analysis, and reporting of water-related information to fill the existing knowledge gap on water flows and fluxes. In this study, Water Accounting Plus (WA+) framework is applied to the western region of Lake Urmia, a dying hyper-saline lake, to assess water use and crop water productivity (CWP) from 2010 to 2016. Remotely sensed information along with a distributed hydrological model (SPHY) is used to fill the information gap on water resources and inform effective policy actions. Our analysis reveals that the agricultural sector is neither productive nor efficient while there is a considerable scope to ameliorate water productivity and beneficial water use by adopting proper water management practices. Average CWP values for wheat, sugarbeet, vineyard, and apple vary between 0.38 and 0.55, 5.1–5.6, 1.5–1.7 and 1.9–2.3 (kg/m3), respectively while storage changes show consistent depletion, especially during dry year, up to 117 MCM. The results indicate that a 40% reduction in blue water use is achievable to supply additional water to revive Lake Urmia. This study highlights the importance of water accounting and information flow for decision-makers, practitioners, and farming communities to define practical targets and enhance productivity in water-scarce regions.
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| 18. |
- Graham, P, et al.
(författare)
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Using multiple climate projections for assessing hydrological response to climate change in the Thukela River Basin, South Africa
- 2011
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier. - 1474-7065 .- 1873-5193. ; 36:14-15, s. 727-735
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Tidskriftsartikel (refereegranskat)abstract
- This study used climate change projections from different regional approaches to assess hydrological effects on the Thukela River Basin in KwaZulu-Natal, South Africa. Projecting impacts of future climate change onto hydrological systems can be undertaken in different ways and a variety of effects can be expected. Although simulation results from global climate models (GCMs) are typically used to project future climate, different outcomes from these projections may be obtained depending on the GCMs themselves and how they are applied, including different ways of downscaling from global to regional scales. Projections of climate change from different downscaling methods, different global climate models and different future emissions scenarios were used as input to simulations in a hydrological model to assess climate change impacts on hydrology. A total of 10 hydrological change simulations were made, resulting in a matrix of hydrological response results. This matrix included results from dynamically downscaled climate change projections from the same regional climate model (RCM) using an ensemble of three GCMs and three global emissions scenarios, and from statistically downscaled projections using results from five GCMs with the same emissions scenario. Although the matrix of results does not provide complete and consistent coverage of potential uncertainties from the different methods, some robust results were identified. In some regards, the results were in agreement and consistent for the different simulations. For others, particularly rainfall, the simulations showed divergence. For example, all of the statistically downscaled simulations showed an annual increase in precipitation and corresponding increase in river runoff, while the RCM downscaled simulations showed both increases and decreases in runoff. According to the two projections that best represent runoff for the observed climate, increase runoff would generally be expected for this basin in the future. Dealing with such variability in results is not atypical for assessing climate change impacts in Africa and practitioners are faced with how to interpret them. This work highlights the need for additional, well-coordinated regional climate downscaling for the region to further define the range of uncertainties involved.
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| 19. |
- Guo, Renkui, et al.
(författare)
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Diagnosing the impacts of landscape characteristics on hydrologic signatures in the Krycklan catchment in Sweden using a flexible hydrological model
- 2024
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Ingår i: Physics and Chemistry of the Earth. - 1474-7065. ; 134
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated the applicability and performance of a hydrological model (namely FLEXG) for simulating streamflow in boreal catchment, exemplified by the representative Krycklan catchment. The FLEXG simulated daily streamflow for the whole catchment and its sub-catchments. The Kling-Gupta Efficiency (KGE) and Nash-Sutcliffe Efficiency (NSE) demonstrated favorable model performance during the calibration period (KGE = 0.88 and NSE = 0.75) and the subsequent validation (KGE = 0.81 and NSE = 0.63) period for the Krycklan catchment. Notably, a high degree of congruence was observed across eight sub-catchments, with KGE values consistently exceeding the threshold of 0.7 during both calibration and validation periods. These findings underscore the FLEXG model's aptitude for simulating streamflow within boreal catchments, as evidenced by its ability to capture seasonal patterns across the catchment. Additionally, regression analysis was conducted to examine the intricate relationships between model parameters and varied catchment characteristics. These catchment characteristics were identified as pivotal factors influencing streamflow modelling in the study region. Specifically, it was established that catchment size shows a negative correlation with the splitter D (R2 = 0.7), a parameter intimately associated with both fast and slow recession periods. The proportion of forest cover was negatively correlated with the slow response reservoir recession coefficient, Kf (R2 = 0.57), whereas the proportion of wetland cover displayed a positive correlation with Ks (R2 = 0.54). These correlations underscore the substantive impact of land use patterns on streamflow generation dynamics within the boreal catchment context.
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| 20. |
- Holmboe, Michael, 1978-, et al.
(författare)
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Effects of the injection grout Silica sol on Bentonite
- 2011
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 36:17/18, s. 1580-1589
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Tidskriftsartikel (refereegranskat)abstract
- Silica sol, i.e., colloidal SiO2, may be used as a low-pH injection grout for very fine fractures in the construction of deep geological repositories for radioactive waste in Sweden and in Finland. If the bentonite barrier encounters SiO2-colloid particles under conditions favorable for aggregation, there is concern that it will modify the bentonite barrier at the bentonite/bedrock interface. In this study qualitative experiments were performed with mixed dispersions of SiO2-colloids and bentonite or homo-ionic Na/Ca-montmorillonite. Samples were prepared at different colloid concentrations and treated under various conditions such as low and high ionic strength (0.3 M NaCl), as well as dehydration and redispersing. Free swelling and settling experiments were performed in order to qualitatively compare the conditions in which SiO2-colloids affect the bulk/macro properties of bentonite. In order to study specific SiO2-colloid/montmorillonite interactions and preferred type of initial aggregation, dilute dispersions of homo-ionic montmorillonite dispersions mixed with varying concentrations of SiO2-colloids were prepared and selected samples were characterized by PCS, SEM/EDS, AFM and PXRD. The results from this study show that bentonite and montmorillonite particles can be modified by SiO2-colloids when mixed in comparable amounts, due to dehydration or high ionic strength. Some indications for increased colloidal stability for the SiO2-colloid modified clay particles were also found. From the AFM investigation it was found that initial attachment of the SiO2-colloids in Na+ dominated samples seemed to occur on the edges of the montmorillonite layers. In Ca2+ dominated samples not subjected to excess NaCl, SiO2-colloid sorption onto the faces of the montmorillonite layers was also found. In all, contact between the bentonite barrier and ungelled Silica sol should preferably be avoided.
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| 21. |
- Ikeagwuani, C. C., et al.
(författare)
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Improvement of soft clay soil with a combination of pre-gelatinized corn starch and nanoparticle agro waste : A multi-objective grey wolf optimizer approach
- 2024
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 135
-
Tidskriftsartikel (refereegranskat)abstract
- The present study aimed to assess the potential of a bio-inspired algorithm, multi-objective grey wolf optimization algorithm (MOGWO), to optimize the strength properties (California bearing ratio (CBR) and unconfined compressive strength (UCS)) of an expansive subgrade soil. This optimization process involves the use of two additives, namely a bio-polymer, pregelatinized corn starch (PGCS), and a nanoparticle agro waste, rice husk ash (RHA), blended with the soil in different mix ratios determined by a 32 factorial experimental design. The CBR samples were cured for 7 days, while the UCS samples were cured for 1, 7, and 28 days. To optimize the expansive subgrade soil strength, regression models were developed using PGCS and RHA as predictors for CBR and UCS, serving as fitness functions in the slightly modified MOGWO optimization technique. Next, the optimization analysis produced non-dominated solutions. The results obtained from the laboratory experiments and optimization analysis revealed that there was significant improvement in the UCS and CBR of the soil. These improvements can be attributed to the pozzolanic reaction between the soil-RHA matrix, the formation of intercalated and exfoliated nanocomposites, and the hydrophilic interaction of PGCS. By applying the slightly modified MOGWO technique, the study achieved optimal enhancements in UCS (710.3 kN/m2) and CBR (24.2%) when the expansive subgrade soil was mixed with 0.2637% PGCS and 12.2413% RHA. The results demonstrate the potential of the MOGWO technique in improving the properties of expansive subgrade soil.
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| 22. |
- Isaksson, E, et al.
(författare)
-
Ice cores from Svalbard :useful archives of past climate and pollution history.
- 2003
-
Ingår i: Physics and chemistry of the earth. Part A. - : Elsevier BV. - 1464-1895 .- 1873-4642 .- 1474-7065. ; 28:28-32, s. 1217-1228
-
Tidskriftsartikel (refereegranskat)abstract
- Ice cores from the relatively low-lying ice caps in Svalbard have not been widely exploited in climatic and environmental studies due to uncertainties about the effect of melt water percolation. However, results from two recent Svalbard ice cores, at Lomonosovfonna (1250 m asl) and Austfonna (750 m asl), have shown that with careful site selection, high-resolution sampling and multiple chemical analyses, it is possible to recover ice cores with partly preserved annual signals. These cores are estimated to cover at least the past 600 years and have been dated using a combination of known reference horizons and glacial modeling. The δ18O data from both Lomonosovfonna and Austfonna ice cores suggest that the 20th century was the warmest during the past 600 years. A comparison of the ice core and sea ice records from this period suggests that sea ice extent and Austfonna δ18O are linked over the past 400 years. This may reflect the position of the storm tracks and their direct influence on the relatively low altitude Austfonna. Lomonosovfonna may be less sensitive to such changes and primarily record atmospheric changes due to its higher elevation. The anthropogenic influence on Svalbard environment is illustrated by increased levels of non-sea-salt sulphate, nitrate, acidity, fly-ash and organic contaminants particularly during the second half of 1900s. Decreased concentrations of some components in recent decades most likely reflect emission and use restrictions. However, some current-use organic pesticide compounds show growing concentrations in near surface layers.
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| 23. |
- Juma, B., et al.
(författare)
-
Analysis of rainfall extremes in the Ngong River Basin of Kenya : Towards integrated urban flood risk management
- 2020
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier. - 1474-7065 .- 1873-5193.
-
Tidskriftsartikel (refereegranskat)abstract
- Extreme rainfall events are a major cause of highly disruptive flooding in small urban watersheds with limited flood risk management systems. In the Ngong River Basin of Kenya, such floods affect more than 0.5 Million residents within the Kibera informal settlements of Nairobi. However, there is paucity of information about the characteristics of the extreme rainfalls to support flood risk management. This study investigated the best-fit probability distribution models for the extreme rainfalls of the Ngong Basin using Block Maxima approach as a basis for anticipatory flood risk management. Daily rainfall data for the period between 1968 and 2017 were acquired from the existing two rainfall stations to support the analysis at monthly, seasonal and annual timescales. The Gamma, Pearson Type III, Gumbel and Generalized Extreme Value distributions were selected and applied to each timescale. Parameters of the distributions were determined using the Maximum-Likelihood estimator. The validity of the fitted probability models was tested using the Kolomogorov- Smirnov, Anderson-Darling and Cramer von Misses measures for Goodness of Fit. The best-fit probability distributions were subsequently used to establish the rainfall frequencies and return levels at annual timescales. The results show that Pearson Type III provided the best fit at monthly timescales during the dry spell months, while the Generalized Extreme Value distribution provided best results during the wet periods. At seasonal timescales, the Gamma distribution was noted to be the best-fit model. The return levels developed could essentially support the design of urban flood control structures for appropriate flood risk management.
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| 24. |
- Juma, Benard, et al.
(författare)
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Flooding in the urban fringes : Analysis of flood inundation and hazard levels within the informal settlement of Kibera in Nairobi, Kenya
- 2023
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 132, s. 103499-
-
Tidskriftsartikel (refereegranskat)abstract
- Overlapping conditions of rapid urbanisation and climate change across developing countries are threatening the capacity of cities to manage climate risks, especially in the flood-exposed low-income peripheral areas. Limited studies have applied hydrodynamic flood models in ascertaining flooding conditions, supportive of risk-informed decisions in such urban fringes. Against this backdrop, we assessed plausible flooding and hazard conditions in the low-lying villages of Lindi and Silanga in Kibera informal settlement. The coupled one-dimensional and two-dimensional hydrodynamic model, customised from the Hydrological Engineering Centre's River Analysis System (HEC-RAS) was parameterised for flood simulation under different hydrological regimes and scenarios associated with flooding in Kibera. Volumetric flow estimates and a computed energy slope were used to define the upstream and downstream modelling boundary conditions respectively. Trial-and-error adjustment of the flow resistance coefficients from land-use features was applied in model calibration, and the results compared to the surveyed flood of 23rd April 2019. Results show that proximal areas to the Ngong River and Nairobi dam face high flood risks. A flood volume of 11.7×105m3 from a 2.5h, 50 mm rainfall could potentially inundate about 2.0% and 8.3% of areas in Lindi and Silanga respectively, while a volume of 48.9×105m3 from a 100-year storm of 172 mm could inundate about 10.6% of Lindi and 29.1% of Silanga. Upstream steeply sloping topographies of the villages increase flood velocities and risk of drowning, while the lower reaches at relatively flatter topographies, experience attenuated flow and rapid accumulation of flood waters, hence, higher flood depths. These results can support policy interventions for integrated flood risk management in Kibera, as a way of mainstreaming the underserved urban communities in climate risk management.
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| 25. |
- Juma, Benard, et al.
(författare)
-
Simulation of flood peak discharges and volumes for flood risk management in the ungauged urban informal settlement of Kibera, Kenya
- 2022
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 128
-
Tidskriftsartikel (refereegranskat)abstract
- In spite of the increasing extremity and adverse consequences of urban floods under climate change, flood characteristics in most developing countries are still largely unknown due to lack of continuous monitoring. This portentous uncertainty stances high flood risk, especially to a majority low-income urban population inhabiting the flood-prone informal settlements. Physically-based hydrologic models, whose parameters are derivable from catchment features, are often used for hydrological analysis in the ungauged regions. In this study, the Hydro-logic Engineering Centre's-Hydrologic Modelling System (HEC-HMS) was used for rainfall-runoff simulation in the upper Ngong River Basin of Kenya, draining into the Kibera informal settlement, for purposes of estimating flood peak discharges (FPDs) and direct runoff volumes (DRVs), often required for flood risk management. The Soil Conservation Service-Curve Number (SCS-CN), SCS-Unit Hydrograph (SCS-UH) and Muskingum models were used for hydrological simulation from four (4) observed and fifty-four (54) hypothetical extreme rainfalls. The results obtained indicated that a 50 mm rainfall event with a duration of 2.5 h has the potential of producing FPD and DRV of about 90m3s-1 and 1.17 x 106m3 respectively at the Ngong River confluence at Sokomoko in Kibera. On the other hand, the non-intermittent 100-year storm event of about 172 mm in depth, occurring over a period of about 4 h, potentially generated FPD of about 460m3s-1 and DRV of about 4.89 x 106m3, portending calamitous impacts in the basin. These results can offer preliminary information on potential flood character-istics, that can be used as a baseline to support local-level flood risk mitigation measures in the ungauged Ngong River Basin.
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| 26. |
- Karlberg, Louise, et al.
(författare)
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Exploring potentials and constraints of low-cost drip irrigation with saline water in sub-Saharan Africa
- 2004
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 29:15-18, s. 1035-1042
-
Tidskriftsartikel (refereegranskat)abstract
- Irrigation with saline water could provide an interesting opportunity to meet increasing food demands without competing with other pressing needs for fresh water such as domestic and industrial water use in water scarce regions. In sub-Saharan Africa, saline groundwater could be a plentiful and under-utilised resource; however, there is a lack of data to confirm this assumption. Saline water is deliberately and successfully used for irrigation of field and garden crops in several countries. The water saving characteristics and the distribution patterns of water in the soil under drip irrigation make this water application technique suitable for use in combination with saline water. Low-cost drip irrigation has already been successfully implemented in sub-Saharan Africa. It is suggested that low-cost drip irrigation with saline groundwater for the cultivation of horticultural crops can be a feasible option under conditions of water shortage, and has the potential to contribute to improved and sustainable crop production for smallholder farmers.
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| 27. |
- Karnland, Ola, et al.
(författare)
-
Experimentally determined swelling pressures and geochemical interactions of compacted Wyoming bentonite with highly alkaline solutions
- 2007
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 32:1-7, s. 275-286
-
Tidskriftsartikel (refereegranskat)abstract
- The estimated quantity of cement for construction and sealing purposes is around 9E5 kg in the planned Swedish KBS3 repository for nuclear waste. The highly alkaline cement pore fluid (pH > 12) may affect other components in the repository, and especially the bentonite buffer is of concern. In this study, we simulated possible interactions between cement and bentonite by contacting highly compacted bentonite with high molar hydroxide solutions in a series of laboratory experiments. Wyoming bentonite (MX-80) and purified homo-ionic Na- and Ca-montmorillonite were used for tests with 0.1, 0.3 and 1.0 M NaOH and saturated Ca(OH)2 solutions. Pressure cells with permeable filters were loaded with compacted discs of bentonite at the proposed buffer density (2000 kg/m(3) at full water saturation). A hydroxide solution was circulated on one side of the cell and an isotonic chloride solution on the other during a minimum of 45 days. Swelling pressure and solution pH were monitored during the tests and the change in the solution composition and bentonite mineralogy were determined after completed tests. No effect on swelling pressure was observed in tests with 0.1 M NaOH (pH 12.9) or saturated Ca(OH)2 solutions (pH 12.4) and the mineralogical/chemical changes of the clay were minimal. The bentonite swelling pressure was significantly reduced in the tests with 0.3 (pH 13.3) and 1.0 M (pH 13.8) NaOH solutions. The reduction seems to be due to an instant osmotic effect, and to a continuous dissolution of silica minerals, resulting in mass loss and, consequently, a decrease in density. At these high pH, the release of silica was dominating and the CEC of the clay increased by 20-25%. The structural formula of the smectite and X-ray diffraction tests for nonexpandability (Greene-Kelly test) provided strong evidence that the dissolution of montmorillonite proceeds incongruently through an initial step of beidellitization. The calculated rate of silica release from montmorillonite is 1.6E-9 g g(-1) clay s(-1) for 1.0 M and 5E-10 g g-1 clay s-1 for 0.3 M NaOH solutions. The Si release rate is, however, not a straightforward measure of the montmorillonite dissolution rate due to the non-stoichiometric dissolution. Upon contact between bentonite and NaCl solutions, ion-equilibrium is established between the external solution and the exchangeable cations of the clay. A similar initial pressure response on exposure of bentonite to NaOH solutions indicates that such equilibrium may establish also with an external NaOH solution. If so, the OH-concentration of the clay pore water will be lower than that of the external solution, which would explain that dissolution rates in our experiments with highly compacted bentonite are lower than those reported for batch experiments with hydroxide solutions of the same concentration. (C) 2006 Published by Elsevier Ltd.
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| 28. |
- Karpouzoglou, Timothy, et al.
(författare)
-
A global and regional perspective of rainwater harvesting in sub-Saharan Africa's rainfed farming
- 2014
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 72-75, s. 43-53
-
Tidskriftsartikel (refereegranskat)abstract
- In semi-arid and sub-humid sub-Saharan Africa highly variable rainfall, frequent droughts and low water productivity are consistently undermining food security. Rainwater harvesting technologies (RWHTs) help utilise water more productively whilst raising yield levels. In this article it is argued that realising the potential of RWHTs for resilience building and climate adaptation requires a better understanding of global and regional processes influencing RWHTs adoption combined with pre-existing analysis at the household scale. On the basis of a systematic literature review, processes of influence in the diffusion and uptake of RWHTs are identified. These relate to shifting ideology associated with food production systems; the scope of investments in agriculture science and technology; emergent actors shaping development assistance; and patterns of farmer mobility. Drawing insights from theory on transformations for sustainability and development, this article adds to the understanding of connectedness between farm-level adoption of RWHTs, and regional to global level actors, institutions and processes.
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| 29. |
- Liu, Longcheng
(författare)
-
A model for the viscosity of dilute smectite gels
- 2011
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier. - 1474-7065 .- 1873-5193. ; 36:17-18, s. 1792-1798
-
Tidskriftsartikel (refereegranskat)abstract
- A simple yet accurate model describing the viscosity of dilute suspensions of sodium montmorillonite in dilute homoionic solutions is presented. Taking the clay particle and the surrounding clouds of ions as a whole as an uncharged but soft, coin-like particle, the Huggins’ equation for a suspension of uncharged particles is extended in the model to account for not only the primary and the secondary electroviscous effects, but also the multi-particle interaction. The agreements between the predicted and measured results are excellent. The Huggins’ coefficient obtained compares favorably with available data, while the intrinsic viscosity reduces to the Simha’s equation in the large limit of ionic strength, suggesting that the model is robust.
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| 30. |
- Liu, Longcheng, et al.
(författare)
-
Analysis of fluid flow and solute transport through a single fracture with variable apertures intersecting a canister : Comparison between fractal and Gaussian fractures
- 2006
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 31:14-okt, s. 634-639
-
Tidskriftsartikel (refereegranskat)abstract
- Canisters with spent nuclear fuel will be deposited in fractured crystalline rock in the Swedish concept for a final repository. The fractures intersect the canister holes at different angles and they have variable apertures and therefore locally varying flowrates. Our previous model with fractures with a constant aperture and a 90 degrees intersection angle is now extended to arbitrary intersection angles and stochastically variable apertures. It is shown that the previous basic model can be simply amended to account for these effects. More importantly, it has been found that the distributions of the volumetric and the equivalent flow rates are all close to the Normal for both fractal and Gaussian fractures, with the mean of the distribution of the volumetric flow rate being determined solely by the hydraulic aperture, and that of the equivalent flow rate being determined by the mechanical aperture. Moreover, the standard deviation of the volumetric flow rates of the many realizations increases with increasing roughness and spatial correlation length of the aperture field, and so does that of the equivalent flow rates. Thus, two simple statistical relations can be developed to describe the stochastic properties of fluid flow and solute transport through a single fracture with spatially variable apertures. This obviates, then, the need to simulate each fracture that intersects a canister in great detail, and allows the use of complex fractures also in very large fracture network models used in performance assessment.
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| 31. |
- Liu, Longcheng, et al.
(författare)
-
Permeability and expansibility of natural bentonite MX-80 in distilled water
- 2011
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier. - 1474-7065 .- 1873-5193. ; 36:17-18, s. 1783-1791
-
Tidskriftsartikel (refereegranskat)abstract
- Natural bentonite MX-80 differs from the purified and fully Na-exchanged bentonite in that it contains approximately 20.0% accessory minerals, in addition to the montmorillonite particles. Since the accessory minerals and montmorillonite particles have very different physical and chemical properties, natural bentonite MX-80 is found to expand much more slowly in distilled water, leading actually to a three-component system that has very different hydraulic properties from that of the fully Na-exchanged bentonite. To better understand and simulate the special features of expansion of natural bentonite MX-80 in distilled water, the focus is put primarily on the development of a Kozeny-Carman-like equation for its hydraulic permeability in the same way as it was done for Na-exchanged bentonite. With this permeability model, the dynamic force balance model that was originally developed for colloidal expansion of montmorillonite in a two-component system is applied to the natural MX-80 system. Without making any changes to the model, however, two strategies are used to account for both physical and chemical effects of the accessory minerals. The "lumped" strategy assumes that the accessory minerals are stuck onto the montmorillonite particles in such a way that they behave just like one solid component. The "stepwise" strategy changes the pore water chemistry gradually from initially distilled water to eventually achievement of the equilibrium condition. These strategies are simple but proved to function well. The agreement between the simulations and the experimental results indicates that the two-component dynamic force balance model works well in predicting the general features and the behavior of upward expansion of natural bentonite MX-80 in distilled water in a vertical test tube.
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| 32. |
- Magombeyi, M. S., et al.
(författare)
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Rural food insecurity and poverty mappings and their linkage with water resources in the Limpopo River Basin
- 2016
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 92, s. 20-33
-
Tidskriftsartikel (refereegranskat)abstract
- The mappings of poverty and food insecurity were carried out for the rural districts of the four riparian countries (Botswana, Mozambique, South Africa and Zimbabwe) of the Limpopo river basin using the results of national surveys that were conducted between 2003 and 2013. The analysis shows lower range of food insecure persons (0-40%) than poverty stricken persons (0-95%) that is attributable to enhanced government and non-government food safety networks in the basin countries, the dynamic and transitory nature of food insecurity which depends on the timings of the surveys in relation to harvests, markets and food prices, and the limited dimension of food insecurity in relation to poverty which tends to be a more structural and pervasive socio-economic condition. The usefulness of this study in influencing policies and strategies targeted at alleviating poverty and improving rural livelihoods lies with using food insecurity mappings to address short-term socio-economic conditions and poverty mappings to address more structural and long-term deprivations. Using the poverty line of $1.25/day per person (2008-2013) in the basin, Zimbabwe had the highest percentage of 68.7% of its rural population classified as poor, followed by Mozambique with 68.2%, South Africa with 56.1% and Botswana with 20%. While average poverty reduction of 6.4% was observed between 2003 and 2009 in Botswana, its population growth of 20.1% indicated no real poverty reduction. Similar observations are made about Mozambique and Zimbabwe where population growth outstripped poverty reductions. In contrast, both average poverty levels and population increased by 4.3% and 11%, respectively, in South Africa from 2007 to 2010. While areas of high food insecurity and poverty consistently coincide with low water availability, it does not indicate a simple cause-effect relationship between water, poverty and food insecurity. With limited water resources, rural folks in the basin require stronger institutions, increased investments and support to enable them generate sufficient income from their rain-fed farming livelihood to break out of the poverty cycle.
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| 33. |
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| 34. |
- Mangoyana, Robert Blessing
(författare)
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Bioenergy for sustainable development: An African context
- 2009
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 34:1-2, s. 59-64
-
Tidskriftsartikel (refereegranskat)abstract
- This paper assesses the sustainability concerns of bioenergy systems against the prevailing and potential long term conditions in Sub-Saharan Africa with a special attention on agricultural and forestry waste, and cultivated bioenergy sources. Existing knowledge and processes about bioenergy systems are brought into a "sustainability framework" to support debate and decisions about the implementation of bioenergy systems in the region. Bioenergy systems have been recommended based oil the potential to (i) meet domestic energy demand and reduce fuel importation (ii) diversify rural economics and create employment (iii) reduce poverty, and (iv) provide net energy gains and positive environmental impacts. However, biofuels will compete with food crops for land, tabour, capital and entrepreneurial skills. Moreover the environmental benefits of some feedstocks are questionable. These challenges are, however, surmountable. It is concluded that biomass energy production could be an effective way to achieve sustainable development for bioenergy pathways that (i) are less land intensive, (ii) have positive net energy gains and environmental benefits, and (iii) provide local socio-economic benefits. Feasibility evaluations which put these issues into perspective are vital for sustainable application of agricultural and forest based bioenergy systems in Sub-Saharan Africa. Such evaluations should consider the long run potential of biofuels accounting for demographic, economic and technological changes and the related implications.
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| 35. |
- Moreno, Luis, et al.
(författare)
-
Erosion of sodium bentonite by flow and colloid diffusion
- 2011
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier. - 1474-7065 .- 1873-5193. ; 36:17-18, s. 1600-1606
-
Tidskriftsartikel (refereegranskat)abstract
- Smectite gel formed at the outer part of a bentonite buffer in granitic rock could expand into rock fractures with seeping water. Such a gel can release colloids into low ionic strength waters. In addition the gel/sol can itself slowly flow downstream when it has reached a low particle concentration sufficient to decrease the viscosity to allow flow. The erosion due to the combined effects of particle diffusion and gel/sol flow is modelled for a thin fracture into which the gel expands influenced by various forces between and on particles. Some of the forces such as the electrical double layer force and viscous force are strongly influenced by the ionic strength of the pore water. Changes in the ionic strength due to diffusion and dilution of ions in the expanding clay are modelled simultaneously with the gel expansion, flow of gel and colloid release to the seeping water. The model includes description of flow of the seeping fluid, which gradually turns from pure water to sol to more dense gel as the smectite source is approached. The model also describes expansion of the gel/sol and colloid release and flow and diffusion of ions in the system. The coupled models are solved using a numerical code. The results show that the gel will flow with a non-negligible flowrate when its volume fraction is below 1%, but that the erosion and loss of smectite is not much influenced by the concentration of sodium in the clay or in the approaching seeping water, if they are kept below the Critical Coagulation Concentration, CCC.
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| 36. |
- Nickel, D., et al.
(författare)
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Large-scale water resources management within the framework of GLOWA-Danube - The water supply model
- 2005
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 30:6-7 SPEC. ISS., s. 383-388
-
Tidskriftsartikel (refereegranskat)abstract
- The research project GLOWA-Danube, financed by the German Federal Government, investigates long-term changes in the water cycle of the upper Danube river basin in light of global climatic change. Its aim is to build a fully integrated decision support tool "DANUBIA" that combines the competence of eleven institutes in domains covering all major aspects governing the water cycle. The research group "Groundwater and Water Supply" at the Institute of Hydraulic Engineering (IWS), Universitaet Stuttgart, contributes a three-dimensional groundwater flow model and a large-scale water supply model which simulate both water availability and quality and water supply and the related costs for global change scenarios. This article addresses the task of creating an agent-based model of the water supply sector. The water supply model links the various physical models determining water quality and availability on the one hand and the socalled "Actor" models calculating water demand on the other by determining the actual water supply and the costs related, which underlie both technical and physical constraints (e.g., existing infrastructure and its capacity, water availability and quality, geology, elevation, etc.). In reality, water supply within the study is organised through a three-tiered structure: long-distance, regional, and a multitude of community-based suppliers. In order to model this system in which each supply company defines its own optimum, an agent-based modelling approach (implemented using JAVA) was chosen. This approach is novel to modelling water supply in that not only water supply infrastructure but more importantly the decision makers (communities, water supply companies) are represented as generalised objects, capable of performing actions following rules that are determined by the class they belong to. © 2005 Elsevier Ltd. All rights reserved.
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| 37. |
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| 38. |
- Roldugin, Valentin, et al.
(författare)
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Wave-like ozone movements
- 2000
-
Ingår i: Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere. - 1474-7065. ; 25:5-6, s. 511-514
-
Tidskriftsartikel (refereegranskat)
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| 39. |
- Selroos, Jan-Olof, et al.
(författare)
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Radionuclide transport during glacial cycles : Comparison of two approaches for representing flow transients
- 2013
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 64, s. 32-45
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of future, transient ice sheet movement and permafrost development on transport of radionuclides from a proposed repository site is investigated using numerical groundwater flow and radionuclide transport modelling. Two different transport approaches are compared, both utilizing groundwater flow simulations of future climate conditions. The first transport approach uses steady-state particle trajectories representing temperate climate conditions, but modifies the transport velocity along the trajectories according to the changing climate. The second approach is pseudo-transient by performing particle tracking in each individual flow field representing a given time epoch.Two different climate sequences are analyzed. First, a simplified sequence is assessed in order to understand if the two different transport approaches yield significantly different breakthrough characteristics. Second, a sequence representing conditions relevant for real safety assessment applications is considered.Results indicate that the transport approach using fixed trajectories tends to significantly over predict breakthrough during permafrost conditions relative to the pseudo-transient approach. The major difference between the two approaches is related to discharge locations. The fixed trajectory approach yields discharge locations constant in time whereas the pseudo-transient approach is characterized by discharge centres moving in time according to the different climate conditions.
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| 40. |
- Stein, Christian, et al.
(författare)
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A social network approach to analyzing water governance : the case of the Mkindo catchment, Tanzania
- 2011
-
Ingår i: Physics and Chemistry of the Earth. - : Pergamon-Elsevier Science Ltd. - 1474-7065 .- 1873-5193 .- 1464-1909 .- 1873-4677. ; 36:14-15, s. 1085-1092
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Tidskriftsartikel (refereegranskat)abstract
- The governance dimension of water resources management is just as complex and interconnected as the hydrological processes it aims to influence. There is an increasing need (i) to understand the multi-stake- holder governance arrangements that emerge from the cross-scale nature and multifunctional role of water; and (ii) to develop appropriate research tools to analyze them. In this study we demonstrate how social network analysis (SNA), a well-established technique from sociology and organizational research, can be used to empirically map collaborative social networks between actors that either directly or indirectly influence water flows in the Mkindo catchment in Tanzania. We assess how these collabo- rative social networks affect the capacity to govern water in this particular catchment and explore how knowledge about such networks can be used to facilitate more effective or adaptive water resources man- agement. The study is novel as it applies social network analysis not only to organizations influencing blue water (the liquid water in rivers, lakes and aquifers) but also green water (the soil moisture used by plants). Using a questionnaire and semi-structured interviews, we generated social network data of 70 organizations, ranging from local resource users and village leaders, to higher-level governmental agencies, universities and NGOs. Results show that there is no organization that coordinates the various land and water related activities at the catchment scale. Furthermore, an important result is that village leader play a crucial role linking otherwise disconnected actors, but that they are not adequately inte- grated into the formal water governance system. Water user associations (WUAs) are in the process of establishment and could bring together actors currently not part of the formal governance system. How- ever, the establishment of WUAs seems to follow a top-down approach not considering the existing infor- mal organization of water users that are revealed through this social network analysis. Instead of imposing institutional arrangements, we argue that it is more promising to identify and build on existing social structures. Social network analysis can help to identify existing social structures and points for interventions to increase the problem solving capacity of the governance network.
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| 41. |
- Temesgen, Melesse, et al.
(författare)
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Assessment of strip tillage systems for maize production in semi-arid Ethiopia : effects on grain yield, water balance and water productivity
- 2012
-
Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 47-48, s. 156-165
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Tidskriftsartikel (refereegranskat)abstract
- The Maresha, the traditional Ethiopian plow, requires repeated cross-plowing which causes increased surface runoff, less infiltration and hence lower water availability to crops. The main reasons for increased surface runoff and reduced infiltration are plowing along the slope and the formation of a plow pan at shallow depths. Conservation tillage is seen as a way to alleviate these problems. The widely advocated zero-tillage, however, is not feasible for smallholder farmers in semi-arid regions of Ethiopia because of difficulties in maintaining adequate soil cover, the practice of communal grazing, and high costs of herbicides. Strip tillage systems, on the other hand, may offer a solution. This study was initiated to test strip tillage systems and to evaluate the impacts of new tillage systems on the water balance and grain yields of maize. Experiments have been conducted in a semi-arid area called Melkawoba in the central Rift Valley of Ethiopia during 2003–2005. Strip tillage systems involved cultivation along planting lines at a spacing of 0.75 m using the Maresha plow followed by subsoiling along the same lines (STS) or without subsoiling (ST). Results have been compared with traditional tillage involving 3–4 overpasses with the Maresha plow (CONV). Soil moisture has been monitored to a depth of 1.8 m using a Time Domain Reflectometer (TDR) while surface runoff has been measured using a specially designed rectangular trough installed at the bottom of each plot. STS resulted in the least surface runoff (Qs = 18 mm season−1) and the highest grain yields (Y = 2130 kg ha−1) followed by ST (Qs = 26 mm season−1, Y = 1840 kg ha−1) and CONV (Qs = 43 mm season−1, Y = 1720 kg ha−1) provided sowing was carried out within a week after subsoiling. Thus, STS resulted in the highest water productivity, WP = 0.60 kg m−3, followed by ST (WP = 0.52 kg m−3) and CONV (WP = 0.48 kg m−3). The main conclusion of the paper is that even in dry areas reasonable yields can be obtained provided moisture conservation in the root zone is guaranteed. In this regard subsoiling is essential. Moreover, it is concluded that the time between subsoiling and planting is a key factor and should not exceed one week.
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| 42. |
- Wold, Susanna, et al.
(författare)
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Diffusion of humic colloids in compacted bentonite
- 2007
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065 .- 1873-5193. ; 32:07-jan, s. 477-484
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Tidskriftsartikel (refereegranskat)abstract
- Through-diffusion experiments in bentonite with humic colloids in the size range of 1-10 nm were carried out. Bentonite was compacted to 0.6-1.8 g/cm(3) dry density and equilibrated with 0.01 and 0.1 M NaClO4 solutions. Experiments with Eu(Ill) diffusing in the absence and presence of humics were run in parallel, as well as Co(ll) diffusing through compacted bentonite in the presence of hurnics. The hurnic colloid diffusion experiments were run for 60 days and the humic concentration in the outlet solutions measured at time intervals. The experimental breakthrough curves for humic substances (HS) as well as the HS, Co(II) and Eu(III) profiles in the bentonite were simulated using the finite difference based computer code ANADIFF. Regardless of the compaction and ionic strength of solutions, hurnic colloids diffused through the compacted bentonite. The effects of hurnic colloids on both Co(H) and Eu(111) sorption as well as on diffusion were significant. The apparent diffusivity (D-a) increased significantly for both Co(II) and Eu(III) when hurnic colloids were present and the distribution coefficient (K-d) values decreased.
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