Comparing a 1D hydraulic model with a 2D hydraulic model for the simulation of extreme glacial outburst floods   总被引：1，自引：0，他引：1  

Petteri Alho  Juha Aaltonen 《水文研究》2008,22(10):1537-1547

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Impact of Ditching in a Small Forested Catchment on Concentrations of Suspended Material, Organic Carbon, Hydrogen Ions and Metals in Stream Water     

Mats Åström  Eeva-Kaarina Aaltonen  Juhani Koivusaari 《Aquatic Geochemistry》2001,7(1):57-73

Stream-water samples were collected during a 4-year-period in twosmall streams, one whose catchment was ditched for forestry halfway through the sampling period and another nearby reference stream whose catchment was not ditched during this period. The main aim was to study the impact of forest ditching on stream-water quality. Whereas the artificial drainage did not change the hydrograph pattern, it had a large effect on stream hydrochemistry: the concentrations of suspended material, Mn, Ca, Mg and Al increased, theconcentrations of total organic carbon decreased, and pH increased by approximately one unit, from an average of 4.4 to 5.4. The increase in suspended material, Mn and Al concentrations is explainedby the physical mobilisation of mineral particulates/colloids from mineral soils (till) exposed on the ditch slopes beneath the peat layer, while the increase in Ca and Mg loads is explained by the release of Ca²⁺ and Mg²⁺ in exchange reactions in this same soil layer. The increase in pH and decrease in TOC concentrations after ditching are related to changes in hydrological flow paths in the catchments, and most likely to immobilisation of both hydrogen ions and humic substances in the near neutral till horizon exposed beneath the peat layer. Only the aquatic abundance of Fewas not significantly affected by the ditching.  相似文献   

Future fluvial erosion and sedimentation potential of cohesive sediments in a coastal river reach of SW Finland          下载免费PDF全文

Eliisa Lotsari  Juha Aaltonen  Noora Veijalainen  Petteri Alho  Jukka Käyhkö 《水文研究》2014,28(25):6016-6037

This study aims to analyse the combined impacts of future discharges and sea levels on erosion–sedimentation potential, and its seasonal changes, in a ~43‐km‐long coastal river reach of South‐west Finland. To our knowledge, this kind of combined study has not been performed before. In addition to surveying the present erosion–sedimentation conditions, the daily erosion–sedimentation potential is simulated with a one‐dimensional hydrodynamic model for the 1971–2000 and 2070–2099 periods by applying four discharge scenarios. Different sea level stages are also employed in the simulations. All scenarios forecast increasing autumn and winter discharges, but diminishing summer discharges. This indicates increasing river channel erosion, particularly during winters and autumns. Although discharge changes have altogether a greater influence on erosion–sedimentation potential, the importance of sea level changes on sedimentation is noticeable in the estuary. The rising sea level scenarios increase the sedimentation potential. In total, by 2070–2099, the erosion potential may increase in most parts of the study area. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

River ice cover influence on sediment transportation at present and under projected hydroclimatic conditions          下载免费PDF全文

Maria Kämäri  Petteri Alho  Noora Veijalainen  Juha Aaltonen  Mikko Huokuna  Eliisa Lotsari 《水文研究》2015,29(22):4738-4755

A large number of rivers are frozen annually, and the river ice cover has an influence on the geomorphological processes. These processes in cohesive sediment rivers are not fully understood. Therefore, this paper demonstrates the impact of river ice cover on sediment transport, i.e. turbidity, suspended sediment loads and erosion potential, compared with a river with ice‐free flow conditions. The present sediment transportation conditions during the annual cycle are analysed, and the implications of climate change on wintertime geomorphological processes are estimated. A one‐dimensional hydrodynamic model has been applied to the Kokemäenjoki River in Southwest Finland. The shear stress forces directed to the river bed are simulated with present and projected hydroclimatic conditions. The results of shear stress simulations indicate that a thermally formed smooth ice cover diminishes river bed erosion, compared with an ice‐free river with similar discharges. Based on long‐term field data, the river ice cover reduces turbidity statistically significantly. Furthermore, suspended sediment concentrations measured in ice‐free and ice‐covered river water reveal a diminishing effect of ice cover on riverine sediment load. The hydrodynamic simulations suggest that the influence of rippled ice cover on shear stress is varying. Climate change is projected to increase the winter discharges by 27–77% on average by 2070–2099. Thus, the increasing winter discharges and possible diminishing ice cover periods both increase the erosion potential of the river bed. Hence, the wintertime sediment load of the river is expected to become larger in the future. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Direct current (DC) resistivity measurements in long-term groundwater monitoring programmes     

J. Aaltonen  B. Olofsson 《Environmental Geology》2002,41(6):662-671

. Effective leak detection systems are most often needed to enable early warnings of groundwater contamination from landfill areas. In order to monitor the groundwater chemical changes over time direct current (DC) resistivity measurements have been used, since variation in groundwater ion concentration give changes of the electrical potential field. A simple, low-cost system for long-term monitoring has been developed and used for 4 years at an existing operational landfill in central Sweden. The paper describes the construction and operation of the geoelectrical monitoring system based on a fixed electrode Wenner array, situated in a glaciated terrain. The simplicity of the system enables non-experts in geophysics to run the system and evaluate the results. The lateral resistivity variations (up to 10,000% from the mean lateral value) clearly reflect strongly different natural geological conditions, whereas the variations over time (15% from the mean value at each specific point) reflect mainly the seasonal soil humidity and groundwater level variations. Leachates from the landfill have a low resistivity (about 1 ohmm) and the moderate seasonal variations in electrical resistivity favour the possibilities for identification of leakage from the landfill. Evaluation of resistivity data comprises modified double mass calculations versus data from reference measurement sites, which enables detection of contamination although it influences the resistivity less than the natural seasonal variations.  相似文献   

Some considerations in management of computer-processable files of geological data     

P. G. Sutterlin  R. A. Aaltonen  M. A. Cooper 《Mathematical Geosciences》1974,6(4):291-310

Many sets of data in the natural sciences have a hierarchical structure that is either inherent in the data or that is imposed on them during collection. These data structures can be defined using mathematical set-theory notation. If data from two or more computer-processable files are accessed simultaneously, the application of operations of set union and intersection leads to emergence of certain criteria which must be adhered to when managing data files using a generalized, database management system. One of the situations in which these principles come into play is illustrated by the merging of two computer-processable files of geotechnical data, the data for both files having been derived from the same source but structured differently.  相似文献