Fluvial thermal erosion: heat balance integral method

In periglacial regions, frozen river banks are affected by thermal and mechanical erosion. In Siberia, bank retreats of up to 40 m per year are observed. This thermal erosion occurs during a few weeks, at springtime, for high enough water temperatures and river discharges. Until now, models of thermal erosion have been based on the assumption of a constant thermal erosion rate. We have developed a more general model at variable rate, whose solution is calculated using the integral method. Results of this model are compared with experiments, carried out in a cold room. A hydraulic channel allows measurements of the thermal erosion rate of a ground ice sample subjected to a turbulent water flow. Once validated, the model is applied to the periglacial river study case. The model has contributed to better understanding of the roles of each parameter during the thermal erosion process. High water temperature, discharge and ice temperature produce major thermal erosion, whereas the ice content in the soil tends to slow down the thermal erosion process. The effects of water temperature are predominant. An acceleration phase characterized by an increase of the thermal erosion rate occurs at the beginning of the thermal erosion process. The duration of such an acceleration phase is systematically studied. A relatively long acceleration phase is related to a low ablation rate. During the flood season, when the water temperature is increased to 18 °C, this acceleration phase lasts only a few minutes. However, for data typical of periglacial rivers, when the water temperature is close to the melting point, the acceleration phase can last a few days. Copyright © 2007 John Wiley & Sons, Ltd.     

Long‐term growth of a valley‐bottom gully,western Iowa

Growth of a permanent, valley‐bottom gully from 1964 to 2000 was determined annually from survey and sediment‐discharge data and compared with runoff and base?ow discharges. Data were analysed to test the hypothesis that rates of gully growth decay exponentially with time in response to shrinking catchment area caused by gully enlargement. Also, monthly values of growth rates and runoff, averaged over the 36‐year record, were analysed with mass‐wasting data to determine the extent to which colluvium availability affected growth rates seasonally. From 1964 to 2000, the gully volume increased by 9200 m³, accounting for 34 per cent of sediment yield from the watershed. There were tight power‐law relationships between annual growth rates and annual runoff, with runoff exponents of 1·57 and 1·30 for headward and volumetric growth, respectively. Increases in gully length, area, and volume were ?tted successfully assuming an exponential decay in growth rate with time. Rather than being due to a decrease in catchment area, however, the decline in growth rate was caused by a 77 per cent decrease in the ratio of runoff to base?ow, which also widened the gully and reduced the mean slope of its banks. Order‐of‐magnitude seasonal changes in erosion ef?ciency, de?ned as the fraction of stream power used to evacuate sediment from the gully, were roughly correlated with colluvium availability, as indicated by seasonal changes in the number of bank mass‐wasting events. No more than 2·2 per cent of stream power was used to evacuate sediment during any month. This study demonstrates the danger of attributing declining rates of gully growth to a shrinking catchment area if corroborative runoff and base?ow data are not available. Moreover, it illustrates that stream power alone provides only a rough and physically indirect measure of erosion potential. Copyright © 2004 John Wiley & Sons, Ltd.     

Hysteretic freezing characteristics of riparian peatlands in the Western Boreal Forest of Canada

Freezing characteristics were investigated for a sedge covered floating fen and spruce covered swamp located beside a shallow lake in the Western Boreal Forest of Canada. Thermal properties were measured in situ for one freeze‐thaw cycle, and for two freeze‐thaw cycles in laboratory columns. Thermal conductivity and liquid water content were related to a range of subsurface temperatures above and below the freezing thresholds, and clearly illustrate hysteresis between the freezing and thawing process. Thermal hysteresis occurs because of the large change in thermal conductivity between water and ice, high water content of the peat, and wide variation in pore sizes that govern ice formation. Field and laboratory results were combined to develop linear freezing functions, which were tested in a heat transfer model. For surface temperature boundary conditions, subsurface temperatures were simulated for the over‐winter period and compared with field measurements. Replication of the transient subsurface thermal regime required that freezing functions transition gradually from thawed to frozen state (spanning the ?0·25 to ?2 °C range) as opposed to a more abrupt step function. Subsurface temperatures indicate that the floating fen underwent complete phase change (from water to ice) and froze to approximately the same depth as lake ice thickness. Therefore, the floating fen peatland froze as a ‘shelf’ adjacent to the lake, whereas the spruce covered swamp had a higher capacity for thermal buffering, and subsurface freezing was both more gradual and limited in depth. These thermal properties, and the timing and duration of frozen state, are expected to control the interaction of water and nutrients between surface water and groundwater, which will be affected by changes in air temperature associated with global climate change. Copyright © 2009 John Wiley & Sons, Ltd.     

Gelifluction: viscous flow or plastic creep?

This paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw‐related geli?uction. A planar 12° prototype slope was modelled in each experiment, using the same natural ?ne sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N², where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous ?ow is 1/1. If geli?uction is a viscosity‐controlled ?ow process, scaling con?icts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling con?icts are observed, we may conclude that geli?uction is not controlled by viscosity, but rather by elasto‐plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process. Models were saturated, consolidated and frozen from the surface downwards on the laboratory ?oor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze–thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement pro?les re?ecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze–thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and pro?les were also similar to those observed in earlier full‐scale laboratory ?oor experiments. It is concluded therefore that the modelled geli?uction was not a time‐dependent viscosity‐controlled ?ow phenomenon, but rather elasto‐plastic in nature. A ?rst approximation ‘?ow’ law is proposed, based on the ‘Cam Clay’ constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd.     

An experimental and computer simulation study of erosion on a mine tailings dam wall

Mine tailings dams pose a signi?cant risk to the environment if not correctly designed, built and maintained. The effect of erosion on a back‐?lled and capped earthen dam wall was examined by construction of an analogue in an experimental model landscape simulator. The ability of a computer‐based erosion model to simulate erosion processes on the experimental structure was examined. The experimental landscape simulator uses a rainfall simulator to create overland ?ow and erode an arti?cial soil. At the commencement of rainfall, erosion occurred rapidly with deep gullies developing on the dam wall batter. The gullies developed by downcutting, with consequent bank collapse and slumping, and followed ?ow lines towards their source. A physically based erosion model (SIBERIA) was used to simulate erosion on the experimental dam wall. Erosion and consequent development of the experimental structure were modelled by SIBERIA. The ability of SIBERIA to model incision and landscape development in the experimental setting was further examined by use of a simple one‐dimensional experimental catchment. The laboratory experiment and computer simulations demonstrated that erosion on the tailings dam is driven by concentrated runoff and that runoff control is crucial to the long‐term stability of such structures. The study demonstrates that computer‐based erosion models can be used to predict how erosion occurs on the experimental landscapes examined, thus providing con?dence in their use and application. Copyright © 2004 John Wiley & Sons, Ltd.     

A patch hierarchy approach to modeling surface and subsurface hydrology in complex flood‐plain environments

Geomorphology interacts with surface‐ and ground‐water hydrology across multiple spatial scales. Nonetheless, hydrologic and hydrogeologic models are most commonly implemented at a single spatial scale. Using an existing hydrogeologic computer model, we implemented a simple hierarchical approach to modeling surface‐ and ground‐water hydrology in a complex geomorphic setting. We parameterized the model to simulate ground‐ and surface‐water ?ow patterns through a hierarchical, three‐dimensional, quantitative representation of an anabranched montane alluvial ?ood plain (the Nyack Flood Plain, Middle Fork Flathead River, Montana, USA). Comparison of model results to ?eld data showed that the model provided reasonable representations of spatial patterns of aquifer recharge and discharge, temporal patterns of ?ood‐water storage on the ?ood plain, and rates of ground‐water movement from the main river channel into a large lateral spring channel on the ?ood plain, and water table elevation in the alluvial aquifer. These results suggest that a hierarchical approach to modeling ground‐ and surface‐water hydrology can reproduce realistic patterns of surface‐ and ground‐water ?ux on alluvial ?ood plains, and therefore should provide an excellent ‘quantitative laboratory’ for studying complex interactions between geomorphology and hydrology at and across multiple spatial scales. Copyright © 2004 John Wiley & Sons, Ltd.     

Cryogenic Core Collection and Preservation of Subsurface Samples for Biomolecular Analysis

A cryogenic coring system for the collection and preservation of biomolecules in unconsolidated subsurface solid samples is presented here. The sampler is based on existing direct‐push coring technology, with the addition of a cryogenic step to freeze the sample in situ. Once brought to the surface, the frozen cores can be packed in dry ice and shipped to the laboratory for further processing and analysis. The approach prevents redistribution of fluids during sample recovery and shipping, and because the cores are frozen in situ there is little loss of solid material during retrieval to ground surface. To evaluate the performance of the approach, DNA analyses of samples collected by cryogenic coring in a very large physical model are compared with results from water samples and horizontal core samples taken in close proximity. The data indicate that the vertical distribution of DNA within the cryogenic core can be measured at the centimeter scale, providing unprecedented characterization of subsurface biogeochemical interfaces.     

Evaluating model of frozen soil environment change under engineering actions

The change of frozen soil environment is evaluated by permafrost thermal stability, thermal thaw sensibility and surface landscape stability and the quantitatively evaluating model of frozen soil environment is proposed in this paper. The evaluating model of frozen soil environment is calculated by 28 ground temperature measurements along Qinghai-Xizang Highway. The relationships of thermal thaw sensibility and freezing and thawing processes and seasonally thawing depth, thermal stability and permafrost table temperature, mean annual ground temperature and seasonally thawing depth, and surface landscape stability and freezing and thawing hazards and their forming possibility are analyzed. The results show that thermal stability, thermal thaw sensibility and surface landscape stability can be used to evaluate and predict the change of frozen soil environment under human engineering action.     

Interchannel hydraulic geometry and hydraulic efficiency of the anastomosing Columbia River,southeastern British Columbia,Canada

The morphodynamics of the anastomosing channel system of upper Columbia River in southeastern British Columbia, Canada, is examined using an adaptation of conventional hydraulic geometry termed ‘interchannel hydraulic geometry’. Interchannel hydraulic geometry has some of the characteristics of downstream hydraulic geometry but differs in that it describes the general bankfull channel form and hydraulics of primary and secondary channels in the anastomosing channel system. Interchannel hydraulic geometry generalizes these relationships and as such becomes a model of the geomorphology of channel division and combination. Interchannel hydraulic geometry of upper Columbia River, based on ?eld measurements of ?ow velocity and channel form at 16 test sections, is described well by simple power functions: w_bf = 3·24Q_bf^0·64; d_bf = 1·04Q_bf^0·19; v_bf = 0·30Q_bf^0·17. These results, with other related measurements of ?ow resistance, imply that channel splitting leads to hydraulic inef?ciency (higher ?ow resistance) on the anastomosing Columbia River. Because these ?ndings differ from those reported in studies elsewhere, we conclude that hydraulic ef?ciency does not provide a general explanation for anabranching in river channels. Copyright © 2003 John Wiley & Sons, Ltd.     

River ice cover influence on sediment transportation at present and under projected hydroclimatic conditions

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.     

Ice cover of the Amur River and its impact on channel processes

Special features of the Amur R. ice regime in its middle and lower reaches are discussed along with the role of river ice in bank erosion, transport of coarse fragmental material, bottom washout, and water flow redistribution among branches. Numerous and various consequences of the ice drift impact on the banks and floodplain, as well as the intensity of erosion processes in the Amur River channel during winter have been revealed. The water flow redistribution among the Amur River branches near Khabarovsk noticeably changed the ice regime, which was rehabilitated as a result of implementation of a complex of special measures.     

Another Important Factor of Rising Sea Level: Soil Erosion

Global mean sea level is a sensitive factor of climate change. Global warming will contribute to worldwide sea‐level rise from thermal expansion of ocean water, melting of glaciers and polar ice. Consideration of global soil erosion, water vapor cycle, and hydraulic actions suggests that soil erosion is another important factor contributing to sea‐level rise in addition to global warming. Much terrestrial sediment flows into the rivers each year but cannot be replenished, resulting in land surface declines. Moreover, sediment flow into rivers and oceans contributes to rising sea level. Ecological protection measure was proposed to prevent rising sea levels caused by soil erosion. This commentary should be useful to attract attention on rising sea levels caused by soil erosion.     

Glacial conditions that contribute to the regeneration of Fountain Glacier proglacial icing,Bylot Island,Canada

Proglacial icings are one of the most common forms of extrusive ice found in the Canadian Arctic. However, the icing adjacent to Fountain Glacier, Bylot Island, is unique due to its annual cycle of growth and decay, and perennial existence without involving freezing point depression of water due to chemical characteristics. Its regeneration depends on the availability of subglacial water and on the balance between ice accretion and hydro‐thermal erosion. The storage and conduction of the glacial meltwater involved in the accretion of the icing were analyzed by conducting topographic and ground penetrating radar surveys in addition to the modelling of the subglacial drainage network and the thermal characteristics of the glacier base. The reflection power analysis of the geophysical data shows that some areas of the lower ablation zone have a high accumulation of liquid water, particularly beneath the centre part of the glacier along the main supraglacial stream. A dielectric permittivity model of the glacier – sediment interface suggests that a considerable portion of the glacier is warm based; allowing water to flow through unfrozen subglacial sediments towards the proglacial outwash plain. All these glacier‐related characteristics contribute to the annual regeneration of the proglacial icing and allow for portions of the icing to be perennial. Copyright © 2013 John Wiley & Sons, Ltd.     

Photosynthetic capability and Fe,Mn, Cu,and Zn contents in two Moraceae species under different phosphorus levels

The strong adaptability of Broussonetia papyrifera(L.) Vent. to low phosphorus(P) conditions can be attributed to the large amount of root-exuded organic acids and the high ef?ciency of P extraction. However,microelement contents are in?uenced by low-P stress, and their effects on the photosynthetic capability of B. papyrifera remain unknown. In this study, we investigated the effects of low-P treatment on net photosynthetic rate(P_N);chlorophyll a ?uorescence(ChlF) characteristics; and Fe,Mn, Cu, and Zn contents of B. papyrifera and Morus alba L. seedlings. Results show that B. papyrifera exhibited better photosynthetic capability under moderate P de?-ciency(0.125, 0.063, and 0.031 mmol/L P treatments),whereas the photosynthetic capability of M. alba decreased under moderate and severe P de?ciency(0.016 and0 mmol/L P treatments). Under moderate P de?ciency, the decrease in Cu and Zn contents in B. papyrifera was lower than that in M. alba. Under severe P de?ciency, a considerable decrease of photosynthetic capability in B. papyrifera and M. alba was associated with low Cu and Zn contents. The P N of the two Moraceae species exhibited a better correlation with Cu and Zn contents than with Fe or Mn content. P de?ciency could not only decrease cyclic photophorylation and photosynthetic ef?ciency, but could also affect the stability of thylakoid membrane structure and electron transport ef?ciency by in?uencing the contents of Cu or Zn, thereby affecting photosynthesis.     

Hydrodynamics and sediment flux of hoa in an Indian Ocean atoll

Detailed hydrodynamic and sediment ?ux measurements are reported from 11 hoa (shallow cross‐reef channels) in the Cocos (Keeling) Islands, Indian Ocean. All hoa exhibit unidirectional oceanside reef to lagoon ?uxes. These currents are driven by tides, wave set‐up and incident waves, and the presence of islands that generate alongshore gradients so that currents ?ow toward the topographic low points of hoa entrances in the reef rim. Two functional groups of hoa are identi?ed that extend Chevalier's typology of hoa and possess different process signatures. Sediment‐limited hoa (SLH) are ef?cient conduits of sediment transport. They are located close to the reef rim where incident wave energy propagates across the reef crest into the hoa and is able to entrain sediment. Transport‐limited hoa (TLH) are characterized by low rates of sediment transport because incident wave energy is negligible as they are located much further from the reef edge than SLH. In the absence of an entrainment mechanism the oceanside reef ?at is laden with sediment. Storm energy increases transport ef?ciency through hoa. However, the net sedimentation response differs between the two hoa types. Proximity to the reef edge means that frequent storms ?ush sediment from SLH increasing hoa depth and enhancing the potential for erosion of the conglomerate boundary. In contrast, the greater reef width fronting TLH means that sediment transport from reef ?ats to the lagoon is only activated during infrequent storms. The contrasting process signatures account for morphological differences between sediment‐limited hoa (lagoonward decrease in depth and increase in width), and transport‐limited hoa (lagoonward increase in depth). The number and type of functional hoa are found to have signi?cant implications for the rate of lagoon sedimentation in enclosed atolls. In general, an increase in frequency of functional hoa and increased proportion of SLH will promote more rapid rates of lagoon in?ll. Copyright © 2004 John Wiley & Sons, Ltd.     

PREFERENTIAL WATER FLOW IN A FROZEN SOIL — A TWO-DOMAIN MODEL APPROACH

Earlier modelling studies have shown the difficulty of accurately simulating snowmelt infiltration into frozen soil using the hydraulic model approach. Comparison of model outputs and field measurements have inferred the occurrence of rapid flow even during periods when the soil is still partly frozen. A one-dimensional, physically based soil water and heat model (SOIL) has been complemented with a new two-domain approach option to simulate preferential flow through frozen layers. The ice is assumed to be first formed at the largest water filled pore upon freezing. Infiltrating water may be conducted rapidly through previously air-filled pores which are not occupied by ice. A minor fraction of water is slowly transferred within the liquid water domain, which is absorbed by the solid particles. A model validation with field measurements at a location in the middle-east of Sweden indicated that the two-domain approach was suitable for improving the prediction of drainage during snowmelting. In particular, the correlation between simulated and observed onset of drainage in spring was improved. The validation also showed that the effect of the high flow domain was highly sensitive to the degree of saturation in the topsoil during freezing, as well as to the hydraulic properties at the lower frost boundary regulating the upward water flow to the frozen soil and ice formation.     

Bank erosion of an incised upland channel by subaerial processes: Tasmania,Australia

The headwaters of many rivers are characterized by gullies and incised streams that generate significant volumes of sediment and degrade downstream water quality. These systems are characterized by harsh climates, ephemeral flows that do not reach bank top, and bare cohesive banks of clay and weathered bedrock. We investigated the rates and processes of bank erosion in an incised canal that has such characteristics. Detailed measurements of bank position were made over two years with a purpose‐built groundprofiler and photo‐electronic erosion pins (PEEPs). Stage height and turbidity were also monitored. The bare banks eroded at 13 ± 2 mm a⁻¹. Erosion is controlled by subaerial processes that loosen bank material. Observations show that needle‐ice growth is important in winter and desiccation of clays predominates in summer. Flows are unable to erode firm cohesive clays from the banks, and erosion is generally limited by the availability of loosened material. This produces strong hysteresis in turbidity during events. Peak turbidity is related to the number of days with low flow between events, and not peak stage. Rehabilitation with a moderate cover of grass is able to prevent bank erosion by limiting the subaerial erosion processes. Projections of current erosion suggest that without vegetation cover the banks are unlikely to stabilize for many years. Copyright © 2000 John Wiley & Sons, Ltd.     

Seasonal differences in seismic responses of embankment on a sloping ground in permafrost regions

Because of its direct influence on the amount of unfrozen water and on the strength of intergranular ice in a frozen soil, temperature has a significant effect on all aspects of the mechanical behavior of the active layer in which temperature fluctuates above and below 0 °C. Hence seismic responses of engineering structures such as embankment on a sloping ground in permafrost regions exhibit obvious differences with seasonal alternation. To explore the distinctive seismic characteristics of a railway embankment on the sloping ground in permafrost regions, a coupled water-heat-dynamics model is built based on theories of heat transfer, soil moisture dynamics, frozen soil mechanics, soil dynamics, and so on. A well-monitored railway embankment on a sloping ground in Qinghai–Tibet Plateau is taken as an example to simulate seismic responses in four typical seasons in the 25th service year. The numerical results show that seismic acceleration, velocity and displacement responses are significantly different in four typical seasons, and the responses on October 15 are much higher among the four seasons. When the earthquake is over, there are still permanent differential deformations in the embankment and even severe damages on the left slope on October 15. Therefore, this position should be monitored closely and repaired timely to ensure safe operation. In addition, the numerical model and results may be a reference for maintenance, design and study on other embankments in permafrost regions.     

Laboratory study of infiltration into two frozen engineered (sandy) soils recommended for bioretention

Infiltration of water into two frozen engineered soils of different gradation was studied in laboratory soil columns 1.2 m long and 0.1 m in diameter. Prior to testing, the soil moisture was adjusted to two levels, described by the gravimetric water content of 5% or 10%, and soils were compacted to about 80–90% of the maximum dry density and refrigerated to temperatures ranging from ?8 to ?2 °C. Water with temperatures 8–9 °C was thereafter fed on the top of columns at a constant head, and the times of water breakthrough in the column and reaching a steady percolation rate, as well as the percolation rate, were recorded. The soil water content was a critical factor affecting the thawing process; during freezing, soil moisture was converted into ice, which blocked pores, and its melting required high amounts of energy supplied by infiltrating water. Hence, the thawing of soils with higher initial water content was much slower than in lower moisture soils, and water breakthrough and the attainment of steady percolation required much longer times in higher moisture soils. Heat transfer between infiltrating water, soil ice, and frozen soil particles was well described by the energy budget equations, which constitute a parsimonious model of the observed processes. The finer grained soil and more compacted soil columns exhibited reduced porosity and required longer times for soil thawing. Practical implications of study results for design of bioretention facilities (BFs) in cold climate include the use of coarse engineered soils and fitting bioretention facilities with a drain facilitating soil drainage before the onset of freezing weather. Copyright © 2015 John Wiley & Sons, Ltd.     

Transport of water in frozen soil IV. Analysis of experimental results on the effects of ice content

Effects of ice content on the transport of water in frozen soil are studied experimentally and theoretically under isothermal conditions. A physical law, that the flux of water in unsaturated frozen soil is proportional to the gradient of total water content is proposed. Theoretical justification is made by the use of the two-phase flow theory. The experimental results are shown to support the proposed physical law. The results of this study are presented in two parts and this is the second paper describing the theoretical aspects of the study.