Short-term beach–dune sand budgets on the north sea coast of France: Sand supply from shoreface to dunes, and the role of wind and fetch

Three experimental plots, covering the transition from the upper beach to the dune, on the North Sea coast of France were monitored at various intervals over a period of 18–24 months via high resolution terrain surveys in order to determine inter-site sand budget variability, as well as patterns and processes involved in sand exchanges between the upper beach and dune. The wind regime consists of a fairly balanced mix of moderate (80% of winds are below 8 m/s) onshore, offshore and shore-parallel winds. Sustained dune accretion over several years depends on the periodic local onshore welding of shoreface tidal banks that have developed in the storm- and tide-dominated setting of the southern North Sea. The only site where this has occurred in the recent past is Calais, where bank welding has created a wide accreting upper beach sand flat. At this site, significant sand supply from the subtidal sand bank reservoir to the upper beach flat occurred only once over the 18-month survey following a major storm. The bulk of the sand deposited over this large flat is not directly integrated into the adjacent embryo dunes by onshore winds but is progressively reworked in situ into developing dunes or transported alongshore by the balanced wind regime, thus resulting in alongshore stretching of the embryo dune system. The Leffrinckoucke site near Belgium shows moderate beach–dune mobility and accretion, while the Wissant site exhibits significant upper beach bedform mobility controlled by strong longshore currents that result in large beach budget fluctuations with little net budget change, to the detriment of the adjacent dunes. Accretion at these two sites, which are representative of the rest of the North Sea coast of France, is presently constrained by the absence of a shore-attached sand bank supply reservoir, while upper beach–dune sand exchanges are further limited by the narrow wave-affected upper beach, the intertidal morphology of bars and troughs which segments the aeolian fetch, and the moderate wind energy conditions. The balanced wind regime limits net sand mobilisation in favour of either the beach or the dune, and may explain the relatively narrow longshore morphology of the dune ridges bounding this coast.     

A modelling framework for the study of Spatial Data Infrastructures applied to coastal management and planning

The continuous development of Spatial Data Infrastructures (SDI) provides a favourable context for environmental management and planning. However, it appears that the actual contribution of SDIs should also depend on the correlation between users’ expectations and the services delivered to them. Several studies have addressed some organizational, methodological and technological aspects of the development of SDIs. However, only a few studies have, to the best of our knowledge, studied SDI use at large. This article introduces a methodological approach oriented towards the study of the relationship between SDIs and the users interacting with them as part of their professional practices. Our study is applied to coastal zone management and planning in France. This approach combines structural and data flow modelling. The former is based on Social Network Analysis (SNA) and the latter on Data Flow Diagrams (DFD). This modelling approach has been applied to an online questionnaire and semi-structured interviews. The results identify the SDIs, geographical data flows and institutional levels implied in French coastal zone management and planning.     

Complex channel responses to changes in stream flow and sediment supply on the lower Duchesne River, Utah

Channel responses to flow depletions in the lower Duchesne River over the past 100 years have been highly complex and variable in space and time. In general, sand-bed reaches adjusted to all perturbations with bed-level changes, whereas the gravel-bed reaches adjusted primarily through width changes. Gravel-bed reaches aggraded only when gravel was supplied to the channel through local bank erosion and degraded only during extreme flood events.A 50% reduction in stream flow and an increase in fine sediment supply to the study area occurred in the first third of the 20th century. The gravel-bed reach responded primarily with channel narrowing, whereas bed aggradation and four large-scale avulsions occurred in the sand-bed reaches. These avulsions almost completely replaced a section of sinuous channel about 14 km long with a straighter section about 7 km long. The most upstream avulsion, located near a break in valley slope and the transition from a gravel bed upstream and a sand bed downstream, transformed a sinuous sand-bed reach into a braided gravel-bed reach and eventually into a meandering gravel-bed reach over a 30-year period. Later, an increase in flood magnitudes and durations caused widening and secondary bed aggradation in the gravel-bed reaches, whereas the sand-bed reaches incised and narrowed. Water diversions since the 1950s have progressively eliminated moderate flood events, whereas larger floods have been less affected. The loss of frequent flooding has increased the duration and severity of drought periods during which riparian vegetation can establish along the channel margins. As a result, the channel has gradually narrowed throughout the study area since the late 1960s, despite the occasional occurrence of large floods. No tributaries enter the Duchesne River within the study area, so all reaches have experienced identical changes in stream flow and upstream sediment supply.     

A parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment

A new parameterisation for the threshold shear velocity to initiate deflation of dry and wet particles is presented. It is based on the balance of moments acting on particles at the instant of particle motion. The model hence includes a term for the aerodynamic forces, including the drag force, the lift force and the aerodynamic-moment force, and a term for the interparticle forces. The effect of gravitation is incorporated in both terms. Rather than using an implicit function for the effect of the aerodynamic forces as reported earlier in literature, a constant aerodynamic coefficient was introduced. From consideration of the van der Waals force between two particles, it was further shown that the effect of the interparticle cohesion force between two dry particles on the deflation threshold should be inversely proportional to the particle diameter squared. The interparticle force was further extended to include wet bonding forces. The latter were considered as the sum of capillary forces and adhesive forces. A model that expresses the capillary force as a function of particle diameter squared and the inverse of capillary potential was deduced from consideration of the well-known model of Fisher and the Young–Laplace equation. The adhesive force was assumed to be equal to tensile strength, and a function which is proportional to particle diameter squared and the inverse of the potential due to adhesive forces was derived. By combining the capillary-force model and the adhesive force model, the interparticle force due to wet bonding was simplified and written as a function of particle diameter squared and the inverse of matric potential. The latter was loglinearly related to the gravimetric moisture content, a relationship that is valid in the low-moisture content range that is important in the light of deflation of sediment by wind. By introducing a correction to force the relationship to converge to zero moisture content at oven dryness, the matric potential–moisture content relationship contained only one unknown model parameter, viz. moisture content at −1.5 MPa. Working out the model led to a rather simple parameterisation containing only three coefficients. Two parameters were incorporated in the term that applies to dry sediment and were determined by using experimental data as reported by Iversen and White [Sedimentology 29 (1982) 111]. The third parameter for the wet-sediment part of the model was determined from wind-tunnel experiments on prewetted sand and sandy loam aggregates. The model was validated using data from wind-tunnel experiments on the same but dry sediment, and on data obtained from simulations with the model of Chepil [Soil Sci. Soc. Am. Proc. 20 (1956) 288]. The experiments showed that soil aggregates should be treated as individual particles with a density equal to their bulk density. Furthermore, it was shown that the surface had to dry to a moisture content of about 75% of the moisture content at −1.5 MPa before deflation became sustained. The threshold shear velocities simulated with our model were found to be in good agreement with own observations and with simulations using Chepil's model.     

A novel repeat-coring approach to reconstruct recent sediment, phosphorus, and mercury loading from the upper Mississippi River to Lake Pepin, USA

It can be advantageous to revisit coring locations in lakes years after an initial paleolimnological study is completed, to assess environmental changes in the intervening time interval. We revisited sediment core sites in Lake Pepin (Minnesota, Wisconsin) more than a decade after an original set of 10 cores was collected, dated radiometrically, and studied in 1996. Prominent magnetic susceptibility features were used to align the new core set with the older set, such that traditional radiometric dating was not necessary to obtain a chronology for the new cores. The procedure used to align the two core sets accounted for compaction of former surface sediments by burial with new sediment. The amount of new sediment, mercury, and phosphorus accumulated at each core site was determined and extrapolated to the depositional area of the lake to estimate recent (1996–2008) whole-basin loads. Recent sediment accumulation in Lake Pepin compared well (within 3%) with monitored inflow data from a gauging station on the upper Mississippi River just before it enters the lake. Bulk sediment accumulation rate remained very high (772,000 t/year) for the recent period (1996–2008), down slightly from the peak in 1990–1996 (876,000 t/year), and almost an order of magnitude above pre-settlement rates. Total phosphorus deposition remained constant since a peak in the 1960s, but was also well above pre-settlement rates. Mercury continued its precipitous decline since peaking in the 1960s.     

A whole-basin stratigraphic record of sediment and phosphorus loading to the St. Croix River,USA

Lake St. Croix is a natural impoundment of the lowermost 37 km of the St. Croix River in Minnesota and Wisconsin, making this one of a few large river systems in the world possessing a long-term depositional basin at its terminus. The river’s relatively pristine condition led to its designation as a National Scenic Riverway in 1968, but increasing urbanization in its lower reaches has raised concerns about impacts on water quality. This study was initiated to reconstruct historical loadings of suspended sediment and phosphorus (P) from the sediment record in Lake St. Croix. Twenty-four piston cores, with an average length of 2 m, were collected along eight transects of the lake. Dated chronologies from ²¹⁰Pb, ¹³⁷Cs and ¹⁴C were used to calculate the rate of sediment accumulation in the lake over the past 100+ years. Diatom microfossil analysis was used to reconstruct historical lakewater P concentrations over the same time period, and sediment P analysis quantified the amount of P trapped in lake sediments. Using a whole-lake mass balance approach, the loading of sediment and P to Lake St. Croix over the last 100+ years was calculated. Beginning in 1850, sediment accumulation increased dramatically to a peak in 1950–1960 of eight times background rates prior to European settlement. The peak is driven largely by sediment contributions from small side-valley catchment tributaries to the downstream half of the lake. The total P load to the lake increased sharply after 1940 and remains high, at around four times the level of pre-European settlement conditions. The timing of peak sediment and P loading to the lake shows that early settlement activities, such as logging and the conversion of forest and prairie to agricultural land between 1850 and 1890, had only modest impacts on the lake. By contrast, the mid-1900s brought major increases in sediment and P loading to the lake, suggesting that relatively recent activities on the landscape and changes to nutrient balances in the watershed have caused the current eutrophic condition of this important recreational and natural resource. This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue.     

Byers Peninsula: A reference site for coastal,terrestrial and limnetic ecosystem studies in maritime Antarctica

This article describes the development of an international and multidisciplinary project funded by the Spanish Polar Programme on Byers Peninsula (Livingston Island, South Shetlands). The project adopted Byers Peninsula as an international reference site for coastal and terrestrial (including inland waters) research within the framework of the International Polar Year initiative. Over 30 scientists from 12 countries and 26 institutions participated in the field work, and many others participated in the processing of the samples. The main themes investigated were: Holocene changes in climate, using both lacustrine sediment cores and palaeo-nests of penguins; limnology of the lakes, ponds, rivers and wetlands; microbiology of microbial mats, ecology of microbial food webs and viral effects on aquatic ecosystems; ornithology, with investigations on a Gentoo penguin rookery (Pygoscelis papua) as well as the flying ornithofauna; biocomplexity and life cycles of species from different taxonomic groups; analysis of a complete watershed unit from a landscape perspective; and human impacts, specifically the effect of trampling on soil characteristics and biota.Byers Peninsula offers many features as an international reference site given it is one of the largest ice-free areas in the Antarctic Peninsula region, it has a variety of different landscape units, and it hosts diverse aquatic ecosystems. Moreover, the Byers Peninsula is a hotspot for Antarctic biodiversity, and because of its high level of environmental protection, it has been very little affected by human activities. Finally, the proximity to the Spanish polar installations on Livingston Island and the experience derived from previous expeditions to the site make it logistically feasible as a site for ongoing monitoring and research.     

A hybrid representation for modeling,interactive editing,and real-time visualization of terrains with volumetric features

Terrain rendering is a crucial part of many real-time applications. The easiest way to process and visualize terrain data in real time is to constrain the terrain model in several ways. This decreases the amount of data to be processed and the amount of processing power needed, but at the cost of expressivity and the ability to create complex terrains. The most popular terrain representation is a regular 2D grid, where the vertices are displaced in a third dimension by a displacement map, called a heightmap. This is the simplest way to represent terrain, and although it allows fast processing, it cannot model terrains with volumetric features. Volumetric approaches sample the 3D space by subdividing it into a 3D grid and represent the terrain as occupied voxels. They can represent volumetric features but they require computationally intensive algorithms for rendering, and their memory requirements are high. We propose a novel representation that combines the voxel and heightmap approaches, and is expressive enough to allow creating terrains with caves, overhangs, cliffs, and arches, and efficient enough to allow terrain editing, deformations, and rendering in real time.     

Effectiveness of reforestation in erosion mitigation and implications for future sediment yields,East Coast catchments,New Zealand: A review

This paper argues that reforestation of unstable and degraded parts of the East Coast region, predominantly with exotic pines, has successfully stabilised existing erosion forms and prevented the initiation of new ones. Effectiveness is often assessed by capturing erosion scars on aerial photography taken before and after reforestation and any change in scar size is measured in a geographic information system (GIS). Combined with forest age data, modelled reforestation scenarios indicate that sediment generation from earth flows and shallow landslides would be negligible within eight to 10 years after planting, and if all remaining gullies were to be reforested before 2020, sediment yield could halve by 2030 and remain constant thereafter. In a similar time frame, the risk to infrastructure by sedimentation and flooding would likely decrease.     

A 2500 year sediment record from Fayetteville Green Lake, New York: evidence for anthropogenic impacts and historic isotope shift

A series (N = 12) of short (< 1 m) sediment cores were collected from meromictic Green Lake in Fayetteville, New York to investigate potential anthropogenic impacts on the watershed during historic time and environmental change over the past ~ 2,500 years. Stratigraphic data document an abrupt basinwide change during the early 1800's A.D. from brown laminated sediments to grey varved sediments separated by a transition zone rich in aquatic moss. Deforestation of the region by European settlers during the early 1800's A.D. resulted in a flux of nutrients and increased biological productivity followed by a 7fold increase in sediment accumulation rates. Elemental geochemical data document the anthropogenic loading of lead to the to the lake basin via atmospheric fallout. Stable oxygen isotope (¹⁸O calcite) data also provide evidence for an abrupt shift in the isotopic composition of lake water ~ 150–200 years ago. This isotopic shift could have been a local phenomenon related to an increased supply of summer enriched precipitation following removal of forest vegetation, or it might have reflected broader scale climatic changes. We hypothesize that the ¹⁸O calcite shift was the result of the polar front jet stream migrating from a more southerly prehistoric position to a contracted, northerly configuration ~ 150–200 years ago. Such a shift could have been natural, associated with the end of the Little Ice Age or it may have been anthropogenically forced.     

Partnering between a geography department and a community initiative to provide a wind resource assessment for the Blueskin Bay region,Otago, New Zealand

This paper explores the partnership between a community group and a geography department to assess the wind energy potential of the Blueskin Bay region in southern New Zealand. The partnership has provided opportunities for research and is of strategic importance. Year‐long wind observations and numerical modelling have revealed that the hills surrounding Blueskin Bay show potential for wind energy generation. Despite challenges for both parties, the university–community partnership has allowed a successful research platform to be established.     

A Hamiltonian approach to dissipative phenomena between the Earth's mantle and core, and effects on free nutations

The Hamiltonian formalism was recently applied by Getino (1995a,b) for the study of the rotation of a non-rigid earth with a heterogeneous and stratified liquid core. That earth model is generalized here by including the effect of the dissipation arising from the mantle-core interaction, using a model similar to that of Sasao, Okubo & Saito (1980), which includes both viscous and electromagnetic coupling. First, a solution for the free nutations is obtained following a classical approach, which in our opinion is more familiar to most of the readers than the Hamiltonian treatment. This solution provides a theoretical basis clear enough to study both the qualitative and quantitative effects of the dissipations considered in the hypotheses. The main qualitative features are, besides the delays, that the free core nutation (FCN) suffers an exponential damping, while the chandler wobble (CW) is not damped at first order, by the dissipation considered. The numerical values obtained for the complex compliances agree with the most recent experimental computations.
Next, the problem is studied under a Hamiltonian formalism, and a solution equivalent to the above is obtained. Besides its interest from a theoretical point of view, this formalism is necessary in order to apply canonical perturbation methods in order to obtain analytical nutation series.     

A seismological study of normal faulting in the Demirci, Alaşehir and Gediz earthquakes of 1969–70 in western Turkey: implications for the nature and geometry of deformation in the continental crust

Summary. In this study, seismological techniques are combined with surface observations to investigate the faulting associated with three large earthquakes in western Turkey. All involved normal faulting that nucleated at 6–10 km depth with dips in the range 30–50°. The two largest earthquakes, at Alaşehir (1969.3.28) and Gediz (1970.3.28), were clearly multiple events and their seismograms indicate that at least two discrete subevents were involved in producing the observed surface faulting. In addition, their seismograms contain later, longer-period signals that are likely to represent source, not structure or propagation, complexities. These later signals can be modelled by subevents with long time functions on almost flat detachment-type faults.
As a result of these observations, we propose a model for the deformation of the lower crust, in which brittle failure of the top part occurs when high strain rates are imposed during an earthquake that ruptures right through the upper, brittle crust. Under these special circumstances, seismic motion occurs on discrete faults in the lower crust, which otherwise normally deforms by distributed creep. In the case of the normal faults studied here, motion in the uppermost lower crust takes place on shallow dipping faults that are downward continuations of the steeper faults that break to the surface. The faults thus have an overall listric geometry, flattening into a weak zone below the brittle layer at a depth that is probably dependent on the termperature gradient. This interpretation explains why detachment-type mechanisms are not seen in first motion fault plane solutions of normal faulting earthquakes, and suggests an origin for the Metamorphic Core Complexes seen in the Basin and Range Province, which probably represent flat lower crustal faults, analogous to those postulated at Alaşehir and Gediz, that have been uplifted to the surface.