Mapping waterlogging of soils using digital terrain models

Maps of the potential waterlogging of soils were generated using hypotheses about the effect of topography on the soil water regime inspired by Beven and Kirkby's concept of saturation overland flow. The procedure was validated by comparing the simulated maps with maps derived from a 1: 25 000 soil survey for two contrasting catchments. The value and limitations of the method are discussed in the light of this comparison. The approach proposed here is relevant to modelling the distribution of intensely waterlogged soils, provided the relationship between bedrock and the limit values is established. This approach can be used for several purposes: (1) to distinguish positional waterlogging from other types of waterlogging; (2) to control the quality and consistency of waterlogging maps; and (3) to create soil water regime maps for non-surveyed catchments. Conversely, soil water regime maps can be compared with contributing areas simulated by hydrological distributed models for validation purposes.     

Measuring the imprint of orographic rainfall gradients on the morphology of steady‐state numerical fluvial landscapes

We explore the imprint of spatial rainfall patterns on steady‐state landscapes with uniform rock uplift rate. A two‐dimensional (2D) orographic precipitation module is incorporated into the CHILD numerical landscape evolution model to provide a quantitative tool for exploring the co‐evolution of rainfall patterns and fluvial topography. Our results suggest that network organization and planform morphology are strongly impacted by rainfall patterns. Rainfall gradients that are perpendicular to a mountain range front produce narrower watersheds because channels show a tendency to flow along the rainfall gradient, rather than across it. The change in watershed shape is evidenced by smaller values of the exponent on distance in Hack's law and a less peaked width function. Narrower watersheds also lead to an increase in the valley spacing ratio and constrain trunk channels to follow a more direct path to the mountain front. Rainfall gradients also influence the distribution of topography across a watershed. Channel profiles record rainfall patterns in both the channel concavity and the channel steepness index (k_sn). Across short tributaries along which rainfall rate changes little, k_sn decreases systematically with tributary‐averaged rainfall rate. The hypsometric integral (HI), which increases with the amount of topography that is at relatively high elevations within a watershed, is negatively correlated with the profile concavity of the trunk channel. High rainfall rates at the ridge top lead to mainstem channels that have relatively low concavity, and watersheds with relatively higher HI in comparison with landscapes that have uniform rainfall. Finally, we contrast the impacts of rainfall patterns on landscape morphology with those resulting from a linear rock uplift gradient and uniform rainfall. Uplift patterns may have a similar impact on landscape morphology as rainfall gradients, making it challenging to decipher the relative roles of climate and tectonics on landscape evolution without a quantitative assessment of morphologic parameters. Copyright © 2015 John Wiley & Sons, Ltd.     

The design of post‐mining landscapes using geomorphic principles

Nature can provide analogues for post‐mining landscapes in terms of landscape stability and also in terms of the rehabilitated structure ‘blending in’ with the surrounding undisturbed landscape. In soil‐mantled landscapes, hillslopes typically have a characteristic pro?le that has a convex upper hillslope pro?le with a concave pro?le lower down the slope. In this paper hillslope characteristic form is derived using the area–slope relationship from pre‐mining topography at two sites in Western Australia. Using this relationship, concave hillslope pro?les are constructed and compared to linear hillslopes in terms of sediment loss using the SIBERIA erosion model. It is found that concave hillslopes can reduce sediment loss by up to ?ve times that of linear slopes. Concave slopes can therefore provide an alternative method for the construction of post‐mining landscapes. An understanding of landscape geomorphological properties and the use of erosion models can greatly assist in the design of post‐mining landscapes. Copyright © 2003 John Wiley & Sons, Ltd.     

The application of cellular automata to the erosion of landforms

Two approaches to modelling surface erosion are described which can be used to explain the development of geomorphological features. The first approach uses non-linear wave theory and shows how surface gradient discontinuities can arise as the erosion of an initially smooth surface proceeds. For isotropic erosion, surface shapes may be predicted by a simple application of the Huyghens wavefront construction and Snell's law at media boundaries. A second approach uses a computational cellular method. The general shapes predicted by the computer simulations are shown to agree with those determined from the wave approach. The application of the cellular method to problems of geomorphological interest are discussed.     

Hillslope response to knickpoint migration in the Southern Appalachians: implications for the evolution of post‐orogenic landscapes

The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post‐orogenic landscape remain enigmatic. The non‐glaciated Cullasaja River basin of south‐western North Carolina, with uniform lithology, frequent debris flows, and the availability of high‐resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post‐orogenic landscape through the lens of hillslope–channel coupling. This investigation is limited to channels with upslope contributing areas >2.7 km², a conservative estimate of the transition from fluvial to debris‐flow dominated channel processes. Values of normalized hypsometry, hypsometric integral, and mean slope vs elevation are used for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. The transient effect of knickpoint‐driven channel incision on basin hillslopes is captured by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the Cullasaja River. A conceptual model of area–elevation and slope distributions is presented that may be representative of post‐orogenic landscape evolution in analogous geologic settings. Importantly, the model explains how knickpoint migration and channel–hillslope coupling is an important factor in tectonically‐inactive (i.e. post‐orogenic) orogens for the maintenance of significant relief, steep slopes, and weathering‐limited hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.     

Geomorphic evolution of the Southern Alps,New Zealand

The Southern Alps are the topographic expression of late Cenozoic (<8 Ma ago) uplift of the crust of the leading edge of the Pacific plate in South Island, New Zealand. New fission track data on the basement exposed in the Southern Alps quantify the age, amount, and rate of rock uplift, and in combination with geomorphic parameters permit the construction of a new model of the geomorphic evolution of the Southern Alps. The model emphasizes the development over time and space of rock uplift, mean surface elevation, exhumation of crustal section, and relief. The earliest indications of mean surface uplift are between 4 and 5 Ma ago at the Alpine Fault. Mean surface uplift, which lagged the start of rock uplift, propagated southeastward from the Alpine Fault at a rate of 30 km/Ma. By about 4 Ma ago, exhumation had exposed greywacke basement adjacent to and east of the entire 300 km long central section of the Alpine Fault. At 3 Ma ago, greenschist was exposed in the southern parts of the Southern Alps near Lake Wanaka, and since then has become exhumed along a narrow strip east of the Alpine Fault. The model infers that amphibolite grade schist has been exhumed adjacent to the Alpine Fault only in the last 0·3 Ma. The age of the start of rock uplift and the amount and rate of rock uplift, all of which vary spatially, are considered to be the dominant influences on the development of the landscape in the Southern Alps. The Southern Alps have been studied in terms of domains of different rock uplift rate. At present the rate of rock uplift varies from up to 8–10 mm/a adjacent to the Alpine Fault to 0·8–1·0 mm/a along the southeastern margin of the Southern Alps. This spectrum can be divided into two domains, one northwest of the Main Divide where the present rock uplift rates are very high (up to 8–10 mm/a) and exceed the long-term value of 0·8–1·0 mm/a, and another to the southeast of the Main Divide where the long-term rate is 0·8–1·0 mm/a. A domain of no uplift lies immediately to the east of the Southern Alps, and is separated from them by a 1·0–1·5 km step in the basement topography. We argue that this spatial sequence of uplift rate domains represents a temporal one. The existing models of the geomorphic development of the Southern Alps—the dynamic cuesta model of J. Adams and the numerical model of P. Koons—are compared with the new data and evolutionary model. Particular constraints unrealized by these two earlier models include the following: the earlier timing of the start of rock uplift of the Southern Alps (8 Ma ago); the spatial variation in the timing of the start of rock uplift (8 Ma ago to 3 Ma ago); the lower long-term rock uplift rate (0·8–1·0 mm/a) of the Southern Alps for most of the late Cenozoic; the lag between the start of rock uplift and the start of mean surface uplift; and the patterns of the amounts of late Cenozoic rock uplift and erosion across the Southern Alps.     

Digital landscapes of deglaciation: identifying Late Quaternary glacial lake outburst floods using LiDAR

High resolution DEMs obtained from LiDAR topographic data have led to improved landform inventories (e.g. landslides and fault scarps) and understanding of geomorphic event frequency. Here we use airborne LiDAR mapping to investigate meltwater pathways associated with the Tweed Valley palaeo ice‐stream (UK). In particular we focus on a gorge downstream of Palaeolake Milfield, previously mapped as a sub‐glacial meltwater channel, where the identification of abandoned headcut channels, run‐up bars, rock‐cut terrace surfaces and eddy flow features attest to formation by a sub‐aerial glacial lake outburst flood (GLOF) caused by breaching of a sediment dam, likely an esker ridge. Mapping of these landforms combined with analysis of the gorge rim elevations and cross‐section variability revealed a two phase event with another breach site downstream following flow blockage by higher elevation drumlin topography. We estimate the magnitude of peak flow to be 1–3 × 10³ m³/s, duration of the event to range from 16–155 days, and a specific sediment yield of 10⁷–10⁹ m³/km²/yr. We identified other outburst pathways in the lower Tweed basin that help delineate an ice margin position of the retreating Tweed Valley ice stream. The results suggest that low magnitude outburst floods are under‐represented in Quaternary geomorphological maps. We therefore recommend regional LiDAR mapping of meltwater pathways to identify other GLOFs in order to better quantify the pattern of freshwater and sediment fluxes from melting ice sheets to oceans. Despite the relatively low magnitude of the Till outburst event, it had a significant impact on the landscape development of the lower Tweed Valley through the creation of a new tributary pathway and triggering of rapid knickpoint retreat encouraging new regional models of post‐glacial fluvial landscape response. Copyright © 2015 John Wiley & Sons, Ltd.     

Geomorphological surfaces of different age and origin in granite landscapes: an evaluation of the Schmidt hammer test

Granite landforms in Sierra Nevada, California, and the southern part of Sweden were used to test whether a Schmidt hammer can be used to distinguish surfaces of different age and origin. Based on 3260 readings, statistically signi?cant differences were obtained from surfaces formed and/or affected by different geomorphological processes. Aeolian, ?uvial or glacially polished surfaces yield higher values than surfaces exposed to surface weathering, which are distinguishable from surfaces at a weathering front caused by deep weathering. Copyright © 2004 John Wiley & Sons, Ltd.     

Quantitative reconstruction of Late Cenozoic landscapes: a case study in the Sierra de Atapuerca (Burgos,Spain)

We have developed a method to reconstruct palaeorelief by means of detailed geomorphological and geological studies, geostatistical tools, GIS and a DEM. This method has been applied to the Sierra de Atapuerca (NE Duero Basin, Burgos, Spain), allowing us to model a three‐dimensional reconstruction of the relief evolution from the Middle Miocene to the present. The modelling procedure is based on geostatistical recovery of the palaeosurfaces characteristic of each geomorphological evolution stage, using polynomial regressions, trend surfaces and kriging. The modelling of morphology trends has been useful in establishing new geological and geomorphological relationships in the geodynamic evolution of this basin, such as uplift quantification, correlation of erosion surfaces and sedimentary units, and the evolution of fluvial base levels. The palaeosurface reconstruction together with an analysis of the slope retreat have allowed us to reconstruct the palaeoreliefs that define the Late Cenozoic landscape evolution of this area, where the Lower and Middle Pleistocene archaeopalaeontological sites of the Sierra de Atapuerca are located. Copyright © 2007 John Wiley & Sons, Ltd.     

Sensitivity to space and time resolution of a hydrological model using digital elevation data

The space and time resolutions used for the input variables of a distributed hydrological model have a sufficient impact on the model results. This resolution depends on the required accuracy, experimental site and the processes and variables taken into account in the hydrological model. The influence of space and time resolution is studied here for the case of TOPMODEL, a model based on the variable contributing area concept, applied to an experimental 12 km² catchment (Coët-Dan, Brittany, France) during a two month winter period. A sensitivity analysis to space and time resolution is performed first for input variables derived from the digital elevation data, secondly for the optimized values of the TOPMODEL parameters and finally for modelling efficiency. This analysis clearly shows that a relevant domain of space and time resolutions where efficiency is fairly constant can be defined for the input topographic variables, as opposed to another domain of larger resolutions that induces a strong decrease of modelling efficiency. It also shows that the use of a single set of parameters, defined as mean values of parameters on this relevant domain of resolution, does not modify the accuracy of modelling. The sensitivity of the parameters to space and time resolution allows the physical significance of the parameter values to be discussed.     

Drainage basin sensitivity to tectonic and climatic forcing: implications of a stochastic model for the role of entrainment and erosion thresholds

Long‐term average rates of channel erosion and sediment transport depend on the frequency–magnitude characteristics of ?ood ?ows that exceed an erosion threshold. Using a Poisson model for rainfall and runoff, analytical solutions are developed for average rates of stream incision and sediment transport in the presence of such a threshold. Solutions are derived and numerically tested for three erosion/transport formulas: the Howard–Kerby shear‐stress incision model, the Bridge–Dominic sediment transport model, and a generic shear‐stress sediment transport model. Results imply that non‐linearity resulting from threshold effects can have a ?rst‐order impact on topography and patterns of dynamic response to tectonic and climate forcing. This non‐linearity becomes signi?cant when fewer than about half of ?ood events are capable of detaching rock or sediment. Predicted morphology and uplift‐gradient scaling is more closely consistent with observations and laboratory experiments than conventional slope‐linear or shear‐linear erosion laws. These results imply that particle detachment thresholds are not details that can be conveniently ignored in long‐term landscape evolution models. Copyright © 2004 John Wiley & Sons, Ltd.     

How the spatial distribution of grass contributes to controlling hillslope erosion

The aim of this study was to investigate how the spatial distribution of grass influenced run-off and erosion from a hillslope with loess and cinnamon soils in the rocky area of Northern China. We set up a trial to test the two soils with different treatments, including bare soil (BS), grass strips on the upper (UGS) and lower (DGS) parts of the slope, grass cover over the entire slope (GS), and a grass carpet on the lower part of the slope (GC), under simulated rainfall conditions. The results showed that the run-off coefficients for the loess and cinnamon soils decreased by between 4% and 20% and by between 2% and 37%, respectively, when covered with grass. Grass spatial distribution had little effect on the run-off, but more effect on erosion than vegetation coverage degree. The most effective location of grass cover for decreasing hillslope erosion was at the foot, and the high efficiency was mainly due to controlling of rill formation and sediment deposition. The soil loss from GS, DGS, and GC on the loess and cinnamon soils was between 77% and 93% less and 55% and 80% less, respectively, compared with the loss from BS. However, the soil characteristics had little effect on soil erosion for well-vegetated slopes. The results highlight the importance of vegetation re-establishment at the foot of hillslope in controlling soil erosion.     

Evidence of transient topographic disequilibrium in a landward passive margin river system: knickpoints and paleo‐landscapes of the New River basin,southern Appalachians

The upper New River basin of the southern Appalachian Mountains, a major tributary of the modern Ohio River, represents the unglaciated headwaters of the Tertiary Teays River system of eastern North America. Dating of relict fluvial gravels have suggested that New River incision may be outpacing lowering of the surrounding uplands, but physical evidence of transient topographic disequilibrium has yet to be identified. We use focused topographic analysis of the upper New River basin to delineate a perched, low‐relief paleo‐landscape that is experiencing transgressive dissection due to incision by the New River and its tributaries. Accelerated incision has decoupled hillslopes from the drainage network, generating knickpoints which represent the boundary between remnants of the paleo‐landscape and actively adjusting topography downstream. Steepening of hillslopes downstream of knickpoints suggests dynamic headward migration which, along with knickpoint occurrence throughout the drainage network, is inconsistent with the development of fixed stream profile convexities atop strike‐extensive geologic contacts. In the absence of tectonic forcing, we favor a climatically‐forced drop in external base level as driver of the incision pattern we observe. Plio‐Pleistocene glacial damming and diversion of the Teays River to form the modern Ohio River lowered regional base level for the study area, potentially forcing the paleo‐landscape developed during the Teays era to adjust to the modern drainage pattern. The upper New River may therefore represent the potential for glacially‐driven drainage rearrangement to drive transient topographic evolution hundreds of kilometers away from the ice margin, long after the disappearance of ice sheets. Copyright © 2013 John Wiley & Sons, Ltd.     

Application of the normalized surface magnetic charge model to UXO discrimination in cases with overlapping signals

This paper presents an application of the normalized surface magnetic charge (NSMC) model to discriminate objects of interest, such as unexploded ordnance (UXO), from innocuous items in cases when UXO electromagnetic induction (EMI) responses are contaminated by signals from other objects. Over the entire EMI spectrum considered here (tens of Hertz up to several hundreds of kHz), the scattered magnetic field outside the object can be produced mathematically by equivalent magnetic charges. The amplitudes of these charges are determined from measurement data and normalized by the excitation field. The model takes into account the scatterer's heterogeneity and near- and far-field effects. For classification algorithms, the frequency spectrum of the total NSMC is proposed and investigated as a discriminant. The NSMC is combined with the differential evolution (DE) algorithm in a two-step inversion procedure. To illustrate the applicability of the DE–NSMC algorithm, blind test data are processed and analyzed for cases in which signals from nearby objects frequently overlap. The method was highly successful in distinguishing UXO from accompanying clutter.     

One river,two streams: chemical and chromium isotopic features of the Neglinka River (Karelia,northwest Russia)

The physico-chemical and hydrochemical characteristics of run-off of the Neglinka River Basin (northwest Russia) monitored for a year are different for the upstream and downstream sections. The river known hydrologically as the Neglinka, consists hydrochemically of two different streams: one represented by the upstream part of the basin, and the other one by the downstream. The upstream water is characterized by low mineralization (water hardness 0.08–0.43 mmol L^?1) and low δ⁵³Cr values (+0.30 to +0.42‰), whereas the lower part is characterized by high mineralization (water hardness 0.37–3.46 mmol L^?1) and high δ⁵³Cr values (+0.92 to +1.73‰). The difference in chemical composition of the upstream and downstream waters could be due to the underground discharge input. Aqueous chromium (Cr) mobilized from weathering profiles may have been reduced from soluble Cr(VI) to insoluble Cr(III) during the riverine transportation. Partial removal of Cr from the water balance resulted in a decrease in Cr concentration and an increase in δ⁵³Cr values.     

Incorporating landscape features to obtain an object‐oriented landscape drainage network representing the connectivity of surface flow pathways over rural catchments

A topological representation of a rural catchment is proposed here in addition to the generally used topographic drainage network. This is an object‐oriented representation based on the identification of the inlets and outlets for surface water flow on each farmer's field (or plot) and their respective contributing areas and relationships. It represents the catchment as a set of independent plot outlet trees reaching the stream, while a given plot outlet tree represents the pattern of surface flow relationships between individual plots. In the present study, we propose to implement functions related to linear and surface elements of the landscape, such as hedges or road networks, or land use, to obtain what we call a landscape drainage network which delineates the effective contributing area to the stream, thus characterizing its topological structure. Landscape elements modify flow pathways and/or favour water infiltration, thus reducing the area contributing to the surface yield and modifying the structure of the plot outlet trees. This method is applied to a 4·4‐km² catchment area comprising 43 955 pixels and 312 plots. While the full set of 164 plot outlet trees, with an average of 7 plots per tree, covers 100% of the total surface area of the catchment, the landscape drainage network comprises no more than 37 plot outlet trees with an average of 2 plots per tree, accounting for 52 and 7% of the catchment surface area, when taking account of linear elements and land use, respectively. This topological representation can be easily adapted to changes in land use and land infrastructure, and provides a simple and functional display for intercomparison of catchments and decision support regarding landscape and water management. Copyright © 2011 John Wiley & Sons, Ltd.     

Sensitivity of mean transit time estimates to model conditioning and data availability

Mean transit times (MTTs) can give useful insights into the internal processes of hydrological systems. However, varying model conditioning assumptions and data availability can limit the use of MTT, particularly in terms of comparing the results of studies using different assumptions and data records of varying lengths. We present a systematic analysis of sensitivity of MTT estimates to different methods of artificially extending the data record, varying model warm‐up period lengths and varying sampling intervals for a small upland catchment in the Scottish Highlands. The analysis was based on Cl^? data in conjunction with the convolution integral model using the gamma distribution as transit time distribution. It could be shown that three out of four different methods to artificially extend the data record and to generate a warm‐up period give mostly equivalent results. The required minimum warm‐up period length to reliably estimate MTT for a 3‐year period of data was observed to be about 2 years or 3 times the MTT, implying that ～95% of the tracer signal entering the stream at day 1 of the warm‐up period has to be recovered by the end of the warm‐up period in order to avoid significant deviations from the best available MTT estimates. It was furthermore found that sampling intervals of up to 4 weeks can produce MTT estimates within about 0·25 times the best available MTT estimate, albeit with potentially increased process misrepresentation in terms of the gamma distribution parameter α. Copyright © 2011 John Wiley & Sons, Ltd.     

Sensitivity analyses of a distributed catchment model to verify the model structure

Sensitivity analyses are valuable tools for identifying important model parameters, testing the model conceptualization, and improving the model structure. They help to apply the model efficiently and to enable a focussed planning of future research and field measurement. Two different methods were used for sensitivity analyses of the complex process-oriented model TAC^D (tracer aided catchment model, distributed) that was applied to the meso-scale Brugga basin (40 km²) and the sub-basin St Wilhelmer Talbach (15.2 km²). Five simulations periods were investigated: two summer events, two snow melt induced events and one summer low flow period. The model was applied using 400 different parameter sets, which were generated by Monte Carlo simulations using latin hypercube sampling. The regional sensitivity analysis (RSA) allowed determining the most significant parameters for the complete simulation periods using a graphical method. The results of the regression-based sensitivity analysis were more detailed and complex. The temporal variability of the simulation sensitivity could be observed continuously and the significance of the parameters could be determined in a quantitative way. A dependency of the simulation sensitivity on initial- and boundary conditions and the temporal and spatial variability of the sensitivity to some model parameters was revealed by the regression-based sensitivity analysis. Thus, the difficulty of transferring the results to different time periods or model applications in other catchments became obvious. The analysis of the temporal course of the simulation sensitivity to parameter values in conjunction with simulated and measured additional data sets (precipitation, temperature, reservoir volumes etc.) gave further insight into the internal model behaviour and demonstrated the plausibility of the model structure and process conceptionalizations.     

Sensitivity of seismic hazard evaluations to uncertainties determined from seismic source characterization

The sensitivity and overall uncertainty in peak ground acceleration (PGA)estimates have been calculated for the city of Tabriz, northwestern Iran byusing a specific randomized blocks design. Eight seismic hazard models andparameters with randomly selected uncertainties at two levels have beenconsidered and then a linear model between predicted PGA at a givenprobability level and the uncertainties has been performed. The inputmodels and parameters are those related to the attenuation, magnituderupture-length and recurrence relationships with their uncertainties.Application of this procedure to the studied area indicates that effects ofthe simultaneous variation of all eight input models and parameters on thesensitivity of the seismic hazard can be investigated with a decreasingnumber of computations for all possible combinations at a fixed annualprobability. The results show that the choice of a mathematical model ofthe source mechanism, attenuation relationships and the definition ofseismic parameters are most critical in estimating the sensitivity of seismichazard evaluation, in particular at low levels of probability of exceedance.The overall uncertainty in the expected PGA for an annual probability of0.0021 (10% exceedence in 50 yr) is expressed by a coefficient ofvariation (CV) of about 34% at 68% confidence level for a distance ofabout 5km from the field of the major faults. The CV will decrease withincreasing site-source distance and remains constant, CV = 15%, fordistances larger than 15 km. Finally, treating alternative models on theoverall uncertainty are investigated by additional outliers in input decision.