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1.
Digital flow networks derived from digital elevation models (DEMs) sensitively react to errors due to measurement, data processing and data representation. Since high‐resolution DEMs are increasingly used in geomorphological and hydrological research, automated and semi‐automated procedures to reduce the impact of such errors on flow networks are required. One such technique is stream‐carving, a hydrological conditioning technique to ensure drainage connectivity in DEMs towards the DEM edges. Here we test and modify a state‐of‐the‐art carving algorithm for flow network derivation in a low‐relief, agricultural landscape characterized by a large number of spurious, topographic depressions. Our results show that the investigated algorithm reconstructs a benchmark network insufficiently in terms of carving energy, distance and a topological network measure. The modification to the algorithm that performed best, combines the least‐cost auxiliary topography (LCAT) carving with a constrained breaching algorithm that explicitly takes automatically identified channel locations into account. We applied our methods to a low relief landscape, but the results can be transferred to flow network derivation of DEMs in moderate to mountainous relief in situations where the valley bottom is broad and flat and precise derivations of the flow networks are needed. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

2.
The increasing popularity of remote sensing techniques has created numerous options for researchers seeking spatial datasets, especially digital elevation models (DEMs), for geomorphic investigations. This yields an important question regarding what DEM resolution is most appropriate when answering questions of geomorphic significance. The highest possible resolution is not always the best choice for a particular research aim, and DEM resolution should be tailored to fit both the scale of investigation and the simplicity/complexity of modelling processes applied to the dataset. We find that DEM resolution has a significant effect on a simple model of bed load sediment connectivity in the Lockyer Valley, Queensland. We apply a simple bed load transport threshold to catchment DEMs at three different resolutions – 1 m, 5 m, and 25 m. We find that using a 1 m resolution DEM generates numerous disconnections along tributary channel networks that underestimates the sediment contributing area, i.e. effective catchment area (ECA), of seven tributary basins of Lockyer Creek. Utilizing a coarser (lower‐resolution) DEM helps eliminate erroneous disconnections, but can reduce the detail of stream network definition. We find that the 25 m resolution DEM provides the best measure of ECA for comparing sediment connectivity between tributary catchments. The utility of simple models and coarse‐resolution datasets is important for undertaking large, catchment‐scale geomorphic investigations. As catchment‐scale investigations are becoming increasingly entwined with river management and rehabilitation efforts, scientists need not embrace an ‘out with the old’ philosophy. Simple models and coarse‐resolution datasets can help better integrate geomorphic research with management strategies and provide inexpensive and quick first‐order insights into catchment‐scale processes that can help focus future management efforts. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

3.
The resolution of a digital elevation model (DEM) is a crucial factor in watershed hydrologic and environmental modelling. DEM resolution can cause significant variability in the representation of surface topography, which further affects quantification of hydrologic connectivity and simulation of hydrologic processes. The objective of this study is to examine the effects of DEM resolution on (1) surface microtopographic characteristics, (2) hydrologic connectivity, and (3) the spatial and temporal variations of hydrologic processes. A puddle‐to‐puddle modelling system was utilized for surface delineation and modelling of the puddle‐to‐puddle overland flow dynamics, surface runoff, infiltration, and unsaturated flow for nine DEM resolution scenarios of a field plot surface. Comparisons of the nine modelling scenarios demonstrated that coarser DEM resolutions tended to eliminate topographic features, reduce surface depression storage, and strengthen hydrologic connectivity and surface runoff. We found that reduction in maximum depression storage and maximum ponding area was as high as 97.56% and 76.36%, respectively, as the DEM grid size increased from 2 to 80 cm. The paired t‐test and fractal analysis demonstrated the existence of a threshold DEM resolution (10 cm for the field plot), within which the DEM‐based hydrologic modelling was effective and acceptable. The effects of DEM resolution were further evaluated for a larger surface in the Prairie Pothole Region subjected to observed rainfall events. It was found that simulations based on coarser resolution DEMs (>10 m) tended to overestimate ponded areas and underestimate runoff discharge peaks. The simulated peak discharge from the Prairie Pothole Region surface reduced by approximately 50% as the DEM resolution changed from 2 to 90 m. Fractal analysis results elucidated scale dependency of hydrologic and topographic processes. In particular, scale analysis highlighted a unique constant–threshold–power relationship between DEM scale and topographic and hydrologic parameters/variables. Not only does this finding allow one to identify threshold DEM but also further develop functional relationships for scaling to achieve valid topographic characterization as well as effective and efficient hydrologic modelling. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

4.
Digital elevation models (DEMs) derived from ground‐based topographic surveys have become ubiquitous in the field of fluvial geomorphology. Their wide application in spatially explicit analysis includes hydraulic modeling, habitat modeling, and morphological sediment budgeting. However, there is a lack of understanding regarding the repeatability and precision of DEMs derived from ground‐based surveys conducted by different, and inherently subjective, observers. This is of particular concern when we consider the proportion of studies and monitoring programs that are implemented across multiple sites and over time by different observers. We used a case study from the Columbia Habitat Monitoring Program (CHaMP), where seven field crews sampled the same six sites, to quantify the magnitude and effect of observer variability on DEMs interpolated from total station surveys. We quantified the degree to which DEM‐derived metrics and measured geomorphic change were repeatable. Across all six sites, we found an average elevation standard deviation of 0.05 m among surveys, and a mean total range of 0.16 m. A variance partition between site, crew, and unexplained errors for several topographically derived metrics showed that crew variability never accounted for > 1.5% of the total variability. We calculated minor geomorphic changes at one site following a relatively dry flow year between 2012 and 2011. Calculated changes were minimal (unthresholded net changes ±1–3 cm) with six crews detecting an indeterminate sediment budget and one crew detecting a minor net erosional sediment budget. While crew variability does influence the quality of topographic surveys, this study highlights that when consistent surveying methods are employed, the data sets are still sufficient to support derivation of topographic metrics and conduct basic geomorphic change detection. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

5.
The resolution and accuracy of digital elevation models (DEMs) can affect the hydraulic simulation results for predicting the effects of glacial lake outburst floods (GLOFs). However, for the Tibetan Plateau, high‐quality DEM data are often not available, leaving researchers with near‐global, freely available DEMs, such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) and the Shuttle Radar Topography Mission data (SRTM) for hydraulic modelling. This study explores the suitability of these two freely available DEMs for hydraulic modelling of GLOFs. Our study focused on the flood plain of a potentially dangerous glacial lake in southeastern Tibet, to evaluate the elevation accuracy of ASTER GDEM and SRTM, and their suitability for hydraulic modelling of GLOFs. The elevation accuracies of ASTER GDEM and SRTM were first validated against field global position system (GPS) survey points, and then evaluated with reference to the relatively high precision of 1:50 000 scale DEM (DEM5) constructed from aerial photography. Moreover, the DEM5, ASTER GDEM and SRTM were used as basic topographic data to simulate peak discharge propagation, as well as flood inundation extent and depth in the Hydrologic Engineering Center's River Analysis System one‐dimensional hydraulic model. Results of the three DEM predictions were compared to evaluate the suitability of ASTER GDEM and SRTM for GLOF hydraulic modelling. Comparisons of ASTER GDEM and SRTM each with DEM5 in the flood plain area show root‐mean‐square errors between the former two as ± 15·4 m and between the latter two as ± 13·5 m. Although SRTM overestimates and ASTER GDEM underestimates valley floor elevations, both DEMs can be used to extract the elevations of required geometric data, i.e. stream centre lines, bank lines and cross sections, for flood modelling. However, small errors still exist in the cross sections that may influence the propagation of peak discharge. The flood inundation extent and mean water depths derived from ASTER GDEM predictions are only 2·2% larger and 2·3‐m deeper than that of the DEM5 predictions, whereas the SRTM yields a flood zone extent 6·8% larger than the DEM5 prediction and a mean water depth 2·4‐m shallower than the DEM5 prediction. The modelling shows that, in the absence of high‐precision DEM data, ASTER GDEM or SRTM DEM can be relied on for simulating extreme GLOFs in southeast Tibet. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

6.
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7.
To quantify landscape change resulting from processes of erosion and deposition and to establish spatially distributed sediment budgets, ‘models of change’ can be established from a time series of digital elevation models (DEMs). However, resolution effects and measurement errors in DEMs may propagate to these models. This study aimed to evaluate and to modify remotely‐sensed DEMs for an improved quantification of initial sediment mass changes in an artificially‐created catchment. DEMs were constructed from photogrammetry‐based, airborne (ALS) and ground‐based laser scanning (TLS) data. Regions of differing morphological characteristics and vegetation cover were delineated. Three‐dimensional (3D) models of volume change were established and mass change was derived from these models. DEMs were modified region‐by‐region for rill, interrill and alluvial areas, based on logical and hydro‐geomorphological principles. Additional DEMs were constructed by combining multi‐source, modified data. Models were evaluated by comparison with d‐GPS reference data and by considering sediment budget plausibility. Comprehensive evaluation showed that DEM usability depends on a relation between the technique used to obtain elevation data, surface morphology and vegetation cover characteristics. Photogrammetry‐based DEMs were suited to quantification of change in interrill areas but strongly underestimated surface lowering in erosion rills. TLS DEMs were best suited to rill areas, while ALS DEMs performed best in vegetation‐covered alluvial areas. Agreement with reference data and budget plausibility were improved by modifications to photogrammetry‐ and TLS‐based DEMs. Results suggest that artefacts in DEMs can be reduced and hydro‐geomorphic surface structures can be better represented by applying region‐specific modifications. Photogrammetry‐based DEMs can be improved by combining higher and lower resolution data in defined structural units and applying modifications based on principles given by characteristic hydro‐geomorphic evolution. Results of the critical comparative evaluation of remotely‐sensed elevation data can help to better interpret DEM‐based quantifications of earth‐surface processes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

8.
The eastern Himalaya syntaxis is located at the southeastern end of the Qinghai-Tibet Plateau and is the area where the Eurasian plate collides and converges with the Indian plate. The Namjabawa is the highest peak in the eastern section of the Himalayas, and the Yarlung Zangbo River gorge is around the Namjabawa Peak. The NE-striking Aniqiao Fault with right-lateral strike-slip is the eastern boundary fault of the Namjabawa syntaxis. Motuo Fault is in the east of and parallel to the Aniqiao Fault, distributing along the valley of the Yarlung Zangbo River. The section of Yarlung Zangbo River valley at the eastern side of the Namjabawa area is located in the southern foothills of the Himalayas and belongs to the subtropical humid climate zone with dense tropical rainforest vegetation. Dense vegetation, large terrain elevation difference, strong endogenetic and exogenic forces, and abundant valley deposition bring enormous difficulty to the research on active faults in this area. Since 1990s, surface morphology can be quantitatively expressed by digital elevation models as the rapid development of remote sensing technology. Geomorphic types and their characteristics can be quantified by geomorphological parameters which are extracted from DEM data, describing geomorphologic evolution and tectonic activity. But to date, researches based on quantitative geomorphic parameters are mainly focus on the differential uplift of regional blocks. In the study and mapping of active faults, surface traces of active faults are acquired by visual interpretation of remote sensing images. It has not been reported to identify the location of active faults via the change of quantitative geomorphic parameters. The distribution map of topographic elevation variation coefficient is suitable to reflect the regional erosion cutting and topographic relief, and the places with higher topographic elevation variation coefficient are more strongly eroded. In this paper, we attempt to identify the active faults and explore their distribution in the Yarlung Zangbo Gorge in the east of the Namjabawa Peak based on the application of two quantitative geomorphic parameters, namely, the topographic slope and the elevation variation coefficient. Using the DEM data of 30m resolution, two quantitative geomorphic parameters of topographic slope and elevation variation coefficient in Namjabawa and its surrounding areas were obtained on the ArcGIS software platform. On the topographic slope distribution map, the slope of the eastern and western banks of the Yarlung Zangbo River near Motuo is steep with a slope angle of more than 30°. Under the background of steep terrain, there are gentle slope belts of 5°~25° distributing intermittently and NE-striking. On the distribution map of topographic elevation variation coefficient, the elevation variation coefficient of the Yarlung Zangbo River near Motuo is greater than 0.9. On the background of the high topographic fluctuation area, it develops gently topographic undulating belts with elevation variation coefficient of 0.2~0.9. The belts are intermittently distributed and northeastern trending. Through the field geological and geomorphological investigation and trench excavation, it is found that the abnormal strips of the above-mentioned geomorphological parameters are the locations where the active faults pass. The above results show that the quantitative analysis of the topographic slope and the coefficient of variation of elevation can help us find active faults in areas with large terrain slope, serious vegetation coverage and high denudation intensity.  相似文献   

9.
Determining the extent of flooding is an important role of the hydrological research community and provides a vital service to planners and engineers. For large river systems located within distant settings it is practical to utilize a remote sensing approach. This study combines a remote sensing and geomorphic approach to delineate the extent of a large hurricane generated flood event in the lower Pánuco basin (98,227 km2), the seventh largest river system draining into the Gulf of Mexico. The lower Pánuco basin is located within the coastal plain of eastern Mexico and has a complex alluvial valley. Data sources included a Landsat 5TM and Landsat 7ETM+ scene, and topographic and particle size data from fieldwork and laboratory analysis. The Landsat 5TM image was acquired after the peak of a large flood event in 1993, whereas the Landsat 7ETM+ scene was acquired during the dry season in 2000. The increasing number of days between flood crest and the date of flood image acquisition along the river valley provided the opportunity to examine several methods of flood delineation and to consider differences in floodplain geomorphology. Backswamp environments were easily delineated in flooded reaches within the Panuco and Tamuin valleys, whereas in the Moctezuma valley more sophisticated methods were required because of the greater time between image acquisition and flood peak, and the complex floodplain topography. This included Principal Component (PC) analysis and image classification. Within the floodplain, residual Holocene terraces complicated flood mapping. Classification of both images allowed consideration of the influence of permanent standing water. Although the flooded areas were greater in the lower reaches of the study area, because this portion of the valley contained large floodplain lakes, the amount of inundation was actually lower. Remote sensing offers the ability to examine large alluvial valleys in distant settings but does not imply that geomorphic criteria should be excluded. Indeed, because of heterogeneous floodplain topography this study illustrates the importance of including field based geomorphic analysis so that the complexity of distinct floodplain environments are considered. The findings from this study are significant because most remote sensing data obtained for the purpose of flood mapping will not coincide with the flood crest. Thus, this study provides an appropriate method for mapping flood inundation in large and complex floodplain settings after flood crest recession.  相似文献   

10.
The horizontal accuracy of topographic data represented by digital elevation model (DEM) resolution brings about uncertainties in landscape process modeling with raster GIS. This paper presents a study on the effect of topographic variability on cell-based empirical estimation of soil loss and sediment transport. An original DEM of 10m resolution for a case watershed was re-sampled to three realizations of higher grid sizes for a comparative examination. Equations based on the USLE are applied to the watershed to calculate soil loss from each cell and total sediment transport to streams. The study found that the calculated total soil loss from the watershed decreases with the increasing DEM resolution with a linear correlation as spatial variability is reduced by cell aggregation. The USLE topographic factors (LS) extracted from applied DEMs represent spatial variability, and determine the estimations as shown in the modeling results. The commonly used USGS 30m DEM appears to be able to reflect essential spatial variability and suitable for the empirical estimation. The appropriateness of a DEM resolution is dependent upon specific landscape characteristics, applied model and its parameterization. This work attempts to provide a general framework for the research in the DEM-based empirical modeling.  相似文献   

11.
We derived a high‐resolution, spatially continuous map of erosion and deposition associated with the debris‐laden flows triggered by the 2011 Las Conchas wildfire and subsequent rainstorms over a 197 km2 area in New Mexico, USA. This map was produced using airborne‐LiDAR‐derived bare‐earth digital elevation models (DEMs) acquired approximately one year before and one year after the wildfire. Differencing of the pre‐wildfire and post‐wildfire‐and‐rainstorm bare‐earth DEMs yielded a DEM‐of‐difference (DoD) map that quantifies the magnitude of ground‐surface elevation changes due to erosion/deposition within each 1 m2 pixel. We applied a 0.3 m threshold filter to our DoD to remove changes that could have been due to artifacts and/or imperfect georeferencing. The 0.3 m value for the threshold filter was chosen based on the stated accuracy of the LiDAR as well as a comparison of areas of significant topographic change mapped in aerial photographs with those predicted using a range of candidate threshold values for the DoD filter. We developed an automated procedure that accepts the DoD map as input and computes, for every pixel in the DEM, the net sediment volume exported through each pixel by colluvial and/or fluvial processes using a digital routing algorithm. An analysis of the resulting sediment volume map for the Las Conchas fire demonstrates that sediment volume is proportional to upstream contributing area. After normalized by contributing area, the average sediment yield (defined as the sediment volume divided by the contributing area) increases as a power‐law functions of the average terrain slope and soil burn severity class (SBSC) with exponents equal to approximately 1.5. Our analysis quantifies the relationships among sediment yield, average terrain slope, and average soil burn severity class at the watershed scale and should prove useful for predicting the geomorphic response of wildfire‐affected drainage basins. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

12.
以皖南山区及大别山区27个中小流域为研究对象,基于数字高程模型DEM提取流域地貌信息,并计算流域平均洪峰滞时.通过建立多元线性回归及通径分析数学模型,探讨地貌因子对流域洪水响应过程的影响.结果表明:在流域系统水平,形状系数、圆度比、流域相对高差、河道分支频率以及森林覆盖率是影响流域平均洪峰滞时的主要指标,其中流域相对高差是相关系数最高的解释变量;各地貌因子间相互作用复杂,其多元线性回归模型对平均洪峰滞时的方差解释量为73.4%,其通径分析模型分别从直接作用及间接作用角度进一步合理阐述各变量对流域平均洪峰滞时的影响.本文可为皖南山区无资料地区分析洪水响应过程提供重要参考,对防洪减灾有显著意义.  相似文献   

13.
Flood hazard maps used to inform and build resilience in remote communities in the Terai region of southern Nepal are based on outdated and static digital elevation models (DEMs), which do not reflect dynamic river configuration or hydrology. Episodic changes in river course, sediment dynamics, and the distribution of flow down large bifurcation nodes can modify the extent of flooding in this region, but these processes are rarely considered in flood hazard assessment. Here, we develop a 2D hydrodynamic flood model of the Karnali River in the Terai region of west Nepal. A number of scenarios are tested examining different DEMs, variable bed elevations to simulate bed aggradation and incision, and updating bed elevations at a large bifurcation node to reflect field observations. By changing the age of the DEM used in the model, a 9.5% increase in inundation extent was observed for a 20-year flood discharge. Reducing horizontal DEM resolution alone resulted in a <1% change. Uniformly varying the bed elevation led to a 36% change in inundation extent. Finally, changes in bed elevation at the main bifurcation to reflect observed conditions resulted in the diversion of the majority of flow into the west branch, consistent with measured discharge ratios between the two branches, and a 32% change in inundation extent. Although the total flood inundation area was reduced (−4%), there was increased inundation along the west bank. Our results suggest that regular field measurements of bed elevation and updated DEMs following large sediment-generating events, and at topographically sensitive areas such as large river bifurcations, could help improve model inputs in future flood prediction models. This is particularly important following flood events carrying large sediment loads out of mountainous regions that could promote bed aggradation and channel switching across densely populated alluvial river systems and floodplains further downstream. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

14.
High-resolution topography data sets have improved the spatial and temporal scales at which we are able to investigate the landscape through the analysis of landform attributes and the computation of topographic changes. Yet, to date, there have been only limited attempts to infer key geomorphic processes in terms of contributions to shaping the landscape. Highly erodible landscapes such as badlands provide an ideal demonstration of such an approach owing to the rapid changes observed over a relatively short time frame. In this technical note we present the Mapping Geomorphic Processes in the Environment (MaGPiE): a new algorithm that allows mapping of geomorphic process signatures through analysis of repeat high-resolution topography data sets. The method is demonstrated in an experimental badland located in the southern central Pyrenees. MaGPiE is a geographic information system (GIS)-based algorithm that uses as input: (a) terrain attributes (i.e. Slope, Roughness and Concentrated Runoff Index) extracted from digital elevation models (DEMs), and (b) a map of topographic changes (DEM of difference, DoD). Initial results demonstrate that MaGPiE allows the magnitude and the spatial distribution of the main geomorphic processes reshaping badlands to be inferred for the first time. © 2020 John Wiley & Sons, Ltd.  相似文献   

15.
As an initial evaluation of the potential of digital elevation models (DEMs) and geographic information systems (GISs) for geomorphic characterization of rocky shorelines, airborne laser scan (ALS) data have been used to characterize shore platforms around Shag Point, southeastern New Zealand. The platforms have been characterized using field‐based techniques in previously published research, and therefore offer an ideal site for evaluation purposes. The main challenge involved the delineation of the shore platform area in terms of landward and seaward extents. The cliff top and landward edge of the shore platform was readily mapped, whereas the seaward edge of platforms was mapped with lesser precision due to difficulties associated with tidal inundation and the interference of wave action and surface water. In the central region of the study area (～0·1 km2) higher platform elevations and dense point cloud data enabled the generation of a high‐resolution (1 m) DEM. In analysing the DEM, ALS offered an advantage over the previous field survey in respect of the ability to assess continuous topography in plan‐view. The extent and form of two distinctive erosional surfaces is clearly apparent and was revealed through classifications based on slope and elevation. The spatial continuity of the upper surface implies that, in addition to the role of rock structure described in previous work, sea level and wave exposure may have been important factors in the generation and preservation of platform morphology at Shag Point. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
Digital elevation models (DEMs) that are used in hydrological applications must be processed to remove sinks, mainly topographic depressions. Flow enforcement techniques include filling methods, which raise elevations within depressions, breaching, which carves channels through blockages, and hybrid methods. Despite previous research demonstrating the large impact to DEMs and subsequent analyses of depression filling, it is common practice apply this technique to flow enforcement. This is partly because of the greater efficiency of depression filling tools compared to breaching counterparts, which often limits breaching to applications of small‐ to moderate‐sized DEMs. A new hybrid flow enforcement algorithm is presented in this study. The method can be run in complete breaching, selective breaching (either breached or filled), or constrained breaching (partial breaching) modes, allowing for greater flexibility in how practitioners enforce continuous flow paths. Algorithm performance was tested with DEMs of varying topography, spatial extents, and resolution. The sites included three moderate sized DEMs (52 000 000 to 190 000 000 cells) and three massive DEMs of the Iberian Peninsula, and the Amazon and Nile River basins, the largest containing nearly one billion cells. In complete breaching mode, the new algorithm required 87% of the time needed by a filling method to process the test DEMs, while the selective breaching and constrained breaching modes, operating with maximum breach depth constraints, increased run times by 8% and 27% respectively. Therefore, the new algorithm offers comparable performance to filling and the ability to process massive topographic data sets, while giving practitioners greater flexibility and lowering DEM impact. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
The effects of large floods on river morphology are variable and poorly understood. In this study, we apply multi‐temporal datasets collected with small unmanned aircraft systems (UASs) to analyze three‐dimensional morphodynamic changes associated with an extreme flood event that occurred from 19 to 23 June 2013 on the Elbow River, Alberta. We documented reach‐scale spatial patterns of erosion and deposition using high‐resolution (4–5 cm/pixel) orthoimagery and digital elevation models (DEMs) produced from photogrammetry. Significant bank erosion and channel widening occurred, with an average elevation change of ?0.24 m. The channel pattern was reorganized and overall elevation variation increased as the channel adjusted to full mobilization of most of the bed surface sediments. To test the extent to which geomorphic changes can be predicted from initial conditions, we compared shear stresses from a two‐dimensional hydrodynamic model of peak discharge to critical shear stresses for bed surface sediment sizes. We found no relation between modeled normalized shear stresses and patterns of scour and fill, confirming the complex nature of sediment mobilization and flux in high‐magnitude events. However, comparing modeled peak flows through the pre‐ and post‐flood topography showed that the flood resulted in an adjustment that contributes to overall stability, with lower percentages of bed area below thresholds for full mobility in the post‐flood geomorphic configuration. Overall, this work highlights the potential of UAS‐based remote sensing for measuring three‐dimensional changes in fluvial settings and provides a detailed analysis of potential relationships between flood forces and geomorphic change. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

18.
Quantifying the morphology of braided rivers is a key task for understanding braided river behaviour. In the last decade, developments in geomatics technologies and associated data processing methods have transformed the production of precise, reach‐scale topographic datasets. Nevertheless, generating accurate Digital Elevation Models (DEMs) remains a demanding task, particularly in fluvial systems. This paper identifies a threefold set of challenges associated with surveying these dynamic landforms: complex relief, inundated shallow channels and high rates of sediment transport, and terms these challenges the ‘morphological’, ‘wetted channel’ and ‘mobility’ problems, respectively. In an attempt to confront these issues directly, this paper presents a novel survey methodology that combines mobile terrestrial laser scanning and non‐metric aerial photography with data reduction and surface modelling techniques to render DEMs from the resulting very high resolution datasets. The approach is used to generate and model a precise, dense topographic dataset for a 2.5 km reach of the braided Rees River, New Zealand. Data were acquired rapidly between high flow events and incorporate over 5 x 109 raw survey observations with point densities of 1600 pts m‐2 on exposed bar and channel surfaces. A detailed error analysis of the resulting sub‐metre resolution is described to quantify DEM quality across the entire surface model. This reveals unparalleled low vertical errors for such a large and complex surface model; between 0.03 and 0.12 m in exposed and inundated areas of the model, respectively. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

19.
Digital elevation models (DEMs) at different resolutions (180, 360, and 720 m) are used to examine the impact of different levels of landscape representation on the hydrological response of a 690‐km2 catchment in southern Quebec. Frequency distributions of local slope, plan curvature, and drainage area are calculated for each grid size resolution. This landscape analysis reveals that DEM grid size significantly affects computed topographic attributes, which in turn explains some of the differences in the hydrological simulations. The simulations that are then carried out, using a coupled, process‐based model of surface and subsurface flow, examine the effects of grid size on both the integrated response of the catchment (discharge at the main outlet and at two internal points) and the distributed response (water table depth, surface saturation, and soil water storage). The results indicate that discharge volumes increase as the DEM is coarsened, and that coarser DEMs are also wetter overall in terms of water table depth and soil water storage. The reasons for these trends include an increase in the total drainage area of the catchment for larger DEM cell sizes, due to aggregation effects at the boundary cells of the catchment, and to a decrease in local slope and plan curvature variations, which in turn limits the capacity of the watershed to transmit water downslope and laterally. The results obtained also show that grid resolution effects are less pronounced during dry periods when soil moisture dynamics are mostly controlled by vertical fluxes of evaporation and percolation. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
The ability to quantify the processes driving geomorphic change in river valley margins is vital to geomorphologists seeking to understand the relative role of transport mechanisms (e.g. fluvial, aeolian, and hillslope processes) in landscape dynamics. High‐resolution, repeat topographic data are becoming readily available to geomorphologists. By contrasting digital elevation models derived from repeat surveys, the transport processes driving topographic changes can be inferred, a method termed ‘mechanistic segregation.’ Unfortunately, mechanistic segregation largely relies on subjective and time consuming manual classification, which has implications both for its reproducibility and the practical scale of its application. Here we present a novel computational workflow for the mechanistic segregation of geomorphic transport processes in geospatial datasets. We apply the workflow to seven sites along the Colorado River in the Grand Canyon, where geomorphic transport is driven by a diverse suite of mechanisms. The workflow performs well when compared to field observations, with an overall predictive accuracy of 84% across 113 validation points. The approach most accurately predicts changes due to fluvial processes (100% accuracy) and aeolian processes (96%), with reduced accuracy in predictions of alluvial and colluvial processes (64% and 73%, respectively). Our workflow is designed to be applicable to a diversity of river systems and will likely provide a rapid and objective understanding of the processes driving geomorphic change at the reach and network scales. We anticipate that such an understanding will allow insight into the response of geomorphic transport processes to external forcings, such as shifts in climate, land use, or river regulation, with implications for process‐based river management and restoration. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

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