1,721,105 research outputs found
Global junction angle dataset
Full text linkA global dataset of channel junction angles.
File is a zipped csv file.
Data is extracted using LSDTopoTools (https://github.com/LSDtopotools). The DEM underlying this data is NASA’s 30 m resolution void-filled Shuttle Radar Topography Mission Digital Elevation Model Version 3 (SRTM-DEM).
Dataset headers: latitude (decimal degrees), longitude (decimal degrees), donor1_stream_order (Horton-Strahler stream order of first tributary), donor2_stream_order (Horton-Strahler stream order of second tributary), receiver_stream_order (Horton-Strahler stream order of the channel formed at the junction), donor1_drainage_area (m2), donor2_drainage_area (m2), this_junction_drainage_area (m2), donors_junction_angle (°), donor1_receiver_junction_angle (°), donor2_receiver_junction_angle (°), gradient_donor1, gradient_donor2, gradient_receiver, ai (aridity index value from Trabucco et al., (2019)), AR (ratio of tributary drainage areas), AI_class (as according to Trabucco et al., (2019))junction_angles_global.zip: A zipped file that contains a single csv file, junction_angles_global.csv
This file contains the headers:
latitude (decimal degrees), longitude (decimal degrees), donor1_stream_order (Horton-Strahler stream order of first tributary), donor2_stream_order (Horton-Strahler stream order of second tributary), receiver_stream_order (Horton-Strahler stream order of the channel formed at the junction), donor1_drainage_area (m2), donor2_drainage_area (m2), this_junction_drainage_area (m2), donors_junction_angle (°), donor1_receiver_junction_angle (°), donor2_receiver_junction_angle (°), gradient_donor1, gradient_donor2, gradient_receiver, ai (aridity index value from Trabucco et al., (2019)), AR (ratio of tributary drainage areas), AI_class (as according to Trabucco et al., (2019)
Reproducible topographic analysis
No full text© 2020 Elsevier B.V. The ability to reproduce the results of an experiment is a fundamental component of the scientific method. However, precisely what is meant by the terms replicable and reproducible often varies between and within disciplines. Here, we present clear definitions of these two terms for geomorphic research and communicate the importance of performing reproducible analysis of remotely sensed topographic data. We argue that the reproducibility of an analysis is not a static, binary state but rather that there is a continuum from irreproducibility to replicability, with reproducibility falling between the two and that the aim of a researcher should be to get as close to reproducibility as possible, favoring a pragmatic rather than dogmatic approach. A brief review of the development of topographic analysis as a discipline is used to highlight the progress made in making topographic analysis more reproducible, and the challenges inherent within common working patterns. The chapter concludes with a series of recommendations on how best to achieve reproducible topographic analysis
Sediment accumulation in embayments controlled by bathymetric slope and wave energy: Implications for beach formation and persistence
Full text linkHigh energy, rocky coastlines often feature sandy beaches within headland‐bound embayments. Not all such embayments have beaches however, and beaches in embayments can be removed by storms and may subsequently reform. What dictates the presence or absence of an embayed beach and its resilience to storms? In this paper, we explore the effect of offshore slope and wind conditions on nearshore sediment transport within idealised embayments to give insight into nearshore sediment supplies. We use numerical simulations to show that sand can accumulate near shore if the offshore slope is >0.025 m/m, but only under persistent calm conditions. Our modelling also suggests that if sediment in an embayment with an offshore gradient steeper than 0.025 m/m is removed during a period of persistent stormy conditions, it will be unlikely to return in sub‐decadal timescales. In contrast, sediment located in embayments with shallower gradients can reform swiftly in both calm and stormy conditions. Our findings have wide implications for contemporary coastal engineering in the face of future global climate change, but also for Quaternary environmental reconstruction. Our simple method to predict beach stability based on slope can be used to interpret differing responses of embayments to periods of changing coastal storminess such as the medieval climate anomaly‐little ice age (MCA‐LIA) transition. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd
How long is a hillslope?
Full text linkHillslope length is a fundamental attribute of landscapes, intrinsically linked to drainage density, landslide hazard, biogeochemical cycling and hillslope sediment transport. Existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope–area scaling, where the hillslope domain transitions into the fluvial domain. Here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model (DEM), based on flow directions calculated using pixel aspect, until reaching the channel network, defined using recently developed channel extraction algorithms. Through comparisons between these measurement techniques, we show that estimating hillslope length from plots of topographic slope versus drainage area, or by inverting measures of drainage density, systematically underestimates hillslope length. In addition, hillslope lengths estimated by slope–area scaling breaks show large variations between catchments of similar morphology and area. We then use hillslope length–relief structure of landscapes to explore nature of sediment flux operating on a landscape. Distinct topographic forms are predicted for end-member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient. Because our method extracts hillslope profiles originating from every ridgetop pixel in a DEM, we show that the resulting population of hillslope length–relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes. We find that across a broad range of sites across the continental United States, topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient
Characteristics of wind waves in shallow tidal basins and how they affect bed shear stress, bottom erosion, and the morphodynamic evolution of coupled marsh and mudflat landforms
No full textA nondimensional relief framework: data
No full textConsidering the relationship between erosion rate and the relief structure of a landscape within a nondimensional framework facilitates the comparison of landscapes undergoing forcing at a range of scales, and allows broad-scale patterns of landscape evolution to be observed. We present software which automates the extraction and processing of relevant topographic parameters to rapidly generate nondimensional erosion rate and relief data for any landscape where high-resolution topographic data are available. Individual hillslopes are identified using a connected-components technique which allows spatial averaging to be performed over geomorphologically meaningful spatial units, without the need for manual identification of hillslopes. The software is evaluated on four landscapes across the continental United States, three of which have been studied previously using this technique. We show that it is possible to identify whether landscapes are in topographic steady state. In locations such as Cascade Ridge, CA, a clear signal of an erosional gradient can be observed. In the southern Appalachians, nondimensional erosion rate and relief data are interpreted as evidence for a landscape decaying following uplift during the Miocene. An analysis of the sensitivity of this method to free parameters used in the data smoothing routines is presented which allows users to make an informed choice of parameters when interrogating new topographic data using this method. A method to constrain the critical gradient of the nonlinear sediment flux law is also presented which provides an independent constraint on this parameter for three of the four study landscapes.Grieve, Stuart; Mudd, Simon; Hurst, Martin; Milodowski, David. (2016). A nondimensional relief framework: data, [dataset]. University of Edinburgh. School of GeoSciences.. http://dx.doi.org/10.7488/ds/1366
Geomorphometric delineation of floodplains and terraces from objectively defined topographic thresholds
Full text linkFloodplain and terrace features can provide information about current and past fluvial processes, including channel response to varying discharge and sediment flux; sediment storage; and the climatic or tectonic history of a catchment. Previous methods of identifying floodplain and terraces from digital elevation models (DEMs) tend to be semi-automated, requiring the input of independent datasets or manual editing by the user. In this study we present a new, fully automated method of identifying floodplain and terrace features based on two thresholds: local gradient, and elevation compared to the nearest channel. These thresholds are calculated statistically from the DEM using quantile-quantile plots and do not need to be set manually for each landscape in question. We test our method against field-mapped floodplain initiation points, published flood hazard maps, and digitised terrace surfaces from seven field sites from the US and one field site from the UK. For each site, we use high-resolution DEMs derived from light detection and ranging (LiDAR) where available, as well as coarser resolution national datasets to test the sensitivity of our method to grid resolution. We find that our method is successful in extracting floodplain and terrace features compared to the field-mapped data from the range of landscapes and grid resolutions tested. The method is most accurate in areas where there is a contrast in slope and elevation between the feature of interest and the surrounding landscape, such as confined valley settings. Our method provides a new tool for rapidly and objectively identifying floodplain and terrace features on a landscape scale, with applications including flood risk mapping, reconstruction of landscape evolution, and quantification of sediment storage routing
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