Combining SfM Photogrammetry and Terrestrial Laser Scanning to Assess Event-Scale Sediment Budgets along a Gravel-Bed Ephemeral Stream

Abstract

Stream power represents the rate of energy expenditure along a stream reach and can be calculated using topographic data acquired via structure-from-motion (SfM) photogrammetry and terrestrial laser scanning (TLS). This study sought to quantitatively relate morphological adjustments in the Azohía Rambla, a gravel-bed ephemeral stream in southeastern Spain, to stream power (ω), critical power (ωc), and energy gradients (∂ω/∂s), along different reference channel reaches of 200 to 300 m in length. High-resolution digital terrain models (HRDTMs), combined with ortophotographs and point clouds from 2018, 2019, and 2020, and ground-based surveys, were used to estimate the spatial variability of morphological sediment budgets and to assess channel bed mobility during the study period at different spatial scales: reference channel reaches (RCRs), pilot bed survey areas (PBSAs), and representative geomorphic units (RGUs). The optimized complementary role of the SfM technique and terrestrial laser scanning allowed the generation of accurate and reliable HRDTMs, upon which a 1-D hydrodynamic model was calibrated and sediment budgets calculated. The resulting high-resolution maps allowed a spatially explicit analysis of stream power and transport efficiency in relation to volumes of erosion and deposition in the RCR and PBSA. In addition, net incision or downcutting and vertical sedimentary accretion were monitored for each flood event in relation to bedforms and hydraulic variables. Sediment sources and sinks and bed armoring processes showed different trends according to the critical energy and stream power gradient, which were verified from field observations. During flows exceeding bankfull discharges (between 18 and 24 m3s−1 according to channel reach), significant variations in ∂ω/∂s values and ω/ωc ratios (e.g., −15< ∂ω/∂s <15 Wm−3; ω/ωc >2 for a peak discharge of 31 m3s−1) were associated with a large amount of bedload mobilized upstream and vertical accretion along the middle reach (average rise height of 0.20 to 0.35 m for the same event). By contrast, more moderate peak flows (≤10 m3s−1) only produced minor changes resulting in surface washing, selective transport, and local bed scouring.

Landslide-Induced Mass Transport of Radionuclides along Transboundary Mailuu-Suu River Networks in Central Asia

“…Besides radioactive contamination of the landslide itself, the run-out or generated impulse wave may further cause damage to nearby houses, infrastructure, or pasture land [24,57]. It was demonstrated that the landslide could cause considerable change in water quality with large increases in the concentration of suspended solids and toxic elements [33,39,58]. Therefore, the instantaneous release of Pb-210 that is associated with the release of the suspended sediment was studied in this paper.…”

Identifying Changes in Sediment Texture along an Ephemeral Gravel-Bed Stream Using Electrical Resistivity Tomography 2D and 3D

“…Often, these bed-forms are composed on poorly sorted sediments with mixed grain sizes (sand, gravel, and pebbles). Deposits of different textures alternate in depth with a general tendency to increase in grain size from the bottom up [11]. This alluvial fill rests mainly on a Miocene marl substrate, the fine texture of which contrasts with that of the overlying coarse detrital materials.…”

“…Electrical resistivity tomography (ERT) is a non-invasive method of rapid application, which is usually used to generate models of distributions of electrical properties of the subsurface, from which the geological structure and hydrogeological variations can be inferred [7][8][9]. Additionally, ERT can be employed to map spatial variations of qualities within a mineral deposit in 3D [10,11]. Several authors conducted ERT surveys to study loose materials, assess mine tailings, and so forth [12][13][14][15].…”

Cultural Heritage Restoration of a Hemispherical Vault by 3D Modelling and Projection of Video Images with Unknown Parameters and from Unknown Locations

“…Although a photograph usually provides the interpretation of any visible element (there are many cases where other types of images result in being more convenient [12]), the laser contributes its geometry with a very high degree of precision, automatically and in a short space of time [13][14][15][16][17]. Due to the laser scanner, the application of both techniques together allows for non-invasive reverse engineering processes where no contact with the element is necessary [18][19][20][21][22], which is especially relevant in heritage studies [23]. Cultural heritage is one of the fields with more different applications of combined techniques (as many different sciences are applied together in restoration works).…”