Use of ground and air-based photogrammetry for soil erosion assessment

Water erosion affects all types of soils around the world at different intensities. However, in tropics water erosion is the most important form of soil erosion and has received much concern in the last decades. The major challenge in soil conservation is the development and implementation of strategies to mitigate the erosion processes in urban and rural areas. Thus, understanding the processes involved in each type of water erosion (sheet, rill and gully erosion), as well as its quantification, is a key factor in managing and developing soil conservation and erosion mitigation strategies. In that way, this thesis aims to investigate the efficiency of ground and air-based photogrammetry for soil erosion assessment, as well as to address some gaps in our understanding of the evolution of erosive processes in its different forms of occurrence. In doing so, we evaluated the factors that influence the development of erosion in micro and macro scales, with experiments in the laboratory and in the field. In the first chapter, it was evaluated the influence of gradient change and runoff volumes on rill erosion process, using digital close-range photogrammetry in a laboratory soil flume. In addition, morphological rill parameters were estimated to allow a better understanding of the rill erosion behaviour under different treatments. The results showed that the flow velocity in rills increased with water flow and slope, showing a strong correlation with the amount of rill erosion. On steep slopes the soil erosion was dominated by the rill erosion with less rill network density while, on low slopes, there were other types of soil erosion occurring together with rill erosion, causing the reduction of soil loss due to rill erosion. The digital close-range photogrammetry technique provided millimetric precision, which is sufficient for rill erosion investigations. In the second chapter aimed to evaluate the efficiency of SfM based on UAV images in obtaining accurate measurements of soil loss in areas of sheet erosion, under natural rainfall, where channelized erosion is not the principal mechanism. The measurements acquired from SfM were compared to the sediments collected in each soil erosion plots. The results of the soil losses obtained by UAV-SfM presented a high correlation with the sediments collected in the plots. This is of great relevance in the context of the monitoring and modelling of water erosion, since the quantification of soil loss around the world is mainly done using plots, a method that presents high operational cost. In addition, the study of laminar erosion through the UAV-SfM allows not only to calculate the soil loss values but to visualize the spatial variation of the erosion process (detachment, transport and deposition) practically in real time along the area. In the third chapter it was evaluated the application of UAV-SfM technique in a gully system. For the first time, a study was carried out evaluating the relative contribution of the different types of erosion (sheet, rill and gully sidewall) in the gully development. This was possible due to the millimetric level of precision of the point clouds, allowing to evaluate even the contribution of the laminar erosion, which is new in gullies studies. As a result, it was possible to quantify sediments volumes stored in the channels and lost from the gully system, as well as to determine the main sediment sources. The study suggests that the main source of sediments in the gully was due to the mass movements, followed by rills and sheet erosion. The UAV-SfM proved to be effective in the gully monitoring. The results findings by this thesis indicate that the use of ground and air-based photogrammetry are precise tools in detecting soil surface changes and can be used to assess water erosion in its various forms of occurrence in nature. In addition, the UAV-SfM has proven to be a very useful technique for monitoring soil erosion over time, especially in hard-to-reach areas

UAVs for the Environmental Sciences

This book gives an overview of the usage of UAVs in environmental sciences covering technical basics, data acquisition with different sensors, data processing schemes and illustrating various examples of application

Multi-Scale detection, mapping, and modelling geomorphic change in gravel-bed rivers with UAV remote sensing

Fluvial science is in particular need of surveying tools which can rapidly and accurately capture topographic data. The use of low-cost, consumer grade UAV (unmanned aerial vehicle) systems and Structure from Motion (SfM) processing methods has seen successful adoption by many other earth surface processes sub-fields however their use for monitoring within the field of fluvial geomorphology remains limited. This study tests the applicability of UAV photogrammetry to fluvial surveying, capturing centimetric resolution data across kilometric scales, providing an ideal perspective for geomorphic process interpretation. For a historically modified UK case study, four series of very high resolution DEMs (digital elevation model) and orthomosaic imagery are produced for a 2km reach of quasi-wandering gravel-bed river. Comparative analyses of DEMs between 2016 and 2018 reveals widening of the incised margin and significant geomorphic evolution characteristic of re-naturalization following the termination of gravel mining, channelization, and resultant aggressive incision. Whole reach volumetric analysis reveals a negative sediment budget approximating a net loss of 250m3/year. Budgetary segregation shows 22% of eroded material is sourced from the banks of the inset wandering margin and is a possible cause of a general fining (30% reduction in mean b axis) of bed material within active channels, detectable by grain scale analysis of high-resolution orthomosaic imagery. Vertical scour is seen to be prevented, even under extreme flows (~100 m3/s-1), by a bed armouring effect which is sustained by liberation of coarse clasts from the floodplain via lateral erosion and bank collapse. Woody debris dynamics, gravel bar creation and migration are intricately modelled throughout the site, their presence seen to be affecting flow-prioritization of sub-channels inside the incised margin. UAV surveying workflows and processing protocols are also developed for fluvial science: A means to neutralize and filter out surface error caused by vegetation occlusion in the SfM workflow, and a method to correct for geo-referencing error in large DEMs. Geomorphic findings at this UK case study hold valuable and transferable insights to river re-naturalization in the context of gravel extraction and channelization

Geomorphometry 2020. Conference Proceedings

Geomorphometry is the science of quantitative land surface analysis. It gathers various mathematical, statistical and image processing techniques to quantify morphological, hydrological, ecological and other aspects of a land surface. Common synonyms for geomorphometry are geomorphological analysis, terrain morphometry or terrain analysis and land surface analysis. The typical input to geomorphometric analysis is a square-grid representation of the land surface: a digital elevation (or land surface) model. The first Geomorphometry conference dates back to 2009 and it took place in Zürich, Switzerland. Subsequent events were in Redlands (California), Nánjīng (China), Poznan (Poland) and Boulder (Colorado), at about two years intervals. The International Society for Geomorphometry (ISG) and the Organizing Committee scheduled the sixth Geomorphometry conference in Perugia, Italy, June 2020. Worldwide safety measures dictated the event could not be held in presence, and we excluded the possibility to hold the conference remotely. Thus, we postponed the event by one year - it will be organized in June 2021, in Perugia, hosted by the Research Institute for Geo-Hydrological Protection of the Italian National Research Council (CNR IRPI) and the Department of Physics and Geology of the University of Perugia. One of the reasons why we postponed the conference, instead of canceling, was the encouraging number of submitted abstracts. Abstracts are actually short papers consisting of four pages, including figures and references, and they were peer-reviewed by the Scientific Committee of the conference. This book is a collection of the contributions revised by the authors after peer review. We grouped them in seven classes, as follows: • Data and methods (13 abstracts) • Geoheritage (6 abstracts) • Glacial processes (4 abstracts) • LIDAR and high resolution data (8 abstracts) • Morphotectonics (8 abstracts) • Natural hazards (12 abstracts) • Soil erosion and fluvial processes (16 abstracts) The 67 abstracts represent 80% of the initial contributions. The remaining ones were either not accepted after peer review or withdrawn by their Authors. Most of the contributions contain original material, and an extended version of a subset of them will be included in a special issue of a regular journal publication

Flow-3D CFD model of bifurcated open channel flow: setup and validation

Bifurcation is a morphological feature present in most of fluvial systems; where a river splits into two channels, each bearing a portion of the flow and sediments. Extensive theoretical studies of river bifurcations were performed to understand the nature of flow patterns at such diversions. Nevertheless, the complexity of the flow structure in the bifurcated channel has resulted in various constraints on physical experimentation, so computational modelling is required to investigate the phenomenon. The advantages of computational modelling compared with experimental research (e.g. simple variable control, reduced cost, optimize design condition etc.) are widely known. The great advancement of computer technologies and the exponential increase in power, memory storage and affordability of high-speed machines in the early 20th century led to evolution and wide application of numerical fluid flow simulations, generally referred to as Computational Fluid Dynamics {CFD). In this study, the open-channel flume with a lateral channel established by Momplot et al (2017) is modelled in Flow-3D. The original investigation on divided flow of equal widths as simulated in ANSYS Fluent and validated with velocity measurements

Multi-scale assessment of shore platform erosion

The morphology and erosion of shore platforms is a pivotal component of rocky coast evolution as these features control both wave transformation and sediment dynamics. Models that predict coastline evolution and efforts to reconstruct past cliff retreat rates from cosmogenic isotope concentrations are forced to simplify platform morphology and commonly treat erosion only implicitly. The lack of an explicit incorporation of platform dynamics into such models reflects a poor understanding of erosion processes that have conventionally been considered to operate at one of two scales: fine scale abrasion captured by sub-mm precision point measurements of vertical change, and step back-wearing and block removal at metre-scale. Neither approach is well suited to informing a generalised model of foreshore erosion that bridges these two scales or that can be applied more widely. As a result without understanding mechanisms of foreshore erosion models which use these data are limited in their utility to address future coastal change under changing sea level and storminess. To address this a multi-scale study was undertaken along the North Yorkshire coast (UK) using high-resolution and high-precision monitoring data collected at the spatial and temporal scales relevant to the processes in action. A novel method was developed to monitor mm-scale platform erosion using Structure-from-Motion (SfM) photogrammetry. The average platform down-wearing rate of 0.528 mm yr-1 was calculated from 15 individual 0.5×0.5 m sites. The volume frequency and 3D-shape distributions of the detachments suggest that erosion occurs predominantly via detachment of fabric-defined platelets. The erosion rate is faster closer to the cliff toe and at those locations where the tide cycles more frequently. Erosion rates calculated from the 2.6 years of data from 22 km of shore platform using high-resolution airborne LiDAR was 3.45 mm yr-1 when derived from individual detachments, or 0.01 mm yr-1 when spatially averaged across the platform. Average lowering of the platform sections containing steps was 0.04 mm yr-1, while in areas with no steps 0.01 mm yr-1. Whilst erosion rate cannot be predicted with confidence for any discrete point on the foreshore, systematic trends in across-shore erosion can be shown, with a peak in rate at 10-18 m from the cliff toe, with erosion intensity gradually decreasing seawards. This new understanding of foreshore erosion has then been used to predict exposure ages from cosmogenic 10Be concentrations at the Hartle Loup platform. This analysis shows that the cliff has been retreating at the steady rate of 0.05 m yr-1 cutting the 300 m wide shore platform in the last 6 kyr. This derives rates of retreat comparable to contemporary erosion monitoring. Platform morphology has been shown not to adjust to an equilibrium shape, but it is rather actively modified depending on the interplay between present morphology, sea level and tidal regime. Importantly, this study provides methods to monitor foreshore erosion, enhances our understanding of mechanisms and controls upon it, whilst the results can be used in models to predict rocky coast evolution by providing an empirically-based assessment of foreshore erosion

Proceedings from the 1992 national conference

Presented at Irrigation and water resources in the 1990's: proceedings from the 1992 national conference held on October 5-7, 1992 in Phoenix, Arizona.Includes bibliographical references.Sponsored by U.S. Committee on Irrigation and Drainage.Interdisciplinary teams for assessing the performance of irrigated agriculture systems -- Putah South Canal remote acoustic water level monitoring and flow measurement -- Decentralized constant-volume control of irrigation canals -- Field manufacture and application of reinforced plastic canal and pipe linings -- Improving channel maintenance methods for Egypt's irrigation systems -- Routing flood water through an irrigation delivery system -- Experience with flexible schedules and automation on pilot projects -- Canal linings used by the Bureau of Reclamation with emphasis on rehabilitation -- The California Farm Water Coalition: telling thirsty Californians why agriculture needs water -- Institutional framework and challenges in management of agricultural water use in South Florida -- Technology transfer lessons from a U.S. water district -- Management of water conservation through irrigation system modernization and rehabilitation -- Artificial recharge of groundwater -- Long-term storage through indirect recharge -- Mitigating agricultural impacts on groundwater through desalination -- Agriculture's impact on water resources in Eastern Europe: Bulgaria, Hungary, and Romania -- How probiotic fertilizers improve irrigation efficiency, buffer salts, and reduce nitrate infiltration into groundwater -- Drought, supply shortages and E.S.A.: can the farmer survive? -- Avoiding pitfalls in canal automation -- AZSCHED computer software for irrigation scheduling -- Determination of irrigated crops consumptive water use by remote sensing and GIS techniques for river basins -- GIS and conjunctive use for irrigated agriculture -- Mapping technology in the '90's for GIS applications to irrigation and drainage