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Bedrock rivers shape the surface of the planet and respond to changes in tectonic and climatic forcings. The rate of bedrock river incision is set by the local channel morphology, rock material strength, and the flux and caliber of sediment in the landscape. Both the erodibility of in-channel bedrock and the grain size of sediment supplied to the channel can be influenced by rock properties, leading to a complex suite of local and non-local lithologic controls on channel morphology. Quantifying each property at the landscape scale is challenging, as rock strength and channel morphology can vary over small spatial scales, and local sediment properties vary over time. Recent advances in small uncrewed aerial vehicle (UAV) technology and structure from motion photogrammetry enable mapping at high enough resolution to resolve patterns in sediment cover, channel geometry, and rock properties, while mapping across large enough spatial scales to integrate across reach scale heterogeneity. In addition, repeat surveys enable tracking sediment transport and channel adjustment through time. Here, I take advantage of natural gradients in metamorphic grade and exhumation depth in the Taiwan Central Range to characterize how rock material properties develop across an orogen and influence channel morphology and sediment. Paired UAV photogrammetry and field surveys span over 53 kilometers of river channel, with 30 km confined to of bedrock-bound channels, and over 10 kilometers of repeat surveys. These surveys sample systematically across all formations and lithologies present in the range. I directly measured channel morphology and sediment cover in each surveyed channel and tributary from 1-5 cm resolution 3D models and orthoimagery. I then use repeat surveys to analyze patterns in clast mobility. These measurements reveal that the size and number of boulders supplied to the channel from hillslope mass wasting systematically increase across both the west to east gradient in metamorphic grade and the south to north gradient in exhumation depth. Channel morphology (slope, width, and depth) is highly variable both within individual reaches, and across the orogen. The increase in boulder size locally steepens the channel, implying that the addition of coarse sediment increases thresholds for incision. However, while the measured grain sizes and slopes both increase from south to north, there is no observed trend in orogen scale relief. On the other hand, while Taiwan has substantial variation in channel width, boulder abundance and size do not set channel width at the reach or orogen scale. Instead, variations in channel width are primarily controlled by bedrock anisotropy and variations in bedrock wall lithology. Finally, repeat surveys reveal that boulder transport and abrasion occurs during 1-3 year storm events. Bed reorganization enhances boulder abrasion, and the selective transport of large clasts imply that boulder residence time in this system is likely shorter than the timescale of bedrock river incision. Ultimately, high resolution surveys reveal local and regional controls on bedrock river incision, set by the interplay of rock strength, sediment, and channel morphology. These observations provide a critical link between theory derived from physics at the local scale, and models of erosion at the landscape scale.
Interpreting spatial patterns in rates of fluvial incision from river channel elevation long profile data requires an assumption that tectonic uplift rate governs river channel slope. However, application of the most mechanistically explicit description of river incision [Sklar and Dietrich,2004] suggests that sediment flux and sediment grain size, not rock uplift rate, control river channel slopes in many settings. Because it is usually difficult to independently constrain sediment supply, tectonic interpretations of river elevation long profiles are necessarily uncertain. Here we exploit a natural experiment in Boulder Creek, a ~ 30 km2 drainage in the Santa Cruz Mountains,CA USA in order isolate the affect of grain size and relative sediment supply on river channel slope in an actively uplifting landscape along a restraining bend in the San Andreas Fault.
"The Liwu River runs a short course; its channel head at the water divide in Taiwan's Central Range is a mere 35 km from its outflow into the Pacific Ocean. But in those short 35 km, the Liwu has carved one of the world's geographic wonders: the spectacular Taroko Gorge with marble and granite walls soaring nearly 1000 m above the river channel. Taroko Gorge was a fitting venue for a 2003 Penrose Conference that addressed the coupled processes of tectonics, climate, and landscape evolution. The young mountains, extreme weather, and dramatic landforms provided an appropriate backdrop to wide-ranging discussions of geomorphic processes, climate and meteorology, sediment generation and transport, the effects of erosion on tectonics, and new analytical and modeling tools used to address these processes and problems. This volume's papers extend that discussion, reaching across fields that have experienced rapid advances in the past decade."--Publisher's website.
Libro de abstracts del congreso celebrado en Santander en junio de 2013.
Australian Landscapes provides an up-to-date statement on the geomorphology of Australia. Karst, desert, bedrock rivers, coasts, submarine geomorphology, biogeomorphology and tectonics are all covered, aided by the latest geochronological techniques and remote sensing approaches. The antiquity and enduring geomorphological stability of the Australian continent are emphasized in several chapters, but the cutting-edge techniques used to establish that stability also reveal much complexity, including areas of considerable recent tectonic activity and a wide range of rates of landscape change. Links to the biological sphere are explored, in relation both to the lengthy human presence on the continent and to a biota that resulted from Cenozoic aridification of the continent, dated using new techniques. New syntheses of glaciation in Tasmania, aridification in South Australia and aeolian activity all focus on Quaternary landscape evolution.
Rivers are important agents of change that shape the Earth's surface and evolve through time in response to fluctuations in climate and other environmental conditions. They are fundamental in landscape development, and essential for water supply, irrigation, and transportation. This book provides a comprehensive overview of the geomorphological processes that shape rivers and that produce change in the form of rivers. It explores how the dynamics of rivers are being affected by anthropogenic change, including climate change, dam construction, and modification of rivers for flood control and land drainage. It discusses how concern about environmental degradation of rivers has led to the emergence of management strategies to restore and naturalize these systems, and how river management techniques work best when coordinated with the natural dynamics of rivers. This textbook provides an excellent resource for students, researchers, and professionals in fluvial geomorphology, hydrology, river science, and environmental policy.
With contributions from key researchers across the globe, and edited by internationally recognized leading academics, Gravel-bed Rivers: Processes and Disasters presents the definitive review of current knowledge of gravel-bed rivers. Continuing an established and successful series of scholarly reports, this book consists of the papers presented at the 8th International Gravel-bed Rivers Workshop. Focusing on all the recent progress that has been made in the field, subjects covered include flow, physical modeling, sediment transport theory, techniques and instrumentation, morphodynamics and ecological topics, with special attention given to aspects of disasters relevant to sediment supply and integrated river management. This up-to-date compendium is essential reading for geomorphologists, river engineers and ecologists, river managers, fluvial sedimentologists and advanced students in these fields.
The morphology of mountainous areas is strongly influenced by stream bed incision rates, but most studies of landscape evolution consider erosion at basin scales or larger. The research here attempts to understand the smaller-scale mechanics of erosion on exposed bedrock channels in the conceptual framework of an established saltation-abrasion model by Sklar and Dietrich [2004]. The recirculating flume used in this experiment allows independent control of bed slope, water discharge rate, sediment flux, and sediment grain size all factors often bundled together in simple models of river incision and typically cross-correlated in natural settings. This study investigates the mechanics of erosion on exposed bedrock channels caused by abrasion of transported particles. Of particular interest are saltating particles, as well as sediment near the threshold between saltation and suspension - sediment vigorously transported but with significant interaction with the bed. The size of these erosive tools are varied over an order of magnitude in mean grain diameter, including a sand of D50 = 0.56 mm, and three gravel sizes of 3.39, 4.63, and 5.88 mm. Special consideration was taken to prevent any flow conditions that created a persistent alluvial cover. The erodible concrete substrate is fully exposed at all times during experiments reported here. Rates of erosion into the concrete substrate (a bedrock proxy) were measured by comparing topographic data before and after each experimental run, made possible by a precision laser mounted on a high speed computer-controlled cart. The experimental flume was able to produce flow discharge as high as 75 liters per second, sediment fluxes (of many varieties) up to 215 grams per second, and bed slopes up to 10%. I find a general positive correlation is found between erosion rate and bed slope, shear stress, grain size, and sediment flux.