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Reservoir sedimentation
Published in Willi H. Hager, Anton J. Schleiss, Robert M. Boes, Michael Pfister, Hydraulic Engineering of Dams, 2020
Willi H. Hager, Anton J. Schleiss, Robert M. Boes, Michael Pfister
Re-establishing the sediment continuum in a river is one of the main purposes of any SBT. They allow for conveyance of sediments, both bed and suspended loads, from the upstream river and reservoir to the downstream reach having the potential to enhance river morphology of the often sediment-depleted river stretches downstream of dams. The routing of large sediment loads around the reservoir during flood events resembles the natural riverine conditions leading to a reduced erosion and river incision potential in the downstream reach. This in turn may affect the river ecosystem, altering the habitat conditions for the biota, particularly fish and macroinvertebrates (Facchini et al., 2015). Therefore, the downstream effects and the bypassing efficiency of SBT operations become more and more important. The downstream morphology and ecology should be monitored to optimize the SBT operation both in terms of the downstream effects on fauna and flora, and regarding the bypassing efficiency, i.e. the ratio of bypassed to incoming sediment volumes. The downstream situation should be compared with undisturbed river reaches upstream of the reservoir to assess the ecological effect of SBT operation.
Sediment replenishment as a measure to enhance river habitats in a residual flow reach downstream of a dam
Published in Jean-Pierre Tournier, Tony Bennett, Johanne Bibeau, Sustainable and Safe Dams Around the World, 2019
S. Stähly, A.J. Schleiss, M.J. Franca, C.T. Robinson
Sediment dynamics are an often neglected but essential linkage in the nexus between water-food-energy and ecosystems (Wohl et al., 2015). Flow and sediment dynamics are two interlinked key abiotic drivers in riverine ecosystems hosting a large variety of habitats. Water storage through dam construction in rivers are vital infrastructures to guarantee food and energy production (Schleiss, 2017), however these have a severe impact on both abiotic drivers. They regulate the flow and interrupt the longitudinal transport of sediment along the river bed. Deposited sediments in a reservoir cause the loss of storage capacity. On the other hand, a lack of sediment causes river incision downstream of the dam, streambank erosion, pauperization of morphology and loss of habitats and fluvial connectivity (Kondolf, 1997). In extreme cases, downstream sediment depletion can affect sub-surface waters. Different measures to mitigate the downstream lack of sediments are applied in practice such as flushing, sediment bypassing and artificial replenishment of sediments, although with limited results and viability. Including the sediment dynamics in catchment management contributes to socially and environmentally sustainable water, food, and energy security, contributing directly to Agenda 2030 of the United Nations in several of its targets (Nerini et al., 2018).
The sediment challenge of Swiss river corridors interrupted by man-made reservoirs
Published in Wim Uijttewaal, Mário J. Franca, Daniel Valero, Victor Chavarrias, Clàudia Ylla Arbós, Ralph Schielen, Alessandra Crosato, River Flow 2020, 2020
C. Mörtl, S.L. Vorlet, P. Manso, G. De Cesare
Downstream of the reservoir, changes in sediment transfer and flow regime can result in substantial geomorphological adjustments (Petts & Gurnell, 2005), (Juez et al., 2018). Those channel alterations (e.g river incision/degradation, loss of morphological diversity) provoke potential hydrological, groundwater and ecological risks, that can have far-reaching effects all along the course of the river.
Improved landslide susceptibility mapping using unsupervised and supervised collaborative machine learning models
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2023
Chenxu Su, Bijiao Wang, Yunhong Lv, Mingpeng Zhang, Dalei Peng, Bate Bate, Shuai Zhang
The geomorphic features of the study area are largely determined by the development of complex faults, folds, structural fissures, etc. The altitude of the mountains is generally between 1000 and 3000 m, and the relative elevation difference of the deep, precipitous valley is about 1000. Determined by the geological structure, the mountains mostly have NE-SW orientation. The area features significant river incision phenomena and generally “V”-shaped valleys. The bedrock primarily consists of magmatic rock and metamorphic rock. The study area is highly prone to rockfalls, landslides and debris flows. The lithological properties include a composition of mainly diorite, medium fine-grained granite and alluvium. The fairly steep topography of the study area is due to the hard rocks. Meanwhile, on the west of the study area starting from the Maoxian–Wenchuan fault, the lithological composition turns into phyllite, sandstone and limestone. Such a peculiar lithological contrast contributes to the disparate landslide scenarios, leading to explicit landslide boundaries. Strongly weathered rock slopes with outward inclined joint sets are widely spread on both sides of the PR303 in the study area, particularly on the upper part of gullies.
Hydro-geomorphic assessment of erosion intensity and sediment yield initiated debris-flow hazards at Wadi Dahab Watershed, Egypt
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2021
Sara M. Abuzied, Biswajeet Pradhan
The channel erosion could be determined using the MPSIAC equation (Equation (18)). The channel erosion could be delineated in the MPSIAC using the relationship between annual rainfall and gully erosion based on the BLM method. However, the channel erosion could be delineated in the EHM using an effective relation between stream power index (SPI) and proximity to erosive streams. The SPI represents the stream erosion power and is considered as a parameter affecting the slope stability within WDW (Figure 19). The SPI is an essential parameter monitoring slope erosion, since the erosive power of runoff straightly affects river incision and slope toe erosion. The SPI can be attained from the relation between the specific catchment area (A) and the local slope gradient in degrees (β) using Equation (19).
Landscape evolution of the Blue Mountains revealed by longitudinal river profiles and Cenozoic basalts and gravels
Published in Australian Journal of Earth Sciences, 2020
The locations of the knickpoints on the major rivers therefore mark the transition between the more vigorous erosion downstream, and the slower erosion of the older landscapes upstream. The presence on the Shoalhaven Plain of an incised middle Eocene, paleo-Shoalhaven River (Nott, 1992) and very low denudation rates of 0.2–1 m (Young & McDougall, 1985) is consistent with the interpretation that the landscapes of the upper reaches of this river are of considerable antiquity. A similar conclusion is drawn for the Lachlan River valley where an average river incision rate of 8 m/Ma was inferred by Bishop et al. (1985). It is suggested that the same scenario also holds for the landscapes of the Blue Mountains where more gentle landscapes are present upstream of the knickpoints of the Wollondilly, Coxs and Kowmung rivers and surrounding areas. Downstream of the knickpoints, the deep gorges of the major rivers in the Blue Mountains, reflect the more rapid erosion that has been occurring over the past 30 Ma.