Scour at Bridge Piers Protected by the Riprap Sloping Structure: A Review

Bridge piers on large rivers are often protected from scouring using launchable stone, such as a riprap sloping structure. While such scour countermeasures are effective for pier protection, they significantly alter flow conditions in the bridge opening by overtopping flow and flow contraction, deflecting the formation of the scour hole downstream and exposing the downstream riverbed to additional scour. This paper provides a comprehensive and relevant review of bridge scour estimation methods for piers with a riprap sloping structure installed as a scour countermeasure. Research on empirical methods for bridge scour estimation is reviewed and analyzed with formulae used for comparable structures—complex pier formulae and formulae for river training structures. A summary of relevant formulae applicable to piers with installed scour countermeasures is provided, as well as a discussion on the possible future research directions that could contribute to the field.

Geomechanical Hazards related to River Hydraulics and Remedial Measures: Selected Case Studies in India

River science and engineering has been one of the important study areas for geologists, hydrologists and engineers. The open channel flow and associated hydraulics often initiate several geomechanical hazards including silting and scouring, meandering and migration, floods, etc. Such hazards may lead to disastrous consequences if adequate remedial measures are not undertaken by proper river training works. This paper presents selected case studies in northern and north-eastern parts of India where such hazards occurred due to migration of river channel and flooding of adjacent lands. The two study areas have been the Kosi and the Brahmaputra river basins. In the former study area, hazards took place due to eastward migration, whereas in the latter case, significant damages occurred due to scouring and erosion. The descriptions of the hazards occurred, and the mitigation techniques adopted have been briefly summarized in this paper. A critical analysis with prediction techniques for flood occurrence probability and erosion potential has been conducted as well. The relevant conclusions are drawn therefrom.

Historical River Training Works on the Lower Elbe

The paper deals with river training works built on the reach of the Elbe River between the city of Ústí nad Labem (CZ) and the Czech/German border. Downstream of the Ústí nad Labem, the Elbe in the Czech Republic and in Germany has only been made navigable through river training measures without building weirs. The goal of river training for watercourse navigability is to attain the required waterway parameters through fairway adjustments. This is primarily achieved through channel dredging and the construction of training dams to concentrate the water flow into a narrower but deeper main channel. The paper describes the historical development of river training works during the period from the Middle Ages to the present day. Initially, such works were not meant as part of a unified conceptually designed system of measures. Instead, they were local initiatives aimed to remove natural obstacles from the river bed and to build facilities and structures to aid navigation. Systematic regulation works along the Czech and German sections of the Elbe only started in the early 19th century. The research was focused on studying the original project documents and documentation of the actual design of the training dams since 1894. This historical design documentation was digitised and projected into the maps in the Czech JTSK local coordinate system through the use of advanced geographic information system (GIS) methods. The final atlas of river training works on the Elbe-Vltava Waterway (EVW) along the lower Elbe in the Czech Republic is the first of its kind, utilising geographic information systems to document the locations of technical structures built since the early 19th century in the Elbe River bed in order to make the river navigable and maintain its navigability. The collection of maps also documents the development of the river training works in time based on map data obtained from digitised design documentation from the 19th and 20th centuries, historical aerial photographs dated 1930–1946 and 1950–1964, and present-day maps and orthophotomaps of the Elbe section in question. The atlas of the Elbe-Vltava Waterway river training works is publicly available via a web-based application. The maps are a result of original research and offer a synthesis of interactions between the existing technical structures, the sediment regime of the Elbe and sites that are subject to environmental protection. The research was conducted as part of project no. DG18P02OVV004 entitled “Documentation and presentation of technical cultural heritage along the Elbe-Vltava Waterway” within a support programme for applied research and experimental development of national and cultural identity, funded by the Ministry of Culture of the Czech Republic.

Channel morphology and prediction of mid-line channel migration in the reach of Ganga River using GIS and ARIMA modeling during 1975–2020

The dynamic nature of meandering poses several challenges in a river. The river Ganga shows severe bank erosion in many of its stretches which creates insecurity to the habitats. In the present study, channel morphology and lateral mid-line migration for 1975 to 2020 in 5 years intervals have been studied. The prediction of lateral mid-line migration from 2020 to 2050 by using multi-temporal Landsat satellite images was made by using the ARIMA model. The river reach was divided into 8 bends and 48 cross-sections were identified. The channel length was observed as 224.35 km in 1975 which reduces to 199.96 km in 2020. A decreasing trend was observed for the mean of channel length and meander ratio, and an increasing trend was noted in the mean of sinuosity ratio and tortuosity ratio. A total of 11 cross-sections showed the rightward shifting and 36 cross-sections showed the leftward shifting. Observed and predicted values showed a good R2 value of 0.90 and 0.89 at CS-24 and CS-25, respectively. The results may be used for planning and management of various river training work and understanding the river system dynamics.

Historical cartographic and topo-bathymetric database on the French Rhône River (17th–20th century)

Space and time analyses of channel changes, especially within large rivers subject to high levels of human impact, are critical to address multiple questions about rivers in the Anthropocene era. The reconstruction of long-term (> 150 year) evolutionary trajectories permits an understanding of how natural and anthropogenic factors impact hydromorphological and ecological processes in rivers, helps with the design of sustainable management and restoration options, and may also help in the assessment of future changes. However, the reconstruction of channel changes can be challenging: historical data are often scattered across many archives, and the quantity and accuracy of information generally decreases as one goes back in time. This data article provides a historical database of 350 cartographic and topo-bathymetric resources on the French Rhône River (530 km in length) compiled from the 17th to mid-20th century, with a temporal focus prior to extensive river training (1860s). The data were collected in 14 national, regional, and departmental archive services. A table describes the properties of each archived data item and its associated iconographic files. Some of the historical maps are available in a georeferenced format. A GIS layer enables one-click identification of all archive data available for a given reach of the French Rhône River. This database provides substantial new material for deeper analyses of channel changes over a longer time period and at a finer time step compared with previously available data. The database has several potential applications in geomorphology, retrospective hydraulic modelling, historical ecology, and river restoration, as well as permitting comparisons with other multi-impacted rivers worldwide. The dataset is available at https://doi.org/10.1594/PANGAEA.922437 (Arnaud et al., 2020a). Iconographic extracts of the 350 archived items are available at http://photo.driihm.fr/index.php/category/52 (last access: 2 May 2021).

Hydromorphological evaluation of the river training impact on a multi-thread river system (Belá River, Carpathians, Slovakia)

The paper evaluates the impact of river training works designed to address problems associated with flooding on the braided-wandering Belá River in Slovakian Carpathians. This impact was investigated after the flood event in July 2018 on 11 river reaches where the river engineering and management intervention was applied. We analyzed its impact by spatio-temporal variations in river morphology (12 channel parameters) and changes in cross-section and hydraulic parameters (flow velocity, shear stress, stream power, W/D ratio) between pre- and post-flood management periods. The research hypotheses related to decreasing geodiversity in managed river reaches, a rapid increase in flow velocity during an extreme flood in river reaches where there is no sufficient floodplain inundation due to artificially high banks built by river training works, and increasing erosive force in the channel zone thanks to river management intervention were confirmed. The intervention in the braidplain area of the Belá River resulted in an undesirable simplification of the river pattern, loss of geomorphic diversity, loss of channel–floodplain connectivity, and disturbance and restraint of hydromorphological continuity. Identification of main conflicts of the Belá River management is important for clarifying the different approaches of stakeholders in the study area and aims to provide an objective illustration of their consequences. The presented analyses could help in future management issues as well as in the more critical decision-making process in vulnerable and rare braided river systems on the present when we are losing so many natural rivers by human decisions.

Effects of anthropic changes on the propagation of the Gleno dam break wave in the Valle Camonica floodplain

<p>The catastrophic flood following the Gleno dam break, which occurred in 1923, has been investigated in the literature (Pilotti et al., 2011, Milanesi and Pilotti, 2021) considering the 20 km long steep alpine valley separating the dam location from the hamlet of Corna. In this contribution, we investigate the propagation of the flood wave from Corna, where the computed hydrograph from previous investigation provides the upstream boundary condition, as far as the Lake Iseo outlet in Sarnico, where two controversial documents attest its effect on the lakeshore. In the middle, the flood crossed 30 km of a wide pre-alpine floodplain that has been deeply modified over the last century  and crossed 25 km of a deep lake.</p><p>The simulation has been accomplished by coupling 2 different 2D solver of the Shallow Water Equations: the well-known HEC-RAS 2D software was used to cover the floodplain from Corna up to the Lake Iseo inlet, while a finite volume scheme was used to simulate the lake behaviour in response to the incoming flood. The finite volume scheme used to model the lake is based on the WAF solver developed by Toro (Toro, 2001) and further adapted to account for the geometry of lake Iseo using an unstructured mesh. The scheme used retains shock-capturing capabilities and well-balanced properties able to withstand the constantly changing bathymetry of the lake as well as the unsteadiness of the hydrodynamics modelled. As a first step, the simulation was performed on the topography derived from the LIDAR DTM surveyed in 2008-2009. A computational mesh was built with average grid size of 10 m aligned in correspondence of levees and other singularities. This first simulation dramatically shows how the propagation of the flood wave was affected by the presence of linear structures such as levees and road embankments, absent in 1923 as shown by historical maps. For this purpose, the linear structure that affect the flow was removed from the 2008-2009 DTM and a second simulation was performed in order to compare the different flow hydrograph at the inlet of the lake.</p><p>An important fallout of the modeling effort is the reconstruction of the 1923 original bathymetry of the river in Valle Camonica, to be compared with the present one, affected by 100 years of river training works. The comparison of the flood propagation using the two bathymetries highlights the consequences of systematic hydraulic works on the hazard distribution for the same event. Paradoxically, the residual risk is now much higher than 100 years ago. Moreover, the simulations show that the claim of a 50 cm high bore at the inlet of the Oglio river is unsubstantiated by the model results and that an important request of damages was probably based on a false statement.</p>

Experimental Study on Backflow Patterns Induced by a Bilateral Groin Pair with Different Spacing

Groins are one of the popular manmade structures to modify the hydraulic flow and sediment response in river training. The spacing between groins is a critical consideration to balance the channel-depth and the cost of construction, which is generally determined by the backflow formed downstream from groins. A series of experiments were conducted using Particle Image Velocimetry (PIV) to observe the influence of groin spacing on the backflow pattern of two bilateral groins. The spacing between groins has significant effect on the behavior of the large-scale recirculation cell behind groins. The magnitude of the wake flow induced by a groin was similar to that induced by another groin on the other side, but the flow direction is opposite. The spanwise velocity near the groin tip dictates the recirculation zone width behind the groins due to the strong links between the spanwise velocity and the contraction ratio of channel cross-sections between groins. Based on previous studies and present experimental results, quantitative empirical relationships are proposed to calculate the recirculation zone length behind groins alternately placed at different spacing along riverbanks. This study provides better understanding and a robust formula to assess the backflow extent of alternate groins and identify the optimum groins array configuration.

Rivers Try Harder. Reversed “Differential Erosion” as Geological Control of Flood in the Large Fluvial Systems in Poland

We study cross-sections on the Detailed Geological Map of Poland (SMGP) to find a geologic and geomorphic pattern under river valleys in Poland. The pattern was found in 20 reaches of the largest Polish rivers (Odra, Warta, Vistula, Narew, and Bug) located in the European Lowland, in the landscape of old (Pleistocene, Saalian) glacial high plains extending between the Last Glacial Maximum (LGM) moraines on the North and the Upland on the South. The Upland was slightly folded and up-faulted during Alpine orogeny together with the thrust of Carpathian nappes and the uplift of Tatra Mts. and Sudetes. The found pattern is an alluvial river with broad Holocene floodplain and the channel developed atop the protrusion of bedrock (Jurassic, Cretaceous limestones, marlstones, sandstones) or non-alluvial, cohesive, overconsolidated sediments resistant to erosion (glacial tills, lacustrine or “ice-dammed lake” clays) of Cenozoic (Paleogene, Neogene, Quaternary—Elsterian). We regard the sub-alluvial protrusion as the limit of river incision and scour. It cannot be determined why the river flows atop these protrusions, in opposition to “differential erosion”, a geomorphology principle. We assume it is evidence of geological flood control. We propose an environmental and geomorphological framework for the hydrotechnical design of instream river training.