Fluvial Hydraulics and Sediment Transport

Semiarid climatic conditions prevail over much of southern Africa, with variations in rainfall over seasonal and interannual timescales. This rainfall pattern provides rise to highly variable river discharge regimes from high-energy floods in the wet season to low perennial flow, or isolated remnant pools or dry river beds, in the dry season. These discharge regimes have important implications for river properties as a whole, including water quality, maintenance of ecosystems and biodiversity, pollutant dispersal, and changes in river geomorphology. The latter has been proposed as a means of mapping and classifying river systems in southern Africa, especially in areas with seasonally variable river regimes. The major river reach types identified through such mapping are mixed anastomosing, alluvial braided, mixed pool-rapid and alluvial single thread that describe different combinations of bedrock versus loose sediment within and around the river channel(s). The substrate type and its properties and dynamics have implications for turnover of ecosystem biodiversity, persistence of endemic species, spread of
invasive species and reducing flood risk. Despite such applications, many river systems in southern Africa have not been fully or accurately mapped at this scale, and individual reaches even along the same river can be highly variable in character. For example, along the Limpopo River system, the most common river reach category is low/moderate sinuosity with planform-controlled sand beds (37% of total river length), followed by meandering sand beds (26%) and bedrock-forced meanders (17%). However, different tributaries of the Limpopo have different geomorphic characters, with bedrock-forced meanders being dominant (84%) on the Nzhelele River, meandering sand beds (69%) on the Elephantes River and low-sinuosity fine-grained beds (41%) on the Lotsane River.

Application of the block ramp technique in steep gradient streams for energy dissipation as well as to maintain river stability finds increasing favor amongst researchers and practitioners in river engineering. This paper dwells on a comprehensive state-of-the-art review of flow resistance, energy dissipation, flow characteristics, stability, and drag force on block ramps by various investigators in the past. The forms and equations for each type are thoroughly discussed with the objective of finding the grey areas and gaps. More research is warranted further to improve the equations, which are essential for design analysis. Block ramps can be a promising simple technique to achieve reasonable attenuation of devastating fluvial forces unleashed in gravel-bed streams during cloud bursts.

Development of predictors for frictional resistance in an alluvial channel is a challenging task because of the complex
interaction of fluid, flow and sediment in the channel bed. In the present study, an effort has been made to develop a
functional relationship for friction factor using relevant fluid, flow and sediment parameters. Using field data (years
1984–2002) and the said functional relationship, a predictor for friction factor is proposed for mobile boundary channels.
Proposed predictors for friction factor and cross-sectional properties of a gauging station (Sarangkheda, Tapi
River, India), in turn, have been used to develop stage–discharge relationship for the same station. The proposed relationship
for friction factor and rating curve developed at the Sarangkheda gauging station has been validated using
available independent data for years 2003–2007.

Abstract
The relation between grain-size distribution of the bed and in suspension was critically examined under a uniform flow velocity of 50 cm/s over two beds: one of mainly fine sands and the other of medium sands. Two sections – one 2.85m downstream and the other 6.35m downstream in the experimental channel -were selected for sampling to study the grain-sorting pattern in the vertical direction along the direction of transport. The shape and type of the grain-size distribution pattern were critically studied with height above the bed. The change in the distribution pattern has been attributed to the change of local bed roughness causing scouring against the protruded relatively coarse grains on the bed. Such trends are important to predict the nature of river bed topography. The sand of Bed-1 initially exhibits a log-skew-Laplace distribution at different heights of suspension. The distribution pattern, however, changes but this changing pattern is not consistent along the upstream side. For Bed-2, which initially exhibits a log-normal distribution, the same pattern persists from the height of suspension at 5 cm up to 20 cm. Such consistency in log-normality is also observed at the downstream points of measurement. It is generally expected that the mean grain-size would reduce with increases of suspension height but the results of the experiments, in some occasions, differ significantly from the gradual fining upward trend. This result has been attributed to local changes of bed roughness arising from the protruded relatively coarse grains causing eddies, scouring, and turbulent phenomena which moves coarse particles higher in suspension adding a coarse tail to the distribution increasing the mean grain-size.

Keywords
Flume experiments; Suspension height; Uniform flow velocity; Bed roughness; Grain-size distribution; Bed scouring; Turbulent flow

River sedimentation is an important indicator for ecological and geomorphological assessments of soil erosion within any watershed region. Sediment transport in a river basin is therefore a multifaceted field yet being a dynamic task in nature. It is characterized by high stochasticity, non-linearity, non-stationarity, and feature redundancy. Various artificial intelligence (AI) modeling frameworks have been introduced to solve river sediment problems. The present survey is designed to provide an updated account of the latest and most relevant AI-based applications for modeling the sediment transport in river basin systems. The review is established to capture the subsequent developments in the advanced AI models applied for river sediment transport prediction. Also, several hydrological and environmental aspects are identified and analyzed according to the results produced in those studies. The merits and constraints of the well-established AI models are further discussed in much detail, particularly considering state-of-the art, modeling frameworks and their application-specific appraisal, and some of the key proposed future research directions. Together with the synthesis of such information to drive a new understanding of models and methodologies related to suspended river sediment prediction, this review provides a future research vision for hydrologists, water scientists, water resource engineers, oceanography and environmental planners.

El presente artículo de investigación da a conocer la validación de las ecuaciones empíricas de transporte de sedimentos por arrastre y suspensión empleando para ello mediciones de campo en el rìo Chancay-Lambayeque entre los puentes Pucalá y Monsefú-Éten. La problemática analizada de este trabajo es que al haber un aumento progresivo de los sedimentos en los ríos con material de fondo fino, estos tienden a reducir la capacidad hidráulica de la sección transversal provocando fallas en las riberas del mismo. Respecto a los trabajos de campo se realizaron mediciones de sedimentos con muestreadores manuales tipo Helley Smith y luego se llevaron a laboratorio para estudiar la granulometría, peso específico, velocidad de caída de partícula y concentración de sedimentos. La selección de los métodos se basó en la metodología de mejor ajuste destacando en los resultados con muy buena correlación las ecuaciones de Meyer-Peter y Müller, Schocklistch, Levi y Yalin para el transporte por arrastre y las ecuaciones de Chang, Simons & Richardson, Bagnold y Brooks para el transporte en suspensión que pueden ser aplicables para los ríos del norte del Perú.

Application of block ramp technique in steep gradient streams for energy dissipation as well as to maintain river stability finds increasing favor amongst researchers and practitioners in river engineering. This paper dwells on a comprehensive state-of-the-art review of flow resistance, energy dissipation,flow characteristics, stability, and drag force on block ramp by various investigators in the past. The forms and equations for each type are thoroughly discussed with the objective of finding the grey areas and gaps. While, more research is warranted further to improve the equations, essential for design analysis. Block ramps can be a promising simple technique to achieve reasonable attenuation of devastating fluvial forces unleashed in gravel-bed streams during cloud bursts. Key words | block ramp, drag force, energy dissipation flow resistance, stability HIGHLIGHTS • It disscussed on criticalreview of recent advancement in flow resistance,Energy dissipation, stability and drag forces on block ramps. • Highlights on the grey area and gaps. • The major research gaps are on 3D turbulence study. • flow characteristics. • formulation of block ramp are based on steady flow assumption but in reality flows are highly turbulent with unsteady flow in mountain streams.

River sedimentation is an important indicator for ecological and geomorphological assessments of soil erosion within any watershed region. Sediment transport in a river basin is therefore a multifaceted field yet being a dynamic task in nature. It is characterized by high stochasticity, non-linearity, non-stationarity, and feature redundancy. Various artificial intelligence (AI) modeling frameworks have been introduced to solve river sediment problems. The present survey is designed to provide an updated account of the latest and most relevant AI-based applications for modeling the sediment transport in river basin systems. The review is established to capture the subsequent developments in the advanced AI models applied for river sediment transport prediction. Also, several hydrological and environmental aspects are identified and analyzed according to the results produced in those studies. The merits and constraints of the well-established AI models are further discussed in much d...

Local scour around complex abutment and pier is the main reason for bridges to collapse. Although the complex abutment/pier has been used in most rivers, there is limited research in the literature about the flow pattern and local scour at complex abutment/pier. In this study, a series of experimental test was conducted to predict local scour at complex abutments and provided results were compared with complex piers. The trend of local scour at compound abutments and piers was similar and considerably sensitive to the foundation level (Z). The top of foundation stops development of scour depth for several hours which depends on the abutment/pier size (L), foundation size and its level (Lf and Z). The minimum scour depth was observed for 1.0 < Z/L < 1.5. A novel equation with high accuracy (R 2 = 0.97 and RMSE = 0.06) was developed for prediction of local scour at compound abutment based on effective length. This research highlights that the bridge cost can be reduced with a suitable design for the foundation level.