River Bed Erosion Research Articles

A network scale, intermediate complexity model for simulating channel evolution over years to decades

Excessive river erosion and sedimentation threatens critical infrastructure, degrades aquatic habitat, and impairs water quality. Tools for predicting the magnitude of erosion, sedimentation, and channel evolution processes are needed for effective mitigation and management. We present a new numerical model that simulates coupled river bed and bank erosion at the watershed scale. The model uses modified versions of Bagnold’s sediment transport equation to simulate bed erosion and aggradation, as well as a simplified Bank Stability and Toe Erosion Model (BSTEM) to simulate bank erosion processes. The model is mechanistic and intermediate complexity, accounting for the dominant channel evolution processes while limiting data requirements. We apply the model to a generic test case of channel network response following a disturbance and the results match physical understanding of channel evolution. The model was also tested on two field data sets: below Parker Dam on the lower Colorado River and the North Fork Toutle River (NFTR) which responded dramatically to the 1980 eruption of Mount St. Helens. It accurately predicts observed channel incision and bed material coarsening on the Colorado River, as well as observations for the upstream 18 km of the NFTR watershed. The model does not include algorithms for extensive lateral migration and avulsions and therefore did not perform well in the lower NFTR where the channel migrated across a wide valley bottom. REM is parsimonious and useful for simulating network scale channel change in single thread systems responding to disturbance.

Riverbed erosion of the final 565 kilometers of the Yangtze River (Changjiang) following construction of the Three Gorges Dam

The world’s largest hydropower dam, the Three Gorges Dam (TGD), spans the upper Yangtze River in China, creating a 660-km long and 1.1-km wide reservoir upstream. Several recent studies reported a considerable decline in sediment load of the Lowermost Yangtze River (LmYR) and a rapid erosion in the subaqueous delta of the river mouth after the closure of the TGD in 2003. However, it is unknown if the TGD construction has also affected river channel and bed formation of the LmYR. In this study, we compared bathymetric data of the last 565 kilometers of the Yangtze River’s channel between 1998 and 2013. We found severe channel erosion following the TGD closure, with local riverbed erosion up to 10 m deep. The total volume of net erosion from the 565-km channel amounted to 1.85 billion m3, an equivalent of 2.59 billion metric tons of sediment, assuming a bulk density of 1.4 t/m3 for the riverbed material. The largest erosion occurred in a 100-km reach close to the Yangtze River mouth, contributing up to 73% of the total net eroded channel volume.

Study on the water resources optimal operation based on riverbed wind erosion control in West Liaohe River plain

Abstract. Rivers are drying up most frequently in West Liaohe River plain and the bare river beds present fine sand belts on land. These sand belts, which yield a dust heavily in windy days, stress the local environment deeply as the riverbeds are eroded by wind. The optimal operation of water resources, thus, is one of the most important methods for preventing the wind erosion of riverbeds. In this paper, optimal operation model for water resources based on riverbed wind erosion control has been established, which contains objective function, constraints, and solution method. The objective function considers factors which include water volume diverted into reservoirs, river length and lower threshold of flow rate, etc. On the basis of ensuring the water requirement of each reservoir, the destruction of the vegetation in the riverbed by the frequent river flow is avoided. The multi core parallel solving method for optimal water resources operation in the West Liaohe River Plain is proposed, which the optimal solution is found by DPSA method under the POA framework and the parallel computing program is designed in Fork/Join mode. Based on the optimal operation results, the basic rules of water resources operation in the West Liaohe River Plain are summarized. Calculation results show that, on the basis of meeting the requirement of water volume of every reservoir, the frequency of reach river flow which from Taihekou to Talagan Water Diversion Project in the Xinkai River is reduced effectively. The speedup and parallel efficiency of parallel algorithm are 1.51 and 0.76 respectively, and the computing time is significantly decreased. The research results show in this paper can provide technical support for the prevention and control of riverbed wind erosion in the West Liaohe River plain.

Vulnerability of bridge piers to general and local erosion of river bed

AbstractBridges are large, quite complex, and expensive engineering structures, whose supports, i.e. piers in river beds, are exposed to a series of adverse influences, in particular to the impact of the erosion of a river bed. Disrupted stability of piers or their complete destruction leads to failure of bridge superstructures. We have been witnessing, particularly in recent years, the occurrence of large floods that damaged or even completely destroyed a large number of bridges. In this paper the main causes of general erosion and local erosion have been analysed, with a view toward the ways of determining the depth of local erosion, in order to meet the requirements of a correct selection of foundation depth of bridge piers and of undertaking the corresponding measures to prevent erosion.

Assessment of bridge scour in the lower, middle, and upper Yangtze River estuary with riverbed sonar profiling techniques.

Riverbed scour of bridge piers can cause rapid loss in foundation strength, leading to sudden bridge collapse. This study used multi-beam echo sounders (Seabat 7125) to map riverbed surrounding the foundations of four major bridges in the lower, middle, and upper reaches of the 700-km Yangtze River Estuary (YRE) during June 2015 and September 2016. The high-resolution data were utilized to analyze the morphology of the bridge scour and the deformation of the wide-area riverbed (i.e., 5-18km long and 1.3-8.3km wide). In addition, previous bathymetric measurements collected in 1998, 2009, and 2013 were used to determine riverbed erosion and deposition at the bridge reaches. Our study shows that the scour depth surrounding the bridge foundations progressed up to 4.4-19.0m in the YRE. Over the past 5-15years, the total channel erosion in some river reaches was up to 15-17m, possessing a threat to the bridge safety in the YRE. Tide cycles seemed to have resulted in significant variation in the scour morphology in the lower and middle YRE. In the lower YRE, the riverbed morphology displayed one long erosional ditch on both sides of the bridge foundations and a long-strip siltation area distributed upstream and downstream of the bridge foundations; in the middle YRE, the riverbed morphology only showed erosional morphology surrounding the bridge foundations. Large dunes caused deep cuts and steeper contours in the bridge scour. Furthermore, this study demonstrates that the high-resolution grid model formed by point cloud data of multi-beam echo sounders can clearly display the morphology of the bridge scour in terms of wide areas and that the sonar technique is a very useful tool in the assessment of bridge scours.

Numerical Analysis Study of Sarawak Barrage River Bed Erosion and Scouring by Using Smooth Particle Hydrodynamic (SPH)

Smooth Particle Hydrodynamic is the three-dimensional (3D) model. In this research work, three cases and one validation have been simulate using DualSPHysics. Study area of this research work was at Sarawak Barrage. The cases have different water level at the downstream. This study actually to simulate riverbed erosion and scouring properties by using multi-phases cases which use sand as sediment and water. The velocity and the scouring profile have been recorded as the result and shown in the result chapter. The result of the validation is acceptable where the scouring profile and the velocity were slightly different between laboratory experiment and simulation. Hence, it can be concluded that the simulation by using SPH can be used as the alternative to simulate the real cases.

The analysis of factors influencing the dynamics of lowland riverbed erosion downstream of the Jeziorsko reservoir dam (central Poland)

Increased riverbed erosion could recently be observed in close vicinity of hydrotechnical constructions in many lowland rivers. The immediate effect of erosion in this case is a very significant reduction of the riverbed level over a considerable distance, downstream of large reservoir dams. This process is influenced simultaneously by both hydraulics of river flow and geotechnical properties of soil eroded. The paper presents an analysis of parametric changes in the level of river bottom and grain size of bed material, and the relative density in the context of changes in hydrological conditions and diversity of engineering-geological conditions. As the result, a multiparametric model of erosional potential of riverbed sediments has been proposed, which can significantly help in proper planning of locations and construction of correction thresholds under given hydraulic conditions of the river.

Particle size distribution of bed materials in the sandy river bed of alluvial rivers

The particle size distribution of bed materials in the sandy river bed of alluvial rivers is important in the study of topics such as friction, river bed evolution, erosion, and siltation. It also can reflect the dependency relation between river bed sediment and flow intensity. In this paper, the critical pattern of sediment movement in the near-wall region of a sandy river bed was analyzed. According to the principle of momentum balance, the critical settling-rising condition of bed material in a sandy river bed was found to be instantaneous turbulent velocity equal to 2.7 times the sediment settling velocity in quiescent water. Based on a vertical instantaneous turbulent velocity with a Gaussian distribution, a theoretical relation for calculating the particle size distribution of bed materials in a sandy river bed without pre-known characteristic grain sizes was developed by solving a stochastic equation. The formula is verified using measured data, and the results show that the proposed formula was in accordance with the measured data. This study has theoretical significance and practical value for determining the bed material particle size distribution of the sandy bed of alluvial rivers.

River slopes on basalts: Slope-area trends and lithologic control

River incisions in continental basalts are distinct and heterogeneous. Knickpoints and the predominance of erosion by plucking contribute to that distinction, whereas significant differences in the vesicularity and jointing of basaltic flows are suggested as controls on the heterogeneities of incisions. We investigated 11 small river channels (<80 km long) installed on continental basalts of the Paraná Volcanic Province, South Brazil, using slope-area analysis (S = ksA−θ), to explore the possible relationships of steepness (ks) and concavity (θ) indices with characteristics of flow basalts. Channels were chosen that did not present signs of significant tectonic interference on a longitudinal profile, i.e., convex reaches and prominent knickpoints. The data were extracted in a Geographic Information System (GIS) environment from digital topographic maps at a scale of 1:50,000. Basaltic flow zones and morphologies, jointing styles, as well as river bed morphologies and erosion processes were surveyed in the field. The longitudinal profiles of the rivers are stepped, and the lower slope reaches are associated predominantly with vesicular basalts and basaltic breccias. Knickpoints are generated by contrasts in the erodibility of the substrate due to vesicular-massive differences and the partial insertion of channels in tectonically fractured zones (lineaments). The normalized steepness index (ksn) is positively correlated (R2 = 0.8) with the knickzone index (the ratio between the number of knickzones and the channel length). Rivers occurring in simple basaltic flows have distinct upper and lower limits of the steepness index (ks), which are represented by massive and vesicular basalts, respectively. The average concavity index (θ) is 0.56 ± 0.16, and its range is from 0.34 to 0.82. The range in θ is inversely related to the rate of downstream variation in the drainage area (discharge). However, the greatest control is exerted by the proportion of basalts that are more resistant to erosion (massive), with which there is also an inverse relationship (R2 = 0.64). The results indicate that, although basalts have an apparent uniformity in the geomorphological response, differences in jointing and vesicularity may generate different behaviors detectable by slope-area indices.

Estimating the Scouring Depth of Bridge Pier Using Self-Organizing Neural Networks (SOM)

Scouring is caused as a result of erosion of river bed by water flow and materials carried by water. This research estimates the scouring depth using self-organizing neural network (SOM). The obtained findings were compared with findings of other models. It was found that self- organizing neural network (SOM) has higher correlation coefficient (0.98), compared to other methods. It was also found that root mean square error (RMSE = 0.112) is less than other methods. Estimating the depth of scouring using self-organizing neural network (SOM) method indicated that this method gives better findings, in a way that correlation coefficient in implementing the program with dimensional data is higher value compared to state in which program is implemented with non-dimensional data. In addition, Root Mean Square Error (RSME = 0.09) was seen less in the state of dimensional data. In the current research, using the sensitivity analysis showed that when SOM program is implemented with dimensional data, it will be more sensitive to parameter of average diameter of particles.

Predicting the sequent depth ratio of a B-F hydraulic jump on a river-bed rock chute

Rock chutes are widely used to control erosion of river beds because of their high energy loss, low environmental impact, simple construction and low cost. They typically include a negatively sloped stilling basin, which leads to formation of a little-understood ‘B-F’ hydraulic jump. This has its toe located on the upstream positive slope of the chute and its roller length ending on the downstream negative slope of the stilling basin. In this study, a general equation for computing the sequent depth ratio of a B-F jump was developed using Buckingham dimensional analysis and the incomplete self-similarity theorem. A new non-dimensional parameter, E0, including the effects of the jump toe and the location of the end of the roller length, was introduced. Laboratory experiments of B-F hydraulic jumps were conducted for a wide range of upstream Froude numbers, relative bed roughness, three different upstream channel slopes and three different negative downstream channel slopes. The sequent depth ratio on rough rocky beds was found to be considerably smaller than those on a smooth concrete bed. Two new prediction equations, for smooth and rough bed slopes, are presented and the results show that the predictions agree reasonably well with the experimental data.

Математическое моделирование руслового потока для прогнозов влияния строительства в поймах на гидрологический режим

Issues of forecasting of construction works on floodplains impact on hydrological and bed processes at adjacent ranges of major rivers have been considered. Mathematical models of flows and bed processes at the river ranges with complicated morphometry of the bed and floodplain have proposed. Their application enables to solve a significant scientific/practical problem of assessment of the construction works impact on flooding floodplain territories and the Ob River bed erosion in the vicinity of the city of Barnaul. Calculations for the Ob River range under consideration have been done according a computer hydrodynamic model produced with the use of hydrological data, outcomes of bed surveying and geodesic investigations. The planning construction work impact on the water levels, flow velocities and the river bed erosion in case of different Ob River flows has been shown. The bed and hydrological processes impact on the site of the designed facility has been assessed.

Environmental impact assessments of the Xiaolangdi Reservoir on the most hyperconcentrated laden river, Yellow River, China.

The Yellow River is the most hyperconcentrated sediment-laden river in the world. Throughout recorded history, the Lower Yellow River (LYR) experienced many catastrophic flood and drought events. To regulate the LYR, a reservoir was constructed at Xiaolangdi that became operational in the early 2000s. An annual water-sediment regulation scheme (WSRS) was then implemented, aimed at flood control, sediment reduction, regulated water supply, and power generation. This study examines the eco-environmental and socioenvironmental impacts of Xiaolangdi Reservoir. In retrospect, it is found that the reservoir construction phase incurred huge financial cost and required large-scale human resettlement. Subsequent reservoir operations affected the local geological environment, downstream riverbed erosion, evolution of the Yellow River delta, water quality, and aquatic biodiversity. Lessons from the impact assessment of the Xiaolangdi Reservoir are summarized as follows: (1) The construction of large reservoirs is not merely an engineering challenge but must also be viewed in terms of resource exploitation, environmental protection, and social development; (2) long-term systems for monitoring large reservoirs should be established, and decision makers involved at national policy and planning levels must be prepared to react quickly to the changing impact of large reservoirs; and (3) the key to solving sedimentation in the LYR is not Xiaolangdi Reservoir but instead soil conservation in the middle reaches of the Yellow River basin. Proper assessment of the impacts of large reservoirs will help promote development strategies that enhance the long-term sustainability of dam projects.

Recent sedimentary record of storms and floods within the estuarine-inner shelf region of the East China Sea

Although extreme weather events make a strong impact in shallow marine sedimentary environments, there is still a paucity of past records for the Holocene period. Estuarine-inner shelf mud regions deposited from rivers that transport a large amount of suspended sediment represent an important archive of the Holocene. Two cores (S5-2 and JC07) retrieved from the estuarine-inner shelf regions of the East China Sea provided an opportunity to use sensitive grain size and 210Pb dating to reconstruct a history of extreme weather events in the Yangtze River basin. Here, we show that the average sedimentation rates of the two cores, S5-2 (1930–2013) and JC07 (1910–2013), were estimated to be 3.11 and 1.56 cm/yr, respectively. The results indicated that sediment supply played an important role in sedimentation of the estuarine-inner shelf mud region of the East China Sea. Sand content strongly increased in the late 1980s, a result of downstream riverbed erosion of the Yangtze River and submerged deltas. The grain size versus the standard deviation method was used to identify grain-size intervals with the highest variability along a sedimentary sequence. The Yangtze estuary mud area coarse population correlated well with historical literature on Yangtze River floods since AD 1930. Extreme storm events corresponded well with historical literature on the Zhe-Min mud region of the East China Sea. The spectral analyses of the sample core coastal population demonstrated that flood and storm events were consistent with a ~3–8 a periodic change of El Niño Southern Oscillation (ENSO), suggesting that the flood events usually follow ENSO years in the Yangtze River. Consequently, sediment records preserved in the two cores demonstrated different sedimentary responses to Yangtze River floods and storms, which is important to recover centennial scale flood events, to infer extreme precipitation, and to understand climate change in the estuarine-inner shelf of the East China Sea. Nevertheless, more efforts are still needed to simulate paleo-flood and predict future flood events in the context of global warming.

Effects of weir height and reservoir widening on sediment continuity at run-of-river hydropower plants in gravel bed rivers

This study conducted scaled physical model tests of a run-of-river hydropower plant (RoR). The physical model represented an idealized gravel bed river with a width of 20m, a slope of 0.005, a mean annual flow of 15m3s−1 and a 1-year flood flow of 80m3s−1. Substrate and bed load had a characteristic grain size dm of 56mm. The model scale was 1:20. The study was designed to test the effects of weir height and reservoir widening on sediment continuity and flushing efficiency at low-head RoR plants. Three different weir heights and two reservoir widths were investigated to assess and quantify their influence. As long as equilibrium conditions had not been established in the reservoir the flushing efficiency was low and thus the sediment continuity was not met. The experiments revealed that both parameters had a significant effect regarding the time needed to reach equilibrium conditions. The equilibrium slope that established was independent of weir height. Weir height, however, determined the starting point from where the equilibrium slope was built up. Accordingly, an increase in weir height will increase the reservoir bed levels by the same amount. A large weir height leads to huge sedimentation volumes and thus to a lack of sediments and to river bed erosion downstream of the hydropower plant. It could also considerably increase the flood risk at the head of the reservoir. This calls for regular maintenance work to re-establish flood safety. The experimental results suggest new concepts of low weir heights and cross sectional reservoir widths in the design of low-head RoR plants to facilitate frequent and efficient flushings, to enhance sediment continuity, and to reduce maintenance and operational costs.

Sediment Transport Dynamic in a Meandering Fluvial System: Case Study of Chini River

Sedimentation in river reduces the flood carrying capacity which lead to the increasing of inundation area in the river basin. Basic sediment transport can predict the fluvial processes in natural rivers and stream through modeling approaches. However, the sediment transport dynamic in a small meandering and low-lying fluvial system is considered scarce in Malaysia. The aim of this study was to analyze the current riverbed erosion and sedimentation scenarios along the Chini River, Pekan, Pahang. The present study revealed that silt and clay has potentially been eroded several parts of the river. Sinuosity index (1.98) indicates that Chini River is very unstable and continuous erosion process in waterways has increase the riverbank instability due to the meandering factors. The riverbed erosional and depositional process in the Chini River is a sluggish process since the lake reduces the flow velocity and causes the deposited particles into the silt and clay soil at the bed of the lake. Besides, the bed layer of the lake comprised of cohesive silt and clayey composition that tend to attach the larger grain size of sediment. The present study estimated the total sediment accumulated along the Chini River is 1.72 ton. The HEC-RAS was employed in the simulations and in general the model performed well, once all parameters were set within their effective ranges.

Estimation of maximum scour depth near a spur dike

Scour is a natural phenomenon in rivers caused by the erosive action of the flowing water on the bed and banks. Spur dikes are constructed across the flow to protect the bank from erosion by shifting of the river away from the bank. The spur dike undermines due to river-bed erosion and scouring, which is generally recognized as the main cause of spur dike failure. In this study, accuracy of existing equations for the computation of maximum scour depth has been checked with available data in the literature and data collected in the present study using graphical and statistical performance indices. Three new relationships are also proposed to estimate the maximum scour depth and maximum scour length upstream and downstream of spur dike. This new relationship for maximum scour depth is shown to perform better than other existing equations.

Analysis of Prognosis of Lowland River Bed Erosion Based on Geotechnical Parameters

Abstract The river erosion is a complex process, the dynamics of which is very difficult to predict. Its intensity largely depends on hydraulic conditions of the river channel. However, it is also thought that natural resistance of the subsoil has a great influence on the scale of the erosion process. Predicting the effects of this process is extremely important in the case of constructing a piling structure (for example, artificial reservoirs). The partition of the river channel causes significant lowering of the river channel bed downstream the dam which threatens the stability of hydro technical and engineering (bridges) buildings. To stop this unwanted phenomenon, stabilizing thresholds are built. However, random location of thresholds significantly reduces their effectiveness. Therefore, taking under consideration natural geotechnical conditions of the subsoil appears to be extremely important. In the light of the current development of in-situ tests in geotechnics, an attempt to use results from these tests to predict the bed erosion rate was made. The analysis includes results from CPTU and DPL tests, which were carried out in the Warta River valley downstream the Jeziorsko reservoir. In the paper, the general diagrams for the procedure of obtaining and processing the data are shown. As a result, the author presents two multidimensional bed erosion rate models built based on hydraulic data and results from CPTU or DPL tests. These models allow taking more effective actions, leading to the neutralization of the effects of the intensive bed erosion process.

Challenges of river basin management: Current status of, and prospects for, the River Danube from a river engineering perspective

In the Danube River Basin multiple pressures affect the river system as a consequence of river engineering works, altering both the river hydrodynamics and morphodynamics. The main objective of this paper is to identify the effects of hydropower development, flood protection and engineering works for navigation on the Danube and to examine specific impacts of these developments on sediment transport and river morphology. Whereas impoundments are characterised by deposition and an excess of sediment with remobilisation of fine sediments during severe floods, the remaining five free flowing sections of the Danube are experiencing river bed erosion of the order of several centimetres per year. Besides the effect of interruption of the sediment continuum, river bed degradation is caused by an increase in the sediment transport capacity following an increase in slope, a reduction of river bed width due to canalisation, prohibition of bank erosion by riprap or regressive erosion following base level lowering by flood protection measures and sediment dredging. As a consequence, the groundwater table is lowered, side-arms are disconnected, instream structures are lost and habitat quality deteriorates affecting the ecological status of valuable floodplains. The lack of sediments, together with cutting off meanders, leads also to erosion of the bed of main arms in the Danube Delta and coastal erosion. This paper details the causes and effects of river engineering measures and hydromorphological changes for the Danube. It highlights the importance of adopting a basin-wide holistic approach to river management and demonstrates that past management in the basin has been characterised by a lack of integration. To-date insufficient attention has been paid to the wide-ranging impacts of river engineering works throughout the basin: from the basin headwaters to the Danube Delta, on the Black Sea coast. This highlights the importance of new initiatives that seek to advance knowledge exchange and knowledge transfer within the basin to reach the goal of integrated basin management.

Assessment of Displacement Flow at Ketandan Creeks to Optimizing Land Use in Jember New City Housing

Displacement flow will caused a change in the flow characteristics such as flow depth, discharge, river slope and width of the river surface. If not carefully examined, it will cause the riverbed erosion, sedimentation and risk of flooding. This paper aims to assess the hydrology and hydraulics of the river flow changes in Ketandan creek in optimizing the use of land housing for Jember New City (JNC). Hydrology modelling studies conducted for the return period rainfall include a 2 year as normal discharge, and 100 year as flood condition. Simulation of flood designs used to assess changes in the flow regime in the channel and the risk of flooding with HEC-RAS program. The results of the study showed that for the flood design 3,1 m 3 /sec and 12,8 m 3 /sec will give the effect of critical water surface. In order to keep the flow of the river bed of critically needed as the drop-structure and spillway construction