River Bank Slope Research Articles

The Use of Modified Composite Materials in Building Hydraulic Engineering Structures

The article describes hydraulic engineering structures which are built in low-head water power hydro systems and which can also be used to stabilize river bank slopes. The paper gives information on the condition of riverbanks in Samara region and underlines the necessity to increase the amount of works on bank-stabilization. The paper stresses the importance of decreasing the expenses on building bank-stabilizing hydraulic engineering structures without any loss in their reliability and safety. Authors propose to build such structures using composite materials and their modifications and take geosynthetics, polymer-impregnated concrete and waste-/by-products as their constituents. The research also describes how the properties of composite materials change when they are modified for building hydraulic engineering structures.

Toppling and wedge failures in Malekhu River area, Malekhu, Central Nepal Lesser Himalaya

A huge landslide was identified on the right bank of the Malekhu River at about 1 km upstream from the Malekhu Bridge of the Prithvi Highway, and was named Malekhu Landslide. The landslide area consists of quartzite with sericite partings, chlorite schist and amphibolite of the Robang Formation of the Kathmandu Complex. The landslide extends for about 200 m along the river bank slope and its crown and toe have elevation respectively of 429 m and 361 m a.s.l. The major portion of the hillslope has been altered by landsliding as evidenced from the different geometry of slopes consisting of very steep scarp slope, steep to moderate slope with toppled and wedge failure debris, and several wedges and gullies. The right-side up layers have an average dip direction of 167° and a plunge of 56-90°, whereas the overturned layers have an average dip direction and plunge of 316°/32°. The direction towards which the toppling had occurred is 167°. The overturned layers had rotated to 36°, during which the layer dip direction had rotated counterclockwise to an amount of 31° from the major direction of toppling, and this rotation should have occurred during sliding of the toppled block. The Malekhu Landslide is a complex landslide experiencing more than one mode of failure of which the most prominent one is the toppling. It is a kind of flexural toppling of passive mode and had already occurred and now is suspended. The second mode of failure is the wedge sliding. The kinematic analysis of discontinuities on the slope for evaluating possibility of landsliding has indicated that the wedge failure is potential due to the presence of a line of intersection produced by the discontinuity parallel to the foliation of the right-side up layers and the overturned layers. This suggests that the toppled blocks may further slide. It is required to protect the slope from landsliding as there have been extended two unpaved roads one along the crown and the other along the toe of the landslide, and due to existence of the Malekhu Bridge in the downstream stretch of the river. DOI: http://dx.doi.org/10.3126/bdg.v16i0.8881 Bulletin of the Department of Geology Vol. 16, 2013, pp. 21-28

Characteristics and Mechanism of Concentrated Unloading in Bank Slope of Yangqu Hydropower Station

Abstract Based on the study of field background, tectonic evolution and development history of the Yellow River valley, the authors made an in-depth study of the distribution and formation mechanism of the deep concentrated unloading of a typical bank slope developed in broad basin, and found that the concentrated unloading ranges from 2520 to 2650 m at El, the horizontal depth is 40 to 90 m in left bank and 40 to 60 m in right bank. It showed that these deep cracks in concentrated unloading zone generally dip towards the river or to the inner slope with high angle, and the cause of formation due to the category of unloading. The concentrated unloading is the product of the epigenetic deformation along the original tectonic structural planes accompanied by the stress release of slope during the formation process of river bank slope.

BED-LOAD SEDIMENT PROFILE AND EFFECT OF RIVER BANK EROSION ON RIVER CROSS-SECTION

The processes of lateral and riverbank erosion are among the elements of river morphology dynamic resulting from natural processes and human activities. This process has been studied in detail throughout the research for four months starting from 7 October 2009 to 26 January 2010. In this research, technique of erosion pins were applied at five plots selected along the Chini River in Pahang, Malaysia in order to evaluate the rate of for lateral and river bank erosion. The results in the lateral erosion indicates that, the average highest erosion was recorded at plot 4 (3 cm), followed by plot 3 (2.3 cm), plot 2 (1.42 cm), plot 1 (1.2 cm) and plot 5 recorded the lowest average which is 0.59 cm respectively. Overall, the total average of lateral erosion recorded at all five plots is 8.51 cm. Meanwhile, results obtained from river cross-section variation indicated that plot 1 and 2 show changes from the V shape in early observation to U shape at the end of the observation period. This shows that side-erosion was active in the entire process. Furthermore, plot 3, 4 and 5 remained U shape until the latest observation but it was found that the riverbed was getting shallow. For the regression analysis, two independent variables were selected to relate with rate of river bank erosion namely steep gradient bank height of the bank. These independent variables show a positive relationship with the rate of the side and river bank erosion where the value of r2 is 0.820 and 0.645 for both variable of gradient and height. For the analysis of soil particle distribution, the mean value is a sand and very coarse with phi ø -2.00 to phi ø 0.00. The standard Deviation (D) indicates of worst deposition, between phi ø 1.00 to phi ø 4.00. Skewness (S) shows very small size to oversize which is between phi ø -1.00 to phi ø +1.00 and the value of Kurtosis (K) for this river is dominated by grain size mesokurtic and platikurtic. Therefore, the Slope Stabilization or river bank slope protection of River Chini area is proposed to reduce the river bank erosion and sediment production.

Discussion on the Mechanism Research of Pioneer Plant Roots in Riverbank Soil Conservation and Slope Stabilization in the Three Gorges Reservoir Area

The change of fluctuating rhythm of water level resulted from the construction of the Three Gorges Hydropower Project impacts the composition and structure of riverbank plant communities and plant growth in the reservoir area, which further affects the effects of plant root systems on soil conservation and slope stabilization. The changing trends of riverside ecological environment and vegetation in the reservoir area were analyzed in this paper, so was the study of mechanism on plant root systems in soil conservation and slope stabilization. Some suggestions were put forward finally for the mechanism research of pioneer plant roots in riverbank soil conservation and slope stabilization. It was suggested that the effects and mechanism of plant roots in soil conservation and slope stabilization in the Three Gorges reservoir area could be evaluated and uncovered by studying the temporal and spatial dynamics of root tensile strength, erosion resistance, shear resistance, soil physical and chemical properties, and their relationship with dynamics of the pioneer plant root structure responding to environmental changes induced by the construction of the hydropower project. The study also should include field investigation and simulated experiments in laboratory. The field investigation could reveal the changes of temporal and spatial dynamics of pioneer plant roots’ tensile strength, erosion resistance, shear resistance, and soil physical properties. The simulated experiments could evaluate quantitatively the relationship between plant root structure and their effects on soil conservation and slope stabilization.

Rock slope stability evaluation in static and seismic conditions for left bank of Jinsha River Bridge along Lijiang-Xamgyi’nyilha railway, China

Jinsha River Bridge is located along the Lijiang-Xamgyi’nyilha railway on the southeastern Tibet plateau; it is an area with a high prevalence of earthquakes. The bridge abutments were designed to be constructed in river bank slopes, where rocks are controlled by two sets of joint planes that significantly influence the stability of the left bank slope. According to the engineering-geological conditions and the characteristics of discontinuities, strength properties of the rock mass were obtained based on Barton model and direct shear test. Numerical analyses were performed using FLAC3D software to examine the slope’s response to seismic loading. Then in order to evaluate the damage trends of the rock mass under the different loading conditions, a calculation model based on the geological parameters and slope stability was simulated and analyzed using the discrete element numerical simulation program UDEC (Universal Distinct Element Code), and the effect of degradation of discontinuities on the slope stability was investigated. The results show that the destruction of rock mass under the gravity, bridge foundation, and seismic load are mainly concentrated within 30 m depth of slope, and the slope under loading may slide along joint planes. In addition, the dynamic analysis by amplification of the input loading indicates that instability occurs to the bank slope at a height of about 200 m, and rock blocks will fail under seismic load. Therefore, to prevent the slope from deformation under the engineering loading and strong earthquakes, the bridge foundation should be strengthened.

The role of vegetation in the daily and yearly small tilt variations of the Danube's high bank, Hungary

In this paper relationships between vital processes of plants and small movements of a river bank slope are investigated. For monitoring the movements, two geodetic test sites were established on the high loess bank of the river Danube at Dunafoldvar and Dunaszekcső in Hungary. At both sites two highly sensitive borehole tiltmeters were installed for continuous monitoring of movements. The recorded daily tilt amplitudes were compared with the precipitation and the potential evapotranspiration of the area. It was pointed out that the daily tilt amplitudes are in close connection with the vital processes of the plants. The precipitation effect on the seasonal variations of the tilt amplitudes is of minor importance which means that the vegetation has a much more important role in the water balance of the upper soil layer than the precipitation. Our investigation showed that the vegetation can be effective in hindering landslides occurrence since the infiltration of the precipitation into the deep soil layers and so the moistening of the high bank can be significantly diminished by planting appropriate vegetation on slopes.

하천 제방 비탈면 녹화용 자생 지피식물의 종자발아 특성에 관한 연구

To investigate the attributes of seed germination of the plants for greening of river bank slope, low-temperature treatment, chemical treatment, plant hormones treatment, and stratification were conducted using the seeds of 6 herbs growing naturally around river banks, such as Setaria glauca and faberii, Imperata cylindrica var. koenigii, Miscanthus sinensis, Pennisetum alopecuroides, Lespedeza cuneata and the seeds of 3 shrubs, such as Lespedeza bicolor., Rosa multiflora, Spiraea prunifolia for. simpliciflora. The findings are as follows. In case of herbs, Setaria glauca and faberii. have stone seeds. In the treatment with , they were germinated through dormancy breaking, even though there were some differences depending on immersion time, and the germination rate of Setaria faberii was a bit higher than that of Setaria glauca. The germination rate of Imperata cylindrica var. koenigii was low in the treatment with , NAA, and the plant hormone, but the seed germination rate has improved and the germination rate of Miscanthus sinensis and Pennisetum alopecuroides showed the improved seed germination rate in low temperature treatment. In case of Lespedeza cuneata and bicolor, the leguminous plants, the treatment with was most effective for the improvement of seed germination and the decrease in germination time. Only Spiraea prunifolia for. simpliciflora, the rose among 3 woody plants showed the seed germination rate above 50% without any additional treatment. Thus, it was thought to be appropriate for greening. Rosa multiflora showed the attribute of germination in a dark condition at low temperature through stratification, despite its low germination rate. Based on the results as above, with respect to the greening using directly collected seeds, Miscanthus sinensis, Pennisetum alopecuroides, and Spiraea prunifolia for. simpliciflora are suitable for greening, because they do not need any additional treatment, and Lespedeza cuneata and bicolor are also suitable for greening because it is possible to improve the germination rate and reduce the germination time through the treatment on the seeds before sowing.

Incipient motion of cohesionless sediments on riverbanks with ground water injection

This study investigates the influence of ground water injection on the initial movement of non-cohesive sediment particles on a riverbank slope analytically and experimentally. By including the hydraulic gradient in the force analysis, the critical condition was derived to account for the effect of seepage flow, showing that the seepage hydraulic gradient and the riverbank slope are governing parameters in modifying the incipient motion of sediments on a riverbank slope. Experimental investigations were performed in an open-channel flume for various riverbank slopes and hydraulic gradients of injection, showing that the critical shear stress increases with decreasing riverbank slopes and vise-versa, while injection reduces the critical value. All experimental data agree well with the theoretical derived expression of the critical condition in the case of injection.

Species Distrbution within Riparian Landcape along Mayo Kam of Gashaka Taraba State, Nigeria

The study examines species density and diversity distribution in riparian landscape along 18km stretch of Mayo Kam. Total of 117 Samples quadrants of 125m2 (46), 225m2 (25), and 275m2 (46) from strata 5m (zone A), 9m (zone B), and 11m (zone C) respectively away from the Channel Bank Edge (CBA) through the Hydraulic Floodplain (HFP) and the Genetic Floodplain (GFP) were delineated and detailed survey was carried out. Data was collected on river bank morphology, altitude a.m.s.l., slope gradient, soil type, and tree species density and diversity. Result of species distribution revealed mean densities and diversities in zones A, B, and C as, 10 and 4 per 125m2, 10 and 3 per 225m2, and 23 and 5 per 275m2 respectively. Accordingly, density and diversity per 625m2 show maximum of 83 and 8 and minimum of 5 and 5 on outer convex bank and inner straight bank. Brachystigia eurycoma, Vetix doniana, Andria enermis and Diospyrus spp are the obligates of zone A. Characterizing zone B are Anogeisus leocarpus, Peninari excelsa, Crossoptyx februfuga and Nauclea latifolia species while, common species in zone C are Uapaka togoensis, Terminalia glaucoscens, and Grewia mollis. The dense and diverse pattern in the distribution within the three zones is importantly due to relative location of stratum from channel flow (variation in moisture availability), morohologic form, soil type and slope gradient.Key Words: Bank form, density, diversity, landscape, Mayo Kam, riparian, species

An Analysis of River Bank Slope and Unsaturated Flow Effects on Bank Storage

Recognizing the underlying mechanisms of bank storage and return flow is important for understanding streamflow hydrographs. Analytical models have been widely used to estimate the impacts of bank storage, but are often based on assumptions of conditions that are rarely found in the field, such as vertical river banks and saturated flow. Numerical simulations of bank storage and return flow in river-aquifer cross sections with vertical and sloping banks were undertaken using a fully-coupled, surface-subsurface flow model. Sloping river banks were found to increase the bank infiltration rates by 98% and storage volume by 40% for a bank slope of 3.4° from horizontal, and for a slope of 8.5°, delay bank return flow by more than four times compared with vertical river banks and saturated flow. The results suggested that conventional analytical approximations cannot adequately be used to quantify bank storage when bank slope is less than 60° from horizontal. Additionally, in the unconfined aquifers modeled, the analytical solutions did not accurately model bank storage and return flow even in rivers with vertical banks due to a violation of the dupuit assumption. Bank storage and return flow were also modeled for more realistic cross sections and river hydrograph from the Fitzroy River, Western Australia, to indicate the importance of accurately modeling sloping river banks at a field scale. Following a single wet season flood event of 12 m, results showed that it may take over 3.5 years for 50% of the bank storage volume to return to the river.

Active surface faulting or landsliding in the Lower Tagus Valley (Portugal)? A solved controversy concerning the Vila Chã de Ourique site

The Lower Tagus Valley has experienced significant (M 6–7) historical seismicity, evidencing the presence of seismogenic faults. These are still deficiently known due to the low strain rates and the recent alluvial sedimentation of the Tagus River that buries most of the structures, though Paleoseismic evidence was allegedly found by a research team in the Tagus valley, at a site 60 km N of Lisbon, near Vila Chã de Ourique (VCO). According to this team, trenching at the VCO site exposed an active thrust fault, evidencing the surface rupture of a large earthquake that occurred in 1531. Our studies performed at this site, comprising field observations with a reappraisal of the trench outcrops previously excavated, borehole drilling, soil mechanics laboratory testing, and seismic reflection acquisition, pointed to the alternative interpretation that the outcropping structures are gravitational and not of tectonic origin. The interpretation of new outcrops crosscutting the structures exposed at the trenches, as well as newly acquired high-resolution seismic reflection data, definitely exclude the active thrust fault explanation and support a gravitational slip model for all the observed structures. Gravitational slip in the river bank slope was promoted by low shear strength clays and high pore water pressure coupled with slope toe river erosion. Gravitational slides must have occurred prior to development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by borehole data and estimations of sedimentation rates.

Incipient Motion of Riverbank Sediments with Outflow Seepage

Based on a force analysis, an expression is derived to describe the critical Shields number for incipient motion of uniform cohesionless sediment particles on a riverbank slope in terms of flow parameters, outflow seepage, and physical and mechanical properties of sediments. Parametric studies were conducted to investigate quantitatively the effects of hydraulic gradient of seepage, slope angle, and flow direction on the critical Shields number. The results show that the critical Shields number decreases with an increase in the hydraulic gradient. Where bank collapse is concerned, the most dangerous direction of hydraulic gradient of outflow seepage is at an angle equal to the effective internal angle of friction of the sediment mass with respect to slope surface. At a certain value of hydraulic gradient, the critical Shields number decreases with increasing slope angle. Open flow becomes more erosive when the current direction changes from horizontally parallel with the riverbank line to turning downward.

Control of Chemotherapy-Induced Emesis with 5-Hydroxytryptamine-3 Antagonists

The paper presents a probabilistic study aimed at investigating the role of the soil hydraulic response on the stability of existing river embankments, for which the uncertainty and the inherent variability of geotechnical and hydraulic properties are typically greater when compared to new flood defence structures. The study has been carried out with reference to a specific, thoroughly investigated 20 m-long segment of the river Secchia banks (northern Italy), which experienced a catastrophic sudden failure after a period of intense rainfall, in January 2014. By taking such well-documented case as a base, the proposed probabilistic analyses consider three key aspects, typically disregarded in routine risk assessment procedures: i) transient seepage flow through earth structures due to time dependent hydraulic loads, ii) unsaturated conditions of soils forming the river embankment, iii) uncertainty of the soil model parameters, with special emphasis placed on the impact of intrinsic variability of unsaturated soil parameters. The numerical results, obtained from the application of the Point Estimate Method, allow identifying the crucial role of suction distribution on the probability of failure of the riverbank slopes and clearly show that such probability can be significantly underestimated when the variability of hydraulic parameters is neglected.

The effects of human impact on spatial structure of the riparian vegetation along the Ashida river, Japan

A vegetation map was prepared to clarify both the differences of patch size in each vegetation type and the changes of patch size in each river reach in the Ashida river running through the east part of Hiroshima Prefecture, Japan. With use of this map, the area and perimeter of each patch were measured. The microscale landform and distance from the river mouth of each patch were also recorded to analyze the habitat of vegetation and land-use. The vegetation and land-use types in the river were reflected in different patch size distributions. These were roughly divided into following four groups by cluster analysis: group A characteristic of large size patches occupying the major part; group B comprising a variety of patches from large size to small size; group C consisting of small patches covering the major part and group D with small number of patches. The vegetation types in group A tended to be observed mainly on river bank slope and major bed, while group B had a trend to occur mainly on minor bed and waterside lowland. For further scrutinization, the distributions of patch size in vertical course of the river were addressed after dividing the major part of the stream into four sections namely, 0–10, 11–20, 21–30 and 31–43 km from the river mouth, respectively. The smaller patches become dominant as the river reaches go upstream. The major vegetation types in group A were observed on artificial lands including bank slope and major bed, suggesting that human impacts such as flood protection works and regular mowing affected the spatial structure of riparian vegetation.

Field Experiment on Erosion-Resistance of Embankment of Ichinoseki Flood Detention Basin against Overflow.

Erosion resistance of a river bank slope with variety of plants was exeperimentally investigated. The experiment was carried out on a natural embankment of Ichinoseki Flood Detention Basin under rapid overflow condition. It is found that erosion resistance of embankment is governed by not only difference of distribution of plants but also mole holes in the bank.

The effects of litter displacement on riverbank vegetation

The hypotheses that litter deposition on riverbanks would depend on riverbank features and that litter mass would affect riverbank vegetation were tested by sampling vegetation, litter, and soil along a seventh-order stretch of the unregulated Vindel River in northern Sweden. Sampling was carried out within a horizontal litter gradient at the top of the riverbank where most of the litter deposition occurs. The amount of leaf litter left on the riverbank after flooding was significantly correlated (P < 0.05) with soil organic matter. In contrast, wood litter mass and total litter mass were not correlated (P > 0.05) with riverbank features such as soil organic matter, riverbank slope, or stem density. Species richness, species diversity, and the proportions of stemmed and nonstemmed species showed quadratic relationships (P < 0.05) with leaf litter mass, whereas ground vegetation cover decreased monotonically (P < 0.05) with increasing leaf litter mass. Tall, stemmed species were most frequent at eroded sites with low amounts of leaf litter and at sites where leaf litter had accumulated. In contrast, the highest proportion of low-growing species was found at sites with intermediate leaf litter masses. Community characteristics such as species richness, species diversity, and the proportions of stemmed and nonstemmed species (but not ground vegetation cover) were less strongly correlated with wood litter mass and total litter mass. Linear equations explained about half of the variation in ground vegetation cover along gradients of wood and total litter masses. Density and richness of seeds increased with increasing litter mass. We discuss the litter effects in terms of productivity and disturbance and conclude that flooding in pristine rivers may exert a considerable influence on riverbank vegetation as a result of litter displacement.