Flexible Dam Research Articles

Drag Coefficient of Emergent Flexible Vegetation in Steady Nonuniform Flow

AbstractFlexible vegetation plays key roles in the natural channel and riparian ecology. This paper investigates the drag coefficient Cdf of an emergent flexible vegetation array in a steady nonuniform flow. Laboratory flume tests of five vegetation densities exposed to a constant flow rate were conducted, and the variation in the water surface was accurately measured. The Saint‐Venant equation was applied to explore vegetation hydrodynamics under nonuniform conditions, and a more widely applicable formula for the vegetated drag of nonuniform flow was proposed. Furthermore, the flexible drag coefficient factor αb was used to represent the flexibility and drag reconfiguration, which were explored from the perspective of material mechanics. The results reveal that the calculated values of Cdf exhibit nonmonotonic variation with increasing Reynolds number along the streamwise direction due to the flow nonuniformity. There are two effects of blockage and sheltering in the emergent vegetated patch: The blockage effect increases the drag coefficient, while the sheltering effect—especially at the leading edge and tail of the vegetated patch—reduces the drag of the flexible canopy due to bending deformation. These two effects achieve equilibration in dense flexible canopies. Finally, by relating αb to flexibility through the slenderness Cauchy number CYS, a nonmonotonic pattern can be obtained for each test. A fitting formula was proposed based on αb as a function of CYS. The results presented in this study can potentially support applications related to the plant flexible dams and vegetated filter strips for river ecosystems.

Pisha sandstone: Causes, processes and erosion options for its control and prospects

Pisha sandstone is a special kind of soft rock in the semiarid region along the up and middle reaches of Yellow River and Loess Plateau and is severely eroded by wind, rainfall and gravity force. Pisha sandstone region is called “the most severe water loss and soil erosion in the world” and referred to as the “Earth Cancer” by local residents and experts both at home and abroad. The plan for the control of Pisha sandstone started in the 1950s. Since then a series of projects have been implemented, both engineering and vegetation measures have been developed and widely used to protect Pisha sandstone from erosion. Since seabuckthorn was introduced as a viable approach for soil erosion protection and its implementation resulted in a breakthrough to control Loess Plateau, it was considered as an important and efficient measure. Then the seabuckthorn flexible dam was proposed for coarse sediment retention and fine sediment deposition. And then a new comprehensive control model using consolidation materials combined with vegetation was proposed and promising results were achieved both in laboratory and field demonstrations. In the future, the complex erosion mechanism and ecological carrying capacity should be studied further and more efficient and practical comprehensive measures shall be developed. Moreover, monitoring systems shall be used to predict and detect the changes in the Pisha sandstone slope and structure.

Effectiveness of Flexible Dam Operation and Sediment Replenishment at Managawa Dam, Japan

A field demonstration project on flexible dam operation at the Managawa dam in the Kuzuryu River Basin has been implemented since 2000. The goal is to restore flow and sediment regimes in the Managawa River, which flows along the Ono-city and is located below the dam. Flexible dam operation stores inflow discharge into a reservoir, which generally uses part of the flood control capacity and appropriately discharges the stored water to the river, also known as the “flood pulse,” for restoring dynamic fluvial systems and the resulting ecological processes. In addition, other options have been carried out in combination with flexible dam operation, for example, sediment replenishment since 2003 and channel rehabilitation since 2007. This article reveals the positive impacts and effectiveness of flexible dam operation, sediment replenishment, and channel rehabilitation, and discusses challenges and future prospects toward translating the field demonstration project into dam management on the ground level. First, we classified reach types to identify the impact of various management options, e.g., flexible dam operation, sediment replenishment, and channel rehabilitation. These management options can influence respected reaches. We conducted a macro-scale analysis to understand the relationship between the aforementioned management options and dynamic fluvial systems, addressing changes in gravel riverbed, vegetation, and habitat types (riffles and pools). Second, a micro-scale analysis was conducted to understand the relationship between the management option and changes in attached algae to sediment and macro-invertebrates, etc. The results show the effectiveness of the middle-scale flood pulse to restore dynamic fluvial systems, increase habitat diversity, and sustain ecological processes. Furthermore, we discussed the impacts of such options on the flow and sediment regimes in Managawa River and revealed that flexible dam operation reduces the occurrence of low flow and midscale floods. It was also revealed methods such as sediment replenishment and channel rehabilitation play an important role in increasing the effectiveness of the middle-scale flood pulse and restoring dynamic fluvial systems, even though sediment replenishment is not sufficient to restore sediment regimes (i.e., bring then back to pre-dam conditions).

Experimental study on mechanism and shape characteristics of suspended flexible dam

Hydraulic structures such as groin, longitudinal dike and seawall are common in water conservancy and water transportation engineering projects at home and abroad, which have long been dominated by solid mass structural form. With brush and stone as building materials, this kind of structure has an obvious engineering effect. However, it not only requires huge capital investments, but also has negative impacts on the ecological environment. The suspended flexible dam is an innovative engineering measure, and few theoretical and experimental researches of this type dam can be found at present. This paper studies the mechanism and shape characteristics of this dam and obtains the dynamic equilibrium equation of flexible dam, the float buoyancy expression, and the condition for transformation among three forms of the underwater shape of the dam. The results are valuable in engineering application and can be used as the reference for the future work due to the distinctive design philosophy, the small negative effects on environment and the consistency for sustainable development.

Spatial Variation of Soil Organic Matter in Gully Bed with the Seabuckthorn Flexible Dam: A Case Study of EG1 in Zhun-Ge-Er County of Inner Mongolia, China

In this paper, based on geostatistics and GIS techniques, spatial variation characteristics of soil organic matter (acronym: SOM) on a small scale were analyzed and discussed in east-one-branch gully (EG1) bed with the seabuckthorn flexible dam and the contrastive gully bed (which is non-vegetated any vegetation) located in zhun-ge-er county, Erdos, inner Mongolia, which belongs to the typical Pisha Sandstone area. The results show that the seabuckthorn can significantly increase SOM in the small catchment gully bed in the Pisha sandstone area, and the mean SOM content in gully bed with the seabuckthorn flexible dam is approximate 1.75 times that in the contrastive gully. Apparent spatial variation characteristics of SOM were found in the gully with the seabuckthorn flexible dam and the contrastive gully bed, moreover, the medium spatial autocorrelation of SOM was detected in gully bed with the seabuckthorn flexible dam, and the spatial variation of SOM was together led to by the structural and random variation at 1-6.5 m range, and of which the random variation accounts for 40%. Additional, the spatial autocorrelation of SOM in the contrastive gully bed is higher, the spatial variation of SOM was dominantly brought about by the structural variation at 1-4.5 m range, and of which the random variation accounts for 37%. Furthermore, the fractal dimension values reveal that dependence of SOM of the gully bed with the seabuckthorn flexible dam on spatial is weaker than that of the contrastive gully bed. It is judged that the seabuckthorn has an obvious effect on spatial distribution patterns and heterogeneity of SOM on a small scale.

Simulation of sediment retention effects of the double seabuckthorn plant flexible dams in the Pisha Sandstone area of China

The Pisha Sandstone area is located in the triangle region close to Shanxi Province, Shaanxi Province, and Inner Mongolia Autonomous Region in Northwestern China. This area is the main source of coarse sediment entering into upper and middle reaches of Yellow River of China. The area is often called as “the most severe soil and water loss area in the world” and compared to “the cancer of the earth” due to the extremely serious soil and water loss and poor eco-environment. To control the coarse sediment delivering into Yellow River and restore the ecology of this area, the seabuckthorn plant flexible dam, a new ecological engineering, was proposed and used widely in this area. In this paper, the sediment retention effects of the double seabuckthorn flexible dams (“SFDs”) after seven years in the Pisha Sandstone gully were simulated using one-dimensional sediment and water mathematical model. Based on the computational results, several major design and planting parameters and their values were analyzed and discussed, including the dam length, the dam gap, the roughness as well as the slope of gully bed. The interaction among these parameters was also discussed according to the simulation results. We found that the sediment retention effects of the double seabuckthorn plant flexible dams were also dependent on the rainfall events and the gully topography. This study provides the theoretical proof for the design and planting of the double seabuckthorn flexible dams (i.e., a new ecological engineering) in the Pisha Sandstone area.

Numerical modelling of hydrodynamic pressures on dams

This paper discusses several considerations related to appropriate numerical modelling of the reservoir hydrodynamic pressures on dams. The reservoir is modelled with 8-noded isoparametric displacement based solid finite elements. The study includes both stiff and flexible dams with vertical and sloped upstream faces under ramp, harmonic and random acceleration loads. The numerical results were compared and found to be in good agreement with available closed-form solutions. The same approach may be used in analyses of other waterfront structures such as quay walls.

Simulation of sediment retention effects of the single seabuckthorn flexible dam in the Pisha Sandstone area

Pisha Sandstone area is located in an adjacent region close to Inner Mongolia Autonomous Region, Shaanxi and Shanxi province of northwestern China, which covers an area of more than 11,000km2. Pisha Sandstone is a kind of loosely bonded sandstone formed during the tertiary period. It is very hard when it is dry but becomes loose when wet. Due to the nature of that, this area of northwestern China is plagued with a high erosion rate (over 20,000tkm−2yr−1) as well as poor vegetation. In order to reforest gullies and to control erosion in this area, the seabuckthorn flexible dam that is actually a new biological measure focused on by many people was successfully used to reduce the erosion rate of the area. This paper aims at the identification and/or determination of the major impact factors which essentially influence the sediment retention effects of the seabuckthorn flexible dam. Firstly, the sediment retention effects of the single seabuckthorn flexible dam were simulated using one-dimensional sediment-flow model in this study. Then, based on the computational results, two major impact factors, i.e. roughness and dam length of the seabuckthorn flexible dam, were found. Finally, according to the sediment retention effects under various roughness and dam lengths condition, a series of the suitable length ranges of the seabuckthorn flexible dam were given in corresponding to a series of the seabuckthorn flexible dam's roughness. The results show that the seabuckthorn flexible dam can strikingly and effectively reduce sediment loss from the gully. An emphasis is placed on widely spreading and planting of the seabuckthorn flexible dam in the Pisha Sandstone area in the future to prevent soil and water loss and to achieve at least good ecological status.

Block Sand Mechanism Experiment and Analysis of Vegetation Flexible Dam

By the indoor flume model experiment, this paper analyzed the block sand mechanism of turbid water appearance. The experiment was done under 1/150, 1/100 and 1/50 three base slopes with 5.09L/s, 9.08L/s and 13.08L/s three discharges. Carried on an observation to the variety that vegetation dam’s in front and back single grain sediment sport speed, and silted up appearance with the sediment in the dam to carry on analysis before the dam to the plant. The experiment showed that the base slope is more big, the damping extent in sport in sediment in upper stream of vegetation dam’s reduce more small, the sediment attains to lose the sand early more equilibrium, and the blocks sand result of vegetation dam is more bad.

댐-호소계 비선형 지진응답의 직접시간영역 해석기법

이 논문에서는 댐-호소계의 선형 및 비선형 지진응답 해석을 시간영역에서 엄밀히 수행할 수 있는 해석법을 제시하였다. 댐-호소계는 (1) 선형 또는 비선형으로 거동하는 댐체와 (2) 깊이가 균일하다고 가정한 호소 원역 및 (3) 댐체와 호소 원역 사이 불규칙한 형상의 근역의 세가지 부구조물로 구성된 연계 시스템으로 정식화되었다. 댐체는 선형 또는 비선형 유한 요소로 모델링되고, 호소 원역은 무한 영역으로의 에너지 방사를 엄밀하게 표현할 수 있도록 주파수영역에서 개발된 변위기반 전달경계를 시간영역에서의 포갬적분으로 변환하여 시간증분법과 결합이 용이하게 하였다. 호소 근역을 댐체와 호소 원역이라는 두 개의 부구조물 사이에 저장된 압축성 유체로 모델링하였다. 이 논문에서는 세 개의 부구조물로 구성되는 댐-호소계에 대해 비선형 시간영역 해석을 용이하게 하는 시간증분법을 유도하여 제시하였고 개발된 해석법을 다양한 형상의 댐-호소계의 지진응답 해석에 적용하여 그 정확성을 검증하였다. 이에 추가하여 제시한 기법을 콘크리트 댐의 비선형 지진응답 해석에 적용하여 손상 정도와 부위를 해석 결과로서 보여주었으며 동시에 제시한 기법이 내진성능 평가 등 실무에 바로 활용될 수 있음을 입증하였다. An analysis method is proposed for the transient linear or nonlinear analysis of dynamic interactions between a flexible dam body and reservoir impounding compressible water under earthquake loadings. The coupled dam-reservoir system consists of three substructures: (1) a dam body with linear or nonlinear behavior; (2) a semi-infinite fluid region with constant depth; and (3) an irregular fluid region between the dam body and far field. The dam body is modeled with linear and/or nonlinear finite elements. The far field is formulated as a displacement-based transmitting boundary in the frequency domain that can radiate energy into infinity. Then the transmitting boundary is transformed for the direct coupling in the time domain. The near field region is modeled as a compressible fluid contained between two substructures. The developed method is verified and applied to various earthquake response analyses of dam-reservoir systems. Also, the method is applied to a nonlinear analysis of a concrete gravity dam. The results show the location and severity of damage demonstrating the applicability to the seismic evaluation of existing and new dams.

Hydrodynamic pressures behind flexible and rigid dams

During earthquakes, hydrodynamic pressures are generated by the impounded reservoir on the dam face. The magnitude and distribution of the hydrodynamic pressures vary with factors such as frequency and intensity of earthquake-induced ground motion, depth of impounded reservoir, stiffness of dam and geological conditions. It is difficult to obtain experimental data on hydrodynamic pressures from the field owing to uncertainties associated with earthquake loading. This paper aims at using dynamic centrifuge modelling to measure hydrodynamic pressures behind both relatively stiff and flexible model dams. Comparisons of the experimental data with theoretical hydrodynamic pressures show that Westergaard's equation gives a conservative estimation of hydrodynamic pressures. Comparison with Chopra's method revealed that it underpredicts hydrodynamic pressures for low reservoir depths but gives reasonably good predictions for higher depths of reservoir. It is concluded that dynamic centrifuge modelling may be an effective experimental method to estimate the hydrodynamic pressures acting on a dam.

Rockfall Protection as an Integral Task

Among the different natural hazards, rockfall has an important place even though other natural hazards could affect more people or have greater consequences. The phenomenon may be further classified according to the size of the largest blocks and the total rock mass involved. The risk management procedure can be divided into (a) hazard identification and description, (b) hazard assessment and (c) risk management and treatment. Initiation zones of rockfall are identified and characterized by using geodetic, geomorphic, geotechnical and historical data. Trajectories are analyzed and boulder impacts are modelled to identify endangered areas. A variety of methods exist to estimate the frequency of rockfall events. Finally, hazard maps are produced that indicate the hazard level based on the intensity and probability of rockfall events. Together with indications on the occupancy and vulnerability of buildings and infrastructure, risks can be calculated and compared with acceptable values for new projects and tolerable ones for existing assets. The most effective countermeasure is land-use planning to avoid dangerous areas. If this is not possible or existing assets have to be protected, geotechnical and structural mitigation measures are justified. They cover measures in the initiation zone, along the propagation path and in the deposit zone. The types of structure used are flexible barriers, galleries, embankments and dams, depending on the position of the protective measure and the available space, the energy to be absorbed and other functions the structures should fulfill. Structures are dimensioned to withstand the impact of a design block, taking into account the damping effect of a possible cushion layer and the dynamic response of the structure itself.

Research and application of flow visualization technique in large-scale hydraulic models

With the rapid development of computer and optical technique, as a powerful measuring method in hydrodynamics, flow visualization technique is able to get much flow field information in practical engineering. It also has an important meaning to projects and environmental areas. The image processing is the key to flow visualization for gaining flow field information. In terms of the PIV principles, the algorithm of PIV based on Fast Fourier Transformation (FFT) is studied, and the image mosaic program based on genetic algorithm has been compiled. The flow field of seabuckthorn flexible dam has been calculated and analyzed by using those methods as above-mentioned, and in the meanwhile, the application of flow visualization technique to measure the outdoor flow field has been studied exploringly, which proves that it is feasible to apply this technique to measure the large-scale outdoor flow field.

Representation of radiation damping in a dam–reservoir interaction analysis based on a rational stiffness approximation

In this paper, the dam–reservoir interaction problem is solved directly in the time-domain by modelling a part of the reservoir as a semi-infinite fluid-channel. Radiation damping is taken into account rigorously using an analytical solution with respect to the direction of wave propagation. The key step of the method consists of approximating the resulting modal flux–pressure relationship by a rational function in i Ω, which can be replaced by a system of linear equations in the frequency-domain. Two algorithms for the calculation of the coefficients of the rational function are described and compared. Finally, a system of first-order differential equations in the time-domain is obtained which completely represents the semi-infinite fluid-channel and can be coupled to the equations of motion of a dam and a bounded reservoir. The proposed strategy is verified considering a rigid dam. Moreover, the results of an earthquake analysis of a coupled flexible dam–reservoir system are presented.

Earthquake‐Induced Base Sliding of Concrete Gravity Dams

Analytical procedures are developed considering hydrodynamic effects to determine the response history of earthquake-induced sliding of a gravity dam monolith supported without bond on a horizontal, planar surface of rock. The results presented indicate that the permanent sliding displacements of dams induced by ground motions with peak acceleration of 0.5g may range from a few inches to a couple of feet. Also examined in this work is the possibility of estimating the sliding displacement of a flexible dam due to ground acceleration by analyzing the sliding response of a rigid dam due to an average (over height) acceleration computed from linear analysis of the flexible dam without sliding at the base. The results presented indicate that this approximate procedure, which has been widely used in estimating the deformations of embankment dams, can provide an order-of-magnitude estimate of the concrete dam sliding displacement, which is conservative for most cases when this displacement is practically significant.

A note on the shapes of flexible dams

Flexible dams are in use as both temporary and permanent structures in a number of countries and consist of a flexible membrane secured to the channel bed. The membrane of the more common inflatable ones is secured at both ends and the dam inflated with air or water. Parachute dams in which the upper end of the membrane is fixed to a floating boom and restrained by guys are also discussed. The paper deals with the theoretical calculation of the shape of these dams when the retained water level is just at the crest of the dam, (i.e. with no overflow). In particular it deals with how the shape of a dam changes with increasing inflation and hence with the selection of the design parameters (the length of the membrane, the distance between the anchorages and inflation pressure) for a dam required for a given purpose.

Flexible Dams Inflated by Water

An inflatable dam is a tube of flexible material inflated by water or air to impound water. The profile of the water inflated dam is obtained numerically. The relationships between the parameters that govern the shape of dam are presented in the form of charts.

The theory of flexible dams by water pressure

The theory of flexible dams by water pressure