Beaver dams attenuate flow: A multi-site study     

Alan Puttock  Hugh A. Graham  Josie Ashe  David J. Luscombe  Richard E. Brazier 《水文研究》2021,35(2):e14017

Beavers can profoundly alter riparian environments, most conspicuously by creating dams and wetlands. Eurasian beaver (Castor fiber) populations are increasing and it has been suggested they could play a role in the provision of multiple ecosystem services, including natural flood management. Research at different scales, in contrasting ecosystems is required to establish to what extent beavers can impact on flood regimes. Therefore, this study determines whether flow regimes and flow responses to storm events were altered following the building of beaver dams and whether a flow attenuation effect could be significantly attributed to beaver activity. Four sites were monitored where beavers have been reintroduced in England. Continuous monitoring of hydrology, before and after beaver impacts, was undertaken on streams where beavers built sequences of dams. Stream orders ranged from 2nd to 4th, in both agricultural and forest-dominated catchments. Analysis of >1000 storm events, across four sites showed an overall trend of reduced total stormflow, increased peak rainfall to peak flow lag times and reduced peak flows, all suggesting flow attenuation, following beaver impacts. Additionally, reduced high flow to low flow ratios indicated that flow regimes were overall becoming less “flashy” following beaver reintroduction. Statistical analysis, showed the effect of beaver to be statistically significant in reducing peak flows with estimated overall reductions in peak flows from −0.359 to −0.065 m³ s⁻¹ across sites. Analysis showed spatial and temporal variability in the hydrological response to beaver between sites, depending on the level of impact and seasonality. Critically, the effect of beavers in reducing peak flows persists for the largest storms monitored, showing that even in wet conditions, beaver dams can attenuate average flood flows by up to ca. 60%. This research indicates that beavers could play a role in delivering natural flood management.  相似文献   

Estimating the fluvial sediment input to the coastal sediment budget: A case study of Ghana     

Isaac Boateng  Malcolm BrayJanet Hooke 《Geomorphology》2012,138(1):100-110

Knowledge of fluvial sediment supply to the coastal sediment budget is important for the assessment of the impacts on coastal stability. Such knowledge is valuable for designing coastal engineering schemes and the development of shoreline management planning policies. It also facilitates understanding of the connection between rivers in the hinterland and adjoining coastal systems. Ghana's coast has many fluvial sediment sources and this paper provides the first quantitative assessments of their contributions to the coastal sediment budget. The methods use largely existing data and attempt to cover all of Ghana's significant coastal rivers. Initially work was hindered by insufficient direct measured data. However, the problem was overcome by the application of a regression approach, which provides an estimated sediment yield for non-gauged rivers based on data from gauged rivers with similar characteristics. The regression approach was effective because a regional coherence in behaviour was determined between those rivers, where direct measured data were available. The results of the assessment revealed that Ghana's coast is dissected by many south-draining rivers, stream and lagoons. These rivers, streams and lagoons supply significant amounts of sediment to coastal lowlands and therefore contribute importantly to beaches. Anthropogenic impoundment of fluvial sediment, especially the Akosombo dam on the Volta River, has reduced the total fluvial sediment input to the coast from about 71 × 10⁶ m³/a before 1964 (pre-Akosombo dam) to about 7 × 10⁶ m³/a at present (post-Akosombo dam). This sharp reduction threatened the stability of the east coast and prompted an expensive ($83 million) defence scheme to be implemented to protect 8.4 km-long coastline at Keta. Sections of Ghana's coast are closely connected to the hinterland through the fluvial sediment input from local rivers. Therefore, development in the hinterland that alters the fluvial sediment input from those local rivers could have significant effects on the coast. There is the need, therefore, to ensure that catchment management plans and coastal management plans are integrated or interconnected.  相似文献   

THE INFLUENCE OF RIPARIAN VEGETATION COVER ON DIFFUSE LATERAL SEDIMENT CONNECTIVITY AND BIOGEOMORPHIC PROCESSES IN A MEDIUM‐SIZED AGRICULTURAL CATCHMENT,AUSTRIA     

RONALD E. POEPPL  MARGRETH KEILER  KIRSTEN VON ELVERFELDT  IRENE ZWEIMUELLER  THOMAS GLADE 《Geografiska Annaler: Series A, Physical Geography》2012,94(4):511-529

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泥石流沟谷坊坝群治理效应——以地震极重灾区北川县化石板沟为例     

周海波  陈宁生  卢阳  李兵 《山地学报》2012,(3):347-354

谷坊坝是泥石流治理的重要工程措施之一。化石板沟泥石流治理工程共设13座谷坊坝,组成梯级谷坊坝群;坝体主要分布在泥石流形成区和流通区,混凝土结构,轴向两端嵌入沟道两侧基岩0.5～1 m。通过对比化石板沟谷坊工程修建前后沟床纵坡比降、沟道两侧斜坡稳定性及泥石流侵蚀速率等方面的差异,证明谷坊工程能够有效拦蓄松散固体物质、稳固沟床和岸坡、降低沟道纵坡比降、降低泥石流流速和耗散流体能量、抬高沟道上游泥石流侵蚀基准面。研究发现,化石板沟谷坊坝群共拦截固体物质2.76×104 m3,仅占流域物源总量574.9×104 m3的0.5%,占近期可供给泥石流活动的物源量85×104 m3的3.3%;稳固沟床松散物质4.37×104 m3,仅占流域物源总量的0.76%,占近期可供给泥石流活动的物源量的5.2%;稳固沟道两侧坡体松散物质134.07×104 m3,占流域物源总量的23.3%,泥石流物源减少;回淤的沟道比降为原比降的60%～75%,相同频率下泥石流流速、峰值流量降低,沟道侵蚀速率下降,泥石流输沙量减少35%～57%;上游泥石流支沟侵蚀基准面抬升0.3～0.5 m。泥石流呈现从粘性到稀性,再到含沙水流的趋势发展。  相似文献   

Evaluation of Plasticity Models’ Ability to Analyze Typical Earth Dams’ Soil Materials     

C. J. Loupasakis  B. G. Christaras  G. Ch. Dimopoulos  T. N. Hatzigogos 《Geotechnical and Geological Engineering》2009,27(1):71-80

The selection of the constitutive laws reproducing the response of geomaterials usually becomes a very complicated procedure; especially during the analysis of geostructures containing coarse grained materials. The objective of this study, is the evaluation of models based on the perfect and hardening plasticity theory, regarding their ability to analyze the behaviour of soil materials, used for the construction of earth dams. The evaluated constitutive laws are the elastic–perfect plastic model based on the Mohr–Coulomb failure criterion and the isotropic hardening CAP model based on the same criterion. The data used for the evaluation of the models, originate from the body of the Sfikia earth dam. This dam is considered suitable, because of the specialized laboratory tests’ available data, regarding the materials of every zone. The availability of those data, as well as the variety of the construction geomaterials, allows the deduction of generalized conclusions, concerning the ability of the specific models to simulate a variety of similar earth constructions.  相似文献   

Asymptotic formulae for correcting finite element predicted natural frequencies of gravity and embankment dams     

Chongbin Zhao  G.P. Steven 《Soil Dynamics and Earthquake Engineering》1996,15(3):161-169

Extraction of natural frequencies of a gravity dam or an embankment dam plays an important role in the seismic design of the dam because the seismic response of a dam is dependent largely on the dynamic characteristics of the dam. Owing to the lack of exact solutions and the geometry of a dam, numerical methods such as finite element methods have been often used to extract the natural frequencies of the dam. Since the finite element method is an approximate one, the resulting finite element solution to the natural frequency of a dam cannot be safely used unless its accuracy is evaluated within the acceptable range for the seismic design of the dam. To solve this problem, some asymptotic formulae for correcting the finite element predicted natural frequencies of a gravity dam and an embankment dam have been developed in this paper. Since the present asymptotic formulae are derived from the fact that the finite element solution tends to the exact one if the finite element size used approaches zero, they provide a corrected solution of higher accuracy for the natural frequency of a dam so that the accuracy of a finite element solution can be evaluated against this corrected solution. After the correctness and usefulness of the present formulae are assessed, two practical examples have been given to show how the asymptotic formulae can be used to correct and evaluate the discretization error for the finite element predicted natural frequencies of gravity dams and embankment dams.  相似文献   

Seismic hazard evaluation for dams in northern Colorado, U.S.A.     

Ute R. Vetter  Jon P. Ake  Roland C. Laforge 《Natural Hazards》1996,14(2-3):227-240

A seismic hazard evaluation for three dams in the Rocky Mountains of northern Colorado is based on a study of the historical seismicity. To model earthquake occurrence as a random process utilizing a maximum likelihood method, the catalog must exhibit random space-time characteristics. This was achieved using a declustering procedure and correction for completeness of recording. On the basis of the resulting a- and b-values, probabilistic epicentral distances for a 2 × 10^–5 annual probability were calculated. For a random earthquake of magnitude M _L 6.0–6.5, this distance is 15 km. Suggested ground motion parameters were estimated using a probabilistic seismic hazard analysis. Critical peak horizontal accelerations at the dams are 0.22g if median values are assumed and 0.39g if variable attenuation and seismicity rates are taken into account. For structural analysis of the dams, synthetic acceleration time series were calculated to match the empirical response spectra. In addition, existing horizontal strong motion records from two Mammoth Lakes, California earthquakes were selected and scaled to fit the target horizontal acceleration response spectra.  相似文献   

Seismic fragility assessment of concrete gravity dams     

Paulos B. Tekie  Bruce R. Ellingwood 《地震工程与结构动力学》2003,32(14):2221-2240

Many concrete gravity dams have been in service for over 50 years, and over this period important advances in the methodologies for evaluation of natural phenomena hazards have caused the design‐basis events for these dams to be revised upwards. Older existing dams may fail to meet revised safety criteria and structural rehabilitation to meet such criteria may be costly and difficult. Fragility assessment provides a tool for rational safety evaluation of existing facilities and decision‐making by using a probabilistic framework to model sources of uncertainty that may impact dam performance. This paper presents a methodology for developing fragilities of concrete gravity dams to assess their performance against seismic hazards. The methodology is illustrated using the Bluestone Dam on the New River in West Virginia, which was designed in the late 1930s. The seismic fragility assessment indicated that sliding along the dam–foundation interface is likely if the dam were to be subjected to an earthquake with a magnitude of the maximum credible earthquake (MCE) specified by the U.S. Army Corps of Engineers. Moreover, there will likely be tensile cracking at the neck of the dam at this level of seismic excitation. However, loss of control of the reservoir is unlikely. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

修筑寒区小型水利工程的经验回顾     

Rudolf V. Zhang 《冰川冻土》2004,26(Z1):12-20

The paper provides a review of experience with the construction of hydraulic projects in the permafrost regions. Principles for construction, operation and maintenance of earth dams are refined and formulated. High priority needs for improving the stability of structures are identified.  相似文献   

Continuous ambient‐vibration monitoring of the arch dam of Mauvoisin     

Georges R. Darbre  Jean Proulx 《地震工程与结构动力学》2002,31(2):475-480

This paper presents the experimental programme and results of a continuous ambient vibrations recording programme carried out on the 250 m arch dam of Mauvoisin. This project follows a series of previous measurements completed for seven different water levels. An automated system was set up on the dam and the ambient vibrations were recorded twice daily for a period of 6 months. Frequency shifts were tracked throughout the testing period and the effects of the varying water level were identified. The results confirmed the behaviour observed in previous ambient‐ and forced‐vibration tests. The added‐mass effects are overcome by the stiffening of the dam due to increasing hydrostatic pressure for lower reservoir levels. This trend is then reversed for higher water levels. Any temperature‐related effects were not identified. The experimental techniques are briefly described and the frequency identification process and its limitations are discussed. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献