Effects of vegetation channel banks and gravel size on flow structure

Vegetation on river banks and bed roughness are important factors affecting flow structure, sediment transport, erosion and geomorphology in rivers. In this experimental study, the impacts of vegetation on flume walls, grain size of bed gravels and aspect ratio on characteristics of shear stress distribution, Coles' wake parameter, the kinematic energy correction factor (α) and the momentum correction factor (β) have been assessed. Reynolds stress distribution illustrates a three-layer pattern when the aspect ratio is smaller than 2. In addition, the aspect ratio and changes of vegetation affect α, β as well as the Coles' wake parameter Π.     

Scour prevention in bottomless arch culverts

Bottomless arch culverts are employed as ecological bridges at road crossings with their most common application being fish passage.The simulated culvert streambed should mimic the existing natural cha...     

Effects of accelerating and decelerating flows in a channel with vegetated banks and gravel bed

Experiments were conducted in an 8 m long,40 cm wide,and 60 cm deep re-circulating fiume with vegetated banks and gravel bed to study the effects of accelerating and decelerating flows on the flow stru...     

Graded and uniform bed load sediment transport in a degrading channel

Twenty runs of experiments are carried out to investigate non-equilibrium transport of graded and uniform bed load sediment in a degrading channel. Well-sorted gravel and sand are employed to compose four kinds of sediment beds with different gravel/sand contents, i.e., uniform 100%gravel bed, uniform 100% sand bed, and two graded sediment beds respectively with 53% gravel and 47% sand as well as 22%gravel and 78%sand. For different sediment beds, the experiments are conducted under the same discharges, thereby allowing for the role of sediment composition in dictating the bed load transport rate to be identified. A new observed dataset is generated concerning the flow, sediment transport and evolution of bed elevation and composition, which can be exploited to underpin devel-opments of mathematical river models. The data shows that in a degrading channel, the sand greatly promotes the transport of gravel, whilst the gravel considerably hinders the transport of sand. The promoting and hindering effects are evaluated by means of impact factors defined based on sediment transport rates. The impact factors are shown to vary with flow discharge by orders of magnitude, being most pronounced at the lowest discharge. It is characterized that variations in sand or gravel inputs as a result of human activities and climate change may lead to severe morphological changes in degrading channels.     

Experimental study of depth-limited open-channel flows over a gravel bed

Laboratory experiments of depth-limited open-channel flows over a gravel bed were conducted in the study.Two gravel patches with identical individual element size and different lengths(3.81 m and 7.5 m)were tested.The depth-limited uniform flow regime with relative submergence S_r(= D/k_s) ranging from2.68 to 5.94 was produced by adjusting the tailgate weir.The velocity profiles were measured by using both an ultra-sound velocity profiler(UVP) and an acoustic Doppler velocimeter(ADV).The conventional methods used to determine the zero-plane displacement and estimate the bed shear velocity were then reviewed and compared.The measured double-averaged(DA) velocity profiles were found to fit well with the log law and defect law with a non-universal Karman constant κ./κ-value remains nearly constant and in the range from 0.2 to 0.3 for the long patch(LP) cases and κ-values are scattered within a wider range from 0.3 to 0.5 for the short patch(SP) cases.While the Br-value in log law remains constant and equal to 8.5 for LP cases,the Br-value was found to decrease with the increase of the dimensionless roughness height k_s~+ for SP cases.The streamwise turbulence intensity distributions were found to be independent on the patch length and agree well with the available experimental data in the intermediate region and wall region.The Manning resistance coefficient and Darcy-Weisbach friction factor were analyzed.The κ-value decreases to 0.22 for the fitting of the logarithmic flow resistance law under small relative submergence.The value of the integration constant Ar in the logarithmic law falls within the normal range between 3.25 and 6.25.     

Sand and gravel mining: effects on ground water resources in Hancock county,Maine, USA

Based on this preliminary study, existing sand and gravel mining regulations (in Maine, USA) can be inferred to provide some protection to water resources. Sand and gravel deposits are important natural resources that have dual uses: mining for construction material and pumping for drinking water. How the mining of sand and gravel affects aquifers and change aquifer vulnerability to contamination is not well documented. Mining regulations vary greatly by state and local jurisdiction. This study test metrics to measure the effectiveness of mining regulations. The sand and gravel aquifer system studied is covered with former and active gravel pits to nearly 25% of its areal extent. Data from homeowner interviews and field measurements found scant evidence of changes in water quantity. Water quality analyses collected from springs, streams, ponds and wells indicate that the aquifer was vulnerable to contamination by chloride and nitrate. However, water quality changes can not be related directly to mining activities.     

碎石土振动压实动态监测方法研究

根据结构振动理论,分析了振动压实机械与被压土体的相互作用机理,研究了碎石土振动压实动态监测的理论依据,建立了一套适用于加速度监测仪的振动压实动态监测数据采集系统．在大量室内试验数据的基础上,研究了振动压实过程中加速度电信号响应随碎石土密实度的变化规律,发现二者具有显著的线性相关性．研究结果为实现快速有效的碎石土路基密实度实时动态监测提供了理论依据和工程指导．     

Distribution and provenance of the Baginton Sand and Gravel in the Wreake Valley,northern Leicestershire,England: Implications for inter-regional correlation

The Baginton Sand and Gravel is traced along the lower Wreake Valley as a continuous water-laid stratum at the base of the drift succession. Its properties closely resemble those previously described from the proto-Soar valley, namely an upward fining sequence and a composition dominated by pebbles of Triassic and Carboniferous origin. Such a provenance is consistent with the idea that the proto-Soar once followed a route eastwards past Melton Mowbray, and that the drainage along the lower Wreake Valley has been reversed in the course of Pleistocene times. However, the slope of the sand and gravel train appears to be to the west rather than the east, and the rockhead relief is also inconsistent with an eastward-flowing proto-Soar. Until this enigma is resolved, it would be imprudent to use the Baginton Sand and Gravel as the basis for inter-regional correlations. The issue is further complicated by the preservation at Brooksby of earlier interglacial or interstadial deposits whose temporal affinities remain unclear.     

Impacts of reforestation and gravel mining on the Malnant River, Haute-Savoie, French Alps

The Malnant River is a rapidly incising river with a French name that translates as “bad creek,” reflecting local opinion of the hazards from dramatic channel changes that have occurred in the last few centuries. Downcutting in the last three decades has created severe problems for farmers in this small watershed (16 km²) as bridges are undermined, streamside roads are threatened, and irrigation diversion structures are rendered unusable. The purpose of our study was to determine the extent and causes of downcutting. A detailed landcover map dated 1732 revealed that forest cover had been reduced by that time to 10% of the present-day cover. The Malnant was strongly affected by floods and debris torrents during the 18th and 19th centuries that delivered massive amounts of sediment. During the 20th century, reforestation reduced the sediment delivery from hillslopes. In addition, gravel extraction in the Malnant and in the Fier River (of which the Malnant is a tributary) has lowered the base level for the river. This initiated a knickpoint that moved upstream. Weirs placed in the Malnant in 1968 were used to measure rates of bed incision in the field. With a mean width of 4.0 m and degradation up to 36 cubic meters per meter channel length, the lower 4.5 km of the Malnant has experienced a net loss of approximately 163,000 m³ of bed material. Above the 4.5-km point on the Malnant, bedrock controls exist that have arrested the upstream-progressing degradation.