Hydraulic analysis of cell-network treatment wetlands     

Huaguo Wang  James W. Jawitz 《Journal of Hydrology》2006,330(3-4):721-734

When individual cells of a multiple-cell treatment wetland are hydraulically connected, the wetland has a cell-network structure. The hydraulic performance of treatment wetlands is often characterized using tracer residence time distributions (RTDs) measured between the wetland inlet and outlet, such that the wetland is considered as a single hydraulic unit, regardless of the extent of networking between individual internal cells. This work extends the single hydraulic unit approach to enable the specification of moments and RTD parameters for individual cells, or clusters of cells, within the cell-network based on inert tracer tests with injection only at the network inlet. Hydraulic performance is quantified in terms of hydraulic efficiency and travel time dimensionless variance using both the method of moments and RTD modeling. Cell-network analysis was applied to a case study from the Orlando Easterly Wetland (OEW), demonstrating the improvement in hydraulic performance of individual wetland cells following wetland restoration activities. Furthermore, cell-network analysis indicated that the location of water quality sampling station locations within the cell network can significantly affect the accuracy of pollutant removal effectiveness estimation when the individual sample station RTD does not represent the hydraulic unit RTD. At the OEW, it was determined that historical nutrient removal effectiveness estimation may be underestimated for one area and overestimated for another, and recommendations were provided for sample station locations to minimize future performance estimation errors.  相似文献   

The dynamics of a channel-fed lava flow on Pico Partido volcano, Lanzarote     

Duncan Woodcock  Andrew Harris 《Bulletin of Volcanology》2006,69(2):207-215

A short length of channel on Pico Partido volcano, Lanzarote, provides us the opportunity to examine the dynamics of lava flowing in a channel that extends over a sudden break in slope. The 1–2-m-wide, 0.5–2-m-deep channel was built during the 1730–1736 eruptions on Lanzarote and exhibits a sinuous, well-formed channel over a steep (11° slope) 100-m-long proximal section. Over-flow units comprising smooth pahoehoe sheet flow, as well as evidence on the inner channel walls for multiple (at least 11) flow levels, attest to unsteady flow in the channel. In addition, superelevation is apparent at each of the six bends along the proximal channel section. Superelevation results from banking of the lava as it moves around the bend thus causing preferential construction of the outer bank. As a result, the channel profile at each bend is asymmetric with an outer bank that is higher than the inner bank. Analysis of superelevation indicates flow velocities of ~8 m s^–1. Our analysis of the superelevation features is based on an inertia-gravity balance, which we show is appropriate, even though the down-channel flow is in laminar flow. We use a viscosity-gravity balance model, together with the velocities calculated from superelevation, to obtain viscosities in the range 25–60 Pa s (assuming that the lava behaved as a Newtonian liquid). Estimated volume fluxes are in the range 7–12 m³ s^–1. An apparent down-flow increase in derived volume flux may have resulted from variable supply or bulking up of the flow due to vesiculation. Where the channel moves over a sharp break in slope and onto slopes of ~6°, the channel becomes less well defined and widens considerably. At the break of slope, an elongate ridge extends across the channel. We speculate that this ridge was formed as a result of a reduction in velocity immediately below the break of slope to allow deposition of entrained material or accretion of lava to the channel bed as a result of a change in flow regime or depth.  相似文献   

Hydraulic and compaction characteristics of leachate-contaminated lateritic soil   总被引：2，自引：0，他引：2  

Sitaram Nayak  B.M. Sunil  S. Shrihari   《Engineering Geology》2007,94(3-4):137-144

Large quantities of leachate-contaminated lateritic soil results from dump yards in the southwest coast of India. These dump yards receive large quantities of municipal solid waste which includes chemical, industrial and biomedical wastes. Large areas of land are currently being used for this purpose. An extensive laboratory testing program was carried out to determine the compaction characteristics and hydraulic conductivity of clean and contaminated lateritic soil. Batch tests were used to study the immediate effect of leachate contamination on the properties of lateritic soil. Contaminated specimens were prepared by mixing the lateritic soil with leachate in the amount of 5%, 10% and 20% by weight to vary the degree of contamination. The results indicated a small reduction in maximum dry density and an increase in hydraulic conductivity due to leachate-contamination. The change induced by chemical reaction in the microstructure of the soil was studied by scanning electron microscope before and after contamination of soil with leachate. The structure of the leachate contaminated soil sample appeared to be aggregated in scanning electron microscope analysis. The aggregated structure increases the effective pore space and thus increases the hydraulic conductivity. Fifty percent increase in hydraulic conductivity was observed for specimens prepared at standard Proctor density and mixed with 20% leachate. Compaction characteristics did not change much with the presence of leachate up to 10%. With 20% leachate the maximum dry density decreased slightly indicating excess leachate in the soil. However the changes are not significant.  相似文献   

Roughness control on hydraulic conductivity in fractured rocks   总被引：1，自引：0，他引：1  

Laura Scesi  Paola Gattinoni 《Hydrogeology Journal》2007,15(2):201-211

The influence of joint roughness on the typologies of fluid flow inside fractures is well known and, thanks to experiences in the field of hydraulics, it has been studied from both a physical and mathematical point of view. Nevertheless, the formulations adopted by traditional hydraulic models are hardly applicable in the geological field, because of the difficulty encountered in the roughness parameter estimation. Normally this parameter can be estimated using the joint roughness coefficient (JRC), which considers both the asperity height and its regularity and directional trend. The main advantage in using the JRC arises from the fact that it can easily be obtained from geological-technical surveys and from comparison with the standard Barton profiles. Some relationships have been built up that allow for the estimation of the hydraulic conductivity tensor (an essential parameter for understanding water flow in fractured rock masses), not only as a function of traditional parameters like aperture, spacing, dip and dip direction, etc., but also of joint roughness, precisely expressed in terms of the roughness coefficient. These relationships have been studied initially from a theoretical point of view and then practically, through laboratory investigations.

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Resumen  Se conoce muy bien la influencia de la rugosidad de las grietas en las tipologías del flujo de fluidos a lo interior de las fracturas y gracias a las experiencias en el campo de hidráulica ha sido posible estudiarla desde puntos de vista matemáticos y físicos. Sin embargo, las formulaciones adoptadas por los modelos hidráulicos tradicionales tienen poca aplicabilidad en el campo geológico debido a la dificultad relacionada con la estimación del parámetro de rugosidad. Normalmente este parámetro puede estimarse usando el coeficiente de rugosidad de grieta (JRC) el cual considera tanto la altura de la aspereza como su regularidad y tendencia direccional. La principal ventaja de utilizar el JRC se deriva del hecho que puede obtenerse fácilmente de levantamientos técnico-geológicos y de la comparación con los perfiles Standard Barton. Se han construido algunas relaciones que permiten la estimación del tensor de conductividad hidráulica (un parámetro esencial para el entendimiento del flujo de agua en masas de roca fracturadas), no solo en función de parámetros tradicionales como apertura, espaciado, buzamiento y dirección de buzamiento, etc., sino también en función de la rugosidad de la grieta estimada con precisión en términos del coeficiente de rugosidad. Estas relaciones se han estudiado inicialmente desde un punto de vista teórico y luego de modo práctico a través de investigaciones de laboratorio.

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Résumé  L’influence de la rugosité des joints sur les types d’écoulement de fluide dans les fractures est bien connue et a été étudiée aussi bien du point de vue physique que mathématique grace à des expériences menées dans le domaine de l’hydraulique. Cependant les formulations adoptées dans les modèles hydrauliques traditionnels sont difficilement applicables dans le domaine de la géologie à cause de la difficulté rencontrée pour estimer la rugosité. Ce paramètre peut normalement être apprécié grace au coefficient de rugosité du joint (JRC), lequel prend en compte à la fois la hauteur de l’aspérité ainsi que sa régularité et sa direction. Le principal avantage dans l’utilisation du JRC réside dans le fait qu’il peut facilement être obtenu à partir d’études techniques-géologiques et par comparaison avec la classification de Barton. Des relations qui permettent une estimation du tenseur de conductivité hydraulique (un paramètre essentiel pour comprendre l’écoulement de l’eau dans les masses rocheuses fracturées) ont été élaborées, pas seulement en fonction de paramètres traditionnels tels que l’ouverture, l’espacement, l’inclinaison et la direction d’inclinaison, etc , mais aussi en prenant en compte la rugosité des joints à travers le coefficient de rugosité. Ces relations ont initialement été étudiées d’un point de vue théorique puis expérimentalement à travers des recherches en laboratoire.

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储层水动力学数值模拟系统的研究及应用     

徐士进  王汝成 《江苏地质》1998,22(1):46-49

油气在盆地中产生和运移过程中,水动力因素起着重要的控制作用［１］,如何确定这一作用的实际影响,是一个值得研究的问题。通过数学推导,得出储层中的稳态油层和非稳态油层两种情况下的水动力理论模型,并且对水动力圈闭、深度－压力系统和流体势等作出理论模拟,将其用于油气勘探中,结果与实际情况较相符。  相似文献   

Holocene profile changes along a California coastal stream     

William W. Haible 《地球表面变化过程与地形》1980,5(3):249-264

Walker Creek in Marin County, California is a coastal stream draining to Tomales Bay, which lies in the San Andreas Rift Zone. Its valley contains an alluvial fill with a basal gravel dated at 5000 years BP. In upstream parts of the watershed, channels are incised arroyo-like in the fill leaving the valley floor standing as a high terrace averaging 5·5 m (18 ft) high. Below this terrace is an inner terrace of historic age that stands 2·4 m (8 ft) above the streambed. The stratigraphy and morphology of this valley are seen in others nearby, and indicate that in the last half of Holocene time in this region a single episode of valley alluviation was followed by two episodes of valley cutting. The second episode of valley cutting is occurring in the present time. During the last 60 years the flow has become seasonal, the stream has incised 1·5 m (5 ft) below the inner terrace in upstream reaches, aggraded 1·2 m (4 ft) in downstream reaches, and extended its estuary. Incision upstream has begun to re-expose the bedrock valley floor and is associated with aggradation downstream that has caused the flood plain to overtop both terraces. This has decreased the stream's gradient. Using a stream that is currently effecting major changes in its valley and channel morphology, two aspects of hydraulic adjustment in fluvial systems are examined. The changes in the average slope of the longitudinal profile are small but measureable. Profile concavity has not changed measurably. The various profiles that have existed in Holocene time show that stream gradient can be, but is not necessarily, slightly adjusted during valley filling and cutting. Flow measurements at a high discharge show that the channel has begun to assume the hydraulic geometry of an ephemeral channel. Adjustments of depth, velocity, and roughness appear to be hydraulic adjustments in response to changing watershed conditions.  相似文献   

Hydraulic parameters and solute velocities in triple-porosity karstic-fissured-porous carbonate aquifers: case studies in southern Poland     

A. Zuber  J. Motyka 《Environmental Geology》1998,34(2-3):243-250

 Rock and flow parameters of three karstic-fissured-porous aquifers in the Krakow-Silesian Triassic formations were measured using various methods and compared. Though cavern and fissure porosities are shown to be very low (cavern porosity below 0.5% and fracture porosity below 0.2%), they contribute dominantly to the hydraulic conductivity (from about 1.3×10^–6 to about 11×10^–6 m/s). Matrix porosity (2–11%) is shown to be the main water reservoir for solute transport and the main or significant contributor to the specific yield (<2%). Though the matrix porosity is shown to be much larger than the sum of the cavern and fissure porosities, its contribution to the total hydraulic conductivity is practically negligible (hydraulic conductivity of the matrix is from about 5×10^–11 m/s to about 2×10^–8 m/s). On the other hand, the matrix porosity (for neglected cavern and fissure porosities) when combined with tracer ages (or mean travel times) is shown to yield proper values of the hydraulic conductivity (K) by applying the following formula: K≅(matrix porosity×mean travel distance)/(mean hydraulic gradient×mean tracer age). Confirming earlier findings of the authors, this equation is shown to be of great practical importance because matrix porosity is easily measured in the laboratory on rock samples, whereas cavern and fracture porosities usually remain unmeasurable. Received: 21 February 1997 · Accepted: 13 May 1997  相似文献   

煤层底板原位综合测试及突水危险性评估     

董书宁 《工程地质学报》2010,18(1):116

在实施井下钻孔水压致裂地应力测量的同时,评价岩层阻水性能,确定导升带高度,做到一孔多用。测试区实际观测表明,泥岩、粉砂岩、中砂岩、灰岩阻水性能由大到小,导升高度则由小变大,平均导升高度约32m; 地应力测量表明,该测试区原始地应力状态为SH＞Sv＞Sh,最大水平主应力方向NE至NEE。突水临界指数评价表明,-550m水平采煤工作面掘进时突水的可能性较大,应当采取防范措施。  相似文献   

Effect of macropore tortuosity and morphology on preferential flow through saturated soil: A Lattice Boltzmann study     

《Computers and Geotechnics》2014

Unlike micropores where water moves upward or downward based on hydraulic gradient, in macropores, water flows predominantly downward due to the gravity. Therefore, models based on capillary flow are not capable of simulating macropore flow. There are attempts to model the macropore flow using two domains, one for capillary flow and another one for macropores. These models use Richard’s equation for capillary flow and Poiseuille’s law for macropores in which the macropore is approximated to be cylindrical or planar. This study quantifies the magnitudes of the errors induced by this assumption. Influence of macropore shapes and tortuosity was quantified by using a 3D Lattice Boltzmann model, which is capable of simulating fluid flow in micropores as well as macropores of cracked clays. Artificial macropores of constant sectional area and volume, but different shapes were generated in 3D and the influence of macropore shapes, shape related parameters, and tortuosity were systematically investigated. Macropore flow rate decreases with different shapes compared to cylindrical macropores and increase in aspect ratio of sectional shape leads to decrease in macropore flow rate. The maximum effect of bends/turnings along the tortuous macropore was about 25% on overall decrease of flow rate due to tortuosity. However, more detailed study is required on the influence of bends on macropore flow rate. The macropore flow rate reduces by about 70% for tortuosity of 1.41. A prediction equation is verified to predict the flow rate of different shapes and tortuous macropores based on straight cylindrical macropore using aspect ratio and tortuosity factor.  相似文献   

地窝堡机场东南大风特征及其大气结构     

杨洪儒  王楠 《干旱气象》2014,(3):393-398

按照民航系统气象行业标准要求,结合乌鲁木齐国际机场的具体情况,给出乌鲁木齐机场东南大风的定义,并应用乌鲁木齐机场1978~2012年间逐时观测的风速风向对机场东南大风的特征进行分析,然后再引入水跃理论和Froude数,对机场东南大风发生时的大气结构做解析。结果表明:(1)1980年代与2000年代至今,为东南大风的兴盛期,1990年代为东南大风的低值期;(2)东南大风主要集中出现在春秋季,其中尤以4月出现次数最多,占总出现次数的36.4%;(3)早晨至中午期间,东南大风多发且风速较大;午后至夜间,东南大风发生次数少,且风速也相对较小;(4)东南大风的持续时间以低于5 h为主,其次为持续11 h以上的大风,而持续时间在5~11 h之间的大风出现最少;(5)对于4月和11月而言,大风发生时达坂城与本场的气压差与同时次本场的温度垂直递减率存在显著的线性关系。  相似文献