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1.
Artificial tracer experiments were conducted in the mature karst system of Jeita (Lebanon) under various flow conditions using surface and subsurface tracer injection points, to determine the variation of transport parameters (attenuation of peak concentration, velocity, transit times, dispersivity, and proportion of immobile and mobile regions) along fast and slow flow pathways. Tracer breakthrough curves (TBCs) observed at the karst spring were interpreted using a two-region nonequilibrium approach (2RNEM) to account for the skewness in the TBCs’ long tailings. The conduit test results revealed a discharge threshold in the system dynamics, beyond which the transport parameters vary significantly. The polynomial relationship between transport velocity and discharge can be related to the variation of the conduit’s cross-sectional area. Longitudinal dispersivity in the conduit system is not a constant value (α?=?7–10 m) and decreases linearly with increasing flow rate because of dilution effects. Additionally, the proportion of immobile regions (arising from conduit irregularities) increases with decreasing water level in the conduit system. From tracer tests with injection at the surface, longitudinal dispersivity values are found to be large (8–27 m). The tailing observed in some TBCs is generated in the unsaturated zone before the tracer actually arrives at the major subsurface conduit draining the system. This work allows the estimation and prediction of the key transport parameters in karst aquifers. It shows that these parameters vary with time and flow dynamics, and they reflect the geometry of the flow pathway and the origin of infiltrating (potentially contaminated) recharge.  相似文献   

2.
溶质暂态存储是岩溶地下水溶质运移过程中的普遍现象。为揭示岩溶管道与裂隙介质间溶质暂态存储机制,本文构建室内管道-裂隙物理模型,开展集中补给条件下的定量示踪试验,运用双区对流弥散模型实现溶质运移过程模拟。研究表明：随着集中补给水动力条件的增强,裂隙暂态存储水量呈线性增加趋势,溶质穿透曲线由单峰型向双峰型转变;管道和裂隙中的平均流速呈负相关关系,溶质在管道和裂隙中的滞留时间差决定了穿透曲线的形态;溶质暂态存储引发了穿透曲线的拖尾效应和双峰现象,对岩溶地下水溶质运移过程具有重要的控制作用。  相似文献   

3.

Simultaneous short-pulse injections of two tracers (sodium bromide [Br–] and fluorescein dye) were made in a losing reach of Snake Creek in Great Basin National Park, Nevada, USA, to evaluate the quantity of stream loss through permeable carbonates that resurfaces at a spring approximately 10 km down drainage. A revised hydrogeologic cross section for a possible flow path of the infiltrated Snake Creek water is presented, and the results may inform water management in the region. First arrival and peak concentration of the two tracers occurred at 9.5 and 12.7 days after injection, respectively. Fracture transport simulations indicate that Br– preferentially diffuses into immobile regions of the aquifer, and this diffusive flux is likely responsible for the major differences in the breakthrough curves. When considering the diffusive tracer flux, total apparent Br– and fluorescein dye recoveries were 16.9–22.1% and 21.7–24.3%, respectively. These findings imply that consideration of diffusive flux and long-term monitoring in fracture-dominated flow may support accurate quantification of tracer recovery. In addition, the apparent power law slopes of the breakthrough tails for both tracers were steeper at early times than have been attributed to heterogeneous advection or channeling in meter-scale tests, but the late-time Br– power law slope becomes less steep than has been attributed to diffusive exchange. These deviations may reflect fracture transport patterns that occur at larger scales.

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4.
The Doosti Dam was built across the Harirood River on the border between Turkmenistan and Iran. During the reservoir impounding, leakage occurred as new springs through the sandstone layers of the Pesteleigh Aquifer and limy sandstone and limestone layers of the Neyzar–Kalat Aquifer, at the right abutment of the dam. To evaluate the grout curtain operation, a tracer test was carried out by injection of Uranine in a borehole located at the upstream of grout curtain in the Pesteleigh Aquifer. Tracer test results demonstrated a diffuse flow component through the grout curtain in the Pesteleigh Aquifer, but no tracer was detected at the main leakage point, SP1 Spring, emerged downstream of grout curtain from the Neyzar–Kalat Aquifer. Using the spectral coherency function, the lag time between changes in the water level of the injection borehole and water level in the tracer detected boreholes or discharge of the tracer detected springs was determined. Linear regression analyses indicated that the estimated lag time by the time series analysis was close to the first arrival time of the tracer. Therefore, the estimated velocities based on the lag time of time series could be considered close to the calculated velocities based on the first arrival time of the tracer. The estimated groundwater velocities based on the time series analysis ranged from 3.91 to 20.31 m h?1, showed that diffuse flow dominated pathways from the reservoir toward the downstream boreholes in the Neyzar–Kalat Aquifer, while conduit flow was present within the pathways toward the SP1 Spring. Regarding the reservoir volume, the negligible amount of leakage at the maximum water level of the reservoir confirmed well overall operation of the grout curtain at the dam site.  相似文献   

5.
The seepage occurrence from the reservoir on the right bank of the Akde?irmen Dam located in Afyonkarahisar province in the Turkey has been investigated. When the reservoir began to fill with water, a large amount of water seepage occurred at the dam. The seepage developed at the base of the spillway and the right downstream slope of the dam. The various attempts have been made to reduce the seepage using grouting. Although the additional grouting operations was reduced the seepage at the base of the spillway, there has not been a reduction in seepage at the water outlet location at the downstream slope. Electrical resistivity measurements along the eight lines with the dipole–dipole array and dye tracer tests were performed in order to identify the seepage locations. The interpretation of electrical resistivity data showed the distribution of strata and the seepage zone along the right downstream of the dam. Groundwater flow rates calculated from dye tests indicated that there is an excessive seepage south-eastwardly on the downstream slope of the dam. Integrated interpretation of resistivity data and dye tests indicate that the seepage paths are in the direction from NW to E and SE.  相似文献   

6.
屋顶雨水回灌裂隙岩溶含水层连通示踪试验   总被引：1，自引：0，他引：1  
雨水回灌后对岩溶水的影响分析和效果需要对回灌井和下游的观测井监测数据说明。由于岩溶含水层中岩溶发育极不均匀,在测定地下水位并判定出地下水流向的基础上,连通示踪试验是选择与回灌井相对应的观测井的有效办法。用氯化钠作为示踪剂,监测不同测井不同埋深地下水电导率随时间变化的方法确定了岩溶水观测井选址、岩溶含水层的结构及水文地质条件。示踪试验结果表明,3#观测井(西院井)可用来监测雨水回灌效果,并计算出该地区的地下水势流速在9 m/h～20 m/h之间。该成果对北方地区岩溶含水层回灌和环境评价具有重要的参考价值。  相似文献   

7.
The sinuosity factor (SF) is a critical value in karst systems in terms of estimating their hydrodynamic parameters including groundwater velocity, coefficient of dispersion, etc., through dye tracer experiments. SF has been used in a number of different dye tracer experiments in karstic systems to estimate a representative flow path. While knowing SF is crucially important in the estimation of hydrodynamic parameters, its calculation is associated with significant uncertainty due to the complexity of subsurface karstic features. And yet, only a few studies have discussed its uncertainties, which might lead some errors in estimation of hydrodynamic parameters from dye tracer experiment. In this study, dye tracer experiments were conducted in two consecutive years (2003 and 2004) representing low and high flow conditions in the Beyyayla sinkhole (Eski?ehir, Turkey) where the flow path is well known. Uranine was used in experiments as a tracer and QTRACER computer program was used to determine the hydrodynamic properties of the Beyyayla karst system as well as to gain insights into the effects of SF from dye tracer experiments on estimated parameters. The results showed that the breakthrough curve follows a unimodal and a bimodal distribution in low and high flow conditions, respectively. These different distributions stem from the water transport mechanisms, where velocities were calculated as 58.2 and 93.6 m h?1 during low and high flow conditions observed in a spring emerging from the south side of the studied system. The results also show that the coefficient of dispersion, Reynolds number, and Peclet number increased and longitudinal dispersivity decreased with the higher flow rate. Furthermore, the estimated parameters did not vary with either the flow conditions or the tracer transit time, but they have shown some variations with SF. When SF was increased by 50 %, a change in these parameters was obtained in the range of 50–125 %.  相似文献   

8.
Tracer concentration data from field experiments conducted in several carbonate aquifers (Malaga province, southern Spain) were analyzed following a dual approach based on the graphical evaluation method (GEM) and solute transport modeling to decipher flow mechanisms in karst systems at regional scale. The results show that conduit system geometry and flow conditions are the principal factors influencing tracer migration through the examined karst flow routes. Solute transport is mainly controlled by longitudinal advection and dispersion throughout the conduit length, but also by flow partitioning between mobile and immobile fluid phases, while the matrix diffusion process appears to be less relevant. The simulation of tracer breakthrough curves (BTCs) suggests that diffuse and concentrated flow through the unsaturated zone can have equivalent transport properties under extreme recharge, with high flow velocities and efficient mixing due to the high hydraulic gradients generated. Tracer mobilization within the saturated zone under low flow conditions mainly depends on the hydrodynamics (rather than on the karst conduit development), which promote a lower longitudinal advection and retardation in the tracer migration, resulting in a marked tailing effect of BTCs. The analytical advection-dispersion equation better approximates the effective flow velocity and longitudinal dispersion estimations provided by the GEM, while the non-equilibrium transport model achieves a better adjustment of most asymmetric and long-tailed BTCs. The assessment of karst underground flow properties from tracing tests at regional scale can aid design of groundwater management and protection strategies, particularly in large hydrogeological systems (i.e. transboundary carbonate aquifers) and/or in poorly investigated ones.  相似文献   

9.
A new mode of interconnecting karst systems separated by impermeable bed due to karst collapse was discovered in the study of dam site in Guizhou, South China. Karst flow may be diverted from conduits in one layer to another, thus forming a connected karst system. Comprehensive methodology and techniques used in the investigation included surface geological surveys, geophysical investigations, special drilling, and tracer tests. In the stage of preliminary study, the karst conduits were considered to be developed separately along individual karstified layers. However, further investigation shows that karst collapse may be associated with conduit and cavern development, damaging the impermeable bed and its watertight function. Accordingly, a new pattern of karst conduit system was reestablished. The results obtained enable the dam designer to plan a reliable alternative for seepage protection.  相似文献   

10.
Mathematical simulations on dam break or failure using BOSS DAMBRK hydrodynamic flood routing dam break model were carried out to determine the extent of flooding downstream, flood travel times, flood water velocities and impacts on downstream affected residences, properties and environmental sensitive areas due to floodwaters released by failure of the dam structure. Computer simulations for one of the worse case scenarios on dam failure using BOSS DAMBRK software accounted for dam failure, storage effects, floodplains, over bank flow and flood wave attenuation. The simulated results reviewed a maximum flow velocity of 2.40 m/s with a discharge of approximately 242 mз /s occurred at 1.00 km downstream. The maximum discharge increased from 244 m3/s (flow velocity = 1.74 m/s occurred at 8th. km) to 263 m3/s (flow velocity = 1.37 m/s occurred at 12th. km); about a 39% drop in flow velocity over a distance of 4.00 km downstream. If the entire dam gives way instantly, some spots stretching from 0.00 km (at dam site) to approximately 3.40 km downstream of the dam may be categorized as “danger zone”, while downstream hazard and economic loss beyond 3.40 km downstream can be classified as “low” or “minimal” zones.  相似文献   

11.
为进一步了解堰塞坝溃坝过程,开展了9组水槽模型试验,对溃口纵向下切和溯源发展过程进行了系统分析,并讨论了上溯源点移动速度与溃口水深之间的关系。研究发现：非黏性堰塞坝溃坝过程中,冲刷面与底床的夹角时刻发生变化,上、下溯源点位置不固定但也不能完全发展到坝踵;上、下坡面坡度增大到最大值1：1.5时,下溯源点到下游坝趾的最大距离与坝体沿水流方向长度的比值（xp*/xd*,反映下溯源点最终相对位置）对应降低到最小值0.24和0.18;坝体相对尺寸从1减小到1/2时,xp*/xd*值从0.38增大到0.47。上溯源点的无量纲移动速度是不断变化的,在无量纲时刻为0.13时,其x,y分量分别达到峰值0.94和0.32;上溯源点处溃口水深出现时刻相对移动速度峰值点出现时刻有延迟,大概延迟0.04个无量纲时间。  相似文献   

12.
To better understand the movement and transport of water and pollution through the coarse gravel unsaturated zone, the presented research was conducted to estimate water flow and transport processes with a tracing experiment in a lysimeter in the Selniška Dobrava. A combined tracing experiment was performed with deuterated water and the fluorescent dye—uranine. The fastest and dominant flow velocities were calculated based on injection time, the first tracer appearance time and the time of highest concentration. Mean flow velocity and vertical dispersion were estimated by an analytical best-fit method using one-dimensional convection–dispersion model. Deuterium was confirmed as an ideal conservative tracer and a more suitable tracer than dye (uranine) for the study of water flow in the unsaturated zone of a coarse gravel aquifer. The retardation factor of the dye as compared with deuterium was 1.13–1.75, which is in agreement with previously published results. Artificial tracers, especially deuterated water, were also identified as a very useful tool to assess other properties and differences in water flow in the unsaturated zone of a coarse gravel aquifer such as velocity and dispersion.  相似文献   

13.
Karst aquifers contribute to supplying drinking water to almost a quarter of the world´s population. Their complex dynamics requires specific approaches aimed at recognizing their singularities, analyzing its vulnerability, and ensuring water resources quality. In this paper, the results of processing and modeling five breakthrough tracer curves obtained under different hydrodynamic conditions in the main conduit of Egino karst aquifer (Basque Country, Spain) are analyzed together with those involving pressure injections of the tracer in the saturated zone of the karst massif recharge area. In the conduit, transport is immediate and highly efficient (recovery rates above 84% and dispersion coefficients from 15.04 to 84.35 m2/min); tracer retentions increase as flow rates decrease and no significant contributions to its surroundings are observed. In contrast, tracer transport from the massif recharge area is more complex: after injection at a pressure of 1 MPa, most tracer remains in the surrounding of the injection borehole, retained in a saturated medium of low effective fracture porosity (? f ?=?1.02?×?10?4, assuming a radial divergent flow model); subsequently, the main tracer mobilization to the spring was registered with the first rains, with 0.088 m/min mean velocity and high concentrations per unit mass being injected (C p /M0?=?0.03 mg/L/kg), which is evidence that the tracer reaches soon the karst conduit network. In any case, a decreasing tracer presence is registered at the injection zone during a hydrological cycle. In both cases, the observed non-linearity of transport processes should be considered in the development of vulnerability approaches, modeling efforts, and mapping. Furthermore, in the case of karst massif recharge areas, as the presence of pollutants may have a significant impact on the springs and persist over time, their management and protection needs must be revised in each specific site. Simultaneously, quality-monitoring programs at the springs must be adapted to the aquifers recognized dynamics.  相似文献   

14.
Seepage phenomena through the karstic limestone foundation of Kalecik Dam are investigated. The dam, designed as a rock-fill dam with a height of 77 m, is already used for irrigation. The foundation consists of Mesozoic ophiolite, Paleocene allochthonous units composed of different lithologies, and Miocene conglomerate. The conglomerate lies unconformably on the other units. Quaternary basaltic lava patchily covers the others. Seepage from upstream to downstream occurs through the allochthonous karstic limestone. This limestone, which is overlain by conglomerates, has a thickness increasing towards the right abutment.

To prevent seepage at the right abutment, a 200-m long and 60-m deep grout curtain along the dam axis was constructed. After the impoundment, some springs occurred downstream, and for this reason, extra grouting was performed. However, the seepage problem could not be solved. In order to determine the seepage direction and karstification pattern, hydrological studies have been done. Additional investigation boreholes have been drilled to observe fluctuations of the groundwater level and to analyze hydrochemistry. Also, dye tracer tests have been carried out.

As a result of these hydrogeological studies, seepage paths were observed in the karstic limestone located between the dam and the spillway. As those carbonate rocks continue beneath the spillway, the seepage problems are enjected to continue.  相似文献   


15.
桂林毛村地下河流域雨季与旱季定量示踪分析   总被引：3，自引：2，他引：1  
以典型岩溶地区广西桂林市毛村地下河流域为例,基于在线高分辨率监测进行雨季与旱季定量示踪试验,精细刻画流域内含水介质特征。根据示踪试验研究及毛村地下河系统内地下水的径流和分布特征,可将毛村地下河系统划分为社更岩、扁岩地下河系统,大冲里-背地坪系统和大岩前落水洞-毛村出口系统。这三个子系统分布于毛村流域的上游和下游,其示踪剂浓度历时曲线为陡升陡降的尖峰,地下管道相对单一,无较大岔道和溶潭发育。各段地下河水动力作用以对流作用为主,且水流一般呈现为紊流流态。雨季流速快、流量较大,平均运移时间短,示踪剂回收率比旱季高。流域中游含水介质相对均匀,无管道发育,地下水主要赋存于溶蚀裂隙。   相似文献   

16.
Temporary dams can be formed by the sudden injection of debris flow into main streams by some favorable geomorphologic and hydraulic conditions, resulting in extensive inundations upstream and catastrophic floods downstream due to dam breaches and consequently dramatic changes of channels and valleys. Expeditious means of assessing dam-forming potential are necessary, particularly in geologically active regions. Complete blockages or dam formations are significantly related to the discharge ratio and velocity ratio between the tributary and the main stream, the bulk density of the debris flow, confluent angles and the degree of unevenness of grain sizes. In order to set up a critical index/C for dam formation, 19 groups of flume tests were conducted. The results showed that there were three types of blockage in the intersections, and dam-forming processes were mainly controlled by the product of the dimensionless momentum ratio and the degree of unevenness of grain sizes in the debris flow. Complete blockages or dam formations occurred when C > 83.4, whereas semi-blockages were formed or no dams were formed when C < 71.5, which had been judged to be feasible by historical instances of dam formation in China. Dam failures commonly resulted from overtopping. No piping was observed in the course of dam failure, and the time elapsed between dams can be denoted by a linear relation with the momentum ratio.  相似文献   

17.
以青木关岩溶地下河为例,利用在线高分辨率示踪技术获取基础数据来探寻岩溶地下河形态特征,估算水文地质参数。试验中示踪剂回收率高达99 %,示踪剂历时浓度曲线有两个孤峰,前后峰值浓度分别为37.63 μg/L和1.21 μg/L, 两个孤峰的偏度和峰度均大于0,据此推测青木关岩溶地下河并无较大溶潭发育,且地下河流态为紊流流态。根据试验所得数据结合地下河地理空间信息,以经验公式估算得到地下河平均流速、摩擦系数、雷诺数、舍伍德数、施密特数等水文地质参数,分别为204 m/d、0.26、127 980、4 165、1 140,表明青木关地下河管道内部结构复杂,地下水环境比较脆弱,且估算得到的雷诺数所表征的地下河水流态与示踪剂历时浓度曲线得到的结果一致。   相似文献   

18.
为研究径流式低坝影响下的水流流动与泥沙淤积特性,开展水槽试验,基于图像测量技术,获取并解析坝附近区域流场信息及典型淤积形态。结果表明：坝前附近流段纵向流速在垂线上出现衰减区,减幅随水流强度增大而减小;坝顶断面纵向和垂向流速沿垂线的分布均呈现显著的分区特性,分区界限几乎不受水流强度的影响;随坝顶水深增加,坝下游漩涡涡心向下游及河底移动,面积和强度皆增大;坝上游淤积形态特性对水流强度的变化非常敏感,在较低强度来流下,呈接近坝体的稳定曲面斜坡,而在高强度来流下,不形成稳定淤积体;坝下游形成动态稳定的淤积斜坡,纵剖表面线呈抛物线规律,随来流强度变异程度小。  相似文献   

19.
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20.
为研究径流式低坝影响下的水流流动与泥沙淤积特性,开展水槽试验,基于图像测量技术,获取并解析坝附近区域流场信息及典型淤积形态。结果表明:坝前附近流段纵向流速在垂线上出现衰减区,减幅随水流强度增大而减小;坝顶断面纵向和垂向流速沿垂线的分布均呈现显著的分区特性,分区界限几乎不受水流强度的影响;随坝顶水深增加,坝下游漩涡涡心向下游及河底移动,面积和强度皆增大;坝上游淤积形态特性对水流强度的变化非常敏感,在较低强度来流下,呈接近坝体的稳定曲面斜坡,而在高强度来流下,不形成稳定淤积体;坝下游形成动态稳定的淤积斜坡,纵剖表面线呈抛物线规律,随来流强度变异程度小。  相似文献   

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