Water supply potential and optimal exploitation capacity of karst aquifer systems

The management of groundwater flow systems in karst regions appears, at present, to be the most important procedure for solving water deficiency problems during periods of low rainfall. Faced with a lack of data for characterizing the water supply potential of karst aquifers, analyses of spring hydrographs may provide valuable indirect information regarding the structure of karst hydrogeological systems. To estimate the optimal exploitation capacities of karstic sources, a stochastic-conceptual approach was applied in case studies from the Serbian karst. Water supply potentials were initially evaluated on the basis of groundwater budgets. Further steps towards defining optimal “exploitable” regimes included analyses of storage changes in karst water reservoirs under natural conditions and calculation of the potential expansion of currently tapped sources. The results obtained through these analyses are a significant contribution to feasibility studies and aid in the avoidance of problems of overexploitation.     

Post-drilling destabilization of temperature profile in borehole Yaxcopoil-1, Mexico

As part of the International Continental Scientific Drilling Program (ICDP), the 1.5-km-deep borehole Yaxcopoil-1, located in the Chixculub meteor impact structure in Mexico, has undergone further study after drilling operations ceased. Temperature logs were repeated ten times at intervals 0.3–0.8, 15, 24 and 34 months after borehole shut-in. The logs bear a distinct signature of transient heat transfer by groundwater flow manifested by a gradual distortion of the linear temperature profile when a cold wave of 0.8–1.6°C amplitude was detected propagating downward from 145 to 312 m at a rate of 4–6 m/month. To understand the nature of this moving anomaly, a 20-day monitoring of the cold wave was carried out at a depth of 307 m that showed further cooling of 0.6°C during the first 16 days of the passage followed by temperature stabilisation. As an explanation of this unusual phenomenon, a theory is proposed, whereby the drilling mud has accumulated within the overlying and cooler highly porous and permeable karstic rocks during the drilling and migrates downward. The observed migration rate suggests a permeability higher than 10^?11 m². This indicates a high vulnerability to contamination of the only freshwater aquifer in the Yucatan region.     

Spatial pattern of Karst rock desertification in the Middle of Guizhou Province,Southwestern China

Karst rocky desertification is a typical type of land degradation in the Southwestern China. It has great ecological and economical implications for the local people. Landsat images from the middle of Guizhou Province collected in 1974, 1993 and 2001 were used for change detection of the pattern of Karst rocky desertification. The results show the following findings: (1) Desertification area expanded drastically in 27 years, at an increasing rate about 116.2 km²/year. (2) High areas (900–1,500 m) are the most affected. (3) Areas with the slope <5° or >25° are also easily tend to be Karst rocky deserted. (4) The process of Karst rocky desertification is nearly irreversible. Few areas of Karst rocky desertification could be meliorated to non-desertification land. (5) Most of the degraded lands are located in the south and the central of the study region, and the meliorated land areas are sparsely located in the east and the west part of the region. All these findings would provide bases for the decision-making of the local government to improve the Karst rocky desertification     

Dynamic of the freshwater–saltwater interface in a karstic aquifer under extraordinary recharge action: the Merida Yucatan case study

A hydraulic analysis of the interface between freshwater–saltwater behavior was done in the Merida Yucatan zone, two machines that constantly register the groundwater levels were installed, and three electric conductivity logs were taken from wells. When comparing the measured results with the ones obtained using theoretical equations developed to calculate the freshwater–saltwater interface position, it was proved that in some cases these equations can be applied, and in others not. Two effects that rule the behavior of karst aquifers in extraordinary conditions were found.     

Tracer methods used to verify the hypothesis of Cvijić about the underground connection between Prespa and Ohrid Lake

Prespa Lake and Ohrid Lake constitute a hydraulic system shared between Albania, FYR of Macedonia and Greece. Karst rocks separate both lakes. The elevation of Prespa Lake is about 150 m higher than that of Ohrid Lake. Considering these facts, Cvijić formulated in 1906 the hypothesis that Prespa Lake recharges the St. Naum and Tushemisht springs at Ohrid lakeside. Environmental isotopes demonstrated that Prespa Lake recharges about 37–42 and 52–54% of water emerging in St. Naum, and Tushemisht springs, respectively. An artificial tracer experiment carried out in 2002 physically demonstrated the underground connection between both lakes. This experiment confirmed the supposed underground connection and brought important information about the groundwater velocity, transit time, and karst water conduits development.     

How can the epikarst zone influence the karst aquifer hydraulic behaviour?

The role of an epikarst zone in the karst aquifer hydraulic behaviour was brought into focus in our studies referring to the catchment area of the Hubelj spring (SW Slovenia). This study points out the significance of effects of the fast preferential flow—epiflow, which is the main factor controlling solute/contaminant transport towards the aquifer saturated zone. The so-called epikarstic hypothesis is verified on the basis of the most significant research results that are supported by the most important findings from the literature.     

威连滩冲沟砂黄土的风蚀与降雨侵蚀模拟实验

 通过风洞与模拟降雨实验，研究了风力与降雨对青海省贵南县威连滩冲沟砂黄土的复合侵蚀作用。实验得出：①风蚀后的降雨使砂黄土表面在风干过程中形成了一层较为坚硬的结壳，增大了土壤的抗蚀性，降低了第二次风洞实验后期的风蚀率;②土壤水分与人为扰动是影响土壤风蚀的两个重要因素。当土壤水分较小时，风蚀率受人为扰动影响巨大;当土壤水分较大时，人为扰动对土壤风蚀的影响较小;③在持续降雨的实验条件下，砂黄土的产流、产沙量随着雨强的变化而改变。这种变化与表土的侵蚀率、可蚀性物质的多少、土壤水分以及土壤的入渗率等都有很大的关系。     

隧道支护新技术——水平旋喷成拱法

介绍了水平旋喷成拱工艺，分析了工艺参数对旋喷的影响，并采用该方法在鞍子河电站成功地进行了工程施工，为软弱地层隧道预衬砌提供了一个新途径。     

云南蒙自五里冲水库岩溶及其工程处理

五里冲水库个旧组（T2^cg)灰岩，岩溶极其发育，其中尤以洼地深、峰丛高、溶洞多又大，地下河管道单一较长、岩溶总体发育历史悠久为特点，以更新世以来岩溶最为发育，现今地下河管道主要形成于晚更新世至今。因区域地壳持续抬升，岩溶没有成层发育的规律，但自上向下递减现象明显。工程上五里冲水库是以帷幕高压灌浆技术为主辅以其它多种方法处理溶洞及封堵地下河，利用天然盲谷成库的一座无大坝中型水库。帷幕高压灌浆技术先、便捷、可靠。水库蓄水己达设计水位，发挥了效益。一年可向蒙自县供水8161万m^3，可增加灌溉面积10万亩，改善灌溉2.3万亩，向城市及工业供水1210万m^3，使蒙自水利化程度由37%提高到70%以上。     

隧（巷）道测量瞄准误差与觇标选取

根据隧（巷）道双欠观测值的统计资料，分析觇标对瞄准误差的影响，提出觇标的选取方法的观测中注意的问题。