The emerging water crisis in Bulgaria

Climatic records for the last 15 years indicate that Bulgaria is experiencing a period of exceptionally low precipitation. During 1993, significant water supply problems emerged, approaching crisis proportions in Sofia, the nation's capital, by the end of 1994. The record-setting drought of 1993 can be explained from a synoptic climatic perspective. Whether consequences of the continuing drought could have been foreseen is arguable. That these consequences were fully realized only in 1994 may be understood through examination of Bulgarian water use since the end of the socialist era in 1989. If Bulgaria had experienced the same levels of industrial activity and irrigation as occurred in 1989, the current situation would have been national catastrophe, a situation that could quickly emerge in coming years should climatic patterns persist.     

Effects of concrete cracking on the earthquake response of gravity dams

Tensile stresses exceeding the tensile strength of concrete can develop in concrete dams subjected to earthquake ground motion. This study examines the earthquake response of gravity dams including tensile cracking of the concrete. The interaction between the dam and compressible water is included in the analysis using a numerical procedure for computing the non-linear dynamic response of fluid-structure systems. The crack band theory is used to model tensile cracking with modifications to allow for the large finite elements necessary for dam analysis. The earthquake response of a typical gravity dam monolith shows that concrete cracking is an important non-linear phenomenon. Cracking is concentrated near the base of the dam and near the discontinuities in the face slope. The extensive cracking, which develops due to ground motion typical of maximum credible earthquakes, may affect the stability of dams during and after strong earthquakes.     

A wind tunnel study of mean and fluctuating concentrations in a plume dispersing over a two-dimensional hill

This paper describes an experimental investigation of the behaviour of the statistics of concentration fluctuations in a passive plume dispersing over a two-dimensional hill of moderate steepness. Recently developed high frequency response Flame Ionization Detector (FID) technology with a frequency response in excess of 200 Hz was utilized to obtain an extensive set of measurements of the mean and fluctuating plume concentrations. Plumes dispersing over flat terrain and over a hill with a maximum slope of 0.3 were studied. For both cases, extensive turbulent flow measurements were also carried out.The measured mean plume concentration profiles were of a generally Gaussian form and showed the expected effects of surface reflection for the flat terrain and hill. Plume intermittency and concentration fluctuation intensity were calculated at all measurement locations. Conditional and unconditional plume concentration statistics were calculated. The conditional (in-plume) concentrations and intensities were more uniform with height than for the unconditional ones.     

Oxygen Transfer Through Flexible Tubing and Its Effects on Ground Water Sampling Results

A model for the diffusion of gases through polymeric tubing was derived which predicts that the amount of gas transferred is proportional to the tubing length and inversely proportional to the pumping rate. The model was experimentally tested and confirmed for oxygen transfer through fluorinated ethylene-propylene copolymer (FEP) tubing using tubing lengths and flow rates typical of ground water sampling. Diffusion can introduce measurable concentrations of oxygen into initially anoxic water. Diffusive loss of carbon dioxide from water that is oversaturated with respect to atmospheric CO₂ does not measurably affect pH under similar usage conditions.