Abstract:

Groundwater connectivity test was conducted to investigate the hydraulic connection between caves in the upstream and the downstream, and to quantitatively determine the ratio of water flow into the downstream caves. Rhodamine, which would be fluorescent illuminated by light of certain wavelengths, was used as tracer medium. Fluorescence spectrophotometer was employed to detect the intensity of fluorescence in the tracer solution, hence obtaining the curve of concentration vs. fluorescence intensity. The tracer was put at the entrance of Karst cave in the upstream, and water samples were collected at the exit in the downstream to detect the fluorescence intensity and measure the flow. According to the obtained curve, the tracer quality in the sample was calculated. Subsequently, the water allocation ratio was derived from the law of mass conservation and the theory of tracer transport and diffusion. Results showed that during the test period, 89% of the water flowed from caves in the upstream into the downstream. The relation between fluorescence intensity and tracer concentration is also believed to be feasible for quantitative analysis. The test method could be a reference for similar engineering practices.  

Key words: tracer, connectivity tests, fluorescence intensity, spectrophotometer