Leakage is a common phenomenon in dams, and its early detection is critical for dam safety. In the present study, a new method based on tracer tests is applied to detect and quantify leakage in the Wanyao Dam, Jiangshan City, China. The objective is to detect the leakage zone of a dam wall by combining the natural tracer test and the artificial tracer test. Temperature, electrical well-logging tests with nature tracers, and the artificial tracer test with salt (NaCl) were conducted using 48 and 5 pre-existing boreholes, respectively. Using natural tracer tests, the 48 boreholes are categorized into 4 leakage classes: (1) Class 1, high connectivity within whole borehole; (2) Class 2 high connectivity at lower depths; (3) Class 3, weaken connectivity; and (4) Class 4, safe boreholes with no connectivity. Using the proposed method, specific leakage rates of some boreholes were estimated. The results of the new method are validated by comparison with those from natural tracer tests, site-investigation, and historical observation data. Overall, the new tracer test has the following merits: (1) low cost, (2) environment friendliness, and (3) is simple to apply. Moreover, the proposed method improves the accuracy of traditional tracer tests for detecting leakage zones.

With the rapid growth of the global demand for low-carbon energy, the development of hydropower has ushered in new development, but the ecological and environmental problems caused by this cannot be ignored. Taking the safe and efficient operation of water conservancy projects as the goal, this paper took the Maling Water Conservancy Project (MWCP) as an example to predict and evaluate the ecological environment risks of water conservancy projects. Based on the on-site geological surveys and experiments, the big well method and the long narrow horizontal tunnel method were used to estimate the water inflow from the underground caverns. The contaminant migration model was used to predict and analyze the groundwater quality. The impact of the MWCP on the surrounding environment was systematically analyzed and evaluated. The results showed that the estimated water inflow from the underground powerhouse and the water conveyance pipeline was about 7403.6 m³/d during the construction period. The groundwater level in the reservoir area could recover after a short drop, which had little effect on the surrounding vegetation. The groundwater quality was affected obviously because the migration speed of contaminants was very fast under abnormal conditions. During the operation period, it had little effect on groundwater level and had certain influence on groundwater flow field in local area. The source of sewage was mainly a small amount of domestic sewage, which could be ignored after taking anti-seepage measures. After storing water in the reservoir area, there was a possibility of small-scale immersion on the right bank. Most of the reservoirs had good stability conditions but the stability of the upper fault valley was poor; however, the possibility of leakage was very small. Overall, the project had little impact on the surrounding environment. The research results could also provide some references for other hydroelectric projects within the basin.

For the characterization of heterogeneous aquifers, transient hydraulic tomography (THT) was proposed as a promising method to obtain the distribution of hydraulic parameters with satisfying spatial resolution using different approaches. These include hydraulic travel time, attenuation inversions, thermal tracer tomography, and geostatistical inversion with successive linear estimator (SLE). For the same hydrogeological test, different inversion methods tend to use different sub-data sets to obtain different hydraulic parameters. Up to now, however, few studies have focused on revealing the respective characteristics of these inversion methods and attempted to improve the accuracy of aquifer characterization by bridging the shortcomings of the inversion methods. The main objective of this study was to evaluate the utility of multiple inversion techniques on aquifer heterogeneity characterization. A series of warm water injection tests were first simulated in a fluvial aquifer analogue outcrop. The calculated head and temperature datasets from these tests were fully utilized to reveal the aquifer heterogeneity by using all of the four above-mentioned inversion methods. The results show that the thermal tracer tomography, hydraulic travel time, and attenuation tomography characterized the high permeability zones more accurately within the well area, whereas the geological statistical method tended to depict the overall distribution of $K$ values for a larger area. By comparison analysis and combinations of the individual inversion results, the scientific and economic complementarity can be studied and some valuable advice for the choice of different inversion methods can be recommended for future practices.

Hydraulic tomography (HT) based on the successive linear estimator (SLE) offers the high-resolution characterization of aquifer heterogeneity but conventionally requires prolonged pumping to achieve steady-state conditions, limiting its applicability in contamination-sensitive or low-permeability settings. This study bridged theoretical and practical gaps (1) by identifying spatial periodicity (hole effect) as the mechanism underlying divergences in steady-state cross-correlation patterns between random finite element method (RFEM) and first-order analysis, modeled via an oscillatory covariance function, and (2) by validating a novel short-term sampling strategy for SLE-based HT using field experiments at the University of Göttingen test site. Utilizing early-time drawdown data, we reconstructed spatially congruent distributions of hydraulic conductivity, specific storage, and hydraulic diffusivity after rigorous wavelet denoising. The results demonstrate that the short-term sampling strategy achieves accuracy comparable to that of long-term sampling strategy in characterizing aquifer heterogeneity. Critically, by decoupling SLE from steady-state requirements, this approach minimizes groundwater disturbance and time costs, expanding HT’s feasibility to challenging environments.