Structure and water storage capacity of a small karst aquifer based on stream discharge in southwest China

- Three discharge recession models were evaluated in the small karst catchment.
- Effective porosities of conduit, fracture, and matrix were quantified for karst aquifer.
- Conduit system was not very developed but highly connected.

SummaryKarst spring/stream discharge reflects the global configuration of the aquifer. However, quantitative description of the aquifer structure such as effective porosity (neff) and water storage capacity by the discharge analysis is difficult because of the complex conduit/fracture system. This study attempted to quantify the characteristics of karst aquifer based on discharge recession and time series analysis methods. Three recession models, including modified Maillet, Mangin and Boussinesq models, were evaluated to choose the most suitable one for analyzing the aquifer structure, and auto-correlation and cross-correlation functions were applied to study the aquifer response in both year and rainfall event time scales. The results showed that the modified Maillet model was more suitable in the study catchment with Mangin model overestimating and Boussinesq model underestimating the discharge. The neff was 3.73% for the total aquifer, and it was 0.07%, 0.33% and 3.33% for the conduit, fracture and matrix, respectively. Based on a case study of a rainfall event with precipitation of 68 mm, the water volumes drained by the three media were 25.43%, 33.40% and 41.17%, respectively. This indicates that, although conduit network is not very developed with lower neff, it is still an important water transmissive element (draining more than a quarter of water after the rainfall event). The memory time of the aquifer was 4 days for the year scale and 8 h for the rainfall event (68 mm) scale. This demonstrates that the aquifer has a well developed drainage system with a quick response to the rainfall. The above results provide further insights for hydrological processes modeling and water resources management for the small catchment in karst regions.