Characterizing subsurface hydraulic heterogeneity of alluvial fan using riverstage fluctuations

Yu-Li Wang1, Tian-Chyi J. Yeh1, Jet-Chau Wen2, Shao-Yang Huang3, Yuanyuan Zha4, Jui-Pin Tsai5, Yonghong Hao6, Yue Liang7

1Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, Arizona

2Department of Safety, Health, and Environmental Engineering, National Yunlin University of Science and Technology, Douliu, Taiwan

3Research Center for Soil and Water Resources and Natural Disaster Prevention, National Yunlin University of Science and Technology, Douliu, Taiwan

4State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, China

5Department of Civil Engineering, National Chiao-Tung University, Hsinchu, Taiwan

6Key Laboratory for Water Environment and Resources, Tianjin Normal University, Tianjin, China

7National Engineering Research Center for Inland Waterways, Chongqing Jiaotong University, Chongqing, China

The objective of this study is to demonstrate the ability of riverstage tomography to estimate 2-D spatial distribution of hydraulic diffusivity (D) of Zhuoshui River alluvial fan, Taiwan, using groundwater level data from 65 wells and stream stage data from 5 gauging stations. In order to accomplish this objective, wavelet analysis is first conducted to investigate the temporal characteristics of groundwater level, precipitation, and stream stage. The results of the analysis show that variations of groundwater level and stream stage are highly correlated over seasonal and annual periods while that between precipitation is less significant. Subsequently, spatial cross-correlation between seasonal variations of groundwater level and riverstage data is analyzed. We found that the correlation contour map reflects the pattern of sediment distribution of the fan. This finding is further substantiated by the cross-correlation analysis using both noisy and noise-free groundwater and riverstage data of a synthetic aquifer, where aquifer heterogeneity is known exactly. The ability of riverstage tomography is then tested with these synthetic data sets to estimate D distribution. Finally, the riverstage tomography is applied to the alluvial fan. The results of the application reveal that the apex and southeast regions of the alluvial fan are areas with relatively high D and the D values gradually decrease toward the shoreline of the fan. In addition, D at northern region of the alluvial fan is slightly larger than that at southern. These findings are consistent with the geologic evolution of this alluvial fan.

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