Vertical hydraulic gradient (VHG) provides detailed information on
3D groundwater flows in alluvial fans, but its regional mapping is complicated
by a lack of piezometer nests and uncertainty in conventional well data.
Especially, determining representative depth of well screen in each well is
problematic. Here, a VHG map of the Toyohira River alluvial fan, Sapporo,
Japan, is constructed based on groundwater table elevation (GTE), using
available well-data of various screen lengths and depths. The water-level data
after 1988, when subway constructions are mostly completed in the city, are divided
into those of shallow wells (≤20 m deep), and those of deep wells (>20 m
deep). First, the GTE map is generated by kriging interpolation of shallow well
data with topographic drift. Next, the individual VHG value of each deep well
is calculated using its top, middle, and bottom elevations of the screen
depths, respectively. The VHG maps of three cases are then obtained using
neighborhood kriging. The VHG map of the bottom screen depths has proven most
valid by cross-validation. The VHG map better visualizes that downward flows of
groundwater are predominant over the fan. Positive area of VHG is mostly
vanished around the fan-toe, indicating urbanization effect such as artificial
withdrawals. A negative
 S. G. Hu, T. Kobayashi, E. Okuda, A. Oishi, M. Saito, T. Kayaki and S. Miyazaki, “Alluvial Fans-Importance and Relevance: A Review of Studies by Research Group on Hydro-Environments around Alluvial Fans in Japan,” In: M. Taniguchi and I. P. Holman, Eds., Groundwater Response to Changing Climate, CRC Press, AK Leiden, 2010, pp. 131-139. doi:10.1201/b10530-12
 W. A. McIlvride and B. M. Rector, “Comparison of Short- and Long-Screen Monitoring Wells in Alluvial Sediments,” Proceedings of the Second National Outdoor Action Conference on Aquifer Restoration, Ground Water Monitoring and Geophysical Methods, Dublin, 1988, pp. 375-390.
 Y. Sakata, “Geostatistical Reservoir Modeling of Trending Heterogeneity Specified in Focused Recharge Zone: A Case Study of Toyohira River Alluvial Fan, Sapporo, Japan,” PhD Dissertation, Hokkaido University, Sapporo, 2013.
 S. G. Hu, S. Miyajima, D. Nagaoka, K. Koizumi and K. Mukai, “Study on the Relation between Groundwater and Surface Water in Toyohira-Gawa Alluvial Fan, Hokkaido, Japan,” In: M. Taniguchi and I. P. Holman, Eds., Groundwater Response to Changing Climate, CRC Press, AK Leiden, 2010, pp. 141-158. doi:10.1201/b10530-13
 Y. Sakata and R. Ikeda, “Quantification of Longitudinal River Discharge and Leakage in an Alluvial Fan by Synoptic Survey Using Handheld ADV,” Journal of Japan Society of Hydrology and Water Resources, Vol. 25, No. 2, 2012, pp. 89-102. doi:10.3178/jjshwr.25.89
 L. Nikroo, M. Kompani-Zare, A. R. Sepaskhah and S. R. F. Shamsi, “Groundwater Depth and Elevation Interpolation by Kriging Methods in Mohr Basin of Fars Province in Iran,” Environmental Monitoring and Assessment, Vol. 166, 2010, pp. 387-407. doi:10.1007/s10661-009-1010-x
 T. Hengl, “A Practical Guide to Geostatistical Mapping of Environmental Variables,” JRC Scientific and Technical Reports, Office for Official Publications of the European Communities, Luxembourg, 2007.
 B. Minasny and A. B. McBratney, “Spatial Prediction of Soil Properties Using EBLUP with the Matérn Covariance Function,” Geoderma, Vol. 140, No. 4, 2007, pp. 324-336. doi:10.1016/j.geoderma.2007.04.028