The Heifangtai is located on the fourth terrace of the Yellow River, c. 60 km to the west of Lanzhou City, Gansu Province, China (Fig. 1a). The terrace has an area of 13.7 km2 and, since the 1960s, has been used as farmland by the people relocated from areas affected by the construction of the Liujiaxia Dam and its associated reservoir on the Yellow River. Large-scale irrigation on the terrace resulting from agricultural land use since the relocation has elevated groundwater levels by c. 20 m as a result of the presence of a relatively...

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