Subsurface drainage in a soil overlying an impermeable layer

Hasegawa, Shuichi; Osozawa, Seiko

doi:10.1080/00380768.1994.10414291

Cited by 1 publication

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“…Joso Clay, an alternation of clayey layers with a thickness, in general, of 1–4 m and a maximum thickness of 5–6 m (Kanno et al. 1976; Kikuchi 1981) is widely recognized as the low‐permeability layer (aquitard) (Hasegawa and Osozawa 1994; Nagatsuka and Oba 1982; Shimada et al. 1990; Yasuhara and Marui 1993; Yasuhara et al.…”

Section: Introductionmentioning

confidence: 99%

Field scale determination of the aquifer–aquitard boundary in Joso Clay by cone penetrometry

Eguchi

Sawamoto

Shiba

2009

Soil Science and Plant Nutrition

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A few number of soil profile studies have pointed out that Joso Clay, a thick clayey layer underlying the shallow groundwater bodies in the diluvial uplands of southern Ibaraki and northern Chiba prefectures, Japan, has a structured surface layer in which the hydraulic conductivity is one to several orders of magnitude higher than that of the underlying massive layer. The spatial distribution of the boundary between the structured and massive clay layers should be determined as the aquifer-aquitard boundary; however, such attempts have not been made. In the present study, dynamic cone penetrometry was used to determine the spatial distribution of the aquifer-aquitard boundary in Joso Clay at a field scale in Tsukuba-Inashiki Upland, Ibaraki prefecture, Japan. The dynamic cone penetration index N d5 , every 5-cm depth average of the number of hammer strikes required for the tip cone to enter into the soil per unit of depth, was determined to a depth of 3.1-3.7 m at 54 rectangular grid points with approximately 5-m spacing in a field with an area of 943 m 2 . The field-scale N d5 profile data suggested that prismatic structures with N d5 values of up to 50-60 m -1 are widely distributed in the uppermost layer of the Joso Clay. Accordingly, a criterion of N d5 > 60 m -1 was proposed for determining the underlying aquitard in this field. The depth to the aquifer-aquitard boundary was determined to be 2.58 m on average, ranging from 2.40 to 2.89 m. Furthermore, annual water table monitoring at each grid point showed that the thickness of the structured layer, varying from 0.30 to 0.75 m, occupied 61-100% of the annual average shallow aquifer thickness, which varied from 0.40 to 0.87 m. These results demonstrate the significance of the uppermost structured layer in the Joso Clay as the major part of the shallow aquifer at a field scale in this upland.

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Section: Introductionmentioning

confidence: 99%