Geoderma, 45 (1989) 19-29 19 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands Characterizing Spatially Variable Hydraulic Properties of a Boulder Clay Deposit in The Netherlands* J. BOUMA, A.G. JONGMANS, A. STEIN and G. PEEK Department of Soil Science and Geology, Wageningen Agricultural University, P.O. Box 37, 6700 AA Wageningen (The Netherlands) (Received August 5, 1988; accepted after revision February 15, 1989) ABSTRACT Bouma, J., Jongmans, A.G., Stein, A. and Peek, G., 1989. Characterizing spatially variable hy- draulic properties of a boulder clay deposit in The Netherlands. Geoderma, 45: 19-29. Morphological and statistical methods were used to define the heterogeneity of a reddish brown boulder clay deposit in The Netherlands in terms of: (1) depth of occurrence below the surface; (2) areas occupied in cross-sections by the dense groundmass; and (3) areas occupied by sandy soil material around frost fissures. Physical measurements of K-sat were made separately in both materials with two methods, one using small infiltrometers and the other gypsum-encased undis- turbed blocks of soil that were carved out in situ. Both types of measurements yielded average K- sat values of 0.3 m/day for the groundmass and 6.9 m/day for the sandy soil material around fissures. K-sat measurements on horizontal undisturbed areas of 1200 cm2 yielded values of ap- proximately 0.5 m/day which could successfully be estimated by determining areas occupied by both materials in cross-section and by considering the proportional contribution of both materials to K-sat. This method of estimation was next used to demonstrate the effect of different hypo- thetical sample volumes on K-sat, illustrating the use of soil morphological descriptions to deter- mine optimal sample volume for K-sat measurements in heterogeneous soil materials. INTRODUCTION Glaciation periods in northwestern Europe have a permanent impact on ac- tual soil conditions. For example, occurrence of ground moraine, often referred to as boulder clay, at some depth in sandy soils, still has a profound impact on current soil water regimes. Pedological characterizations of boulder clay, both in terms of spatial occurrence as shown on soil maps and of morphological features, have been reported elsewhere (e.g. Stiboka, 1977; Bouma, 1982). The *Contribution from the Department of Soil Science and Geology, Agricultural University, Wageningen, The Netherlands. 0016-7061/89/$03.50 © 1989 Elsevier Science Publishers B.V.