Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Dann, R. Articles by Francis, G. GeoRef GeoRef Citation

Characterization and Estimation of Hydraulic Properties in an Alluvial Gravel Vadose Zone

^a Institute of Environmental Science and Research, 27 Creyke Rd., Christchurch, New Zealand
^b Crop and Food Research, Private Bag 4704, Christchurch, New Zealand
^c Dep. of Applied Mathematics, Australian National Univ., Canberra, ACT, Australia
^d present address: AquaLinc Research, P O Box 20-462, Bishopdale, Christchurch, New Zealand. G. Francis, present address: AgResearch, Private Bag 4749, Christchurch, New Zealand

Correspondence: ^* Corresponding author (rod.dann{at}esr.cri.nz).

Received for publication 9 December 2008. Understanding the physical and hydraulic properties of the vadose zone is important for modeling land use effects on groundwater quality. This study used a variety of characterization methods to derive conceptual understanding and estimates of hydraulic properties of a coarse alluvial gravel vadose zone in New Zealand. Sandy gravel (SG) material constituted approximately 90% of the vadose zone, with the remainder comprising sand lenses and open-framework gravels. The gravel content of the SG material was approximately 70% (v/v) (range 68–73%). The water content of the bulk SG material (43 samples) ranged from 3.5 to 13.9%. The average bulk density of the SG material was 2.20 g/cm³ (range 2.00–2.33 g/cm³) giving an average calculated porosity of 17%. The average porosity of the open-framework gravels was 34% and these gravels were often coated with 2- to 3-mm-thick deposits of amorphous Fe and Mn oxides. Neutron probe (NP) depth profiles indicated unsteady conditions, with variable water contents with depth and time reflecting the vertical heterogeneity and the variably saturated state of the vadose zone. Time series NP data to 3 m indicated water content in the alluvial gravels responded quickly to soil drainage events, and saturation variability was greater in the sand lenses and the SG material immediately underlying. When compared with derived water retention curves, variability in the water content equated to significant fluctuation in unsaturated hydraulic conductivity (K_unsat). Tension infiltrometer measurements were variable but were within the range of the K_unsat estimates from site-average particle size distribution data. The gravel-transformed, texture-based models used to estimate saturated water content values in this study appeared to underestimate the measured values.

Abbreviations: NNP, neural network prediction • NP, neutron probe • PSD, particle size distribution • SG, sandy gravel • TDR, time domain reflectometry • TI, tension infiltrometer