Aw. Western et al., GEOSTATISTICAL CHARACTERIZATION OF SOIL-MOISTURE PATTERNS IN THE TARRAWARRA A CATCHMENT, Journal of hydrology, 205(1-2), 1998, pp. 20-37
Spatial soil moisture patterns have been measured in the 10.5 ha Tarra
warra catchment in temperate south-eastern Australia on 13 occasions u
sing time domain reflectometry (TDR). Measurements are made on regular
grids of between 500 and 2000 points for each occasion. The spatial c
orrelation structure of these soil moisture patterns is analysed. Samp
le variograms are found to have a clear sill and a nugget. Exponential
variogram models, including a nugget, fit the sample variograms close
ly. The geostatistical structure is found to evolve seasonally. High s
ills (5-25 (% v/v)(2)) and low col relation lengths (35-50 m) are obse
rved during the wet winter period. During the dry summer period sills
an smaller (5-15 (%v/v)(2)) and correlation lengths are longer (50-60
m). This seasonal evolution is explained on the basis of the importanc
e of lateral redistribution of moisture during different seasons. Both
a nugget effect due to measurement error and variability at small sca
les contribute to the variability at the 10 m scale, which is the smal
lest scale in most of the data sets, For one occasion four soil moistu
re patterns containing 514 samples were collected on 10 x 20 m grids.
These patterns are offset by 2 m in an easterly and/or a northerly dir
ection. Variograms for these four patterns are similar which indicates
that variograms used for the structural analysis are highly reliable.
An analysis based on transects subsampled from typical summer and win
ter soil moisture patterns indicates that a substantial number of data
points (more than about 300) are needed to obtain meaningful sample v
ariograms. (C) 1998 Elsevier Science B.V.