






EFFECTS OF MULTIPLE SCALES OF HETEROGENEITY 



This video
demonstrates the effects of multiple scales of heterogeneity, in the absence
of porescale dispersion, on the spreading of a conservative solute plume.
The modeling domain consists of constant head boundaries on the left and
right extremes, and noflow boundaries at the top and bottom. Details are
provided in Table 4.1. 

The following
observations can be made from the video:


Case 1: The
correlation scale of heterogeneity is 500 m, which is much larger than the
initial size of the plume; therefore the plume does not spread greatly. In
such cases, the ln K realization is an important factor that controls
plume migration. Case 2: The
correlation scales of heterogeneity in the first and second scales are 500 m
and 100 m respectively. The initial size of the plume is of the order of 100
m. The plume does not exhibit detailed fingers and tails. However, in
comparison to case 1, spreading is increased. The mean plume displacement is
greater than in case 1, because the plume encounters more preferential paths
(high velocity channels). Case 3: The
correlation scales of heterogeneity in the first, second and third scales are
500 m, 100 m, and 10 m respectively. The third scale is smaller than the
initial size of the plume; most of the heterogeneity is encountered, and thus
plume spreading is greatly enhanced. The mean displacement is greater than in
cases 1 and 2, because the plume encounters more preferential paths (high
velocity channels). A comparison of the
three cases shows that increasing the number of scales of heterogeneity
increases plume spreading. Eliminating smaller scales of heterogeneity from
the model underestimates plume spreading. Incorporating smaller scales
requires higherresolution data, which is costly, and perhaps infeasible.
When only larger scales are modeled, the detailed structure of the aquifer
represented by the smaller scales of heterogeneity is averaged. In this
process of averaging, considerable amount of detail is lost. These details
are critical, and make a huge difference in the prediction of plume
spreading. 