IGW-NET Visualization - Effects of Temporal Variability

Parameter	Case 1	Case 2
Geometric mean conductivity, K_g (m/day)	5	5
ln K variance	0.0	2.0
Correlation scale, λ_x (m)	NA	10
Correlation scale, λ_z (m)	NA	3
Porosity, n	0.3	0.3
Size of model (m)	200 x 100	200 x 100
Grid	251 x 126	251 x 126
Cell size, Δx (m)	0.8 x 0.8	0.8 x 0.8
Time step, Δt(days)	10	10

Temporally varying boundary conditions
Time (days)	Left boundary (m)	Right boundary (m)
0	73	75
30	71.5	74
60	70	72.5
90	70	70
120	69	68
150	68.5	67.5
180	67.5	67
210	68	66.5
240	68.5	68
270	69.5	70
300	70.5	71
330	72	73
360	73	75
The model parameters and inputs are explained below: The average conductivity values are 5 m/d for both cases. The ln K variance for case 1 is 0.0 and for case 2 it is 2.0. The horizontal correlation scale (λ_x), and vertical correlation scale (λ_z) is 10 m and 3 m respectively for case 2. The cell size, Δx, is selected such that the correlation scale, λ, is resolved. Typically, Δx is at least 3 to 4 times smaller than the correlation scale. The time step, Δt, is selected such that the temporal variability of head in the river is resolved. Since the variability is 30 days, a time step of 10 days is used. Download model - 1(To download, right click and select "Save Link As" ) Download model - 2

PLUME TRANSPORT - COMPARISON BETWEEN HOMOGENEOUS AND HETEROGENEOUS AQUIFERS

Problem Statement

This video compares the effect of temporally varying boundary conditions on plume transport in homogeneous aquifers with heterogeneous aquifers. The modeling domain consists of a time-variable head boundary on both left and right extremes. Details are provided in Table 2.8.

Key Observations

The following observations can be made from the video:

Temporally varying boundary conditions cause to and fro motion of the plume in both homogeneous and heterogeneous aquifers.
Plume transport is predominantly reversible in homogeneous aquifers, while it is irreversible in heterogeneous aquifers.
The plume spreads significantly due to the interaction between spatial heterogeneity and temporal variability. In the absence of spatial heterogeneity, the plume does not spread, but undergoes slight distortion in shape.

Additional Observations

Case 1: The average conductivity of the aquifer is 5 m/day. The temporally varying boundary conditions cause the head in the aquifer to fluctuate. As a result, the flow of groundwater changes direction, resulting in to and fro motion of the plume. However, due to the homogeneous properties of the aquifer, there is no spreading of the plume, apart from a slight distortion in the shape of the plume.

Case 2: The geometric mean conductivity of the aquifer is 5 m/day. The temporally varying boundary conditions cause the head in the aquifer to fluctuate. As a result, the flow of groundwater changes direction, resulting in to and fro motion of the plume. Since the aquifer is heterogeneous, the to and fro motion of the plume is irreversible. When a part of the plume enters a low K zone, it is “trapped” and releases the contaminant slowly. As a result, the plume spreads significantly. Compared to case 1, the plume's shape is lost and its position in the aquifer is drastically different. Since the aquifer is anisotropic, plume spreading is predominantly in the horizontal plane, and very little in the vertical plane.