Parameter	Case 1	Case 2	Case 3
Average transmissivity, T (m2/day)	2	20	200
Specific yield, Sy	0.1	0.1	0.1
Storage coefficient	NA	NA	NA
Porosity, n	0.3	0.3	0.3
Starting head - aquifer (m)	5	5	5
Mean head - river (m)	5	5	5
Amplitude, sr (m)	5	5	5
Time period (days)	1	1	1
Size of model (m)	500 x 10	500 x 10	500 x 10
Grid	251 x 6	251 x 6	251 x 6
Cell size, Δx (m)	2 x 2	2 x 2	2 x 2
Time step, Δt(days)	0.1	0.1	0.1
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 (λx), and vertical correlation scale (λz) 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 Download model - 3

 

UNCONFINED AQUIFERS WITH INCREASING TRANSMISSIVITIES

Conceptual Model
This video demonstrates the effect of a sinusoidally oscillating boundary condition on the hydraulic head in unconfined aquifers with increasing transmissivities. The modeling domain consists of a time-variable head boundary on the left extreme, and a no-flow boundary on the right. Details are provided in Table 2.1.
Governing Equations
The following observations can be made from the video: Sinusoidal oscillation at the boundary affects the head in the aquifer sinusoidally. As distance from the boundary increases, the effect on the head decreases. The area that is influenced by the boundary is called the “response zone”. The response zone depends on several parameters, such as transmissivity, storage coefficient, frequency of oscillations, amplitude of oscillations, and distance from the boundary. Lower transmissivity values result in a smaller response zone.
Numerical Model
Case 1: The average transmissivity is 2 m2/day and the specific yield is 0.1. The sinusoidal oscillation of head in the river is characterized by an amplitude of 5 m and a time period of 1 day. Since the aquifer material is not highly transmissive, the resulting transient head distribution in the aquifer is concentrated in a small zone very close to the river. Beyond approximately 20 m from the river, the oscillating head in the river produces no visible effect on the head in the aquifer. Case 2: The average transmissivity is 20 m2/day and the specific yield is 0.1. The sinusoidal oscillation of head in the river is characterized by an amplitude of 5 m and a time period of 1 day. Since the aquifer material is more transmissive than in case 1, the resulting transient head distribution in the aquifer is concentrated in a larger zone compared to case 1. Beyond approximately 50 m from the river, the oscillating head in the river produces no visible effect on the head in the aquifer. Case 3: The average transmissivity is 200 m2/day and the specific yield is 0.1. The sinusoidal oscillation of head in the river is characterized by an amplitude of 5 m and a time period of 1 day. Since the aquifer material is more transmissive than in cases 1 and 2, the resulting transient head distribution in the aquifer is concentrated in a larger zone compared to cases 1 and 2. Beyond approximately 100 m from the river, the oscillating head in the river produces no visible effect on the head in the aquifer.