Recharge enters the system at a rate of 10 -9 m/s. Vertical flow would be parallel to the edge of the model and would be a valid no-flow boundary for horizontal flow. However, flow observations in the rivers show that groundwater is discharging to the rivers and unless the geologic units provide a substantial barrier to flow, groundwater flow in the vicinity of the river is likely to be vertical. In the case of the boundary on the right, this might not be correct because the geologic units continue beyond the area shown on the cross section. The right, and bottom boundaries are treated as no-flow boundaries. The rivers will be treated as constant-head boundaries. The uppermost geologic unit is missing for approximately half of the cross section and all but the bottom unit are missing at the far left. The colored lines are the boundaries between different geologic units and the blue areas on either end represent rivers. The black line represents the ground surface. In this example, we will model the monocline illustrated below.

Even if you will eventually need to use a three-dimensional model, starting with a two-dimensional model may provide you with insights into the system that will be helpful in three-dimensional modeling. Because a cross sectional model will typically have far fewer cells than an equivalent three-dimensional model it can be run and calibrated much more quickly.

In many cases, a cross sectional model can be a good approach to a modeling problem.

Geologic cross section software