Lecture 31

Regional Ground-water Flow

Fetter 8.1 - 8.2

Know water moves to lower potential energy.

Flow nets are very useful for displaying regional flow.

	Solution to Laplace Equation
	Solve mathematically J. Toth (1962, 1963)
	Numerically Freeze and Whiterspoon (1966, 1967)
	using different boundary conditions

Recharge

	Topographical high areas
	Usually deep unsaturated zone.
	Flow lines diverge

Discharge area-

	Topographical low areas
	Usually shallow water table
	Flow lines converge(except coast lines)

*Vegetation may be indicator of seeps, springs , lakes , streams.

M.K.Hubbard (1940)

developed "The Theory of Groundwater flow"

Figure 8.1 Cross-sectional flow net in an isotropic, homogeneous aquifer.

The aquifer is much deeper than the diagram.

Figure 8.2 Piezometers superimposed on the previous diagram. The water

level in the piezometer will rise to the elevation of the hydraulic head, which

is represented by the equipotential line at the open end of the piezometer.

The Theory of Ground-Water Motion

Josef Toth-

	Developed a closed form of analytical solution to the Laplace equation.
	Assumed Homogeneous and Isotropic.
	No flow Boundaries right, left, bottom, linear slope to water table.
	Ground-Water discharge through ET, not one discharge point.

The potential field and flow lines in the vicinity of a stagnation point, which

will develop at the intersection of three flow systems.

A. Equipotential field and flow lines in a region where a high-conductivity

body in buried in a lower-conductivity aquifer.

B. the water table and the potentiometric profile of a line of piezometers,

each ending at the same elevation along line A-A’ of part A.

Figure 8.3 Regional flow pattern in an area of sloping linear topography

and water table. The flow pattern is symmetrical about the midline.

Figure 8.4 The effect of increased basin depth is shown on these

two figures. In Part A, basin depth/length ratio is 1:20; in Part B,

it is 1:2. The shallow basin has only local flow systems, whereas

the deep basin has local, intermediate, and regional flow systems.

The water-table configuration is the same for both basins.

Figure 8.5 The amplitude of the undulations of the water table controls the

depth of the local flow systems. For shallow basins, this can determine

whether both local and regional flow systems will develop (Part A), or,

with deeper undulations, only local flow systems will form (Part B).

ENV 302 - Lectures