Lecture 15

Lecture 15

Flow Lines

Fetter 5.11

Flow lines

An imaginary line tracing a path that water flows in an aquifer.

Isotropic

Flow lines and equipotentials cross at right angles.

Flownet

A graphical solution to the two dimensional Laplace equation.

	Assume
	(1.) Homogeneous

	(2.) Isotropic

	(3.) Fully saturated

	(4.) No change in potential with time

	(5.) Soil and water incompressible

	(6.) Flow is lamilar and Darcy’s Law valid

	(7.) All Boundary conditions known

Boundaries

No flow - flow lines parallel to boundary.

Constant Head equipotentials parallel to boundary.

Water table known head, flow lines are oblique to water table if recharge.

Flow net is a family of equipotentials with enough flow lines to form a pattern of

"square" figures.

	(1.) Identify boundaries and label type and hydraulic head.

	(2.) Sketch boundaries to scale

	(3.) Identify known equipotential and flow line positions

	(4.) Draw trial set of flow lines

	outer lines parallel to no-flow boundaries

Rules

(1.) Flow and equipotential lines intersect at right angles and are chosen to form curvilinear squares.

a circle drawn in any curvilear square should touch all four sides at a tangent.

(2.) Flow quantity between all pairs of adjacent flow lines is the same.

(3.) Energy loss between all pairs of equipotentials is the same.

(4.) Velocity and hydraulic gradient are a function of spacing between flow and equipotential lines.

(5.) Lines within the net are smooth curves.

Flow net can be used to determine quantity of water flowing through area.

q’

	q’ = Total volume discharge per unit width of aquifer ()

	K = Hydraulic conductivity

	p = Number of flow paths bound by adjacent pairs of streamlines.

	h = Total head loss over length of streamlines (L)

	f = Number of squares bounded by any two adjacent streamlines covering the entire length of flow.