Lecture 22

Non Radial Flow Equation in

a Confined Aquifer - Jacob

Method

Fetter 7.4.3.2

Jacob Straight-Line Time Drawdown Method-

C.E. Jacob and H.H. Cooper (Cooper and Jacob 1946, Jacob 1950)

Observed that u becomes small and higher terms of infinite series become

negligible with time if u< 0.05, then u = , ignore all higher powers and

or

Convert to base 10 log

	® Log equation plots as straight line on semi log paper.

Generally u condition met for large t , or small r .

	Use method after sufficient time has elapsed.
	Closer observation wells.

Semi log graph

	(2.) Draw straight line through data points and extend backwards
	to zero drawdown axis.
	Must intercept s=0 at some time ® to
	(3.) Find amount of drawdown (h0 - h) or s for 1 log interval.
	(4.) Calculate T =
		T - ft2/d or m2/d
		Q - ft3/d or m3/d
		D (h0 - h) - Drawdown / log cycle (ft)
	(5.) Calculate S =
		S = storativity
		r = radial distance to well (ft)
		t0 = time where straight line intersects the zero drawdown axis (days)

Graphical Methods

 Nonequilibrium Radial Flow-Confined

Drawdown Measurements at three or more observation wells at the same time.

Pumped Well

Observation Well

Drawdown versus distance diagram

	(3.) Draw line through wells closest to the observation well till it intercepts zero drawdown.
				distance from pumping well where s = 0
	(4.) Find drawdown/ log cycle
	(5.) Calculate
		T =
		S =
					T = ft2/d
					Q = ft3/d
					D (h0 - h) = ft
					r0 = distance at which straight line intercepts zero drawdown axis(ft)
					t = days

Graphical Solution

ENV 302 - Lectures