Environmental Engineering FOURTH EDITION

Water Supply 111

Flow 0 A

d d

Area A ample

Figure 6-3. Permeameter for Example 6.1.

EXAMPLE 6.1. A soil sample is installed in a permeameter as shown in Fig. 6-3. The

length of the sample is 0.1 m, and it has a cross-sectional area of 0.05 m2. The water

pressure placed on the sample is 2 m, and a flow rate of 2.0 m3/day is observed. What

is the coefficient of permeability?

Using the above equation, and solving for K, we have

2.0

K= Q- - = 2 m3/rn2-day.

A(Ah/AL) 0.05 x (2/0.1)

An aquifer confined between two impermeable surfaces (aquacludes) is called a

con.ned aquifer and can be thought of as a very large permeameter. The pressure loss

due to the flow can be determined by measuring the water level in two wells, the second

one being directly downstream of the other.

EXAMPLE 6.2. A confined aquifer is 6 m deep and the coefficient of permeability in
the soil is 2m3/day-m2. The wells are lOOm apart, and the difference in the water
elevation in the wells is 3.0 m. Find the flow rate and the superficial velocity through
the aquifer.
The slope of the pressure gradient, AhlAL = 3/100 = 0.03, and the flow rate for
a section of aquifer 1 m wide is

TI 1

AL I ---4