Water and the Hydrogeology of Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 91

Rise
Run = Slope

Slope

Rise
(dH)

(dH)
(dL) = Slope

Run
(dL)

I =hydraulic head=dH/dL

FIGURE 3.31
Calculating the hydraulic head.

This information is needed to determine the general direction of groundwater flow
between the three wells:

• Relative geographic position of the wells
• Distance between the wells
• Elevation of water in each well

Calculating the direction of groundwater flow involves the following steps (Heath 1983),
and an example of the procedure is shown in Figure 3.32:

Well 1
Head= 26.26m

(26.26m)

N N

(26.26 - 26.20) (26.26 - 26.07)

=

215

X

X= 68m

26.20m
Contour line

(26.20m)

Well 2
Head= 26.20m

Intermediate head

130m

26.20 - 26.07
130

Hydraulic gradient = 0.001m/m

(26.07m)

Well 3
Head= 26.07m

0 25 50 100 0 25 50 100

Groundwater
flow direction

Scale in meters

Scale in meters

Steps 1 and 2 Steps 3 through 5

FIGURE 3.32
Determining the direction of groundwater flow. (Modified from Heath, R.C., Basic Ground-Water Hydrology ,
United States Geological Survey, Water Supply Paper 2220, United States Government Printing Office,
Alexandria, VA, 1983.)