Environmental Engineering Reference
In-Depth Information
1. Identify the well with the intermediate water level.
2. Interpolate the location of the intermediate water level well along a straight line
between the wells having the highest and lowest relative water levels.
3. Create a line segment of equal potential to the intermediate well by drawing a
straight line from the well with the intermediate water level to its water equivalent
elevation plotted along the straight line between the wells having the highest and
lowest relative water elevations.
4. Draw a perpendicular line to the water-level contour just plotted with the well
of highest or lowest water elevation. This line parallels the general direction of
groundwater flow.
5. Calculate the difference between the water level of the well and the intermedi-
ate well-level contour by using the distance between the well and the contour to
reveal the hydraulic gradient.
3.5.9 Estimating the Rate of Groundwater Flow
Calculating the rate or velocity of groundwater flow requires site-specific knowledge or
estimation of the following parameters:
• Hydraulic conductivity (K) of the saturated geologic strata
• Effective porosity (n e ) of the saturated geologic strata
• Hydraulic gradient (dH/dL) or slope of the groundwater surface
Once the above parameters are measured or estimated, the rate or velocity of groundwater
flow can be calculated using the stream economy equation and Darcy's law. The stream
economy equation is
(3.4)
Q Av
=
where
Q is the discharge (volume of water per unit time (cm 3 /s)
A is the cross sectional area (at right angle to the water flow direction) cm 2
v is the velocity (cm/s)
dH
dL
Q K A
=
×
×
(3.5)
where
K is the hydraulic conductivity (cm/s)
A is the area (cm 2 )
dH/dL is the hydraulic gradient
Step 1 of Equation 3.6 demonstrates how groundwater velocity can be computed by sub-
stituting Av (which equals Q) in Equation 3.4 for the Q in Equation 3.5. After the area (A) is
cancelled on both sides of the equation, the velocity (v) is equal to hydraulic conductivity
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