Hi, I’m Jesse Dickinson, a hydrologist with the US Geological Survey. We’re here in
the San Pedro Basin in Southeastern Arizona, and we’re going to demonstrate how to measure
hydraulic head in an artesian well. Materials:
The materials needed include: A pipe wrench, A plug for the well, A clear
plastic column that can be attached vertically to the opening of the well , Plumbers tape
to ensure a tight fit to the well and to minimize leaking, A pencil or pen if using a water
level field form, or a device for electronic data entry, A ruler or tape for measuring
the height of water in the plastic tube, A level to ensure that the ruler or tape is
perpendicular to the land surface Instructions:
Step 1) Determine you are at the correct well from the well description and locate the documented
measuring point(s) and land surface datum from well photo or diagram.
Step 2) If necessary, use a pipe wrench or other tool to remove any plugs in order to
gain access to the well. Step 3) Apply plumbers tape to ensure a tight
fit between the well opening and the plastic pipe to minimize leaking.
Step 4) Connect a length of transparent plastic pipe tightly to the well.
Step 5) Gradually close any other opening to the flowing well. If pressure is applied
suddenly, the well could be permanently damaged by the “water-hammer effect” by caving
of the aquifer material, breakage of the well casing, or damage to the distribution lines
or gauges. Step 6) Ensure that all flow from the well
stops so that a static water-level measurement can be made.
Step 7) Rest the ruler or measuring tape on the measuring point (MP) and use the level
to check that the ruler or tape is perpendicular to the land surface. Use the scale to read
the height above the measuring point that the water has risen in the plastic pipe.
Step 8) Record the date and time of the measurement on a Water Level Measurement Field Form or
a digital screen input form. Because the water level is above the measuring point, this is
a negative number. Step 9) Record the measuring point (MP) correction
length on the “MP correction” row of the field form or select the MP used from the
electronic data entry form. Subtract the MP correction length from the true “water level
below measuring point” value to get the depth to water above the land surface datum
as a negative number. The MP correction is positive if the MP is above the land surface,
or negative if it is below the land surface. On the field form, record the water level
in the “WL below LSD” column. Step 10) Make a check measurement by performing
the previous steps. Record the check measurement on the field form or electronic data entry
form. If the check measurement differs from the original measurement by greater than 0.1
or 0.2 foot, continue to measure the water height until the reason for a lack of agreement
is determined or the results are found to be reliable. Complete the “final measurement
for GWSI” portion of the paper or digital field form.
Step 11) Gradually remove any plugs to the flowing well. If pressure is applied or released
suddenly, the well could be damaged. Step 12) Remove the clear plastic pipe from
the opening of the well. Step 13) Attach any other plugs to well openings.
Limitations: Keep in mind the following limitations of
this method. Low-pressure head measurements are most feasible
when the head is less than six feet above the land surface.
Measurements are commonly accurate to 1/10th of a foot.
All flow from the well should be shut down so that a static water level measurement can
be made. However, the time required to reach a static pressure after flow discontinues
may range from hours to days. Since a true static measurement may be impractical,
record the time after shutting off the flow for each measurement.
Advantages: An advantage of a method for low pressure
measurement is that it is generally simpler, faster, safer, and more accurate than a method
for high pressure measurement. Disadvantages:
A disadvantage is that this method may be impractical for wells with heads greater than
5 to 6ft above the land surface.