The water table is the top surface of the saturated zone of water in an aquifer. It fluctuates as water enters or leaves it and is usually measured in two ways: depth to water and height above sea level. Water table levels are monitored worldwide. They indicate the availability of drinking water and the potential to irrigate farmlands. Nearly every major city on earth depends on water derived from the aquifer. Its waters recharge the wells used to give life to cities and its levels determine how deep a well must be drilled.
- Skill level:
Things you need
- Metal tape measure
- Water well
- Online USGS water levels
- Sinker weight
- Local environmental records
- GPS (optional)
Method 1: USGS resource website
Research the USGS resource. The water tables throughout the United States are continuously monitored. Input the locations of interest and the available real-time water level data will stream to your computer.
Method 2: Measure the level of nearby surface water
Most of the time, the height of the nearest surface water is the water table level. Use a GPS at the water's surface and read the elevation. The exception to this is if the underlying geological structure is an impermeable layer, such as clay. The surface of the water will not be indicative of the water table. In this case, the water is being held up--not by the surface of the water table but by that of the impermeable stratum.
Obtain access to the location of the nearest monitoring well; there are usually many (government or private) in any given area. Access may require permission. Monitoring wells are often discreet concrete pads, flush to the ground, with a capped PVC pipe centred in it. All government monitoring well locations are documented at the appropriate state office. While there are no set rules, the easiest way obtain well information is to go to the USGS website and research the area of interest. The nearest DERM, county or state records departments may also have water data for additional queries. Unfortunately, there is no consistency from location to location on the way environmental data is presented, preserved or collected.
Attach the sinker to the end of the tape measure and chalk the end of the metal tape so a foot is coloured. Gradually guide the tape down the well until just after you hear the sinker strike the water. Hold the tape still and record the depth from the top of the well (M1). Gently reel the tape back up and read the distance where the water washed the chalk off (M2). Subtract M2 from M1 for the depth to the water table.
Determine the elevation of the water table above sea level by subtracting the depth to the water table from land surface elevation you found in step 2.
Tips and warnings
- Chalk the tape up thickly.
- Guide the tape measure down as evenly as possible.
- Avoid splashing.
- Close the well upon conclusion of the measurement
- Obtain permission for these measurements where required.
- Do not introduce any harmful contaminants.
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