Measure groundwater level
The groundwater level as measured in a pipe or hole is a surface that does not occur in the soil. Between the soil particles in the soil, there are spaces, the so-called pores. These are, viewed from top to bottom, filled with air, filled with air and water, and completely filled with water. (see figure 9). The groundwater level measured in a pipe or hole is where all pores are filled with water. We can measure these groundwater levels through boreholes and monitoring wells.
A drill hole can be made to measure the behavior of the groundwater level for several days or weeks in a row. This gives a reasonably reliable impression of the rise and fall of the groundwater level. Drill holes are less suitable for measuring a longer period. In the meantime, they can be damaged or (partly) collapse. The risk of collapse depends on the type of soil and soil structure as well as on the fluctuation of the groundwater over time.
Monitoring wells are needed to measure the groundwater level over a longer period. These often consist of plastic tubes and can differ greatly in diameter and length. Usually, the diameter varies from two to four to five centimeters. There are tubes which are provided with perforations over a fairly great length around which a nylon stocking is attached. Here the groundwater can flow over the entire length of perforations in the pipe. This can mean that water flows in from highly permeable layers that occur high in the profile. If you are measuring the groundwater level in the pipe, it is not known from which depth the groundwater originates. To gain insight into this, it is possible to provide the monitoring wells with perforations only over a limited length.
To measure the water level in boreholes or monitoring wells, it is necessary to use a level gauge. These can be used to a depth of up to 10 meters. For greater depths, there is also a gauge light (up to about 50 meters) or a gauge with sound signal (up to about 200 meters deep). The water level can be recorded incidentally, for example, once a day, per week, month or quarter, but also continuously. So-called divers are placed for this, which can be read remotely.
After making the borehole or installing a monitoring well, you should wait at least 24 hours before measuring for the first time. The location of the boreholes and/or monitoring wells depends on which data is desired. To check the influence of the ditch level in a plot, an observation can be made at a distance of, for example, 2, 10, and 50 meters from the ditch. (figure 10 a) Figure 10b shows that the measurement can also take place at a fixed distance from the ditch, right next to a drain. This way the course of the groundwater can be measured near a drain. The influence of the drain length to the end pipe can also be examined. In figure 10c the setup shows that the influence of the drain on the groundwater level can be measured. A reasonable impression of the functioning of ditches and drains are shown in figures 10a, 10b, and 10c.
Examples of flooding and application of the control
Puddles in drained lots may or may not have been caused by compacted topsoil. In addition to a possible observation via the soil profile, it is also possible to derive from the behavior of the groundwater level. This is one of the purposes of placing a monitoring well, or boreholes can be made just around the pools and it is also possible to make them from drain to drain as shown in figure 10. A day later it can be determined whether the topsoil is compacted. For example, if the groundwater around the ponds is clearly below ground level (for example, more than 30 cm), then there is compaction. Besides, the influence of the drains is noticeable due to differences at the location of the drain compared to the center between the drains. Even when there are puddles up to the edge of the plot while the ditch level is, for example, more than 1.00 meters below ground level, there is almost certainly compaction. If the groundwater level is the same as the water in the puddles, the drainage will not function optimally, unless there is a substantial discharge from the end pipe at that moment (figures 11A and 11B). The cause may be that the total profile has been compacted, but also that the drainage has been disturbed.
By examining the most recent use of the plot and assessing the soil profile, the occurrence of soil compaction can be properly estimated.
When it is a drainage failure, puddling only occurs very locally. After all, a drainage system that has always functioned well is rarely disrupted across an entire plot. If there are puddles shortly after the drainage has been installed, this could be a malfunction in one of the drains. Placing monitoring wells or making boreholes from drain to drain and / or along the length of the drain at a fixed distance to the end pipe can clarify this. During all this, the discharge is also checked.
If there is a suspicion of a malfunction, the drain can be punctured, flushed, or measured. Piercing is the simplest form of control. Flushing is a combination of checking and cleaning in one operation. Measurement provides insight into the location, accessibility, and elevation. If a fault is found in this way, the problem can be solved, for example by excavating the fault or by installing a completely new drain.