Construction & the effect on Groundwater
All construction affects groundwater and a water management plan will be required.
From deforestation to urbanisation, from holes to heaps and dams to drains, they all have an affect on the groundwater.
Deforestation causes an increase in the rate of run off of rainwater resulting in lower percolation of precipitation into the soil and a consequent increase in soil erosion leading to slope instability, hence land and mud slides. The increased rate of run off can cause small streams and large rivers to rise and flood in a shorter time, but also to dry up sooner.
These conditions cause great difficulties for subsistence farmers in developing countries.
Urbanisation also causes faster run off because of the non permeable surfaces such as roads, roofs and car parks. This also creates drainage problems that can lead to contamination and erosion of natural water courses.
Quarries and mines often need dewatering because they extend down into the local aquifers causing water to enter the workings. This water has to be removed so that the work of extraction can continue. While the water is not lost, it is removed from the aquifer which may cause a drop in groundwater levels that can affect such local interests as agriculture and domestic and commercial wells.
Excavating for deep footings and basements may need dewatering during the construction phase.
The groundwater (pore water) within the soil body of the saturated zone, can, depending on soil type, contribute significantly to the bearing capacity of the soil.
Lowering, even temporarily, the groundwater (piezometric) level can have serious affects on adjacent structures.
The construction of large earth structures such as dams, berms and embankments also influence the pore water pressures beneath these large structures.
These pore water pressures can be critical to the safety of the dam. If the impounded water upstream of the dam rises or falls to rapidly the pore water pressures will respond and could cause the dam to fail.
The pore water (groundwater) pressures should be constantly monitored beneath critical large earth structures.
The monitoring program may include installing piezometers that allow the water level to be checked manually on a regular basis using a Heron dipper-T or Water Tape water level indicator noting changes in level. Alternatively by using the dipperLog ground water data logger placed strategically within and around the structure, a much higher sampling frequency with the ability to set alarm levels and initiate corrective procedures may be the most prudent course.
The Heron Instruments dipperLog ground water monitoring system when used in the
4/20 mA mode can be used to monitor, log, warn and initiate actions via the users PLC system.
The Heron Instruments dipperLog (stand alone) can also be used for monitoring and recording ground water levels in stand pipes and piezometers.
The dipperLog system allows 32000 data sets of groundwater level & temperature between downloads at timed intervals from one second to several hours.