Annex C

(informative)

Example of groundwater pressure derivations based on a model and long term measurements

(1) The natural groundwater pressure is part of the hydro logical cycle being influenced by the precipitation, evapotranspiration, snow melting, surface run-off etc.

(2) In order to establish a model of the groundwater situation for a building or a civil engineering project site and the surrounding area, available hydrogeological information should be compiled and compared to the actual groundwater measurements. Such information could be:

• water level fluctuations;
• geohydrological maps;
• previous measurements in the surroundings;
• typical water levels of surface water or in wells;
• long term measurements in similar aquifers.

(3) The groundwater measurements for a project normally only contain a short series of measurements. In these cases it is important to make a prediction of the expected groundwater pressure for the actual design situation and site. Such a prediction can be based on the model mentioned above and on long term measurements of the groundwater in a similar aquifer in the same region as the project in combination with a short term measurement on the site.

(4) By using statistical methods, it became possible to predict the groundwater pressure within a few kPa based on 15 years measurements in a reference system and a 3 month measuring period on the actual site, see Figure C.1.

(5) It is also possible to simulate the groundwater fluctuations by a conceptual model. Precipitation and air temperature can be used as input in the model. The groundwater response is calibrated against long term measured groundwater fluctuations in the region.

NOTE For additional information and examples, see X.2.

A) reference pipe	B) prediction pipe

Key

• 1 maximum groundwater levels measured in the reference pipe through 15 years.
• 2 minimum groundwater levels measured in the reference pipe through 15 years.
• 3 measured groundwater levels in the reference pipe during the same year as the observations in the prediction.
• 4 pipe on the actual test site.
• 5 predicted maximum groundwater level in the prediction pipe on the actual test site.
• 6 predicted minimum groundwater level in the prediction pipe on the actual test site.
• 7 measured values of groundwater level in (he prediction pipe on the lest site from time t₀ through t₁

NOTE The diagram on the left is the maximum and minimum groundwater level for a reference pipe. The diagram on the right is the actual measurements together with the predicted maximum/minimum groundwater levels.