GW_VOL ; The EXPECT Groundwater Level Module

The groundwater module uses linear source-receptor relationships between groundwater abstraction rate of a well and changes in hydraulic head and seepage in grid blocks. The relationships are based on calculations with the RIVM groundwater model for the Netherlands (LGM). Source-receptor relationships are derived for all combinations of 1*1 km grid cells and abstraction wells. Effects of different abstraction wells on one grid cell are summed. Because of the non-linear relationship between hydraulic head in the upper aquifer and flux to the surface water system used in LGM, the source-receptor relationships are only an approximation of the LGM results.

The ratio between the variance explained by the model and the total variance has been calculated for each grid cell as an indication of the accuracy of the results calculated with source-receptor relationships. Effects of several groundwater abstraction scenarios have been calculated with both the groundwater module and LGM, to get an impression of the differences in results.The conclusion is that, if groundwater abstraction scenarios do not include changes in abstraction rates larger than in the scenarios discussed in chapter 4, GW_VOL can be used successfully to calculate changes in groundwater level and seepage.