The Brumunddal sandstone is located some 150 km north of Oslo in the county of Hedemark in Southeastern Norway. Groundwater is a major resource of water both for consumption and agricultural use in Brumunddal. Ground water from the unconfined sandstone aquifer is continuously pumped. The usage of huge amount of water has effects on the level of ground water and hence on the amount of water stored in the aquifer from time to time. As groundwater and surface water are connected, the viability of groundwater dependent ecosystem and the base flow component of river flows can also be impacted. The river Brumunda which is fed by the aquifer joins lake Mjøsa, the largest Lake in Norway.
Groundwater balances provide information on the quantities of the most significant inflow and outflows, which is important for assessing the sustainability of a ground water management regime. Ground water is essentially a hidden resource and there are many gaps in the available data; therefore, studies of groundwater under both natural and artificial conditions have employed modeling techniques. Groundwater models describe groundwater flow using mathematical equations that are based on certain simplifying assumptions. Ground water modeling has become a very important process in managing ground water resources.
The objective of this thesis is to develop a 2-dimensional map-view ground water model to determine the direction of groundwater flow, quantify the inflow and outflow and to determine the relationship between the aquifer and the Brumunda river.
COMSOL Multiphysics, formerly known as FEMLAB, is a computer software that makes possible to numerically solve partial differential equations. The numerical solution relies on the Finite Element Method (FEM). The Darcy’s Law application mode of COMSOL Multiphysics version 3.4 was used to quantify water balances for the aquifer.
The model was calibrated to the average 2007 (summer) groundwater levels for 33 privately owned wells and 24 stage readings of river Brumunda to match model simulation with actual measurement. About 68 percent of the simulated water levels are within 5 meters of measured water levels and about 20 percent are within 20 meters of measured. The rest are within 40 meters. Model simulations are most sensitive to changes in hydraulic conductivity and less affected by changes in precipitation recharge.
Results from a steady state model showed that the maximum head in the sandstone aquifer is 369m and the minimum head which corresponds to the southern part of the study area is 178m. The hydraulic conductivity which gives the best fit of the observed and calculated head is 1.26e-7 m/s. The transmissivity calculated is proportional to the thickness of the aquifer. The maximum transmissivity is found to be 9.69e-5 and the minimum is 7.28e-5 m2/s. The total amount of water recharging the aquifer was estimated to be 2598566 m3/year. The total amount of discharge from the aquifer to the river Brumunda was estimated to be 649642 m3/year. This accounts for 25 percent of the recharge. The total discharge through the Public Narud water supply well is 1063000 which accounts for 41 percent of the total recharge. The rest water of the recharge which is about 885924 m3/year is pumped by the private wells for agriculture and consumption purposes. This is equivalent to 34 percent of the total recharge.
The calibrated steady state model can be used to predict effects for different pumping scenarios.