The major problems of groundwater hydrology in Latvia are related to:
- change of groundwater table due urban and industrial water consumption;
- pollution of horizons by leakage from waste deposits and polluted water pumping sites;
- operation of underground gas reservoir in Inčukalns;
- filtration processes nearby the reservoirs of hydropower plants (HPP).
Although solution of all above problems is subject to extensive modelling efforts, only the groundwater flow investigations nearby the largest HPP in Latvia, Pļaviņu HPP, is illustrated hereafler.
The largest HPP on the River Daugava is built on the floodplain of the river; the main earth dam is located on the riverbed, but wing dams lie on the bedrock hills of Devonian age. The main building of HPP is located on the ancient valley, filled with low permeability moraine. It ensures low filtration rates, however causes problems due:
- high filtration through the deluvial and proluvial sediments on the slopes of buried valley;
- necessity to lower pore pressure in sandy loam to preserve mechanical stability of moraine.
The system of complex hydrological measures including concrete injections into dolomites, drainage blankets, relief wells etc. are being continuously developed and adjusted. The three-dimensional groundwater filtration model is developed for the 4 to 4 km region around the HPP to serve as a tool for hydrogeological engineering. Several thousands survey boreholes and few hundreds of observation wells (time series of piezometric heads and discharges since 1968) allowed to build a geological structure with spatial resolution up to several cm (three dimensional finite element mesh encounters a quarter of million tetraedrs), and calibration up to 1 m accuracy between calculated and observed piezometric heads.
Daugava HPP Cascade, SJSC UP Latvenergo