The main Latvian stream, the River Daugava is a trans-boundary river. Its length is 1005 km, area of drainage basin 87900 square kilometers. The discharge of the River varies seasonally from 95 (winter low-flow) 105 (summer low-flow) cubic meters/s to 8000 cubic meters/s (spring snow-melt period) while the mean annual discharge is ca. 600 cubic meters/s. The River Daugava has different flow conditions along its longitudinal section in territory of Latvia: slow stretches (slope few cm/km) interchange with rapids (bottom slope up to 1 m/km), and reservoirs of the cascade of HPPs. The largest reservoir of Pļaviņas HPP has volume 0.5 cubic kilometers, water level is raised by 40 m. The cross-profiling of the River Daugava is done upstream this reservoir; regular hydrometric observations as well as monitoring of water quality parameters are carried out for decades along the River. It allows set-up, tuning and calibration of the one-dimensional models of river hydraulics and water quality models. The locations of severe emissions into the river or flooding regions can further be investigated by two-dimensional models. The 20 modelis applied for the River stretch near Līvāni, the effluent site from the proposed pulp mill. The role of the River Daugava as a source of drinking water, the changes in land-use due to the transient socio-economic conditions, changing structure of pollution point-sources are basic reasons for employment of models to forecast the changes in the River Daugava ecosystem.
Institute of Biology (UL) and State Forest Agency