Laboratory for Mathematical Modelling
of Environmental and Technological Processes

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Rivers hydraulics and hydrodynamics

The geographical and geopolitical location of Latvia on the crossing of (European) East-West and North-South routes, the developed rivers’ network, and prolonged Baltic Sea coastline have stimulated the growth of activities dependent on or influencing natural hydrological processes. Consequently, the observation series for different hydrological parameters are available for approx. 100 years. The broad and interrelated spectrum of hydrological processes are extensively studied for decades; however, contrary to central and western Europe, with minor employment of mathematical models. The relevance of hydrological processes, people awareness, availability of data together with plenty of working hypotheses make hydrological studies in Latvia a real challenge for modeller.

Several harbours (Ventspils, Riga) are located in the estuaries of rivers (Venta, Daugava). The mild-sloped rivers of Latvia are influenced by the sea-level fluctuations and saltwater intrusions far upstream. The seasonal run-off cycle is superposed by the daily and weekly cycles of Riga hydropower plant just upstream the estuary of the main Latvian stream, the River Daugava. The flow regime in estuaries is strongly changing during reconstruction and deepening of harbours.

The rivers’ network is well-developed in Latvia. Although it has lost its importance as a part of trade routes, rivers are important drinking water source and energetic resource. Relevant problems of rivers’ hydrology include flooding (interaction of seasonal run-off cycle with regulation by hydropower plants operation), water quality etc.

The hydrology of the mouth regions of Latvian rivers are affected by saltwater edges far upstream in the deepened navigation channels of the River Daugava and Venta; complex structure of deepened terminal sub-basins, interchanging of natural and protected coastline; distinct seasonal runoff cycle with summer low-flow and spring snow-melt flooding; propagation of wind waves far upstream in combination with wave generation in straight stretches. The estuarine region of the River Daugava additionally is influenced by working regime of hydropower plant (HPP), connection of the River Daugava with River Lielupe, and with a chain of inland water basins (acting as reservoirs). The two-dimensional shallow water model is developed for the lower 15 km of Daugava to investigate the hydrologic regime and wave climate in the Riga Seaport as well as to predict the impacts of the ongoing reconstruction measures on the flow regime. The model was in both qualitative and quantitative agreement with the measurements performed in a physical model of the lower River Daugava.

The main Latvian stream, the River Daugava is a trans-boundary river. Its length is 1005 km, area of drainage basin 87900 cquare 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 km3, 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 Livani, 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.

Related projects:

Riga Port Authority - 1
Riga Port Authority - 2
Institute of Biology (UL) and State Forest Agency