Harbour engineering

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.

Latvia has approx. 500-km long, mainly sandy coastline. Fine to medium sand means not only recreational beaches but also reasonable littoral drift, coastal abrasion and accumulation. The net annual northward drift along the coast of the Baltic Proper is caused by prevailing westerly south-westerly winds.

The most distinct manifestation of the littoral transport occurs in its interaction with hydroengineering constructions of seaports (wave breakers, jetties, and sea entrance channels). Main qualitative features are beach growth in upwind side of harbours while downwind areas suffer from erosion. Siltation in sea entrance channels is a real problem for navigation safety requiring annual allocations to perform dredging works. The optimisation of the measures to ensure safe navigation at minimum costs is especially actually for Liepaja and Ventspils harbours exposed for the Baltic winds and waves.

The continuos wave action on the sandy coasts produces cross-shore sand transport by oscillatory velocities; longshore currents with maximum of velocities and littoral longshore transport close to the wave-breaking line. The restructuring of the cross-shore profiles has time scale between single storm period (wash out of sand bar and/or beach) and season (restoration of bar structure). The direction and magnitudes of longshore currents vary continuously. The analysis of the mean sand transport volumes along the coastline allows specifying overall trends, accumulation and erosion zones, which on a longer time scale has respective impact on the shoreline development. A simple one-dimensional model for the predicting cross-shore distribution of the longshore littoral drift is developed. It accounts for wave generation (fetch model), transformation (incl. breaking), current distribution, formation of suspension, development of bed macroforms, bed and suspended load transport. The application of the model for the chain of cross-shore profiles along Latvian coastline shows that. The prevalence of the southwestern winds is responsible for the significant (typically more than 1 million m3) northward load transport near the Latvian coast of the Baltic Proper. The combination of the fetch with coastline orientation yields, generally, converging southward sand transport (annual values below 100 thousand cubic meters) along the coasts of the Gulf of Riga.

The hydrodynamical processes become essentially two or three dimensional in the vicinity of harbours. Typical engineering constructions, which interact with wave fields, water flow patterns and load transport, are wave-breakers, jetties, sediment traps and sea entrance channels of harbours. Two-dimensional model is developed for applications in near-harbour regions (typically up to 10 km zones). It includes two-dimensional, time-dependent description of wave-field, hydrodynamics, bed and suspended load transport, and morphodynamics (bed level changes). The operation of the model in a hind-casting mode allows its calibration and verification.

The operation of the model in forecasting mode allows prediction of the siltation in sediment traps and sea entrance channels during typical and critical seasons; it helps to draw consequences of reconstruction efforts, and is useful for designing of the sediment traps and finding other engineering solutions such as building additional wave-breakers. The applications of described model are found to assist reconstruction of Ventspils and Liepaja harbours.

Related projects:

Ventspils Free Port Authority
Riga Port Authority - 1
Riga Port Authority - 2