Model Estimate of the Coastal Constructions’ Impact on the Hydrodynamic Regime of the Neva Bay Water Area Adjacent to the 300th Anniversary Park of St. Petersburg in August and December 2011

Based on a coupled high-resolution numerical model, changes in the current structure and wind wave field in the northeastern part of the Neva Bay adjacent to the 300th Anniversary Park of St. Petersburg caused by coastal hydrotechnical constructions have been analysed. Using August 2011 conditions, it has been shown that under weak winds conditions, the River Neva runoff is the main contributor to the formation of the current field in this region. The influence of coastal constructions is manifested in the destruction of an anticyclonic vortex near the hydrotechnical structure No. 3 and a in a decrease of current velocity from 15 cm/s to 5 cm/s. For December 2011 conditions, it has been found that under weak southwestern and western winds, the influence of coastal constructions is expressed in a decrease of current velocity by 5–10 cm/s in the beach zone of the park while maintaining the overall structure of the current field. During stormy westerly winds, typical of late December 2011, a considerable southward deflection of the Neva outflow occurs, reducing the outflow current velocity to 20–25 cm/s. At the same time, a current directed along the shoreline from the northwest to the southeast forms in the beach area. The influence of coastal structures in this case leads to a decrease in current velocity by 5 cm/s in the area between hydrotechnical structures No. 2 and No. 3, resulting in the formation of a stagnant zone. Analysis of the wave regime has revealed that coastal constructions create wave shadow zones, thus significantly reducing wave heights in their immediate vicinity, though the protective effect is limited to localised areas. The maximum decrease in wave activity due to the presence of coastal constructions is observed under westerly winds, while the minimum occurs under southerly winds.

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