Sea water level
Wind direction
Ice formation in
the sea
Sensitivity to
erosion during storms
Sand budget in
the coastal belt
Sea water level
Observations made during the past 30 years (1960-1990) at
stations for hydrological monitoring (Liepāja, Pāvilosta,
Ventspils, Kolka, Roja, Daugavgrīva, Skulte, and Salacgrīva) all
show a significant rising trend in the yearly mean water level,
which is most evident at the end of the Gulf of Rīga (Daugavgrīva,
Skulte), and is about 50% slower in open areas of the Baltic sea
coast (Liepāja, Ventspils).
The most drastic, damaging changes (wind and wave
erosion) are associated with storms, when the wind speed in the
coastal belt can exceed 20-25 m/s and the water level can rise by
>1m above the mean level.
The highest water levels in the sea during storm
surges are characteristic of the Baltic Sea coast. During the past
10 years, there have been heavy storms along the Baltic Sea coast in
the years 1992, 1993 and 1999, and on the Riga Gulf coast only in
1992.
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Wind direction
The wind direction in relation to the longshore is a
significant factor that determines the intensity of coastal
geological processes. During the past 10 years, when south-westerly
(from the south-west) and westerly winds dominated, the wind action
directly affected a 180-km-long open segment of Baltic Sea and
partly also the Vidzeme coast of the Gulf of Rīga. The entire
longshore is exposed to wave action only during north-westerly winds.
Ice formation in the sea
The monitoring, conducted between 1922 and 2000, of
the day of first ice, days with ice cover, and day of loss of
ice-melt, suggests warming of the climate. The ice now melts earlier,
which means that the season of active geological processes is
extended over a longer period on the open Baltic seacoast, and
particularly on the Vidzeme coast of the Gulf of Rīga (Salacgrīva).
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Sensitivity to erosion during storms
The amount of sand-gravel material in the beach and foredune belt
is a significant indicator of the sensitivity to erosion during
storms, as it forms a natural protection barrier in front of the
solid, vegetated shore. Increased erosion risk occurs when the
amount of sand of gravel-pebble material in the 10-60-metre-wide
belt of the beach and foredune (if present) does not exceed 60 m3/m
(typical amounts are 10-50 m3/m).
Sand budget in the coastal belt
The sand budget in the coastal belt depends on the amounts
deposited by longshore flows (on flow loads and saturation), on the
onshore transport of material, on erosion of the solid, vegetated
shore, and on river deposition by rivers. In previous centuries, up
until 1940-1980, the transport of sediments from the large rivers
(Venta, Lielupe, Daugava, and Gauja) to the coastal belt was very
significant.
Sediment flows from the Lielupe and Daugava Rivers have become
insignificant during the past 30-40 years, since the sand sediments
in the lower 20-40 km long reaches have been dredged for
construction works, and a series of hydroelectrical dams have been
built on the Daugava. The Venta deposits 115,000 m3 of
sand yearly in the harbour area. The sediments do not reach the
coastal belt because they are dredged in deepening work. Only the
Gauja River deposits sand on the coast, where they form a wide sandy
beach and high foredunes.
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