The Gulf of Riga

The Gulf of Riga is a body of water which is subject to relatively large annual water temperature fluctuations. From the end of June to the middle of August the temperature of the water near the coast generally remains above 18°C. In very warm summers the water temperature here can rise to 26–28°C, and 22–23°C in the middle of the Gulf. The Gulf has some ice cover every winter. True, in very warm winters (e.g. 1960/1961, 1988/1989) only a narrow strip of ice forms in the northern part of the Gulf, between Sõrve Peninsula and Pärnu Bay. Ice cover usually starts to form in shallow bays in the middle of December. In harsh winters this process is brought forward by about a month and in warm winters is postponed by roughly the same amount of time. Pärnu Bay is the first part of the Gulf to freeze over. The pack ice that is piled up on the shore by strong westerly gales has occasionally even threatened the resort buildings on Pärnu beach. The gulf is completely frozen during roughly 60% of winters. Estonia’s thickest coastal ice — 90 cm, was recorded in the eastern part of the Gulf of Riga during the extraordinarily cold wartime winter, 1941/1942. In average winters the ice cover melts by the end of April. In warm winters the whole sea is free of ice by March. In some winters there has been ice in Pärnu Bay for up to 6 months.

The largest fluctuations in sea level along the Estonian coast have also been observed in the Gulf of Riga. Strong and prolonged westerlies raise the water level in the east, and easterlies lower it. In October 1967 the water level in Pärnu Bay rose 253 cm above its average level and caused extensive flooding in the town. In December 1959 the level dropped to 120 cm below the average; as a result many shallow bays dried up and the sea receded hundreds of metres in places.

Currents depend on the direction and speed of the wind, and are therefore very variable. They are fastest in the straits; with an average wind the flow rate in the middle of the straits is 20–25 cm/s, but in strong winds the flow may exceed 100 cm/s. Straits are passages which enable water to be transferred between different parts of the sea. The largest quantity of water flows through the Irben Strait, where the flow rate in strong winds may be as much as 200 000 to 300 000 m3/s, and may top 600 000 m3/s in heavy storms.

One stronger westerly storm may bring 7–10 km³ of water into the Gulf of Riga, which is about 2% of the Gulf’s volume. The volume of water passing through the straits of Suur Väin, between Muhu Island and the mainland, is 4 to 5 times smaller. The waves in the Gulf of Riga are much smaller than on the open sea. Strong winds raise 3–4 m high waves in the deepest part of the Gulf; prolonged storms may occasion wave heights of 5–6 m. The constant addition of large quantities of fresh water by rivers flowing into the Gulf keeps the salt content of the water lower than that out in the open sea; it is 5–6%o on average. During the spring high water the salt content in Pärnu Bay drops to less than 1%o (it is usually 4–5%o at the mouth of the bay).

The Gulf of Riga is an important wintering area for migrating birds. The eastern and northern coastal waters are spawning grounds for Estonia’s most abundant fish species — the Baltic herring.

Pärnu Bay
Pärnu Bay reaches into the mainland in the eastern part of the Gulf of Riga. Its warm water and long bathing season, which begins in the middle of June and lasts for three months, together with its sandy beaches and pine forests, make it an ideal holiday location. The internationally renowned seaside resort at Pärnu was already founded in 1938.

In addition to Pärnu beach, there is an extensive sandy beach to the west of the town, at Valgeranna; this 4 km long beach and Järve beach on Saaremaa Island are the only southern facing beaches in the Baltic States. There is an even longer sandy beach 40 km to the south of Pärnu, between Kabli and Treimani.

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