The numbering of its milestones starts from the estuary of the Danube. The average slope of the channel is 14.5 cm per kilometer, with a width ranging between 20 and 30 meters, and a depth varying from 0 to 8.8 meters. The water velocity depends on the Siófok water release and the backwater effect of the Danube, ranging between 0.5 and 4 km/h. The water level of the channel is not constant. Significant water flow occurs in its upper section only when the lock gates are open in Siófok and water is released from Lake Balaton. The lower section of the channel is mainly influenced by the water discharge of the Kapos River. The Sió Water System (Zala, Balaton, Sió, Kapos, Sárvíz) has a combined catchment area of 14,728 km2. The Sió Canal provides a connection between Lake Balaton and a waterway system spanning approximately 9,000 km across Europe. Currently, the watershed of the Sió Canal is polluted, with vegetation increasingly overgrowing the neglected channel. Navigability, irrigation water management, and occasional water filling of fishponds could be resolved temporarily by releasing water from Lake Balaton. In 1990, plans were already prepared to improve navigability, suggesting that the 16-meter difference in water level between Lake Balaton and the Danube Estuary could be overcome with approximately 4 locks, making the canal continuously navigable. In Siófok, the water release gate is located in the passenger ship harbor, which enables water discharge. The ship lock opens from the Siófok freight port. The two sections of the canal after the two locks in Siófok merge into a common channel after 150 meters. The floodgate, which consists of a water release gate and a ship lock, is situated 2.7 km before the mouth of the Danube. Its main function is to prevent the backwater effect of the Danube and protect the canal from floods.
In the 19th century, plans were made to regulate the water level of Lake Balaton, serving multiple purposes:
- Establishing a navigable waterway connecting the lake to the Danube
- Draining and utilizing the marshes and swamps around Lake Balaton for agriculture
- Ensuring a safer harbor in Balatonfüred
- Protecting the Budapest-Adriatic railway line from water and ice damages.
To regulate the water level of Lake Balaton, a timber dam was built in Siófok. The inauguration of the dam took place on October 25, 1863. In 1867, the water level of the lake rose again, leading to floods as the small capacity of the dam was insufficient to handle the sudden influx of water. Since 1921, numerous records are associated with the history of the dam. In 1965, to prevent flooding along the shoreline, 1791 millimeters of water were released from the lake, equivalent to half of the total water mass of Lake Balaton, which is 1,080 million cubic meters. The most significant water release was recorded in April 1942 when a water volume equivalent to a 26-centimeter decrease in lake level was discharged within one month. This means that, compared to the water release of 4.8 cubic meters per second in the days following September 1, 2005, 60 cubic meters of water per second rushed into the Sió River bed. The dam's primary function is to regulate the maximum water level (reduction) of the lake.
The Siófok Dam is managed by the Environmental and Water Management Directorate of the Central Transdanubian Region, Balaton Water Management Branch.
Photo: Tamás Helényi
