Sioni Reservoir

Sioni Reservoir (სიონის წყალსაცავი), often commonly referred to as Sioni Lake (სიონის ტბა), is a large artificial lake located in the Tianeti Municipality of the Mtskheta-Mtianeti region in eastern Georgia. Situated on the middle course of the Iori River, roughly 45-80 km northeast of Tbilisi, it occupies the Sioni Basin between the townlet of Sioni and the village of Lelovani. Created in the mid-20th century (becoming operational in 1963) by damming the Iori River, the reservoir serves multiple crucial purposes.

With a surface area of approximately 12.8 square kilometers and holding over 325 million cubic meters of water at full capacity (average depth ~25m, max depth ~67m), Sioni Reservoir is a significant water body. Its primary functions are multi-year regulation of the Iori River’s flow for downstream irrigation and supplying water for the Sioni Hydropower Plant, which is part of a small cascade. Beyond its utilitarian roles, the reservoir has become a popular recreational destination due to its scenic beauty – surrounded by forested hills – and its relative proximity to Tbilisi. Activities include fishing (various carp species are common), swimming and boating (especially in summer when surface water warms), picnicking, and camping along its shores. The townlet of Sioni on its bank serves as a local resort center.

The creation of the reservoir had significant historical impact, submerging around eight villages and numerous archaeological sites. Notably, a 5th-century Christian basilica was carefully dismantled before the area was flooded and reassembled at the Tbilisi Open Air Museum of Ethnography. Water levels fluctuate significantly throughout the year, typically lowest in March and highest in July, reflecting its management for irrigation and power generation. Given the current date (April 26, 2025), the reservoir’s water level is likely rising after its winter minimum, making it scenic for visits, though the water would still be quite cool for swimming.

Identification and Location:

• Name: Sioni Reservoir (სიონის წყალსაცავი). Common names: Sioni Lake (სიონის ტბა), occasionally Sioni Sea (სიონის ზღვა).
• Location:
  • Country: Georgia
  • Region: Mtskheta-Mtianeti
  • Municipality: Tianeti
  • Nearest Major Landmark: Located on the Iori River, between the townlet of Sioni and village of Lelovani. Northeast of Tbilisi.
  • Coordinates: Approximately 42.005∘ N latitude, 45.000∘ E longitude (approximate center).
• Relationship to other bodies of water: Artificial reservoir formed on the Iori River. Regulates the river’s downstream flow. Fed by the Iori and other tributaries within its catchment.

Physical Characteristics:

• Surface Area: ≈12.8 km2.
• Maximum Depth: $\approx 67\text{ m}$.
• Average Depth: $\approx 25.4\text{ m}$.
• Volume: Total ≈325.4 million m3; Useful (operational) volume ≈290 million m3.
• Elevation: Surface level fluctuates, generally around $\approx 1000-1041\text{ m}$ above sea level.
• Shoreline Length: Significant and irregular; specific length not readily available.
• Water Source(s): Primarily the Iori River; also smaller streams, precipitation, and runoff from its 587 km² catchment area.
• Outlet(s): Controlled release into the Iori River downstream via the dam, feeding Sioni HPP.
• Water Type: Freshwater.
• Basin Geology: Artificial reservoir occupying the natural Sioni Basin floor within the Iori River valley. The dam created the basin.

Ecological Information:

• Flora (Plant Life): Shoreline features deciduous forests on steeper slopes (upper parts), with areas closer to the water often lacking substantial tree cover due to water level fluctuations. Nearby Sabaduri forest is notable. Aquatic vegetation may exist in shallower, stable bays.
• Fauna (Animal Life): Supports various fish species popular for angling (e.g., Carp, Grass Carp, Crucian Carp). Attracts various water birds. Surrounding forests host typical regional wildlife.
• Trophic Level: Likely Mesotrophic, potentially with Eutrophic tendencies in certain areas or seasons due to riverine nutrient input and local activities.
• Water Clarity: Variable, influenced by river inflow (sediment), seasonal algal growth, and water levels.
• Water Temperature: Exhibits seasonal variation. Surface water warms considerably in summer (reaching over 20°C), suitable for swimming. Cools significantly in winter (down to ~3°C), with only weak or partial ice formation usually observed. Thermal stratification occurs in summer.
• pH Levels: Data not available; likely near-neutral.
• Dissolved Oxygen Levels: Data not available.
• Unique Ecological Features: Large reservoir ecosystem relatively close to the capital, providing important recreational habitat and supporting fish populations.
• Conservation Status: No major specific conservation designation for the reservoir itself, but operates within the broader context of Georgian environmental regulations. The surrounding landscape holds ecological value.
• Invasive Species: Data not readily available, but introduction of non-native fish for angling is possible in such reservoirs.

Human Interaction and Significance:

• Historical Significance: Its creation in the 1950s-60s led to the resettlement of populations from approximately 8 flooded villages (including Saqaraulo, Jigo, Ukugmarti) and the loss of submerged cultural heritage sites. A significant 5th-century Christian basilica was saved by relocation to the Tbilisi Ethnographic Museum prior to flooding.
• Current Uses: Multi-purpose reservoir primarily used for irrigation downstream and hydroelectric power generation (Sioni HPP). Widely used for recreation, including fishing (recreational, possibly some local commercial), swimming, boating, picnicking, and camping. The townlet of Sioni serves as a resort base.
• Environmental Issues: Significant water level fluctuations due to operational management. Potential for pollution from upstream sources (Iori river catchment) or local recreational/settlement activities. Risk of eutrophication. Shoreline erosion. Concerns about waste management from recreational use have been raised.
• Management and Conservation Efforts: Managed by state agencies responsible for water resources, energy, and potentially environmental oversight. Fishing regulations likely apply. Efforts focus on balancing water use demands (irrigation, energy) with environmental and recreational aspects.
• Local Communities: The reservoir is a defining feature for the townlet of Sioni and nearby villages. It supports the local economy through tourism and provides essential water resources, while its creation also caused historical displacement.

Interesting or Unique Facts:

• An artificial lake created by damming the Iori River in the mid-20th century.
• Named after the adjacent townlet of Sioni.
• Its creation required the flooding of multiple villages and archaeological sites.
• An important early Christian basilica (5th century) was moved from the flood zone to Tbilisi.
• Serves critical irrigation and hydropower functions for the region.
• A popular recreational destination for fishing, swimming, and relaxation, easily accessible from Tbilisi.
• Water levels vary significantly throughout the year based on operational needs.