Armağan Dam

Armağan Dam is a dam constructed on the Kocadere Creek, 33 km northeast of Kırklareli Province in northwestern Türkiye, for irrigation and flood control purposes. It has a height of 57.5 metres and a total reservoir capacity of 59 million m³. During and after construction, geotechnical and hydrogeological problems were encountered.

Geology and Soil Structure

The dam is founded on a foundation composed of metamict limestone and argillaceous schists of the Jurassic-aged Dolapdere Formation. The region also contains pre-Permian gneisses and schists, as well as Triassic-aged mahya formations. The metamict limestones are notable for their intense fracturing and karstic structure, with many voids filled with brown kil. These karstic voids are the primary cause of seepage at the dam.

Construction and Early Problems

Initial site selection studies were conducted in 1964. However, due to foundation issues, the original location was changed. The final site was planned in 1981, and before construction of the dam body, superficial alluvium and molasse sediments were removed.

The reservoir began impounding water in 1997. When the water level reached 400 m in 1998, intense flow was observed particularly in the gallery drainage wells on the left bank. Between 1989 and 2003, a total of 103 km of grouting galleries were constructed, and 17,650 kg of cement, bentonite and sand were injected to perform six improvement and curtain grouting operations.

Seepage and Monitoring Studies

Seepage occurred as a result of clay infill within the metamict limestones being washed out by water pressure, leading to the opening of voids. Tracer tests conducted in 2001 and 2005 used Rhodamine and Fluorescein dyes; these confirmed that the karstic system is permeable to water and that water from the reservoir reaches springs at lower elevations. Flow velocities in some areas exceeded 2,000 m/day.

Mineralogical and Hydrogeological Findings

X-ray Diffraction (XRD) and pinhole analyses revealed that the clay emerging from the dam originates not from the dam body itself but from the karstic infill within the metamict limestones. Additionally, water chemistry analyses indicate a mixture between the reservoir water and certain groundwater bodies.

The seepage at Armağan Dam is explained by the gradual washing out of clay infill within karstic structures, leading to the formation and subsequent enlargement of voids. Although grouting operations have been effective in some areas, the dam’s seepage remains sensitive to fluctuations in reservoir level. Therefore, continuous monitoring, re-grouting, and advanced geotechnical studies are recommended to ensure the dam’s impermeability.