Ermenek HPP - groundwater table development during impounding

Currently the reservoir of Ermenek dam is gradually filling. Impounding started already during construction of the 218 m high concrete arch dam located in karstified limestone. Actually the reservoir level has reached approximately 65 % of its final height. The grout curtain alignment was changed and shortened during project execution to a still remarkable total length of 2.2 km in order to anchor the curtain in the impermeable underlying flysch rocks. The single row curtain was upgraded to a double and partly triple row curtain in the vicinity (200 m) of the dam. Within the present contribution the dam monitoring system is described, the observed groundwater pressure conditions correspond to design assumptions and the treatment of local deviations is discussed.
The gradual filling of the reservoir banks is recorded with great care and interest in order to check reservoir and grout curtain tightness. Stepwise interim evaluations confirm reservoir tightness. Total water inflow from drainage holes to the grouting galleries amounts to ~30 l/s, but the inflow is concentrated in zones accompanying fault F2. The elevation of the groundwater level downstream of the curtain is ~50 % of upstream pressure which is higher than expected. In the close vicinity of the dam, where a triple row grout curtain and an additional drainage curtain was executed, the downstream water pressure is below 25 % of the upstream water level. In order to improve the conditions in areas with high seepage and pressure different grouting measures with focus on curtain and link holes are carried out with higher pressure than previously applied.
Other observations like groundwater temperature measurements and ongoing execution of dye test are reported as well; although not all final conclusions can be drawn at the moment as impounding is still going on.