DAM SAFETY IN ARMENIA

The Armenian State Committee of Water System has completed the first phase of its Dam Safety Project, a World Bank financed, nation-wide program for improving the safety of existing dams. Several interesting challenges for remediating unsafe dams arose. There are four uncompleted dams among the 87 dams in Armenia. Two of them – Kaps and Marmarik Dams – represent a danger to the downstream population. For the last two decades the natural stream flow has been passing through the temporary diversion tunnels of these dams. Failure or plugging of these diversion tunnels would cause the flow to overtop and breach the dams, sending a flood wave downstream. In addition the Kechut Dam has inadequate spillway capacity. The Kaps Dam was designed to be 90 m high with 5.8 Mm3 of embankment and a reservoir capacity of 90 Mm3. The dam was completed to full height at the abutments but only to a height of 20 m in the river section when it too was abandoned due to lack of financing. The diversion tunnel was designed as a temporary facility for use during construction. The tunnel has been used for twenty years to pass inflow and needs to be inspected and repaired. The only way to do this is to build the central section of the dam 7 m higher, close the upstream end of the diversion tunnel and raise the water level by 26 m so that it flows out of the reservoir through a tunnel intended for irrigation. Once the diversion tunnel is repaired and re-opened the irrigation tunnel will be retained as a backup spillway should the diversion tunnel ever become plugged. The Marmarik Dam was designed to be 64 m high with 5 Mm3 of embankment and to impound a reservoir of 36.9 Mm3. It failed due to accelerated construction and high pore pressures a few days before impoundment of the reservoir. The downstream slope failed and the crest of the dam slumped 14 m. The Soviet government abandoned the dam after unsuccessful rehabilitation attempts, leaving the dam in an unsafe state. The Armenian government plans to complete the dam to a lower height and provide an irrigation outlet and spillway to discharge inflows. The design challenge was to build a safe dam on top of the one that failed, using as much of the original dam as possible and to ensure that three landslides near the dam and reservoir do not impair the dam’s safety. The Kachut Dam has a glory hole spillway of inadequate capacity. The natural place to locate a new spillway is on the right abutment. However, the space available between the dam and a water supply tunnel is too limited to provide the capacity needed in a normal ungated spillway. This problem will be addressed through the use of fuse gates.