Damming of the Khantaika river

1. The experience of constructin the Khantaika hydroelectric scheme confirmed the practical possibility and economic expediency of using the pioneer method of damming river channels under conditions of the Far North at heads of 5–7 m at the upstream rock embankment. 2. The practical possibility of damming northern rivers during the fall-winter period at river discharges to 500 m3/sec and of achieving a dumping rate from one bank of 400 m3/h with a limited number of vehicles was proved. The rate can be doubled if vehicles are available for dumping from both banks. 3. The pioneer method of damming rivers produces backwater in the upper pool and thus permits regulating the velocity of approach of the stream in order to prevent the entrance of slush and ice into the breach. This method eliminates the need to construct labor-consuming and expensive booms to combat ice. 4. At water velocities in the breach of 6–8 m/sec the use of oversize rocks weighing less than 15–20 tons is ineffective. Rocks of lesser weight should be cabled together into strings of 3–10 each. The volume of oversize rock should be at least 20% of the volume of fill. 5. The construction of approach roads to the site of damming under conditions of narrow canyons with a precipitous bank is accompanied by collapse of a large quantity of oversize rock into the river channel where the embankment abuts the river bank. This can create the danger of concentrated seepage through the retaining cofferdam of the foundation excavation for the plant. Therefore, effective measures should be worked out in the plans to combat seepage at the abutments of the cofferdam.