Page - 1064 - in Book of Full Papers - Symposium Hydro Engineering

7. An overflow spillway with a fixed sill 8. An overflow spillway with a fixed sill combined with raise in the impervious cores 9. Modifications of the existing overflow dams. 10. An emergency spillway with Hydroplus fusegates 11. An emergency spillway with Hydroplus combined with raise in the impervious cores Other factors, such as risks for flooding during construction combined with cofferdams, availability of reservoir for flood regulation during construction including debris and ice, erosion risk in the downstream area, impacts on the dam facility etc were weighed in. The feasibility study favored construction of a new spillway (alternative 2) as the final option for the dam rehabilitation. The spillway was given a width of 18 m, with a sloping chute of ~80 m, followed by a stilling basin. 2.3.2. Ramsele With a more limited objective of preventing further backward erosion near the dam, the following overreaching approaches were evaluated - accepting some erosion but stop it from threatening the dam (undermining) - accepting some erosion but move it to a safe distance from the dam - introducing energy dissipation structures Based on the approaches above, the following measures were evaluated: 1. Classic stilling basin 2. Rock reinforcements (rock bolts) 3. Prolongation of the existing spillway chute 4. Cuf-off wall immediately downstream of the existing chute 5. A few different combinations of No. 2 - 4. The obvious factors that affect the evaluations of the alternatives for Ramsele was cost-efficiency as well as the overall risk reduction and impacts of construction on the existing dam. The feasibility study recommended the third alternative. The prolongation had a linear slope, covering the entire length of the erosion pit ending with a cut-off wall anchored into bedrock. This construction would achieve both goals of limiting backward erosion threatening the dam body as well as relocating erosion areas to a safe distance from the dam. 1064