Page - 70 - in Book of Full Papers - Symposium Hydro Engineering

The 427 m (1400 ft) long FCO Spillway lower chute was heavily damaged by the incident. The damage included two deep scour holes as much as 30 m (100 ft) in depth, including a large scoured erosion channel to the left of the FCO Spillway lower chute, and severely distorted, broken concrete walls and invert slabs downstream of the scour holes (see Fig. 2 and 3). Fig. 3 Aerial view of heavily damaged FCO Spillway lower chute (March 2017) Alternatives for the heavily damaged FCO Spillway lower chute included:  Remove, backfill, and replace  Leave scour holes and erosion channel in place for spillway discharges and only armor sides and bottoms of eroded areas  Construct bridge/aqueduct across scour holes  Construct new FCO Spillway chute These alternatives were further refined and evaluated by OER team in the days following the workshop. Some alternatives were modified or combined with others, while some were eliminated because they did not meet the project objectives, or were simply infeasible. A set of ranking criteria and weighting was developed to evaluate the alternatives. Following the evaluation and ranking of alternatives, the measures recommended for immediate implementation for the FCO Spillway chute were as follows:  The entire FCO Spillway chute, including both the undamaged upper portion and the heavily damaged lower portion, should be completely removed and replaced with new reinforced-concrete walls and invert slabs constructed to modern spillway design standards.  The removal and replacement of the upper chute should proceed by completing as much as could be done by November 1, 2017, in time for the 2017-2018 Winter Flood Season, with the remaining portion 70