INTRODUCTIONThis compendium of case histories provides information on damage that has occurred to hydraulic structures and the various methods of repair that have been used. ACI Committee 210 has prepared this report to help others experiencing similar problems in existing work. Knowledge gained from these experiences may help avoid oversights in design and construction of hydraulic structures and provide guidance in the treatment of future problems.Erosion of concrete in hydraulic structures may occur as a result of abrasive action@ cavitation@ or chemical attack. Damage may develop rapidly after some unusual event such as a flood or it may develop gradually during normal continuous operation or use. In most cases where damage has occurred@ simply replacing the eroded concrete will ensure immediate serviceability@ but may not ensure long-term performance of the structure. Therefore@ repair work usually includes replacing eroded concrete with a more resistant concrete and additional surface treatment@ modifying the design or operation of the structure to eliminate the mechanism that produced the damage@ or both. A detailed discussion of mechanisms causing erosion in hydraulic structures@ and recommendations on maintenance and repair@ is contained in ACI 210R.When damage does occur to hydraulic structures@ repair work poses some unique problems and is often very costly. Direct access to the damaged area may not be possible@ or may be limited by time@ or other constraints. In some cases@ such as repair to spillway stilling basin floors@ expensive bulkheads and dewatering are required. It may not be possible to completely dry the area to be repaired or maintain the most desirable temperature. A great deal of planning and scheduling for repair work are normally required@ not only for the repairs and access@ but also for control of water releases and reservoir levels. If time permits@ extensive investigation usually precedes planning and scheduling to determine the nature and extent of damage. Hydraulic model studies may also be necessary to evaluate possible modifications in the design or operation of the facility.This compendium provides the history on 21 projects with hydraulic erosion damage. They vary in size and cover a variety of problems: 8 with cavitation damage@ 9 with abrasion-erosion damage@ and 4 with erosion damage from chemical attack. Table 1.1 summarizes the projects. Each repair was slightly different. Each history includes background information on the project or facility@ the problem of erosion@ the selected solution to the problem@ and the performance of the corrective action. Histories also contain references and owner information if further details are needed.