Introduction to Addressing Inadequate Conveyance Capacity at Dams: ON-DEMAND

The most common deficiency at dams in North America is inadequate spillway capacity. Inadequate spillway capacity can result in overtopping of a dam during flood events. This is especially a concern for embankment dams where overtopping of the dam embankment can cause breaching of the dam and uncontrolled release of the impounded water. This failure mode accounts for more than 40 percent of recent dam failures. A broad overview of the many approaches, including state-of-the-art technologies, to effectively modify existing dams to meet current spillway capacity requirements will be presented. The various approaches will be illustrated with photographs from recently modified dams and case studies.

Paul G. Schweiger, P.E.

Vice President, Gannett Fleming, Inc.

Paul G. Schweiger, P.E., CFM is a Vice President of Gannett Fleming, Inc. and Manager of the Firm’s Dams and Hydraulics Section. He has over 30 years of consulting engineering experience during which time he has worked on hundreds of dam projects providing the full range of dam engineering services. Mr. Schweiger is a certified Failure Modes Analysis facilitator and a regular ASDSO Dam Owner Workshop instructor. He has published over 50 technical papers and technical manuals, given many presentations on a wide range of dam engineering topics, and is a frequent speaker at national dam safety conferences and specialty technical seminars. He has served on several dam safety committees and work groups including: the National Dam Safety Review Board, the NRCS Study Work Group to evaluate design tools for roller-compacted concrete stepped spillways and embankment armoring, and the FEMA work group for establishing guidelines for the hydraulic safety of dams. He is currently serving as an expert hydrology and hydraulics engineer on an Independent External Peer Review panel for several United States Army Corps of Engineers DSAC I dam projects and managing the FEMA study to convey lessons learned from dam failures and incidents. Paul is also currently serving on the Board of Consultants for the Oroville Dam Spillway Emergency Project.

1. Establishing Design Floods for Dams

a. Why do so many dams have inadequate conveyance capacity?
- i. Brief history of improved understanding of hydrology
- ii. Hazard creep
b. Warning about altering inflow-outflow characteristics at existing dams

2. Making Sense Out of So Many Spillway Options Available for Dams

a. Spillway Types
- i. Principal, Auxiliary, and Emergency Spillways
- ii. Common spillway control structures
b. The weir equation – The Key to Understanding Spillway Design
- i. Improving the weir coefficient
- ii. Increasing the spillway crest length
- iii. Increasing the effective head
c. Special cases
- i. Reservoir attenuation
- ii. Embankment armoring (full and partial)
- iii. New auxiliary spillway(s)
- iv. Siphons
- v. Incremental damage assessment

3. Recent Trends and Lesson Learned