Introduction to Addressing Inadequate Conveyance Capacity at Dams: Download

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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 and Manager, Dams and Hydraulics Section

Gannett Fleming, Inc.

Paul has been with Gannett Fleming for 35 years. During that time, he has provided engineering consulting services for more than 500 dams throughout the United States and Canada. Paul is an approved Federal Energy Regulatory Commission facilitator and Independent Consultant for conducting potential failure modes analysis exercises, Emergency Action Plan exercises, and Part 12 dam assessments. He regularly serves as an expert hydrology and hydraulics engineer on Independent External Peer Review panels for United States Army Corps of Engineers dam and flood control projects and has served on the National Dam Safety Review Board as the Private Sector Representative. Paul is a frequent instructor of Association of State Dam Safety Officials (ASDSO) engineering seminars. He served on the Board of Consultants for the Oroville Spillway Emergency Recovery Project and is currently serving on several boards of consultants for dam projects throughout the United States.

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