Introduction to Addressing Inadequate Conveyance Capacity at Dams: On-Demand

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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, Gannett Fleming, Inc.

Paul is a Vice President of Gannett Fleming, Inc. and Manager of the Firm's Dams and Hydraulics Section in Camp Hill. He has over 33 years of consulting engineering experience and has served as a project engineer or manager for the design of eleven new dams and the design and technical review of many dam rehabilitation projects. He has inspected hundreds of dams across the nation including completing over 200 dam assessment reports. Paul is an approved FERC facilitator for performing potential failure modes analysis exercises for dams, 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 currently serving on the Board of Consultants for the Oroville Spillway Emergency Recovery Project and the Oroville Dam Comprehensive Needs Assessment.

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