Low-Level Conduits – What Can Go Wrong, How to Inspect, How to Repair?

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This course will provide an overview of commonly observed issues associated with the most common type of spillway for relatively small dams (riser and low-level conduit). Importantly, the presentation will summarize methods to evaluate the condition of existing conduits and present common methods to repair and/or replace conduits. At the completion of the course, the participants should be able to identify common issues with low-level conduits, to include inlets and outlets, and have probable courses of action to address the identified issues.

Five Learning Objectives of This Course:

• General dam terminology.

• Risks associated with low-level conduits.

• Common issues with low-level conduit spillways.

• Methods to identify/inspect issues with low-level conduits.

• Methods to repair common issues with low-level conduits.

Joseph S. Monroe, P.E.

Principal, Schnabel

Schnabel Engineering, LLC.

Joe Monroe has 25 years of experience in the design and construction of new and rehabilitation of earthfill dams and concrete gravity dams, including the associated spillway systems. His design experience includes subsurface explorations and geotechnical evaluations, hydraulic and structural design of spillways, and preparation of bidding and construction documents. In addition to design-related functions, he has also provided construction administration duties during the implementation of the design for which he had responsible charge. For remediation projects, Mr. Monroe has been involved with the design and construction of dozens of abandoned and sliplined conduits. He has been involved with dam-related projects throughout the United States and numerous countries throughout the world. Mr. Monroe is a licensed professional engineer in Alabama, Georgia, Maine, North Carolina, South Carolina, Texas, and Virginia.

1. Introduction of Presenters
2. Definitions
- a. What dams fail
- b. What reasons are associated with conduits
- c. Inlet (Cast-in-place versus pre-cast)
- d. Conduit (Cast-in-place versus pre-cast)
- e. Terminal Structure
3. Inspections -Conduits
- a. External – what to look for
- b. Internal – what to look for
4. Maintenance vs Repair
- a. Owner Performed Maintenance
- b. Engineer Required Rehabilitation/Repair
5. Items Requiring Repair - Conduits
- a. Hydraulic considerations
- b. Structural
- c. Settlement
- d. Joint integrity
- e. Seepage
6. ‘Traditional’ Rehabilitation Alternatives - Conduits
- a. Spot Repair
- b. Slip-line and grouting of annular space
- c. Excavate and replace
- d. Permanent abandonment by grouting and construct new spillway
- i. Siphon
- ii. Riser and conduit through/near base of dam
- iii. Short riser with elevated conduit in embankment
7. ‘Non-traditional’ Rehabilitation Alternatives - Conduits
- a. Spin casting
- b. Cured in-place liners
8. Design References
- a. USACE
- b. USBR
- c. NRCS/SCS
- d. FEMA
- e. Other
9. Review