Drainage for dams and associated structures

Drains are important design features for dams and appurtenant structures. It is standard practice to include drains in the design of these structures. They reduce seepage uplift pressures, control seepage for dams, and reduce foundation driving forces on dams and other structures, improving their stability. Drains also provide the secondary benefit of collecting and transporting seepage to a desired outfall location while minimizing impacts due to erosion or aesthetic impacts. There are a variety of drain types and configurations. Factors that influence the type and configuration of drains are the type of structure or foundation, the expected seepage or groundwater locations and volume of drain flows, ease of construction and accessibility of drains. The Bureau of Reclamation (Reclamation) has prepared a manual on drains for dams and associated structures [1]. The manual is currently being used as a working draft within the Bureau of Reclamation. It is planned to solicit comments from users at the end of 2003 and to issue the manual as a final document in 2004. A primary purpose of this manual is to provide information that can be used to establish an effective drain maintenance program. Drains at Reclamation dams have received varying amounts of attention. In most cases, drains that were obviously plugged have been detected during examinations of the dam, and a cleaning program was initiated. Cleaning programs that were initiated have resulted in varying degrees of success. In other cases, instrumentation data have provided a strong indication that drains are plugged, and appropriate action was taken. In still other cases, drains have become plugged without the plugging being detected for a period of time, because the drains could not be easily accessed and visual
and instrumentation evidence did not strongly suggest that the drains were plugging. The drain manual provides guidance for evaluating/inspecting drain systems as well as guidance for maintaining drains. The manual provides: general descriptions and the purposes of various types of drainage systems for dams and appurtenant structures (Chapter 2); design guidelines and analysis methodology on the various drainage systems (Chapter 3); installation methods for drains (Chapter 4); case histories that illustrate the performance of a variety of drainage
systems (Chapter 5); and, guidance on maintaining drains, including a discussion of drain plugging mechanisms, methods for evaluating drain effectiveness, guidelines for drain maintenance, site specific considerations and a summary of drain cleaning methods (Chapter 6). Appendices are also included which contain design examples (Appendix A), detailed case histories (Appendix B) and drain cleaning and inspection equipment (Appendix C). This paper summarizes some of the key information included in the drain manual. Drain plugging is discussed, drain inspection using remote controlled video inspection is described, cleaning methods are summarized, two drain cleaning case histories are presented and a checklist for conducting a drain cleaning program is provided. 15 pp., 2 references.