This course is intended for engineers who need to analyze, design, or retrofit a spillway for a small dam.
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The overall objective of this course is to provide a detailed analysis of the various types of spillways and to explain the hydraulics of each type. There is a also a discussion of the spillway exit channels and a description of sub-critical, critical, and super-critical flows in these channels. After completing this course the engineer should be able to design a spillway using a variety of outlet structures.
We work closely with dam owners to identify and correct potential problems before they become serious. If we find a potentially unsafe condition, we work with the dam owner to address and remedy the condition in a timely manner. When necessary, we may immediately employ any remedial means necessary to protect life and property, or we may impose a reservoir restriction limiting the water surface to a level that is judged safe. We may also direct the dam owner to implement their emergency action plan (EAP).
DSOD established the Spillway Re-evaluation Program in to assess dam appurtenant structures, including spillways, to confirm they meet minimum safety standards. This is an on-going screening process and re-evaluation of spillways at dams, starting with these that potentially pose the highest hazard. This evaluation includes the assessment of the spillway’s design and construction and geologic attributes while concurrently reviewing the dam owner’s maintenance and inspection program, the spillway’s historical performance, and any previous spillway repairs. DSOD is working closely with dam owners to expedite the development of the required assessments and restore any known areas of disrepair.
Our policy requires that dam owners regularly exercise (operate) their outlets in order to demonstrate the ability to draw down the reservoir during an emergency. Outlet controls should be fully exercised at least annually and, in our presence, every three years. Experience has proven that regular exercising of gates/valves helps prevent major maintenance problems from developing and is therefore part of a good maintenance program.
We do not operate the outlet controls themselves nor order their operation during routine inspections. It's the responsibility of the dam owner to develop appropriate plans and make the necessary arrangements when dealing with difficult outlet situations. We accommodate reasonable delays in exercising of outlets so owners have time to complete proper planning, coordinate with other agencies, and perform maintenance and repairs, if necessary.
Dam owners should maintain a log detailing all operation and maintenance activities for their outlet system.
If you believe that your dam’s hazard classification should be different based on the hazard classifications defined in Section 335.4 of the regulations, please send a letter requesting a re-evaluation of the hazard classification, along with supporting documentation to:
Ms. Sharon K. Tapia, P.E.
Division Manager
Division of Safety of Dams
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Gateway Oaks Drive, Suite 300
Sacramento, CA
Please be aware that it could take DSOD up to 60 days to make a determination after receiving all necessary information, and that the existing classification will be in effect until any change in classification is made by DSOD. Dam owners are encouraged to plan accordingly to meet deadlines for submitting EAPs.
A critical appurtenant structure is a water barrier or hydraulic control structure that is 25 feet or greater in height, impounds 5,000 acre-ft or more, or DSOD determines poses a significant hazard. Examples of CAS include saddle dams, spillways, gates on dams, gated low-level outlets, and penstocks. The above-mentioned height and volume criteria are not applicable for the low-level outlets. If you are unsure whether you have a critical appurtenant structure at your dam, please contact your Area Engineer or . Critical appurtenant structures are defined in Section 335.2(a)(3) of the regulations.
When DSOD receives an inundation map and technical study, we send the owner an acknowledgement letter and copy Cal OES. DSOD reviews the map to make sure it complies with the regulations. If DSOD has comments, we will the comments to the owner or consultant, who may revise the map. After comments are addressed and the map meets the requirements contained in the regulations, DSOD will send an approval letter to the owner and again copy Cal OES.
Unfortunately, the legislature did not allocate any funds to help dam owners pay for inundation maps. Cal OES is administering several grants that may be applicable; for more information please contact Steven Larson with Cal OES at or .
DSOD staff continues to research grants and will contact dam owners if a grant may be applicable to inundation maps.
DSOD and Cal OES do not have the authority to extend deadlines; however, DSOD is committed to working with owners toward better emergency preparedness.
Communication is important; if you are concerned that you may not meet the EAP submittal deadline, DSOD encourages you to send letters to DSOD and Cal OES explaining why you can’t meet the deadline, your progress so far, and when you plan to submit the inundation map and EAP.
If an owner does not develop a map and EAP upon order by the Department, then the Department is authorized to prepare a map and EAP and recover costs from the dam owner.
The Department is also authorized to impose penalties and will address enforcement on a case-by-case basis.
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