Spillway Criteria

[treg]

I am looking for guidance on selecting the proper storm for spillway design. The embankment will be 3 or 4 foot high. Probably about and acre. It seems to fall under any state requiements for permitting.

 

[cvg]

If you are in the United States - start with the 100 year inflow hydrograph and route it through the basin and spillway. If it overtops the spillway and flows over the embankment, the embankment will probably fail. Standards in other countries may be different.

 

[johnhan76]

when designing farm ponds - we would route the 2 year rain thru a standpipe. the 25 year rain thru a grassed spillway. Then add 1 foot freeboard from the height of flow in the emergency spillway. this usually amounts to 3-4 feet.

for detention ponds we route the 25 year storm thru the principal structure. for small ponds we make sure the structure can pass the 50 year unrouted (ie clogged orifice with a full pond). For larger ponds we make sure the 50 year doesnt overtop. we rarely use freeboard above the 50 year which im thinking about changing. however in our flat topography it is difficult to get.

 

[RWF7437]

Two places you might try:

The Corps of Engineers has many design guides for dams and spillways. Try searching their website.

In Oregon, the State Water Resources Department regulates small and large dams and has design criteria. What agency in your state performs this function?

 

[treg]

The Department of Water Resources, Division of Dam Safety would be the governing body. They do not regulate dams under 6 ft. high. Embankments that fall under their jurisdiction are required to be designed to pass the 1,000yr. storm. I thnik that is a little too much for this instance.
Thanks