HGL Elevation at Pipe Exit of USBR Type VI Impact Basin

by Charles E. Rice, Res. Hydr. Engr.; Water Conservation Struc. Lab., Agric. Res. Service, U.S. Dept. of Agr., 1301 North Western St., Stillwater, OK 74075,
Kem C. Kadavy, Agric. Engr.; Water Conservation Struct. Lat., Agric. Res. Service, U.S. Dept. of Agr., 1301 North Western St., Stillwater, OK 74075,


Serial Information: Issue 7, Pg. 929-933


Document Type: Journal Paper

Discussion: Blaisdell Fred W. (See full record)
Closure: (See full record)

Abstract: Model tests on a Soil Conservation Service principal spillway with a U.S. Bureau of Reclamation Type VI impact basin for the outlet structure provided an opportunity to establish a relationship to predict the hydraulic grade line (HGL) elevation at the pipe exit as a function of the tailwater (TW) elevation. The relationship is HGL/D = 0.85 + 0.76(TW/D); TW/D > 0.65 or HGL/D > = 1.31, where HGL is the HGL elevation relative to the pipe-exit invert; D is the pipe diameter; and TW is the tailwater elevation downstream of the basin relative to the pipe-exit invert. This relationship permits accurate determination of the head for flow computations. The equation is only valid at design discharge for impact basins designed according to Technical Release No. 49, U.S. Dept. of Agriculture, Soil Conservation Service. Because the results showed that a TW/D = 0.65 had no adverse effect on the HGL elevation, a minimum TW/D = 0.65 is recommended for design because the tailwater reduces water surface roughness and bed erosion.

Subject Headings: Basins | Pipelines | Tailwater | Pipe sizes | Model tests | Hydraulic roughness | Spillways | Soil tests |

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