American Society of Civil Engineers

Estimating Trajectory of Free Overfall Nappe

by Alastair C. Davis, (Engr., Sir William Halcrow and Partners, Hilton House, Lord St., Stockport, U.K.), Richard P. Jacob, (Sr. Lect., Civ. Engrg. Dept., Oxford Brookes Univ., Oxford, U.K.), and Brian G. S. Ellett, (Sr. Lect., Civ. Engrg. Dept., Oxford Brookes Univ., Oxford, U.K.)

Journal of Hydraulic Engineering, Vol. 125, No. 1, January 1999, pp. 79-82, (doi:

     Access full text
     Purchase Subscription
     Permissions for Reuse  

Document type: Technical Note
Abstract: The upper surface profile of a rectangular free overfall is modeled using the free-fall parabolic equation. Empirical and semiempirical relationships for the unknown quantities in this equation are presented. It was found that the resulting simple and straightforward method adequately predicts the position of the upper nappe surface. A relationship for establishing the vertical thickness of the nappe (due to another researcher) is given, thus enabling the entire nappe profile from the brink to be described. The equations are of use in the design of spillways and diversionary structures utilizing a free overfall.

ASCE Subject Headings:
Free flow
Rock masses