ARS | Publication request: Inception point relationship development for stepped spillways

Submitted to: American Society of Civil Engineers Water Resources Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2011
Publication Date: May 23, 2011
Citation: Hunt, S.L., Kadavy, K.C. 2011. Inception point relationship development for stepped spillways [abstract]. In: Proceedings of the ASCE EWRI 2011 World Environmental and Water Resources Congress, May 22-26, 2011, Palm Springs, CA. CDROM.

Technical Abstract: Stepped spillways applied to embankment dams have become a common design practice for the rehabilitation of aging watershed dams, especially those experiencing a hazard classification change from low to high hazard. Traditionally, research on stepped spillways has focused on gravity dams where aerated flow is more likely to develop. For embankment stepped spillways, the non-aerated flow region becomes important. The inception point, the location where the turbulent boundary layer reaches the free surface, signifies the transition from non-aerated to aerated flow. The inception point becomes a key design parameter for stepped spillways. Hubert Chanson developed an inception point relationship for primarily gravity (Theta greater than or equal to 22 degrees) stepped spillways with an ogee crest control section. Researchers have found that Chanson’s relationship tends to overestimate the distance from the downstream edge of a broad-crested weir to the inception point for stepped spillways (Theta less than or equal to 22 degrees) when the Froude surface roughness is less than 10. Physical models of both a 4(H):1(V) and a 3(H):1(V) were tested over a range of discharges and surface roughness (i.e. smooth, solely stepped with one step height, smooth and stepped, solely stepped with multiple stepped heights). Empirical formulas are presented for predicting the inception point location for stepped spillways (Theta less than or equal to 22 degrees) typically designed for embankment dams for a wide range of flow conditions such that the Froude surface roughness is greater than 0.5.