Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2012
Publication Date: 11/1/2012
Citation: Hunt, S.L., Kadavy, K.C. 2012. Closure to "Inception point relationship for flat-sloped stepped spillways" by Sherry L. Hunt and Kem C. Kadavy. Journal of Hydraulic Engineering. 138(11):1004-1005.
Interpretive Summary: Earthen dams are aging, and with age, many dams reflect a change in hazard classification resulting in deficient spillway capacity due to urban sprawl. Flow characteristics in stepped spillways applied to earthen dams behave differently depending on the slope of the spillway. An equation for determining the location where the aerated or "white water" flow begins was developed from research conducted at the USDA-ARS Hydraulic Engineering Research Unit. The equation significantly overestimates the location of "white water" for a specific prototype data point, but only slightly overestimates the location for an independently obtained specific prototype data point. The error observed between the two prototype data points may be due to inflow conditions. Using appropriate engineering judgment, this research could assist design engineers with the final design of stepped spillways with slopes greater than 10 degrees.
Technical Abstract: Stepped spillways applied to embankment dams have become more common for addressing deficiencies in spillway capacity for existing dams. Because flow characteristics behave differently in flat-sloped stepped spillways as compared to steep-sloped stepped spillways, research has increased in this arena. Research at the USDA-ARS Hydraulic Engineering Research Unit resulted in the development of an optimized inception point relationship for flat-sloped stepped spillways with a broad-crested weir crest section. A discusser conveys that a prototype inception point location can be overestimated by a factor of 2 or 3. The authors having conducted recent research under similar parameters (i.e. slope, step height, and unit discharges) found relatively good agreement with the relationship. Differences in the results of the observed prototype data may be affected by differences in inflow conditions. With appropriate engineering judgment, the correlation could be used for final design stages of a stepped spillway with a broad-crested entrance, but because of the potential for air entrapment, it may be suited for stepped spillways with slopes theta > 10 degrees.