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United States Department of Agriculture

Agricultural Research Service

Research Project: ENGINEERING TOOLS FOR SAFE, EFFICIENT HYDRAULIC STRUCTURES AND CHANNELS

Location: Hydraulic Engineering Research

Title: Inception point - key parameter in stepped spillway design

Authors
item Hunt, Sherry
item Kadavy, Kem

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 - key parameter in stepped spillway design [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 with 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, defines where the non-aerated flow ends and the aerated flow begins. For stepped spillways, the inception point becomes a key design parameter, defining flow depth and energy loss. Physical models of both a 4(H):1(V) and 3(H):1(V) stepped spillway were tested for a range of discharges and surface roughness (i.e. solely stepped and smooth and stepped sections). In a 4(H):1(V) stepped spillway, the energy loss increases from 0% at the crest to 30% at the inception point and then continues to increase to about 80% well downstream of the inception point. For the 3(H):1(V) stepped spillway, the energy loss increases from 0% at the crest to 40% at the inception point and then continues to increase to about 80% well downstream of the inception point. As the surface roughness decreases, the inception point moves further downstream of the broad crested weir. Consequently, engineers can minimize or maximize the energy loss in the stepped spillway chute by altering the surface roughness.

Last Modified: 7/25/2014
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