The Ogee spillway (or overflow spillway) is a specialized hydraulic structure designed with an S-shaped crest that mimics the profile of the lower nappe of a freely falling water jet. This design is considered "better" than standard straight-drop spillways because it ensures the water sheet maintains constant contact with the spillway face, effectively eliminating the risk of sub-atmospheric pressure and damaging cavitation. 1. Fundamental Discharge Equation The discharge capacity (
To illustrate the application of the Excel-based design approach, consider a hypothetical ogee spillway design problem. The design requirements are: ogee spillway designxls better
| Module | Purpose | |------------|--------------| | Hydrology Input | Design head, maximum head, upstream slope (vertical, 3:1, etc.), crest length | | Crest Coordinate Generator | Automatically computes x, y from 0 to 4×( H_d ) using WES equation | | Discharge Table | Interpolates ( C ) from H/H_d ratio; checks against maximum expected head | | Pressure Check | Estimates piezometric head at each x; flags potential negative pressures | | Energy Dissipator Sizing | Computes tailwater required for hydraulic jump or flip bucket trajectory | | Plot | Instant scatter plot of crest profile; compares with original nappe curve | The Ogee spillway (or overflow spillway) is a
Downstream Profile: Generally follows the power law equation: Fundamental Discharge Equation The discharge capacity ( To
Excel uses the standard weir equation, but what if your tailwater rises due to a downstream restriction? The spillway becomes submerged, and the discharge coefficient ($C$) drops dramatically. Calculating the submergence reduction factor requires iterative interpolation of complex bi-variate curves (Figure 9-3 in USBR’s Design of Small Dams). Doing this in Excel without a robust User-Defined Function (VBA) leads to manual errors.