Abstract
Hydraulic modeling of a spillway channel can be challenging. When spillway channel geometry is uniform, a simple hydraulic approach may be appropriate and can make analyzing the channel easier. However, if the spillway channel is non-uniform, a different approach may be needed to capture all the channel’s complexities.
This study performs a hydraulic analysis of a spillway channel considering a simple hydraulic approach and a more complex two-dimensional approach. The spillway channel was constructed to the right of a dam embankment by blasting into the bedrock and adjacent hillside. This caused the spillway channel to have non-uniform geometry. The channel bottom is uneven, full of undulations, and has two large drops, which call into question a simple hydraulic approach for simulating spillway flow. Furthermore, the spillway is upstream of a much larger reservoir. When this larger reservoir is at full capacity, it can cause the tailwater downstream of the dam and spillway to reach high water levels within 3.5 feet of the spillway crest elevation. Sedimentation and River Hydraulics in Two-Dimension (SRH-2D), a flow hydraulics program, was used to analyze the hydraulics of the reservoir, spillway, and downstream channel. A hydrology model was created to simulate flow conditions during various design storms, with a focus on the 1000-year design storm. Using SRH-2D, a spillway rating curve was developed for the complex spillway channel and compared to a simple hydraulic approach that assumed the spillway performed like a broad-crested weir. The results showed that the broad crested weir equation was a reasonable assumption for this spillway channel. The differences between the spillway rating curves are believed to be caused by the non-vertical sidewalls. The models’ results also show the changes in flow regime and the effects of tailwater on the water surface profile through the spillway channel. Remarkably, the high tailwater levels do not appear to affect the spillway flow.