Effect of Submergence and Apron Length on Spillway Scour: Case Study

Seungho Hong,Kwang Yoon,Celio Biering,Terry Sturm,Juan Gonzalez-Castro

doi:10.3390/w7105378

Abstract

Large-scale water resources systems are often managed by an integrated set of hydraulic structures that are vulnerable to wider ranges of discharge and tailwater elevation than envisioned in their original design due to climate change and additional project objectives such as fostering healthy ecosystems. The present physical model study explored the performance of a spillway structure on the Kissimmee River, operated by the South Florida Water Management District, under extreme conditions of drought and flooding with accompanying low and high tailwater levels for both gate-controlled and uncontrolled spillway flow conditions. Maximum scour depths and their locations for two different riprap apron lengths downstream of the spillway stilling basin were measured along with the complex flow fields prior to scour. Effects of tailwater submergence, type of spillway flow and riprap apron length on scour results are interpreted in terms of the measured turbulent kinetic energy and velocity distributions near the bed.

Highlights

Spillways have been built in river basins around the world for beneficial purposes such as water supply and flood control and are often operated as systems to maximize effectiveness while subject to constraints such as maximum reservoir levels and minimum releases
This paper focuses on the influence of spillway submergence and length of a riprap apron in controlled and free flows on the maximum scour depth and its location downstream of an ogee spillway in the SFWMD, but the results are presented such that they may be of general interest
The scour depth results for spillway operating conditions tested are shown in Table 1 in prototype units. (In this and succeeding sections, results are given in prototype units unless otherwise noted or in dimensionless form.) The flow types are categorized as uncontrolled submerged (US), uncontrolled free (UF), controlled submerged (CS), controlled free (CF), and uncontrolled jet (UJ)

Summary

Introduction

Spillways have been built in river basins around the world for beneficial purposes such as water supply and flood control and are often operated as systems to maximize effectiveness while subject to constraints such as maximum reservoir levels and minimum releases. Spillways with hydraulic jump stilling basins designed to function within a relatively narrow range of tailwater elevations to ensure adequate energy dissipation in the basin may be subjected either to submerged operation during large floods or hydraulic jump sweep-out during severe droughts as controlled by tailwater elevations. Under these circumstances, the sediment bed downstream of a spillway responds to wide ranges in hydrologic frequency through the geomorphologic processes of deposition and scour. The study presented here relied on the use of a laboratory physical model to examine the changes in flow field and relative range in scour experienced downstream of a spillway as controlled by various degrees of downstream submergence and different lengths of a protected spillway apron for both gate-controlled and uncontrolled spillway flows.

Methods

Results

Conclusion