Author(s): Ali Shirinzad; Sedem Kumahor; Mark Tachie; Haitham Ghamry; Christos Katopodis

Linked Author(s): Ali Shirinzad, Mark Tachie, Haitham Ghamry, Christos Katopodis

Keywords: PIV; Spillway; Turbulence; Downstream Migration

Abstract: Anthropogenic obstructions such as dams with Spillways have adverse impacts on the aquatic habitats and affect the downstream migration of fish. During the migratory cycle of fish, water levels encountered at spillway entrances vary significantly. It is therefore important to understand how changing the water depth over spillways influences hydrodynamic fields and fish behavioral responses. The goal of the present study is to understand the effects of water depth on the hydrodynamic characteristics of the commonly used 90° standard spillway, and relate them to swimming ability, response, and safe passage of fish. The effects of water depth on the hydraulics upstream and over a 90° standard spillway were experimentally investigated using particle image velocimetry in a recirculating open channel flume with streamwise length, spanwise width, and vertical height of 6.00 m, 0.60 m, and 0.45 m, respectively. The spillway height was kept constant at h = 0.15 m and three different upstream water depths, D = 0.245 m (D/h = 1.6), 0.210 m (D/h = 1.4), and 0.180 m (D/h = 1.2) were investigated. The oncoming flow velocities were set to Ue=0.308 m/s, 0.162 m/s, and 0.069 m/s, which corresponded to Reynolds number based on spillway height (Re = Ue h/ν, where ν is the kinematic viscosity of water at 20℃) of 46200, 24300, and 10350, respectively. The Froude number based on the upstream water depth (Fr = Ue/√gD) was 0.199, 0.113, and 0.052. The mean streamlines show a recirculation bubble at the foot of the spillway for all tested water depths. However, the recirculation bubble is apparently larger for the lowest water depth, with separation occurring 1.5h upstream of the foot of the spillway for D/h = 1.2 and 0.6h for D/h = 1.6 and 1.4. Contours of the mean streamwise velocity show that the magnitudes over the spillway increase as the water depth decreases. An elevated region of positive mean vertical velocity is observed upstream of the crest due to the upward deflection of the flow, followed by a sudden change in sign to negative values, which is attributed to the descent of the flow over the crest. The streamwise Reynolds normal stress and vertical Reynolds normal stress also show an increase in magnitude over the spillway as the water depth decreases. Meanwhile, elevated regions of Reynolds normal stresses are concentrated close to the crest of the spillway. In the final paper, the spatial acceleration, turbulent kinetic energy, and strength and size of the large-scale eddies within the flow field are further examined to highlight the effects of water depth on hydraulics upstream and over the spillway.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022925

Year: 2022