Flow Estimations Through Spillways UnderSubmerged Tidal Conditions

The South Florida Water Management District (SFWMD), Florida, USA, operates and maintains about twenty-five coastal spillways that discharge excess runoff water directly into the environmentally sensitive area of Biscayne Bay, south of Miami. Over the past decade serious concerns have been raised regarding the large fluctuations of salinity levels in Biscayne Bay caused by the freshwater releases. At the SFWMD, discharges at gated spillways are computed from an instantaneous stage and operational control information by using basic formulas developed for the estimation of orifice and weir type of flows. However, the accuracy of discharge estimates is compromised whenever flow occurs under submerged conditions and particularly at tidally affected structures. This paper is focused on the estimation of discharges through gated spillways under tidal submerged flow conditions. Data are analyzed using dimensional analysis and an empirical model is developed based on data from two coastal spillways. The model relates the discharge as a function of the tail-water head and the low tide elevation during each tidal cycle. All of the other parameters are treated as constants and lumped into the empirical coefficients.