An Analysis of Drag Coefficient at Hurricane Windspeeds from a Numerical Simulation of Dynamical Water Level Changes in Lake Okeechobee, Florida.

摘要

A time-dependent, two-dimensional storm surge algorithm has been used to estimate the drag coefficient over the windspeed range: 20 < or = W sub < 10 or = 40 meters per second, where W sub 10 is the windspeed 10 meters above MWL. The algorithm represents a vertically integrated physical model which includes nonlinear boundary conditions representing flooding and recession. Wind and water level data for the investigation were gathered in the Lake Okeechobee region. The lake is a roughly circular feature 60 kilom in diameter with a maximum normal depth of 4 m. The effect of extensively grassed, shallow areas of the lake on wind-driven circulation was simulated by a multilayer canopy flow model and included as a subroutine in the numerical analog. The surge model was calibrated for empirical constants with two seiches and quasi-static wind-induced condition within the lake. Two wind-stress relationships, a quadratic one and the Keulegan-Van Dorn expression, were used to model the air-sea interaction. Multiple surge calculations were performed with a range of drag coefficients. Statistical analyses were made of the difference between the observed and computed water levels for the hurricane of Aug. 1949. The results indicate that the Keulegan-Van Dorn wind-stress model yields superior results over the windspeed range. This conclusion was verified by a simulation of the surge associated with the hurricane of Oct. 1950.