Wind tides in small closed channels

Abstract

In addition to the generation of waves, a wind produces a mass transport in a body of water resulting in t h e lowering of the level at t h e windward ~ ide an~ rise at t he leeward side which is called wind tide or setup. Two eff ects of the wll1d are Involved: the s urface t raction on the water, and the form resistance of the waves. This paper presents the t heoretical background of t he subject and expcriment al r es ults. It was di scovered t hat formation of waves in an experimental cha nnel could be inhibited by addin g small amounts of soap or detergent to t he water. !his made it P?ssible to study the sl!rface tracti?n effect separately. The eff ect was studied for both lamlIlar and t urbulent motIOn of the dnft and gravi ty currents produced by the wind. The setup computed from me~s ured wind and water surface veloci ties agreed with theory. Regardless of t he flow regime, the setup was unaffected by viscosity and independent of t he depth-length ratio of t he channel. The additional setup due to presence of waves could be correlated only b y int roducin g a characteristic velocity. This additional setup appears to vary as t h e square root of the d ep th-length rat io. The relation of t he characteristic velocity to t h e criti cal velocity for wind generation is di scussed. The derived empirical formula for setup is compared with obser vations in Lake Erie.