Estimating overwater dispersion in onshore flow upwind of coastal complex terrain
Leopold, Scott A.
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There are many ways to predict dispersion rates of a plume of pollution. One way is the standard deviation of the wind direction, σ[sub θ], a method first used by the Nuclear Regulatory Commission (NRC) to estimate horizontal dispersion. Sigma theta is a measure of turbulence at the altitude of wind direction measurement and can be related to horizontal dispersion by the equation σ[sub θ] = f(x)• σ[sub y] , where σ[sub y] is the actual standard deviation of plume concentration. Values of f(x) for relating σ[sub θ] to σ[sub y] have been found over land, but no relationship has been developed using real data for f(x) during overwater dispersion. For the purpose of modeling plume behavior, overwater dispersion has been assumed to be much less than that over land. This thesis describes how the accepted relationship between σ[sub θ] and σ[sub y] over land is not valid over water, y 6 and that there are two distinct dispersion rates over water and land, one influenced by downwind terrain and the other not affected. These relationships can be used to improve concentration estimates from dispersion models.