Experiments were conducted in a stably stratified towing tank wherein the density gradient was linear and the dividing-streamline height H(D) was half the hill height. Effluent was released at three elevations above H(D). Pairs of tows were made such that, in one tow, the hill (upside-down) was fully-immersed in the water and the towing speed was adjusted to provide a natural H(D) surface. In the second tow of the pair, the hill was raised out of the water to the point where only the top half of the hill was immersed, thus, forcing a flat H(D) surface as is used in some mathematical models. The results suggest that the assumption is a reasonable approximation to make, at least with regard to predicting the locations and values of maximum concentrations and areas of coverage on the windward side of the hill.