Air Pressures Over Reservoir, Canal, and Water Catchment Surfaces Exposed to Wind

Résumé du livre

Surface air pressure differentials that occur over reservoirs, canals, and water-catchment aprons in high-wind conditions were determined by the use of models in a wind tunnel. Such information was needed concerning the magnitude and location of destructive wind forces on water barriers constructed of exposed flexible membrane liners. Rigid models, without a membrane, were used to measure air pressure differentials. Air-pressure differentials were dependent on geometric configuration and were independent of viscous forces above the critical Reynolds number which was determined experimentally. The geometric factors studied with respect to reservoirs and canals included approach slope, approach slope length, leeward slope, and breadth-depth ratio. Those pertaining to water-catchment aprons included breadth-berm height ratio and berm shape. On the leeward slope of reservoirs, favorable (positive) differential pressures were more apt to occur as the approach and leeward slopes decreased (became less steep), but extreme adverse (negative) pressures occurred under the same conditions near the top edge of the slope. As the leeward slope increased the pressure coefficient values were essentially constant over the entire surface. On the reservoir bottom, adverse pressures did not exist when approach and leeward slopes were at the minimum evaluated (1:4). When the leeward and approach slopes increased the average pressure on the bottom became less favorable. The most adverse pressure coefficients generally occurred at the toe of the leeward slope, while maximum favorable pressures on the reservoir bottom generally occurred at the toe of the downwind slope. In most instances, the pressure on the downwind slope was favorable however, adverse pressures were recorded near the top edge of the slope. These adverse or negative pressure conditions were more apt to occur as the breadth-depth ratio increased and the leeward slope decreased. Average pressure values on the interior surface of canals were generally less adverse than...