greater aerodynamic roughness of the forest canopy, resulting in a much more efficient transfer of water vapour away from the surface. According to Gerrits, A.M.J., Interception is the part of the rainfall that is intercepted by the earth’s surface and which subsequently evaporates. In this definition the earth’s surface includes everything that becomes wet after a rainfall event and that dries out soon after. It includes: vegetation, soil surface, litter, build-up surface, etc. How much of the precipitation evaporates depends on land cover characteristics, rainfall characteristics, and on the evaporative demand. Interception can amount up to 15-50% of precipitation, which is a significant part of the water balance. The most important role is as a rainfall reducer, causing a significant amount of rainfall to be directly fed back to the atmosphere which is not available for infiltration DEPRESSION STORAGE Depression Storage is the term applied to the water that is lost because to water that is lost because it becomes trapped in the numerous small depressions that are characteristic of any natural surface. When water temporarily accumulates in a low point with no possibility for escape as runoff, the accumulation is referred to as depression storage. The amount of water that is lost due to depression storage varies greatly with the land use. A paved surface will not detain as much water as a recently furrowed field. The relative importance of depression storage in determining the runoff from a given storm depends on the amount and intensity of precipitation in the storm. Depression storage refers to small low points in undulating terrain that can store precipitation that otherwise would become runoff. The precipitation stored in these depressions is then either removed through infiltration into the ground or by evaporation. Depression storage exists on pervious and impervious surfaces alike; however, depression storage is much greater on undisturbed, pervious surfaces. Standard design and construction practices remove these natural depressions in order to promote drainage, which reduces depression storage. Depression storage assumes that all water has had a chance to infiltrate or evaporate.
College of Engineering Education 2ndFloor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Page 16of 30FIGURE: Depression Storage, Streams, and Lake Let’s Check
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Hydrology, Matina Campus, College of Engineering Education, B&E Building