|Hjelmfelt Jr, Allen|
|VAN MULLEM, J|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 11/20/2001
Publication Date: N/A
Interpretive Summary: This chapter was originally prepared by Victor Mockus in 1964. In the intervening years, the procedures have been interpreted and applied in ways unimaginable to the orginial author. The chapter was rewritten to emphasize what we know to be true concerning the National Resources Conservation Service Curve Number procedure and to discourage use of the procedure in cases where it is inappropriate. This research will be of benefit to water resources engineers and planners who will use it in the analysis of the effects of improved practices on watershed responses to rainfall events.
Technical Abstract: The Natural Resources Conservation Service (NRCS) method of estimating direct runoff from storm rainfall is described in this chapter. The rainfall-runoff relation is developed, parameters in the relation are discussed and applications of the method are illustrated by examples. The NRCS method of estimating direct runoff from storm rainfall was the end product of major field investigation and the work of numerous early investigators (Mockus 1949, Sherman 1942, Andrews 1954, and Ogrosky 1956). A major catalyst for getting this procedure to the field was passage of the Watershed Protection and Flood Prevention Act. The principal application of the method is in estimating quantities of runoff in flood hydrographs or in relation to flood peak rates. These quantities consist of at least one type of runoff. An understanding of runoff types is necessary to apply the method properly in different climatic regions. Four types are distinguished: channel, surface, lateral subsurface flow, and baseflow. All types of runoff do not regularly appear on all watersheds. Climate is one indicator of the probability of the types. In arid regions the flow on smaller watersheds is nearly always surface runoff. Subsurface flow is more likely in humid regions. A long succession of storms, however, may produce subsurface flow or changes in baseflow even in dry climates, although the probability of this occurring is less in dry than in wet climates.