By Environmental and Water Resources Instit, Richard H. Hawkins, Timothy J. Ward, Donald E. Woodward, Joseph A. Van Mullem
The curve quantity (CN) approach for estimating direct runoff reaction from rainstorms was once built to fill a technological area of interest within the Nineteen Fifties. seeing that then, use of the CN technique has prolonged to different purposes, and person event and research have redefined quite a few gains of the unique know-how. In "Curve quantity Hydrology: country of the Practice", an ASCE/EWRI activity Committee investigates the starting place, improvement, position, software, and present prestige of the CN strategy. issues during this record comprise: an advent to curl quantity hydrology; the curve quantity procedure; findings and advancements; constitution of the fundamental equation; soil moisture modeling; calibration equipment; present utilization perform; and proposals. one of many Committee's techniques is assigning a keeper to function the critical resource for in charge details and updates. An appendix presents strategies to the curve quantity equation. This e-book can be worthy to water and environmental engineers eager about hydrology, specially the research of rainwater runoff difficulties.
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Extra resources for Curve Number Hydrology: State of the Practice
1982) of error probabilities associated with the table values of AMC I and AMC III. AMCIII was shown to approximate the direct runoff for a given rainfall for which 90 percent of the runoffs were less; while AMCI approximated the direct runoff for the same rainfall for which 10 percent of the runoffs were less. Reinforcing examples for this notion are given in later papers by Haan and Schulze (1987), and by Hauser and Jones (1991), and Hjelmfelt (1991). Current work by Grabau et al. (2008, in review) further affirms the concept, but refines AMC I and III probabilities as about 12 and 88 percent respectively, leading to about 75 percent of the runoff events falling between ARC I and ARCIII.
The effect is positive: CNII increases as slope increases. 93 CN per unit of slope percent at CNII=50. No goodness-offit information is given for equation  above in the source documents, and a 5% reference slope is not found in NEH4/630. In contrast, Garg et al. (2003) observed a negative relationship between slope and CN (calibrated via the AGNPS model (Young et al. 1989)) over a narrow range (2 CN) for 5 watersheds in south-central Oklahoma. 3 units for each percent of watershed slope. In addition, a recent study by VerWeire et al.
1982) using TR55 (USDA, SCS 1986) came to similar conclusions and extended the findings to derived flood peaks. Even in more complex event models with channel routing, such as HEC-1, CN has been found to dominate in importance over rainfall depth and Manning’s n (Hawkins, 1997). Figure 6 shows comparisons for a typical small urban watershed of 110 acres in Tucson, Arizona. Upon contemplation, this may be an uncomfortable conclusion, insofar as 100 80 Curve Number Percent Change in Peak Flow 60 Manning's 'n' 40 Rainfall Depth 20 0 Impervio us Area -20 -40 -60 -100 -80 -60 -40 -20 0 20 40 60 80 Percent Change in Variable or Input Figure 6.
Curve Number Hydrology: State of the Practice by Environmental and Water Resources Instit, Richard H. Hawkins, Timothy J. Ward, Donald E. Woodward, Joseph A. Van Mullem
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