The runoff curve number (also called a curve number or simply CN ) is an empirical parameter used in hydrology for predicting direct runoff or infiltration from rainfall excess. The curve number method was developed by the USDA Natural Resources Conservation Service , which was formerly called the Soil Conservation Service or SCS — the number is still popularly known as a "SCS runoff curve number" in the literature. The runoff curve number was developed from an empirical analysis of runoff from small catchments and hillslope plots monitored by the USDA. It is widely used and is an efficient method for determining the approximate amount of direct runoff from a rainfall event in a particular area.
17-463: (Redirected from Runoffs ) [REDACTED] Look up runoff or run off in Wiktionary, the free dictionary. Runoff , run-off or RUNOFF may refer to: Runoff (hydrology) , the flow of water over land Channel runoff , the confined flow of water Surface runoff , the unconfined flow of water over land Runoff model (reservoir) ,
34-475: A hydrologic soil group should be done based on measured infiltration rates, soil survey (such as the NRCS Web Soil Survey ), or judgement from a qualified soil science or geotechnical professional. The table below presents curve numbers for antecedent soil moisture condition II (average moisture condition). To alter the curve number based on moisture condition or other parameters, see Adjustments . Runoff
51-402: A mathematical model involving rainfall and runoff Runoff curve number , an empirical parameter used in hydrology RUNOFF , the first computer text-formatting program Runoff or run-off, another name for bleed , printing that lies beyond the edges to which a printed sheet is trimmed Runoff or run-off, a stock market term Runoff voting system, also known as the two-round system ,
68-611: A voting system where a second round of voting is used to elect one of the two candidates receiving the most votes in the first round Instant-runoff voting , an extension or variation of runoff voting where a second round can be rendered unnecessary by voters ranking candidates in order of preference Run-off area , a racetrack safety feature Runoff (2014 film) directed by Kimberly Levin See also [ edit ] Runoff voting (disambiguation) All pages with titles containing "runoff", "run-off" or "run off" Topics referred to by
85-1038: Is affected by the soil moisture before a precipitation event, the antecedent moisture condition (AMC). A curve number, as calculated above, may also be termed AMC II or C N I I {\displaystyle CN_{II}} , or average soil moisture. The other moisture conditions are dry, AMC I or C N I {\displaystyle CN_{I}} , and moist, AMC III or C N I I I {\displaystyle CN_{III}} . The curve number can be adjusted by factors to C N I I {\displaystyle CN_{II}} , where C N I {\displaystyle CN_{I}} factors are less than 1 (reduce C N {\displaystyle CN} and potential runoff), while C N I I I {\displaystyle CN_{III}} factor are greater than 1 (increase C N {\displaystyle CN} and potential runoff). The AMC factors can be looked up in
102-510: Is an event-based calculation, and should not be used for a single annual rainfall value, as this will incorrectly miss the effects of antecedent moisture and the necessity of an initial abstraction threshold. The NRCS curve number is related to soil type, soil infiltration capability, land use, and the depth of the seasonal high water table. To account for different soils' ability to infiltrate, NRCS has divided soils into four hydrologic soil groups (HSGs). They are defined as follows. Selection of
119-426: Is different from Wikidata All article disambiguation pages All disambiguation pages runoff [REDACTED] Look up runoff or run off in Wiktionary, the free dictionary. Runoff , run-off or RUNOFF may refer to: Runoff (hydrology) , the flow of water over land Channel runoff , the confined flow of water Surface runoff ,
136-497: Is different from Wikidata All article disambiguation pages All disambiguation pages Runoff curve number The runoff curve number is based on the area's hydrologic soil group, land use , treatment and hydrologic condition. References, such as from USDA indicate the runoff curve numbers for characteristic land cover descriptions and a hydrologic soil group. The runoff equation is: where The runoff curve number, C N {\displaystyle CN} ,
153-426: Is then related C N {\displaystyle CN} has a range from 30 to 100; lower numbers indicate low runoff potential while larger numbers are for increasing runoff potential. The lower the curve number, the more permeable the soil is. As can be seen in the curve number equation, runoff cannot begin until the initial abstraction has been met. It is important to note that the curve number methodology
170-593: The two-round system , a voting system where a second round of voting is used to elect one of the two candidates receiving the most votes in the first round Instant-runoff voting , an extension or variation of runoff voting where a second round can be rendered unnecessary by voters ranking candidates in order of preference Run-off area , a racetrack safety feature Runoff (2014 film) directed by Kimberly Levin See also [ edit ] Runoff voting (disambiguation) All pages with titles containing "runoff", "run-off" or "run off" Topics referred to by
187-602: The CN runoff equation becomes: In this equation, note that the values of S 0.05 {\displaystyle S_{0.05}} are not the same as the one used in estimating direct runoff with an I a / S {\displaystyle I_{a}/S} ratio of 0.20, because 5 percent of the storage is assumed to be the initial abstraction, not 20 percent. The relationship between S 0.05 {\displaystyle S_{0.05}} and S 0.20 {\displaystyle S_{0.20}}
SECTION 10
#1732854745242204-462: The assumption of I a / S = 0.20 {\displaystyle I_{a}/S=0.20} is usually high. More than 90 percent of I a / S {\displaystyle I_{a}/S} ratios were less than 0.2. Based on this study, use of I a / S {\displaystyle I_{a}/S} ratios of 0.05 rather than the commonly used value of 0.20 would seem more appropriate. Thus,
221-444: The ratio of I a {\displaystyle I_{a}} to S {\displaystyle S} with hundreds of rainfall-runoff data from numerous U.S. watersheds. In the model fitting done by Hawkins et al. (2002) found that the ratio of I a {\displaystyle I_{a}} to S {\displaystyle S} varies from storm to storm and watershed to watershed and that
238-474: The reference table below. Find the CN value for AMC II and multiply it by the adjustment factor based on the actual AMC to determine the adjusted curve number. The relationship I a = 0.2 S {\displaystyle I_{a}=0.2S} was derived from the study of many small, experimental watersheds . Since the history and documentation of this relationship are relatively obscure, more recent analysis used model fitting methods to determine
255-409: The same term [REDACTED] This disambiguation page lists articles associated with the title Runoff . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Runoff&oldid=1259042860 " Category : Disambiguation pages Hidden categories: Short description
272-409: The same term [REDACTED] This disambiguation page lists articles associated with the title Runoff . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Runoff&oldid=1259042860 " Category : Disambiguation pages Hidden categories: Short description
289-448: The unconfined flow of water over land Runoff model (reservoir) , a mathematical model involving rainfall and runoff Runoff curve number , an empirical parameter used in hydrology RUNOFF , the first computer text-formatting program Runoff or run-off, another name for bleed , printing that lies beyond the edges to which a printed sheet is trimmed Runoff or run-off, a stock market term Runoff voting system, also known as
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