Lag Method<\/h2>\n\n\n\n
This is the TR-20 default method where:<\/p>\n\n\n\n Where: Generally used for natural basins with well defined routes for overland flow along bare earth or mowed grass roadside channels. It is similar to the Lag method but will give shorter times compared to the Lag method.<\/p>\n\n\n\n Where: Tc is broken into 3-components or segments as prescribed by TR55 and is also known as the NRCS Velocity method. The final Tc is the sum total of the three components.<\/p>\n\n\n\n Tc = TSheet + TShallow + TChannel (minutes)<\/p>\n\n\n \t\t \r\n \t\t\t\t\tSlopes are inputted in percent in Hydrology Studio, not ft\/ft as in TR55. Hydrology Studio converts your input to ft\/ft. \t\t\t\t<\/p>\r\n \t\t\t \t\t\t\r\n \t\t<\/div>\r\n \t\t\n\n\n\n Flow over plane surfaces and typically ranges between 125 to 150 feet.<\/p>\n\n\n\n Where: After about 100 feet, sheet flow becomes shallow concentrated flow.\u00a0The computed Average Velocity described below is\u00a0based on the solution of\u00a0Manning\u2019s equation with different assumptions for n (Manning\u2019s roughness coefficient) and r\u00a0(hydraulic radius, ft).\u00a0 For example, per TR55, for\u00a0for Paved areas, n is 0.025 and r is 0.2; Unpaved areas, n is 0.05 and\u00a0r is 0.4.\u00a0<\/p>\n\n\n\n Shallow concentrated flow is\u00a0assumed not to have a well-defined channel and has a flow depth of 0.1 to 0.5 feet.<\/p>\n\n\n\n Where: Where: Occurs within channels, swales, ditches, streams or even piped systems. Manning’s equation is used to compute velocity.<\/p>\n\n\n\n Where: Where: Describes methodologies for computing time of concentration, Tc<\/p>\n","protected":false},"author":1,"comment_status":"closed","ping_status":"closed","template":"","format":"standard","meta":{"footnotes":""},"ht-kb-category":[37],"ht-kb-tag":[],"class_list":["post-782","ht_kb","type-ht_kb","status-publish","format-standard","hentry","ht_kb_category-runoff-hydrographs-and-processing"],"_links":{"self":[{"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/ht-kb\/782","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/ht-kb"}],"about":[{"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/types\/ht_kb"}],"author":[{"embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/comments?post=782"}],"version-history":[{"count":14,"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/ht-kb\/782\/revisions"}],"predecessor-version":[{"id":4572,"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/ht-kb\/782\/revisions\/4572"}],"wp:attachment":[{"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/media?parent=782"}],"wp:term":[{"taxonomy":"ht_kb_category","embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/ht-kb-category?post=782"},{"taxonomy":"ht_kb_tag","embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-json\/wp\/v2\/ht-kb-tag?post=782"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/EQLag.png\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/EqUnitLag.png\")
<\/figure>\n\n\n\n
L = Lag time (hrs)
l = Hydraulic length
S = (1000 \/ CN) – 10
Y = Average basin slope (%)
CN = Curve number<\/p>\n\n\n\nKirpich Method<\/h2>\n\n\n\n
![\"\"](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/EqKirpich.png\")
<\/figure>\n\n\n\n
Tc = Time of concentration (min)
L = Hydraulic length (ft)
S = Average basin slope (ft\/ft)<\/p>\n\n\n\nTR-55 Method (NRCS Velocity Method)<\/h2>\n\n\n\n
![\"Tc](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/TR55Runoff.png\")
<\/figure>\n\n\n\nSheet Flow Time<\/h3>\n\n\n\n
![\"\"](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/EQTR55Sheet.png\")
<\/figure>\n\n\n\n
n = Manning\u2019s roughness coefficient
L = Flow Length (must be <=100 ft)
P2 = Two-year 24-hr rainfall (in)
S = Land Slope (ft\/ft)<\/p>\n\n\n\nShallow Concentrated Flow Time<\/h3>\n\n\n\n
![\"\"](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/EqTR55Shallow.png\")
<\/figure>\n\n\n\n
L = Flow Length (ft)
V = Average velocity (ft\/s) and<\/p>\n\n\n\n![\"\"](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/EqTR55Vel.png\")
<\/figure>\n\n\n\n
Cp = 20.328 Paved
Cp = 16.1345 Unpaved, grassed waterways in urban setting
Cp = 9.965 Nearly bare and untilled
Cp = 8.762 Cultivated, straight row crops
Cp = 6.962 Prairie, short-grass
Cp = 5.032 Minimum tillage cultivation, and woodlands
Cp = 2.516 Forest with heavy ground litter
S = Watercourse slope (ft\/ft)<\/p>\n\n\n\nChannel Flow Time<\/h3>\n\n\n\n
![\"\"](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/EqTR55Ch.png\")
<\/figure>\n\n\n\n
L = Flow length (ft)
V = Average velocity (ft\/s) and<\/p>\n\n\n\n![\"\"](\"https:\/\/learn.hydrologystudio.com\/hydrology-studio\/wp-content\/uploads\/sites\/2\/2017\/11\/EqTR55ChVel.png\")
<\/figure>\n\n\n\n
V = Average velocity (ft\/s)
R = Hydraulic radius (ft) = a\/wp
S = Channel slope (ft\/ft)
n = Manning\u2019s roughness coefficient<\/p>\n","protected":false},"excerpt":{"rendered":"