the watershed to reach the drainage point (Thomson et al. 2008). There are three different flow types associated with time of concentration: sheet flow, shallow concentrated flow, and open channel flow. Sheet flow is the flow of water over a plane surface located near the headwaters of a stream, shallow concentrated flow is the path following the sheet flow that stops at the edge of the stream, and the open channel flow is the path following the stream and ends when the channel is drained into a body of water or is merged with another stream. The Tc for each site is calculated by combining the travel time (Tt) of each flow section, which is calculated using the following equations obtained from the Hydrology National Engineering Handbook: Sheet Flow: (1) Tt = travel time (h) = n Manning’s roughness coefficient = length of section (ft) L = 2-year, 24-hour rainfall (in) P2 = slope S Shallow Concentrated Flow: (2) Paved surface: = 0.5 Unpaved surface: = 16.1345 0.5 V S V S 20.3282 ∙ ∙ Tt = travel time (h) = length of section (ft) L = average velocity (ft/s) V Open Channel Flow: (3) (4) Tt = travel time (h) = length of section (ft) L = average velocity (ft/s) V = hydraulic radius (ft) = R = slope S = n Manning’s roughness coefficient
the watershed to reach the drainage point (Thomson et al. 2008). There are three different flow types associated with time of concentration: sheet flow, shallow concentrated flow, and open channel flow. Sheet flow is the flow of water over a plane surface located near the headwaters of a stream, shallow concentrated flow is the path following the sheet flow that stops at the edge of the stream, and the open channel flow is the path following the stream and ends when the channel is drained into a body of water or is merged with another stream. The Tc for each site is calculated by combining the travel time (Tt) of each flow section, which is calculated using the following equations obtained from the Hydrology National Engineering Handbook: Sheet Flow: (1) Tt = travel time (h) n = Manning’s roughness coefficient L = length of section (ft) P2 = 2-year, 24-hour rainfall (in) S = slope Shallow Concentrated Flow: (2) Paved surface: V = 20.3282 ∙ S 0.5 Unpaved surface: V = 16.1345 ∙ S 0.5 Tt = travel time (h) L = length of section (ft) V = average velocity (ft/s) Open Channel Flow: (3) (4) Tt = travel time (h) L = length of section (ft) V = average velocity (ft/s) R = hydraulic radius (ft) = S = slope n = Manning’s roughness coefficient
13-DunningGordonWu.docx