TY - JOUR
T1 - Variations of time of concentration estimates using NRCS velocity method
AU - Fang, Xing
AU - Thompson, David B.
AU - Cleveland, Theodore G.
AU - Pradhan, Pratistha
PY - 2007/7
Y1 - 2007/7
N2 - Time of concentration (Tc) is the time required for runoff to travel from the hydraulically most distant point to the outlet of a watershed. The Natural Resources Conservation Service (NRCS) velocity method commonly is used to estimate Tc for hydrologic analysis and design. The NRCS velocity method applies the physical concept that travel time is a function of runoff flow length and flow velocity. Time of concentration for 96 Texas watersheds is independently estimated by three research teams using the NRCS velocity method. Drainage areas of the 96 watersheds considered in the study are approximately 0.8-440.3 km2 (0.3-170 mi2). Digital elevation models having a grid size of 30m were used to derive watershed physical characteristics using ArcGIS or HEC-GeoHMS. Average channel width was estimated from 1m or 1ft digital orthoimagery quarter quadrangle or aerial photography. Each team made independent decisions to estimate parameters needed for different flow segments for the NRCS velocity method. Estimates of time of concentration made by three research teams are compared, and both graphic comparison and statistical summary demonstrate that time of concentration estimated using the NRCS velocity method is subject to large variation, dependent on the analyst-derived parameters used to estimate flow velocity. Because of the propensity for different analysts to arrive at different results, caution is required in application of the NRCS velocity method to estimate TTc.
AB - Time of concentration (Tc) is the time required for runoff to travel from the hydraulically most distant point to the outlet of a watershed. The Natural Resources Conservation Service (NRCS) velocity method commonly is used to estimate Tc for hydrologic analysis and design. The NRCS velocity method applies the physical concept that travel time is a function of runoff flow length and flow velocity. Time of concentration for 96 Texas watersheds is independently estimated by three research teams using the NRCS velocity method. Drainage areas of the 96 watersheds considered in the study are approximately 0.8-440.3 km2 (0.3-170 mi2). Digital elevation models having a grid size of 30m were used to derive watershed physical characteristics using ArcGIS or HEC-GeoHMS. Average channel width was estimated from 1m or 1ft digital orthoimagery quarter quadrangle or aerial photography. Each team made independent decisions to estimate parameters needed for different flow segments for the NRCS velocity method. Estimates of time of concentration made by three research teams are compared, and both graphic comparison and statistical summary demonstrate that time of concentration estimated using the NRCS velocity method is subject to large variation, dependent on the analyst-derived parameters used to estimate flow velocity. Because of the propensity for different analysts to arrive at different results, caution is required in application of the NRCS velocity method to estimate TTc.
KW - Hydrology
KW - Time of concentration
KW - Travel time
KW - Velocity method
UR - http://www.scopus.com/inward/record.url?scp=34547122923&partnerID=8YFLogxK
U2 - 10.1061/(ASCE)0733-9437(2007)133:4(314)
DO - 10.1061/(ASCE)0733-9437(2007)133:4(314)
M3 - Article
AN - SCOPUS:34547122923
SN - 0733-9437
VL - 133
SP - 314
EP - 322
JO - Journal of Irrigation and Drainage Engineering
JF - Journal of Irrigation and Drainage Engineering
IS - 4
ER -