Estimating Time of Concentration for Overland Flow on Pervious Surfaces by Particle Tracking Method

Abstract

The particle tracking method (PTM) module was added into the open source Full Shallow-Water equations for Overland Flow in a two-dimensional (FullSWOF_2D) program, which has coupled rainfall–runoff and infiltration modules to determine the time of concentration (Tc) for impervious (Tci) and pervious (Tcp) surfaces. The updated program FullSWOF-PTM was tested using observed rainfall events with Nash–Sutcliffe efficiencies ranging from 0.60 to 0.95 (average of 0.75) for simulated runoff hydrographs. More than 400 impervious modeling cases with different surface slope (S0), roughness coefficient (n), length (L), and rainfall intensity (i) combinations were developed and simulated to obtain the Tci for developing the regression equation of Tci as a function of the four input parameters. More than 700 pervious modeling cases with different combinations of S0, n, L, i, and infiltration parameters including the saturated hydraulic conductivity, suction head, and moisture deficit were simulated to estimate the Tcp based on the travel time of 85% of particles arriving at the outlet and the ponding time. The regression equation of Tcp was developed as the sum of Tci and additional travel time as a function of infiltration parameters and i. The Tcp equation can be applied to wide ranges of input parameters in comparison to Akan’s equation.