Experimental surface runoff hydrographs from linear impervious subcatchments for rainfalls of extremely high intensity

Abstract

This study focuses on lab-scale experimental runoff hydrographs from a linear completely impervious plane subcatchment. An improved method of surface runoff physical modelling was developed, allowing for expanded laboratory hydrograph simulations up to a linear scale of 10. Model rains of different intensities and durations were applied, and digital online data processing techniques were employed to ensure high time resolution and accurate flow rate determination. The experimental hydrographs were analyzed in a dimensionless form to facilitate generalization and comparison with widely used nonlinear reservoir method and unit hydrograph method. Wave-like fluctuations of the flow rate were observed in most experimental hydrographs as they approached the maximum runoff. The dimensionless phase time of the experimental hydrographs showed an increasing trend with higher rainfall intensity, and a power-law equation was derived to approximate this relationship. An averaged dimensionless runoff hydrograph was obtained by processing individual hydrographs, and it was approximated by the DR-Hill-Zerobackground model for the initial stage during the rainfall and by the Weibull model for the later stage, after the rainfall stopped. The findings of this study have significant implications for modelling surface runoff from small urban subcatchments, particularly under critical rainfall events with extremely high intensity.

Keywords: High intensity rainfall; Linear subcatchment; Nonlinear reservoir method; Stormwater hydrograph; Surface runoff; Wave effect.

Fig. 1

Surface runoff experimental set-up: 1 – water distribution pipeline; 2 – bypass pipeline; 3 – valve; 4 – interception tray; 5 – hydraulic flume; 6 – water meter; 7 – detention tank; 8 – digital scale AXIS BDU-60; 9 – digital output to the computer; 10 – slope adjuster.

Fig. 2

Experimental curves of volumes and depths of the model runoff for L = 6 m; b = 0.305 m, S = 0.01; n = 0.009, i_r = 1426 mm/h; t_r = 40 s.

Fig. 3

Experimental hydrographs of surface runoff on the physical model: L = 6 m, b = 0.305 m, n = 0.009, S = 0.01.

Fig. 4

Experimental hydrographs of surface runoff on the physical model: L = 6 m, b = 0.305 m, n = 0.009, S = 0.015.

Fig. 5

Experimental hydrographs of surface runoff on the physical model: L = 6 m, b = 0.305 m, n = 0.009, S = 0.02.

Fig. 6

Dimensionless wave amplitudes of experimental hydrographs; error bars ±10 % are specified.

Fig. 7

Dimensionless phase time of waves on experimental hydrographs; error bars ±5 % are specified.

Fig. 8

Experimental dimensionless hydrographs from linear impervious plane subcatchment for model rainfalls of extremely high intensity comparing to other most common methods.