Parametric study of a physically-based, plot-scale hillslope hydrological model through virtual experiments

Figures & data

Fig. 1 A conceptual framework of the hillslope hydrological model.

Fig. 2 Observed overland flow rates for a plot-scale runoff simulation experiment conducted with constant inflow intensity of 97 mm/h and 51 min duration under dense vegetation condition.

Fig. 3 Observed and simulated outflow rates for a plot-scale runoff experiment conducted with constant inflow intensity of 241 mm/h and 30 min duration under moderate vegetation condition.

Table 1 Observed and simulated overland flow characteristics for some of the runoff experiments conducted on the experimental hillslope plot.

Vegetation condition	Inflow intensity (mm/h)	Simulated steady outflow rate (mm/h)	Runoff coefficient
			Observed	Simulated
Sparse	59	22	0.44	0.37
	72	33	0.49	0.46
	79	40	0.54	0.51
	85	35	0.49	0.41
	115	59	0.52	0.51
	128	62	0.49	0.48
	136	71	0.51	0.52
	158	85	0.53	0.54
	167	89	0.54	0.53
	361	238	0.61	0.66
Moderate	80	23	0.35	0.29
	103	35	0.53	0.34
	121	47	0.49	0.39
	174	93	0.54	0.53
	229	84	0.54	0.37
	241	141	0.63	0.59
	270	152	0.67	0.56
	276	115	0.51	0.42
	298	132	0.56	0.44
	339	187	0.56	0.55
	406	190	0.56	0.47
Dense	87	15	0.01	0.17
	89	19	0.06	0.21
	91	21	0.09	0.23
	95	20	0.08	0.25
	97	20	0.04	0.21
	132	34	0.15	0.26
	134	53	0.27	0.40
	184	60	0.21	0.33
	190	50	0.12	0.26
	214	72	0.20	0.34
	300	149	0.42	0.50
	305	127	0.30	0.42
	310	104	0.21	0.34

Table 2 Observed and predicted water table depths above the impermeable layer for an experiment conducted with an average steady recharge rate of 139 mm/h for 48 min duration under dense vegetation conditions. PI: performance index.

Time step (min)	Distance from downstream end of plot (m)	Water table depth above impermeable layer (m)		PI
		Observed	Predicted
17	3	0.05	0.08
	6	0.13	0.13
	9	0.21	0.19	0.065
	12	0.27	0.24
	15	0.34	0.29
27	3	0.12	0.11
	6	0.23	0.19
	9	0.29	0.26	0.045
	12	0.35	0.33
	15	0.39	0.40
42	3	0.18	0.15
	6	0.24	0.26
	9	0.34	0.35	0.034
	12	0.45	0.43
	15	0.56	0.51
57	3	0.16	0.15
	6	0.24	0.24
	9	0.28	0.31	0.031
	12	0.35	0.38
	15	0.42	0.43
72	3	0.12	0.12
	6	0.21	0.19
	9	0.26	0.24	0.023
	12	0.27	0.28
	15	0.31	0.32
87	3	0.10	0.10
	6	0.16	0.15
	9	0.17	0.19	0.033
	12	0.21	0.22
	15	0.23	0.24

Fig. 4 (a)–(c) Three different topographical shapes of hillslope profile.

Fig. 5 (a)–(c) Overland flow hydrographs from different hillslopes under varying rainfall intensities.

Table 3 Effect of change in relief on overland flow hydrographs for i = 150 mm/h.

Hillslope topography	Relief, H = 20 m			Relief, H = 10 m
	Qp (m^3/s)	tp (s)	tr (s)	Qp (m^3/s)	tp (s)	tr (s)
Type 1	0.016	558	351	0.016	682	437
Type 2	0.016	535	233	0.016	657	287
Type 3	0.016	653	179	0.016	743	267

Table 4 Estimated normalized sensitivity coefficients (NSC) for the tested parameters of the model.

Tested parameter	Unit	Base value	NSC
			Overland flow outputs			Subsurface flow outputs
			Qp	tp	tr	Qp(mat)	Qp(mac)	hs
i	mm/h	150	2.121	0.344	0.330	0.739	1.981	0.652
H	m	20	0	0.187	0.189	1.001	0.0004	0
α	–	1	0	0.043	0.506	0.980	0.0004	0
ravg	mm	0.75	–	–	–	0.025	0.376	0.025
N	–	14	–	–	–	0.109	2.205	0.150

Fig. 6 (a)–(c) Subsurface flow hydrographs through soil macropores.

Fig. 7 (a)–(c) Subsurface flow hydrographs through soil matrix.

Table 5 Effect of change in relief on matrix flow hydrographs for i = 150 mm/h.

Hillslope Type	Relief, H = 20 m	Relief, H = 15 m
	Peak matrix flow rate, Qp(mat) (m^3/s)	Peak matrix flow rate, Qp(mat) (m^3/s)
Type 1	3.58 × 10^-08	2.67 × 10^-08
Type 2	1.79 × 10^-06	1.34 × 10^-06
Type 3	1.24 × 10^-05	1.00 × 10^-05

Table 6 Effect of change in soil macroporosity on subsurface stormflow for the Type 2 hillslope.

Rainfall intensity, i (mm/h)	Ravg = 0.00075 m		Ravg = 0.0015 m		Ravg = 0.00075 m
	N	hs (m)	N	hs (m)	N	hs (m)
100	8	0.418	8	0.416	12	0.409
125	9	0.482	9	0.479	14	0.468
150	11	0.544	11	0.540	17	0.525
200	13	0.661	13	0.654	20	0.630
300	18	0.863	18	0.849	27	0.804

Table 7 Maximum height of water table above the impermeable bed under different rainfall intensities.

Hillslope topography	Rainfall intensity, i (mm/h)	Maximum height of water table above the impermeable bed, hs (m)
Type 1	100	0.42
	125	0.48
	150	0.54
	200	0.66
	300	0.86
Type 2	100	0.42
	125	0.48
	150	0.54
	200	0.66
	300	0.86
Type 3	100	0.42
	125	0.48
	150	0.54
	200	0.66
	300	0.86

Table 8 Occurrence of saturation excess overland flow with no lateral macropores for the Type 2 hillslope.

Rainfall intensity, i (mm/h)	Time at which saturation excess overland flow initiated (h)
	Duration of rainfall (0.75 h)	Duration of rainfall (1 h)	Duration of rainfall (1.25 h)
100	No flow	No flow	1.15
125	No flow	1.00	1.00
150	No flow	0.90	0.90
200	0.70	0.70	0.70
300	0.50	0.50	0.50