Integrating hydrogeomorphological concepts in management approaches of lowland agricultural streams: Perspectives, problems and prospects based on case studies in Quebec

Figures & data

Figure 1. Location of the three studied watersheds – the Des Fèves, Lacolle and L’Acadie Rivers – as well as the three sites where crop productivity was assessed near the stream (sites A, B and C).

Table 1. Main characteristics of the three study reaches.

Site	Length (km)	Slope	Drainage area (km^2)	Bottom channel width (m)	Type of soil/crop	Last dredging operation
Des Fèves	4.1	0.0027	3.27	1.6	corn/soy	2013
Lacolle	3.9	0.0011	7.26	3.0	corn/soy	2013
L’Acadie	1.4*	0.0021	2.64	1.9	vegetable (organic soils)	Unknown

^* 480 m in contact with cultivated fields.

Table 2. Detailed information on the streams used to establish regional curves.

Name	Coordinates	Drainage area at the sampling point (km^2)	Year of last dredging operation*
No name; small tributary ditch draining into l’Acadie river	(45°09′02.43′′N, 73°47′14.44′′W)	0.11	Unknown
Small tributary of Norton Creek	(45°02′00.64′′N, 73°34′13.88′′W)	0.56	Unknown
Ruisseau Richard-Gervais(Lacolle)	(45°04′38.65′′N, 73°21′06.93′′W)	3.01	No dredging – aerial photographs of 1930 show nearly the same stream path
Branch 53 of the Des Fèves River (Sainte-Martine)	(45°12′39.92′′N, 73°47′09.11′′W)	3.11	2013 – Downstream portion left undisturbed
Ruisseau Morin (Napierville)	(45°13′34.38′′N, 73°24′29.61′′W)	7.06	2000 – benches left intact
Ruisseau Zénophile-Primeau(Très-Saint-Sacrement)	(45°09′15.33′′N, 73°49′44.99′′W)	9.32	1985
Ruisseau Atkinson(Très-Saint-Sacrement)	(45°08′55.51′′N, 73°48′22.92′′W)	9.60	1996
Des Fèves River(Sainte-Martine)	(45°13′10.66′′N, 73°47′34.37′′W)	51.67
Des Anglais River	(45°09′29.03′′N, 73°49′28.96′′W)	642.21
Des Hurons River	(45°29′26.01′′N, 73°11′09.07′′W)	308.14
L’Acadie River	(45°23′25.05′′N, 73°22′14.98′′W)	366.89
David River	(45°57′15.16′′N, 73°51′34.91′′W)	323.17
Aux Brochets River	(45°09′31.08′′N, 73°03′03.00′′W)	584.26

^* Empty cells indicate natural streams which were never dredged.

Table 3. Four levels of discharge used in hydraulic modelling, along with the calibrated Manning’s n.

Site	Low flow		Medium flow		High flow		Very high flow
	Q (m^3/s)	n	Q (m^3/s)	n	Q (m^3/s)	n	Q (m^3/s)	n
Des Fèves	0.015	0.045	0.11	0.045	0.9	0.045	2.8	0.045
Lacolle	0.04	0.051	0.2	0.051	2.3	0.051	6.5	0.051
L’Acadie	0.02	0.034	0.14	0.034	1.0	0.034	3.2	0.034

Figure 2. (A) Horseshoe wetland design for agricultural fields with a limited riparian buffer such as those typically encountered in Quebec, and (B) integration of horseshoe wetland cross-sections in. Hydrologic Engineering Center's River Analysis System (HEC-RAS).

Figure 3. (A) Diagram showing the dimensions of two-stage channels; (B) regional curves of bankfull channel geometry (Montérégie) for the inset width (W_inset in A) and depth.

Figure 4. Visual representation of a two-stage channel design (3 and 5 times the inset channel width) over an actual cross-section of branch 53 of the Des Fèves River, also showing the location of the deep subsurface drainage outlet measured in the field (the inset channel width is 1.62 m).

Table 4. Additional width required for each bank and corresponding volume of spoil to be removed for two-stage and over-wide ditch designs.

Site	Wfloodplain/Winset	Average additional width (m) (min-max)	Volume of spoil (m^3) for two-stage channel	Volume of spoil (m^3) for over-widened channel
Des Fèves	3	1.3 (0.6–1.9)	6907	10,222
	5	2.6 (1.2–3.7)	12,600	18,763
Lacolle	3	2.8 (2.0–3.5)	30,916	45,775
	5	5.6 (4.3–6.5)	90,458	119,956
L’Acadie	3	1.5 (1.2–1.8)	1414	2148
	5	3.2 (2.7–3.6)	2991	5100

Figure 5. Hydrologic Engineering Center's River Analysis System (HEC-RAS) output for (A) the actual channel configuration of the Lacolle site, (B) the corresponding two-stage profile with 3 times the inset channel width, and (C) the corresponding two-stage profile with 5 times the inset channel width compared to the floodplain width. Values on the right in B and C correspond to the difference in flow stage compared to the actual channel for the four discharge values.

Table 5. Effect of the two-stage profiles on the maximum in-stream discharge (drainage capacity).

Site	Maximum in-stream discharge – current (m^3/s)	Maximum in-stream discharge – 3× (m^3/s) (m^3/s)	Maximum in-stream discharge – 5× (m^3/s) (m^3/s)
Des Fèves	2.4	2.7 (+13%)	3.7 (+54%)
Lacolle	6.5	7.2 (+11%)	8.9 (+37%)
L’Acadie	2.8	3.2 (+14%)	4.3 (+54%)

Table 6. Sensitivity analysis of water stage for the very high flow discharge of the Lacolle site (6.5 m³/s) when increasing Manning’s n.

Manning’s n value	3× stage (m)	5× stage (m)
0.051 (current)	2.03	1.89
0.055	2.12 (+4%)	1.98 (+5%)
0.060	2.21 (+9%) Maximum in-stream flow stage	2.06 (+9%)
0.065	Field flooding	2.14 (+13%)
0.070	Field flooding	2.21 (+17%) Maximum in-stream flow stage

Table 7. Flow characteristics before and after integration of a 3 × 3 m horseshoe wetland on a 6-m wide ditch.

Test	Low flow (Q = 0.2 m^3/s) stage (m)	High flow (Q = 4 m^3/s) stage (m)	Near bank low-flow velocity (m/s)	Near bank high-flow velocity (m/s)	Channel low-flow velocity (m/s)	Channel high-flow velocity (m/s)
Standard ditch	0.29	1.59	0.11	0.32	0.34	1.13
With horseshoe wetland	0.30	1.63	0.00	0.12	0.22	0.31
				(−66%)	(−35%)	(−73%)

Table 8. Comparison of total cost for a traditional dredging approach, self-formed channel approach, two-stage channel and over-widened channel designs.

Site	Traditional clean-out dredging ($)	Self-formed ($)	Two-stage channel ($)	Over-widened channel ($)
Des Fèves	71,000 ($25/m)	38,079 ($13/m)	169,594 ($60/m)	211,922 ($75/m)
Lacolle	98,250 ($25/m)	59,839 ($15/m)	565,924 ($144/m)	798,044 ($203/m)
L’Acadie	12,000 ($25/m)	3708 ($8/m)	17,788 ($37/m)	17,788 ($37/m)

$: 2015 Canadian dollars.

Figure 6. Maize crop yields for different distances to the stream in 2014 at site C (Des Fèves River).