The 2011 flood event in the Richelieu River basin: Causes, assessment and damages

Figures & data

Figure 1. The Lake Champlain and Richelieu River watershed.

Figure 2. Hydrograph (in m³/s), hyetograph (in 0.1 mm) and daily temperature variability (in 0.1°C) recorded by the South Hero weather station and the Fryers Rapids hydrometric station in 2011.

Table 1. Definition and description of hydro-meteorological indicators.

Indices	Period	Description and definition
Qmaxspr	MAM	Maximum daily flow during the spring months from March to May (in m^3/s).
Durfl	Mid-February to September	Number of days when the river flow is above a specific flood threshold (1.7 times the mean inter-annual flow of 395.48 m^3/s for the 1981–2011 period; Saad 2014).
FrThSeq	DJF	Number of days with daily frost and thaw cycles during the winter months (in days); determined by the minimum and maximum daily temperatures.
PrecTOT	November to March (N_M)	Cumulative solid precipitation fallen during the months of November to March inclusively (mm of snow water equivalent).
PrecSol	Winter (DJF & M)	Cumulative solid precipitation fallen during the winter months from December to February and also in March alone (in cm; 1 mm water is equivalent to 1 cm of snow).
PrecLiq	Spring (MAM)	Cumulative liquid precipitation fallen during the winter months from March to April (in mm).
SDIILiq	MAM	Mean intensity of liquid precipitation during the spring months from March to May inclusively (in mm/wet day).
P90pLiq	MAM	90^th percentile of liquid precipitation fallen during the spring months from March to May inclusively (in mm) and calculated using the Cunnane formula (1978); a minimum of 15 days of precipitation (≥1 mm/day) is required.

Figure 3. Dot plot of the inter-annual standardized anomalies of hydrometeorological events according to the 1981–2011 reference period; all abbreviations are defined in Table 1.

Table 2. Scale, shape and location parameters (respectively given in parentheses) of marginal distributions fitted to hydrometeorological indices and stations.

Station/index	Qmaxspr	Durfl	FrThSeq (DJF)	PrecTOT (N-M)	PrecSol (DJF)	PrecSol (M)	PrecLiq (MAM)	SDIILiq (MAM)	P90pLiq (MAM)
Rapides Fryer	Lognormal (6.8,0.2)	Gamma (2.4,0.05)	–	–	–	–	–	–	–
South Hero	–	–	Gamma (37.9,0.7)	GEV (51,0.2, 225)	Gamma (6.8,0.09)	Gumbel (15,15.7)	Inverse Gamma (1163,8.1)	GEV (1.6,0.2,6.7)	Gamma (14.3,0.9)

Table 3. Description of the probable flood attenuating scenarios.

Scenario	Description
1	Reducing the 90^th percentile of spring rainfall from 31.1 mm/day (T = 260 years) to about 15 mm/day (T = 2 years) by subtracting 18 mm of total precipitation from spring days (MAM) with more than or equal to 20 mm of daily precipitation.
2	Reduction in the observed cumulated total precipitation fallen between November and March of 354.7 mm (T = 14 years) to about 226 mm (T = 2 years) by subtracting 20 and 15 mm of total precipitation from days with more than 20 mm, and between 15 and 20 mm of precipitation, respectively, for the months of November to March.
3	Increase in the number of frost/thaw episodes in winter from 19 days (T = 20 years) to 33 days (T = 2 years) by applying an increment of ±2°C to maximum or minimum daily temperatures for days with temperatures within 2°C from the frost/thaw threshold (0°C).
4	Same as scenario 1 in combination with a reduction of the observed cumulated total precipitation fallen between November and March of 354.7 mm (T = 14 years) to about 226 mm (T = 2 years) by subtracting 20 and 15 mm of total precipitation from days with more than 20 mm, and between 15 and 20 mm of precipitation, respectively, for the months of November to March.
5	Combination of scenarios 2 and 3.

Figure 4. Hydrograph of the 2010–2011 observed and simulated daily flows (in m³/s on the vertical axis) from the 2010–2011 observed meteorological conditions and from flood-attenuating scenarios 1 through 5, with respect to the various flood thresholds determined by the Ministère de la Sécurité Publique du Québec (MSP; dashed horizontal lines).

Table 4. The 95% confidence intervals of the estimated return periods of the joint occurrences of the 2011 extreme hydrometeorological events.

Joint return period of 2011’s major flood	Lowest estimate (yrs)	Highest estimate (yrs)
T(P90pLiq_MAMT→260yr* = 31mm/d & QmaxsprT→90yr = 1550m^3/s & PrecTOTN-MT→14yr = 354 mm)	7140	50000
T(PrecTOTN-MT→14yr = 354 mm & QmaxsprT→90yr = 1550 m^3/s & FrThSeq_DJFT→20yr = 19 d)	1852	5000

* Average marginal return period of the 2011 hydrological or meteorological event.

Saad, C. 2014. Analyse hydrométéorologique multivariées et modélisation déterministe des crues de la rivière Richelieu, Québec. Master’s thesis, Institut National de la Recherche Scientifique, Quebec.

 Google Scholar