Lake St. Francois-Xavier

 In the inventory of the MDDELCC’s (Quebec’s Department of Environment) Centre d’expertise hydrique, the X0005087 dam, built in 1900 and modified in 1920, is said to be of "high-capacity" since, among other things, it has a holding capacity of more than 1 million m³.*  And it has just been reclassified on the rise, as a "B", following, for one, the visit of Mr. Éric Martel, representative of the Centre d’expertise, could we learn from the MRC’s recent release.  It has a height of 2.4 m, a length of 103 m;  and it is said to be an "earthen dam".  However, there is no information about its strength; and the level of consequences of its failure is unknown.  It was not the first dam built at the foot of the lake; a previous one must have been dating from the 1880s, at the beginning of the founding of Montfort.  

Engineer Pierre Dumas showed us a cropping of the original bathymetric maps of Dr. Richard Carignan. (They are in possession of the municipal authorities). By following the 2 meters isobath, they show us the Western and Eastern sections of the lake with their corresponding lowered water levels; it must have been the height and initial rough outline of the Lake, before the construction of a dam. Both basins would have then been forming two separate lakes.  You could look at their two hypsometric sheets in the Laurentians lakes web Atlas and see what area and what volume of water that represents. Other data, such as time of renewal and drainage ratio, are also evaluated, Atlas des lacs : Lake St. François-Xavier (West), Atlas des lacs: Lake St. François-Xavier (East). (When following the 2m isobath, looking at the global bathymetric map gives an idea of the former lake contour : Bathymetric map of LSFX)
 In its 1941 report, the Commission of Common Waters of Quebec mentions the existence of two concrete dam sections, a first one of 29 feet. (It was at the entrance of the road access leading to the Montfort Pavilion, where the observation trench has just been dug and where is the fire water intake; but where you will not see much visible traces of still present concrete parts. According to the report, the dam had a hole to let the water pass to a wooden supply line (girdled with iron); its diameter is not specified.
 (Our hypothesis is that the original duct was at least of four feet in diameter. The dam was demolished and replaced by the current dike. A huge funnel, possibly in metal, would eventually be incorporated into the structure to direct water towards the duct, while the wooden one was replaced by a metallic, of only two feet in diameter The latter proved to be insufficient to supply the saw mill and the power plant situated below, without forgetting, at a time, the wooden pool for the orphans. A large diesel Chrysler engine had to be added, as well as a huge reservoir for this hydrocarbon that has had the misfortune to flow into Deer Lake to kill quantity of fish.)
 This duct appears to have been in a straight line, from the opening in the dam to the last concrete pillar.  It borrowed a depression in the land while leaving the dam, at the crossing of route Principale and the access road to the Pavilion, where it passed under a bridge.  A long series of these supporting pillars, spaced by ten feet, are always present at the entrance of the village and join the Main road at Hydro Quebec’s post 14-42. But they are almost completely hidden by shrub lands.  Strangely enough, these pillars are sometimes of arch opening for receiving an about two feet in diameter duct, while others, interspersed in the alignment, are rather designed to receive one of at least four feet; i.e. probably for the earlier wooden conduct but as well used to support the new one.
 The second section of concrete was a 70-foot dam (probably the one blocking the current channel that opens next to the Pavilion), pierced with two openings for overflow, a bottom valve and a wooden sluice 8 feet wide (Is it a door that can be used to remove water during floods?). It was probably the section that was demolished to be replaced by culverts under the Chemin de Lisbourg and on which the boys liked to show fearlessness.
 As we were told by Mr. Mayor Genest, water leaks appeared in downstream of the structure in recent years. On dry weather indeed, several small water leaks are now visible in the observation trench dug for this purpose. The MRC has recently hired Mr. Pierre Dumas, an engineer and consultant in hydraulics, energy and environment, expert in dammed lakes, to conduct a safety study on the century-old dam. We saw the engineer at work on earth and, using a tuba, in the lake, not far from where the fire water intake is located.
 No tree planting should have dressed this structure had already learned Mayor Genest; with decomposition, tree roots, which have drilled deep paths, will eventually leave as many inappropriate channels to pressurized water.  He had also let know that an engineering firm, briefly consulted, was already suggesting a widening of the dam where are the seen leaks, while a second, specialized in dams, would have gone for digging there a trench to be filled with clay.
The rupture of a lake or river dam may occur, as was the case with the artificial Lake Bison (600 meters long) at Saint-Raymond, in Portneuf, which emptied in about five minutes in June, after having yet undergone the prescribed inspections successfully.  Some local residents reported having experience a mini tsunami and believe that water infiltration in the dam could be the cause, while heavy rainfalls had completed the work. The unlikely failure of the dam of Lake Saint-François-Xavier would be of a different order of magnitude; mais dont le Québec a eu de tristes exemples. but Quebec has known sad examples of such.
A first dam and duct were therefore built at Lake St. François-Xavier from the beginning of colonization;  it was essential to the operation of a sawmill that would allow the construction of the village and the orphanage.  That probably was the dam that would have collapsed, as reported by the elders, taking away all the facilities of the mill it served at the time; mais apparemment sans faire de victime. but apparently causing no casualties.
 Thank you to Mr. Gérard Chartier for his valuable collaboration.
 Information and old photos from residents to shed light on the overall picture of this issue would be most appreciated.

* http://www.cehq.gouv.qc.ca/barrages/detail.asp?no_mef_lieu=X0005087
 Carl Chapdelaine

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