Lesson of Saguenay11 May 1998
The Saguenay flood was an event estimated at less than once in 10,000 years. As Anthony Tawil* explains, it resulted in a reappraisal of dam safety in Canada.
The devastation resulting from the unpredicted torrential rains which battered the central and eastern parts of southern Quebec on 18-20 July 1996 was particularly destructive in four watersheds occupying an area of about 210,000 km2, equivalent to the area of England and Scotland combined. Administratively, the area has 24 regional countries which encompass 280 municipalities, and a total population of about 650,000. The greatest devastation affected the largest basin — hosting the Saguenay River and Lake Saint Jean — which has an area of 106,000km2 and a population of 300,000. Lac Saint Jean is 210km north of Montreal and 120km northwest of the city of Quebec, the provincial capital.
The physiography of the disaster area is generally lowlands, at an altitude of 100m to 300m, and highlands. whose maximum relief varies from 800m to 1100m. The lowlands are mainly plains composed of marine clays overlain with fluvio-glacial and fluvio-marine sands. The highlands are composed of granite and gneiss belonging to the Grenville Province of the Precambrian Canadian Shield. Sedimentary rocks are found.
The average annual rainfall in this area varies between 750m and 1450 mm. The area has abundant water resources with many lakes and about 40 significant rivers occupying depressions and valleys separating the hills. The Saguenay–Lac Saint Jean watershed has more than 2000 dams and dykes. The economy in the area is based on forestry, pulp and paper industry, agriculture, hydroelectric generation, mining, wildlife and tourism.
On the fateful Friday, 19 July 1996, the rains began intermittently at 2:00hrs. They intensified later, by 8:00 a.m. and were relentlessly sustained for about 51hrs to 4:00 a.m. on Sunday 21 July. The precipitation was unprecedented and so was the destruction. Rivers and streams ran at four times their natural width, and the sudden swelling flow eroded banks, deepening channels and in some cases carving out new courses. New banks were failing progressively and landsliding in fine-grained soils was prevalent. Dams and dykes were overtopped or failed by loss of abutments. Hydroelectric stations were put out of operation, power and electricity were lost, and hydraulic components destroyed or rendered inoperable. Reservoirs were drained uncontrollably. The 21m high Kénogami earth dam owned by Abitibi-Price Company and used to generate power for the associated paper mill, was completed washed away.
Roads and bridges collapsed, as did railroads. Access to essential services was lost, complicating evacuation and aid to victims. Considerable damage was inflicted on municipal infrastructure including streets, culverts, city parks and recreation facilities and sanitary services. In the Kénogami reservoir basin alone, over 560 houses and cottages were damaged by the flood. Farmers, private property, commercial facilities and service centers were inundated and destroyed. In all, 63 municipalities were struck by the flood and 16,000 people had to be evacuated, housed and cared for. Tragically, five lives were lost, unrelated to dam failure. The cost of the damages was estimated at C$700M.
Inquiry and restoration
The Quebec Government dealt with the consequences of the July flood swiftly and without delay. Barely three weeks after the disastrous event, the government instituted the ‘Scientific and Technical Committee on the Management of Dams’. The mandate was wide and farsighted, in that in addition to investigating the circumstances of the flood, the Committee was called upon to ‘make recommendations to improve the management of dams in Quebec’ It is also noteworthy that the Committee and its inquiry were strictly ‘scientific and technical’. The Committee consisted of five specialists chaired by Roger Nicolet.
As the Saguenay inquiry set about its work, the reconstruction of the rampaged region was already underway. After the rains subsided on Sunday 21 July the widespread dislocation was evident, as was the considerable suffering of people and communities. Restoration work was swift and deliberate and free of the pettiness and delay sometimes inflicted on victims of disasters. Assistance was extended to Quebec from all parts of Canada as well as from the Canadian forces.
The devastation in Saguenay is etched in the minds of Quebecers and Canadians. But in a matter of months, lives were returning to normal and despair was transformed into optimism and hope.
The Committee reports
Floods in Canada are not uncommon occurrences, but loss of life and destruction on a disaster scale have been infrequent. While government inquiries into Canadian floods have been conducted in the past, the work of the Scientific and Technical Committee was the first to deal directly with dams and their management, and by inference, the safety of reservoirs.
The Saguenay Committee submitted its report to the Quebec Cabinet on 14 January 1997, five months after its inception. The work was exhaustive and included analyses of the hydrological phenomenon, public hearings, legal aspects of water and its utilisation, the role of owners and regulators in the management of dams, and public safety. The Committee’s report amounted to 380 pages, plus 80 figures.
The report was published in French. Responding to inquiries from the scientific communities across Canada for an English version, the Canadian Dam Safety Association established a translation committee chaired by Oscar Dascal of hydro-quebec. The English version of the Saguenay Report appeared in September 1997**.
Hydrological aspects of flood
More than one quarter of the Committee’s report was devoted to analyses of the July flood and examination of the eight basins in the area. Rainfall records from ten weather stations, located mainly in the Saguenay region, were used. Highlights of the findings were as follows.
•The precipitation at individual stations on 18-20 July varied from 150mm to 280 mm, which is greater than the medium to long-term total precipitation for July of 125mm. Past precipitation at Chicoutimi from 1871 to 1995, that is over 120 years of measurements, indicated the maximum 24hr and 48hr precipitation were 94.5mm (on 31 August 1893) and 122.4mm (on 30-31 August 1893), respectively. For the same 120 year period, precipitation greater than 80mm in 48hr was recorded only six times. Therefore the July 1996 event was two-to-three times greater than the previous record. Similarly, the intensity of precipitation in the July 1996 event was over 12mm/hr for a few hours, compared to a past average intensity of about 6mm/hr for 48hr. Further, the spatial distribution was notable in that the excessive precipitation of 150mm to 280mm covered an area of several thousand square kilometers.
•For the Kénogami reservoir, the maximum daily inflow for the period 1912 – 1995 was 996m3/s in April 1941; past inflow had exceeded 800m3/s only five times in over 80 years. The maximum daily inflow for 21 July 1996 — 2364m3/s — was more than twice the greatest inflow in over 80 years.
•The probable maximum flood was estimated in 1990 at 3610m3/s. The 10, 000-year flood, estimated in 1988 at 1500m3/s, was much lower than the value of 2364m3/s observed in July 1996. However the statistical distribution is dependent on the number of observations, and the summary in the table above confirms the impact of the July 1996 observations.
•The table gives a summary of the main findings for the rivers for which simulated discharges had been performed. In addition to the variation in average precipitation in the watersheds, the Kénogami reservoir watershed was the most affected. Even for the smaller watersheds, the July 1996 event was extreme.
The Saguenay Committee dealt with eight topics including disaster areas, characteristics of the July flood, public hearings, legal aspects, management of water and dams and public safety. The major conclusions were as follows.
•The July 1996 flood was twice the maximum recorded in more than 120 years. The extensive damage resulting from this unprecedented flood was not surprising, given that infrastructure and service facilities were not built to handle such high flows.
•The spillway capacity in water retaining development was flagrantly inconsistent with the hydrological demands necessary for prudent reservoir operation.
•The care given to hydraulic facilities by owners and operators was uneven. Emergency plans were often incomplete and outdated, and the populace was largely unaware of the hazards. Instrumentation and monitoring were often deficient. There was wide variation in exercising responsibility for hydraulic structures by owners and operators.
•The public showed particular discontent in aspects of water management and use of water including permits, hazard evaluation and mitigating measures.
•The Ministry of Environment and Wildlife, which is responsible for dams and reservoirs in Quebec, experienced difficulties and shortcomings in fulfilling its public responsibility, partly due to its centralised management.
•Regional and municipal authorities displayed serious shortcomings in discharging their responsibility with regards to public safety.
In its report, the Committee submitted 81 main recommendations supplemented by 84 detailed clauses on eight subjects. In many respects, the recommendations were wide-ranging and in some instances, they were radical and innovative. The highlights were as follows.
•Completely revise the existing Quebec Watercourses Act and introduce specific legislation for safety of water-retaining structures, separate from the Act.
•The proposed act on the safety of water-retaining structures should provide for the creation of an Authority Responsible for Safety of Dams (ARSB), which would have extensive powers over all retaining structures in Quebec including tailings dams, irrespective of ownership. The ARSB would be under the jurisdiction of the Ministry of Public Safety. The ARSB would adopt the Dam Safety Guidelines put out by the Canadian Dam Association.
•Prepare a register of dams in Quebec, to include pertinent characteristics.
•Establish public Watershed Committees (WCs) for all rivers hosting hydraulic facilities. The WCs would be responsible for various aspects of the rivers and the drainage basins including co-ordination between the local public authorities and the dam operators.
•Develop new criteria and policies for flood plain management, corresponding to 20- and 100-yr recurrence.
Dam Safety in Canada
All political authority in the Canadian Federation is shared between the Federal Government and the ten Provincial Governments. The sharing of authority is a recognition of the individuality and special concerns of the various regions, and the provinces therefore possess considerable constitutional powers in running their affairs. The management of water resources, mining, forestry, irrigation and flood control all fall under provincial jurisdiction. Therefore, the provinces are responsible for dam safety in their areas, including licensing, safety legislation and public safety.
Canada ranks in the top ten countries in the world in dams higher than 15m. Canadian dams possess an enviable record in safety; and there has been no loss of life related to dam failure.
Quebec is the largest province in Canada and has abundant water resources; it accounts for one-third of the country’s large dams — more than 200.
Alberta was the first Canadian province to enact dam safety legislation, in 1978. As in most other provinces, Quebec does not have specific regulations governing safety of dams.
The recent interest in Canada in dam safety triggered the formation in 1989 of the Canadian Dam Safety Association (CDSA, now the Canadian Dam Association). After three years of preparation, CDSA produced the Canadian Dam Safety Guidelines in 1995. In three short years, the adoption of the guidelines by public and private dam owners, as well as the regulatory agency, has been astonishing. The voluntary applications of the Guidelines has been far more effective than the legislative route. The reality is that to date, safety of dams has not been a priority in the political agenda of the provinces.
The investigation into the Saguenay Flood represents the first public inquiry in Canada into the management of dams, and specifically security of dams and public safety. The recommendations of the Saguenay Committee were favourably received by the Government of Quebec . Action was immediately initiated on the major recommendations, namely the preparation of an inventory for dams in Quebec, the management of flood plains and legislation relating to dams safety. Progress in dam safety legislation is well advanced and public hearings are planned, followed by government consideration later in 1998. It is the expectation of the Canadian dam community that the enactment of safety legislation in Quebec will be duplicated in other jurisdictions.
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|Weather bulletins by the Weather Services Office of Environment Canada for Central Quebec and the Saguenay Region, forecasting the climatological events of 19-21 July 1996. Thursday, 18 July 5:30hrs * Fine and hot today. Rainy and cool Friday. A ridge of fine weather will maintain sunshine over central Quebec. However a depression from the Great Lakes will bring rain Friday. * For Saguenay, today sunny with cloudy periods. Friday, rain heavy at times beginning in the morning and ending in the evening. 14:10hrs * Special Bulletin . . . heavy rainfall warning . . . * The latest analyses indicate that the amounts of rain could reach 40 mm to 70 mm . . . heavy rainfall will begin early Friday morning. 16:30hrs * An intense depression developing over Ontario will cross our regions Friday. Heavy rainfall (close to 50 mm) will fall . . . the rain will end Friday evening. * For Saguenay, heavy rainfall warning in effect for Friday . . . rain strong at times beginning Friday morning. For Saturday, cloudy with 60% probability of showers in the morning. 21:00hrs * For Saguenay, heavy rainfall warning in effect for Friday . . . rain strong at times beginning in the morning. Saturday, 60% probability of showers. Friday, 19 July 5:30hrs * Lots of rain this afternoon . . . a depression developing over the Great Lakes will intensify today. * Large amounts of rain are forecast and heavy rain warning is in effect . . . the rain will end over central Quebec this evening. * For Saguenay, heavy rain warning in effect. Intermittent rain intensifying this afternoon. Saturday . . . rain ending in the evening. Saturday, 20 July 5:30hrs * The intense depression that brought record rainfall Friday is currently over the Gaspé Peninsula. Today it will continue to bring rain. * For Saguenay, heavy rain warning in effect. Today, rain, very cool . . . tonight, cloudy with 40% probability of showers . . . Sunday, cloudy, clearing in the afternoon. 10:57hrs * The intense depression that caused torrential rains to fall on several regions of Quebec will now lose its energy. Rain will persist over few locations with 10 to 20 mm at the most. Sunday, 21 July 5:30hrs * The intense depression that brought torrential rainfall Friday and Saturday has lost a lot of its intensity and is leaving our regions. * Only isolated light showers remain . . . the sun, which has been more than timid these last few days, will return . . . * Monday, sunshine will persist.|