Denver is generally considered a low risk for earthquakes. While the threat is low and there is no documentation of an earthquake event over 6.0 on the Richter scale, the potential for the loss of life, injury and personal damage is present. A large number of residencies and older commercial buildings in the metro area and particularly in Denver are masonry structures. These brick buildings could be susceptible to earthquake damage.
- Flood Watch: Flooding is possible. Tune in to NOAA Weather Radio, commercial radio, or television for information.
- Flood Warning: Flooding is occurring or will occur soon; if advised to evacuate, do so immediately.
- Flash Flood Watch: Rapid rises on streams and rivers are possible. Be prepared to move to higher ground; listen to NOAA Weather Radio, commercial radio, or television for information.
- Flash Flood Warning: Rapid rises on streams and rivers are occurring; seek higher ground on foot immediately.
Flooding has historically been a hazard to the City and County of Denver. Past flooding along the streams in Denver has been well documented by the Corps of Engineers and the Urban Drainage and Flood Control District.
Cherry Creek: From 1942 to present, there have been at least 14 years with major flooding events from Cherry Creek, resulting in flooding of premises and impeding traffic.
Clear Creek: In the Denver area, flooding has been infrequent and typically not severe in the lower reaches. The major flooding has occurred upstream from Denver.
Harvard Gulch: Prior to 1965, Harvard Gulch experienced regular flooding due to summer thunderstorms. The Harvard Gulch Flood Control Project, completed in 1966, was designed for the 10-year flood and has alleviated this problem. The largest flood event since the completion of the project occurred on June 8, 1969. The flow was confined within the drainage improvements.
Because of the extensive mitigation projects completed and the current Flood Control Master Plan now being accomplished by the Urban Drainage and Flood Control District, the threat to life in Denver by flooding has been greatly diminished. There is however, a continued threat to property particularly from flash flooding along Harvard Gulch, Goldsmith, and Westerly Creek. Some potential for property damage exists along Sand Creek, but it is relatively low. There is still some urban street flooding problems, particularly at 38th and Fox Street, I-25 and Evans, and Monaco and Evans. However, recent flood mitigation projects have helped to alleviate some of these problems. While the threat is more to property than life, loss of life and/or injury is always a potential with flooding hazards. The quick developing flash flood and/or failure of one of the major dams in the metro area could still produce serious flooding problems. Loss of either the Cherry Creek or Chatfield Dam could create flooding of historic proportions.
Hail and Lightning:
While tornadoes and flooding have been discussed separately, the storms that produce these threats also include other life threatening and damage producing phenomena. In the Rocky Mountains, thunderstorms occur approximately 70 days per year. These storms produce dramatic displays of lightning and potentially damaging amounts of hail. Hailstorms rarely involve physical injury, but their economic impact can be severe. In 1990, the hailstorm that struck the metro area resulted in approximately $750 million in damages alone. It ranked as the most expensive hail related incident at that time in the country. The damage from hail in Denver can be an annual event. However, new materials for roofing are slowly mitigating the damage from hail. The atmospheric discharge of static electricity in a bolt of lightning has four principle effects:
1) electrocution of living things
2) vaporization of materials along the path of the strike
3) sudden power surges which cause damage to electrical and electronic equipment
4) building fires (In the United States, building fires caused by lightning, account for over $40 million per year in insurance claims).
It should be noted that more people are killed by lightning each year in Colorado than in any other weather related phenomena.
Currently, based on reports filed under Title III of the Superfund Amendment Reauthorization Act (SARA Title III), there are approximately 400 facilities storing reportable quantities of hazardous material on sites throughout the city. In addition to fixed storage sites, hazardous materials are transported along the I-70 and I-25 highway corridors, which pass through densely populated areas of the city. Fire House Magazine has placed the Denver Fire Department Hazmat Response Unit among the top ten busiest units nationwide over the last seven years.
Tornadoes are the most widely feared and publicized natural hazards in Colorado. During 1996, a total of 96 tornadoes occurred in Colorado, heightening concerns that these powerful phenomenons may be increasing to cataclysmic frequencies. The metro area, in particular, serves as a site for the development of severe thunderstorms. Due to the "Denver Cyclone" effect, severe spring weather is a major concern for Denver. These storms create cloud to ground lightning strikes, heavy rain with flooding potential, severe hail, and tornadoes. On June 15, 1988, a group of tornadoes passed over the metro area. Two areas of the city suffered heavy damage due to tornado touch downs. On June 2, 1993, an F-1 rated tornado struck Denver. According to the National Weather Service, there have been 11 tornado touch downs in Denver between 1950 and 1989. The Fujita scale rates intensity of tornadoes with F0 for weak storms with wind rotation below 73 mph, and F5 for violent storms with rotation speeds of 261 to 318 mph. Fortunately, the tornadoes in the Denver area are usually rated F0 to F1 (with rotation speeds of 73 to 112 mph). While the tornadoes that occur in Denver are relatively weak compared to those in the Mid-West, the potential for injury, loss of life and property damage remains high. Most injuries that occur in these events are the result of flying debris, especially broken glass. The tornado threat is with us every spring, and is extremely high during the months of May, June and July. The intensity of these events and the potential for damages and injury should not be underestimated.
The most likely cause of a paralytic event in Denver is a severe winter storm. The city only averages 62.5 inches of snow per season, however there is always the chance of one particular storm producing large snowfall amounts (e.g,. the Christmas Blizzard of '82 produced nearly 2 feet of snow in a 24 hour period, and the October Blizzard of '97 produced 20 inches of snow in a 24 hour period). The disruption of the urban system caused by heavy snow can lead to detrimental economic consequences due to the closures of plants, retail trade centers, schools, communication facilities, and the curtailment of transportation. Major snowfall can even occur during those months with milder temperatures. For example, the average snowfall for September is 1.7 inches, yet in 1936 Denver received 21.3 inches. Snow storms like this, and those in early spring, produce heavy wet snows that break tree limbs and down power lines. Along with snowfall, Denver can also experience extremely cold temperatures, dropping 25 degrees below zero or lower with the wind chill factor. The threat of severe winter storms including cold temperatures and heavy snow, is well documented and even expected in Denver.
The City and County of Denver has made great efforts to manage these events and mitigate their paralytic potential. However, it is easy for some people to become complacent to the threats these hazards pose to life, property, health, and the economy.