WEEKLY WATER NEWS

WEEKLY WATER NEWS

WES WEEK FIVE: 8-12 October 2001

Water in the News

Earth diary - A summary of the week's major environmental events on Planet Earth. [CNN]

Concept of the Week: Artificial Snow

Snow is the essential ingredient for many winter recreational activities including downhill and cross-country skiing, snow boarding, and snowmobiling. No natural snow cover means no cross-country skiing or snowmobiling. But downhill ski hill operators have another option if weather conditions do not provide adequate snow cover—they can generate their own snow. Artificial snow is used to build a base for skiing, refresh snow surfaces, and make skiing possible even during a snow drought, significantly lengthening the ski season. Some ski areas can cover 80% or more of their terrain with artificial snow. Whereas snowmaking offers many economic advantages, some drawbacks stem from alteration of the local water balance.

Artificial snow is actually tiny particles of ice. Snow makers use specially designed snow guns into which flexible hoses feed compressed air and water separately. A jet of compressed air breaks the stream of water into a fine mist of tiny droplets, which if conditions are favorable, freezes to ice crystals. Expansional cooling of the compressed air as it is emitted through the nozzle of the snow gun and into the atmosphere chills the water droplets. Artificial "snowflakes" settle onto the slopes and mechanized snow groomers then till and spread the accumulated artificial snow evenly over the ski slopes.

Many snowmakers add a special protein (commercially known as Snowmax) to the air/water mix to improve both the quality and quantity of artificial snow. A non-toxic and non-pathogenic strain of a bacterium produces the protein that attracts water and promotes formation of ice crystals. Snowmax increases the amount of artificial snow produced at higher temperatures and snowflakes tend to be drier and lighter than other artificial snowflakes.

Ideal weather for snowmaking consists of low air temperature, light winds, and low humidity. Snowmaking is possible even when the air temperature is above 0° C provided that the relative humidity is sufficiently low that the wet-bulb temperature is below 0° C. Recall from pages 65-66 in the WES Textbook that the wet-bulb temperature is the reading obtained through evaporative cooling when water vaporizes from the wetted bulb of a liquid-in-glass thermometer. Some droplets in the fine water spray (emitted by the snow gun) evaporate, tapping latent heat from the air. With sufficient evaporative cooling the air temperature drops to the wet-bulb reading, that is, to freezing or below, and subsequent water droplets freeze to ice crystals.

The significant water demand for snowmaking may impact the local water balance. In Vermont, for example, snowmaking uses about 2 billion gallons of water per year—equivalent to about one-seventh of the volume of the public water supply. To cover an area measuring 500 m by 60 m with 20 cm (8 in.) of artificial snow requires about 2500 cubic meters (658,000 gallons) of water. Streams are the usual source of water for snowmaking but ski areas are typically located high on hill or mountain slopes where stream flow is normally low, especially in winter. In some cases, dams or holding ponds are constructed to ensure an adequate water supply. Diversion of water for snowmaking may cut the supply of water for users downstream. Water that is stored in the winter snowpack on the ski trails runs off to streams during the spring snowmelt, adding to the normally high spring stream discharge and perhaps increasing the potential for downstream flooding.

Concept of the Week: Questions

If the air temperature were above 0° C, artificial snow can be made if the wet-bulb temperature were [(above) (below)] the freezing point of water.
When water droplets evaporate while falling through a layer of relatively dry air, the temperature of the surrounding air [(falls) (rises)].

Historical Events

8 October 1871...Prolonged drought and desiccating winds from the southwest led to the great Chicago fire, the Peshtigo horror, and the Michigan fire holocaust. Fire destroyed more than seventeen thousand buildings killing more than 200 persons in the city of Chicago, while on the same night a fire consumed the town of Peshtigo, WI killing more than 1100 persons. In Wisconsin, a million acres of land were burned, and in Michigan, 2.5 million acres were burned killing 200 persons. "Tornadoes of fire" generated by intense heat caused houses to explode in fire, and burned to death scores of persons seeking refuge in open fields. (David Ludlum) (The Weather Channel)
9 October 1903...New York City was deluged with 11.17 inches of rain in 24 hours at Central Park to establish a state record, while 9.40 inches fell at Battery Park. Severe flooding occurred in the Passaic Valley of New Jersey where more than fifteen inches of rain was reported. (David Ludlum) (The Weather Channel) (Intellicast)
9 October 1967... A cyclone of relatively small dimension with a surface width of only 31 miles, hit India's coast at Orissa and moved to the northeast along the coast for 75 miles. As many as 1000 people and 50,000 head of cattle died. A tidal weave in the storm's wake penetrated 16 miles inland. (Accord Weather Calendar)
10 October 1973...Fifteen to 20 inch rains deluged north central Oklahoma in thirteen hours producing record flooding. Enid was drenched with 15.68 inches of rain from the nearly stationary thunderstorms, which established a state 24 hour rainfall record. Dover, OK reported 125 of 150 homes damaged by flooding. (David Ludlum) (The Weather Channel)
11 October 1846...A very intense hurricane caused great destruction on the Florida Keys. Key West was virtually destroyed with 5 feet of water reported in the city. Fort Taylor was reduced to ruins. (Intellicast)
11 October 1954...A deluge of 6.72 inches of rain in 48 hours flooded the Chicago River, causing ten million dollars damage in the Chicago area. Unofficial reports indicated as much as 12 inches of rain fell. (9th-11th) (David Ludlum) (The Weather Channel)
11-12 October 1995...Heavy rain contributed to flooding along parts of I-75 near Ocala, FL. Five sinkholes up to 10 feet deep and 15 feet wide turned I-75 into a parking lot, as traffic was backed up for more than 5 miles. (Accord Weather Calendar)
12 October 1886...A hurricane made landfall between Sabine Pass, TX and Johnson's Bayou, LA. Tidal waves were said to be as high as 2-story buildings. The surge extended 20 miles inland, with 150 people killed. Survivors clung to trees or floated on mattresses. Two of 100 homes in Sabine Pass were reparable. (Accord Weather Calendar)
14 October 1755...Red dust that was likely transported from the Sahara Desert spread across Europe. Red rain fell at Locarno, Switzerland, while red snow fell on the higher elevations of the Alps. (Accord Weather Calendar)
14 October 1957...Floodwaters roared through a migrant labor camp near the town of Picacho, AZ flooding fifty cabins and a dozen nearby homes. 250 migrant workers lost their shelters. The month was one of the wettest Octobers in Arizona weather history. (The Weather Channel)