 Youngs Branch in Manassas Battlefield on September 6, 2008 |
 Youngs Branch in Manassas Battlefield on September 13, 2008 |
Youngs Branch in Manassas Battlefield on September 6, 2008 |
Youngs Branch in Manassas Battlefield on September 13, 2008 |
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This week, we will explore climate as well as weather. Weather is what you get each day for precipitation and wind and and temperature, while climate is the weather you expect on the average.
If you have lived in Virginia for a year, you already know that we have 4 distinct seasons. August days in Virginia can be - on the average - hot and humid, while January days can be cold and dry. The warmth in the air in early Springtime, and the chill in the air in the Fall, "feel" different from other seasons. That's the climate pattern. However, if you're planning an outdoor event for any particular day in August or January, you'll have to check the weather report within a few days of the event to know the temperature and chance of rain/humidity levels for that one day. The rainfall varies by season. In the summer, we get lots of rain from short, intense thunderstorms. In the winter we get 3-day drizzles and rarely hear thunder. The rain varies by year as well as by season. Some years are wet, some years are dry. In 2002, Virginia experienced a record drought. It was more than just dry - it was record-setting dry. That was followed in 2003 by record high rainfall. |
 Young's Branch on Manassas National Battlefield Park at "bankfull" level, before rising higher and flooding adjacent fields (the "floodplain") in August, 2003 |
In 2003, it rained and rained and rained. Creeks flooded when the volume of water running off the land has exceeded the volume of the normal creek channel. Floods - when the water escapes its normal drainage channels - can cause property damage to facilities built next to the creeks, or threaten lives of people who are in the floodplain.
In August, 2003, several cars were caught in a flash flood at Manassas National Battlefield Park at the Route 29/234 (Stone House) intersection. Drivers had to climb onto the roof of their cars and be rescued from the floodwaters. Normally, Youngs Branch is a minor stream at that location.
In October, 2003, Hurricane Isabel showed that flooding is not the only problem with storms. Tree roots in Virginia's saturated soil could not withstand the long period of strong winds. Massive power outages occured as trees fell on power lines that were not buried underground. In 2004, storms named Gaston and Ivan made September far wetter than average, and created dramatic flooding in some places.
Compare these graphics from the USGS Water Watch - Current water resources conditions (for Virginia):
On September 14, 2002, Virginia reached new low flow levels in rivers across the state, as shown by the red dots on the map below:
Compare 2002 streamflow patterns to 2003:
How Much Is 1 CFS?How many houses can be supplied with 1 cubic foot per second? You can figure this out easily, using your high school math skills. Get a watch, and measure how long it takes you to fill a one-gallon milk jug with water from the sink (or fill a bucket from the hose outside). If your family or housemates are doing a load of wash and taking a shower and flushing the toilet and making breakfast, you could be using as much as 5 gallons/minute in your house. If every drop of Rapidan River water were diverted to the water system, leaving nothing for the fish in the river and letting them die in the sun, then the Rapidan River flowing at 1cfs could supply 450 gallons per minute (7.5 gallons per second x 60 seconds in a minute). If every house was using 5 gallons per minute... how many houses could be supplied by 1 cfs from the Rapidan River? (FYI, there are 11,354 housing units in Orange County. However, most of the houses - separate from the businesses like fast food restaurants - rely upon well water and are not connected to the drinking water system that uses the river water directly.) |
In 2002, Virginia was far drier-than-average. In 2003 and 2004, Virginia was wetter than average... but what's average? Ah, now we're talking climate rather than weather.
