Wet year an `extraordinary' turnaround

Dampest year since 1972 contrasts with '02 drought

October 08, 2003|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

After the deluge come the statistics.

The U.S. Geological Survey says the past 12 months added up to one of the wettest "water years" on record in the Chesapeake Bay region, with a higher flow of fresh water into the bay than in any year since 1972, when Tropical Storm Agnes nearly drowned the place.

It was the second-highest flow to the bay in any year since record-keeping began in 1937.

Heavy snow last winter, persistent rain throughout the past 12 months and Tropical Storm Isabel have also contributed to high stream flows, widespread flooding and the highest groundwater levels in 40 years. And all of it has come on the heels of a historic drought that produced some of the lowest groundwater levels ever recorded in the area.

"This is the first time we've seen this radical a change; it's fairly extraordinary," said Gary Fisher, surface water specialist at the U.S. Geological Survey office in Baltimore.

USGS begins its official "water year" in October, when stream flow and groundwater levels are normally at their lowest, and it runs through September. Recharging of streams and water tables usually occurs during the fall and winter as the demand for water by people and plants declines.

From October last year through September of this year, more than 62 inches of rain fell at Baltimore-Washington International Airport -- almost 20 inches more than normal for the period.

The mean monthly flow of fresh water into the Chesapeake averaged 76.2 billion gallons per day (bgd). That is the most since 1972, the year that saw Tropical Storm Agnes dump as much as 9 inches of rain in the region, helping drive the average flow into the bay that year to a record 78.1 bgd.

The average annual flow is 50.8 bgd.

In the water year ending in September last year, a yearlong drought dropped flows into the Chesapeake to a scant 28.6 bgd. The volumes were below average in every month except May. Near-record lows were reached that August and September.

In the far-wetter year just ended, flows were above average in every month except two, and near-record highs were reached in June through September.

"I think it's important not to read too much into this," Fisher said. "It's just the random nature of the weather. With more analysis, people may look at climate change and there may be more to it. But we just don't know that yet."

All stream-flow and ground-water levels monitored by the USGS in Maryland and Delaware at the end of September were above normal. Three Maryland streams -- the Youghiogheny, Choptank and Pocomoke -- reached record highs for the month.

Flooding was recorded on the Potomac, which experienced 10 times its normal flows for September. The averaged mean monthly flows for the 2003 water year were the second-highest since records began in 1930.

Five monitored ground-water wells in Maryland and Delaware were at the highest levels seen in the past 40 Septembers. Three were at their highest levels ever. Last month also saw four times the normal volume of water rushing into the bay, the third-highest volume on record for the month, the USGS reported.

And as if the fresh water racing into the bay weren't enough, on Sept. 18 and 19, Tropical Storm Isabel shoved a record storm surge into nontidal sections of many tributaries and up onto the low-lying shores.

The surge arrived first at the mouth of the Chesapeake, lifting tides there more than 6 feet above sea level at 2:24 p.m. Sept. 18. Eighteen hours later, the surge reached Fort McHenry, peaking at 7.36 feet above sea level, according to tidal gauges monitored by the USGS and the National Oceanic and Atmospheric Administration.

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