June 27, 2012

Agnes’ historic rainfall taught watershed a concrete lesson

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Aerial view of Riviera Beach in Anne Arundel County. Photo by add1sun

Aerial view of Riviera Beach in Anne Arundel County. Photo by add1sun

By Tom Horton

Bay Journal News Service
You’ll read in various accounts that Tropical Storm Agnes, the great and hurtful deluge that struck Chesapeake Bay 40 years ago in June, was the magnitude of storm that only strikes every two or three centuries on average—maybe even a 500-year storm.

But from the Bay’s standpoint it was arguably unique; nothing else like it in the thousands of years the estuary has existed. To this day, significant parts of the Chesapeake ecosystem have not regained their pre-Agnes health.

Agnes’ winds were nothing much, seldom topping 50 miles an hour after it made Florida landfall on June 20, when it was downgraded from hurricane status.

Historic rainfall, runoff

Agnes was all about historic rainfall, about never-before-recorded runoff, an estimated 25 cubic miles of water dumped in a few summer days into the James, Potomac and Susquehanna River basins. It would have raised the whole Chesapeake 2 feet had there been a dam at its mouth.

The ecological impact of so much water has a lot to do with the watershed it falls on. If there were other Agneses before the historical record began, they fell on a landscape cloaked in deep forest, blanketed with soft, spongy leaf duff, soggy with swamps and the ponded streams of a million beavers.

Agnes fell on a watershed paved and sewered, ditched and drained, fertilized and farmed by 12 million moderns.

Nutrients applied to farmland had doubled and tripled, even since the 1950s, as had concentrations of manure from livestock and poultry.

Sediment, about 20 million tons, trapped for decades by the big Conowingo hydro dam that plugged the Susquehanna in 1928, scoured into the Bay.

Throw in sewage overflows; drums of chemicals washed from as far off as New York state; and farm animal carcasses from West Virginia — the upshot was a massive insult that literally could not have occurred in previous centuries and millennia.

Preceded by dry decades

All of this landscape alteration did not just start in 1972 of course, it had gone on for a long time. But in the decades before Agnes, the consequences of these changes had been minimized because those years had been as extraordinarily dry as Agnes was wet throughout the Bay watershed, minimizing what ran off to the rivers.

From the early 1950s through the early 1970s, only a few years approached average river inflow to the Bay — and several years in the 1960s were so droughty there were fears that the Washington, D.C., region would run out of water to drink.

Agnes, in effect, pulled the trigger on sins that had been abuilding.

Another thing made it uniquely destructive. It happened in June, the only one of the Bay’s historic storms of record to do so. It was a supremely vulnerable time for the Bay’s underwater grasses, then flowering and reproducing. They took a hit from the silt-choked, nutrient-laden water from which they have still not recovered. (This is not just because of Agnes; nutrient and sediment loads remain at unhealthy levels to this day).

Also unable to cope were Bay oysters, which could not keep their shells closed in warm weather to survive the prolonged flows of freshwater that swept most of the way down the Chesapeake.

Historic flooding

Called by federal emergency officials “the most massive flooding in the history of the eastern United States,” Agnes also took a human toll, killing 122.

It destroyed so many homes, bridges and businesses that it remained the most costly storm in U.S. history until Hurricane Andrew battered Florida in 1992.

More than a sixth of downtown Richmond, almost 200 blocks, flooded as the James peaked 70 times above normal flows. Flash flooding drowned 16 along D.C.’s Rock Creek, where flows doubled anything ever recorded. A mother of three toddlers in Baltimore struggled to unbuckle her children from their car seats before the Jones Falls swept her into the limbs of trees downstream and drowned her family.

For a time there were fears that Conowingo Dam might not hold. The dam was evacuated and explosives installed to blow a section if needed. It held, but a crack had opened down one side, shutting U.S. Route 1 across the dam’s top for months while it was re-anchored.

On a personal note, Agnes has been humbling. It was probably the biggest Chesapeake story of my 40-year career, and it happened when I had been reporting for the Baltimore Sun only about six weeks — so green I didn’t even get bylines on my front page stories.

It also reminds us how puny is the human lifespan for understanding the workings of nature. A single event, lasting for days, occurring on the order of centuries — millennia even — may have more impact than everything you might measure during years and decades.

  • Hungrypirana

    Thanks for the story.

    I remember that storm, in the days of just being a kid, listening to Graham Nash, Military Madness and the like.

  • Bob Bauman

    From Bob Bauman JD, former US Representative, 1st District of Maryland:

    Thanks to Tom Horton for an excellent article.
     I had not realized that it was 40 years ago in 1972 that Agnes hit the
    Bay (and killed most of Fletcher Hank’s clams), but I was a State Senator from the five upper Shore counties then and some of my children joined me at Tilghman Island when the Harrison brothers took us on a boat
    tour of the Bay a day or two after Agnes hit.

    I recall seeing
    the Bay looking like a floating, mud colored landfill clogged with ever
    sort of debris from parts of buildings to furniture, trash, trees, logs
    and raw sewage. Most of the junk from New York and Pennsylvania had been
    floated down the Susquehanna on us along with the run off from hundreds
    of thousands of farm acres of fertilizer and topsoil and the salinity
    of the Bay dropped so low that it was thought even the oysters would not
    survive and most of the clams did not. 

    My oldest daughter, Genie, now an attorney in Michigan said: “I
    thought the Bay looked like chocolate milk with junk floating in it-and the
    sky was a weird yellow gray-one my strongest childhood memories.”

    There are many lessons we should have learned from this history.

  • David Eastman

    I remember Agnes well.  I had a first floor apartment in Baltimore and lost everything in the flooding but I fared far better than a lot of other folks. Old town Ellicott City was just about destroyed.  I remember a photo in a Baltimore newspaper of a policeman standing on the roof of his police car with water up to the windows.  I also remember folks with fishing rods trying to hook a London Fog raincoat as the floated down the Jones Falls from the factory that was there at the time.