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Posted at 10:45 AM ET, 06/ 3/2009

Beaver Dams and the Birth of a Pond

By Kevin Ambrose

* Severe T-Storm Watch & Flash Flood Watch In Effect: Full Forecast *
* NatCast | May Recap | Climate Change Kills 300K? *

A newly formed beaver dam has created a small pond that blocks a hiking trail near Dumfries, Va., May 22, 2009.

I was rather surprised on May 22 to find a small pond blocking a hiking trail near Dumfries, Va., that I've used for many years. It was easy to see that the pond was formed by a beaver dam. I knew the dam was recently formed because the pond wasn't there when I walked the trail earlier in the month. I took a few photos of the dam and filed them on my computer. The following weekend, after two heavy rainfalls (2.43" of rain fell at National Airport) and localized flash flooding, I returned to see if the dam had washed away, grown larger, or was the same size as before.

Keep reading for more photos and to find out how the dam fared...

Despite the heavy rain and flash flooding, the beaver dam grew about 6 inches from May 22 (left) to May 30 (right).

Beaver dams are quite strong and resilient to flooding. If a leak occurs in the dam, the beavers will quickly make a patch and rebuild the compromised section. Over time, the dam is further strengthened by vegetation that becomes rooted in the structure of the dam.

Only after the beavers abandon the pond (or are removed) does a beaver dam usually undergo a major failure or leak. It was interesting to see how the dam had grown about six inches in a week's time, despite two heavy rain events. I plan to return over the summer to chart the progress.

A wide view of the new pond formed by beavers near Dumfries, Va.

The beaver dam, which was built across a large portion of a creek's flood plain.

Many small trees were cut down by the beavers to build the dam. This large tree was likely cut down by the beavers, but was probably too big for them to move to the dam. The beavers may have used some of its branches to help build the dam.

The beaver dam at Dumfries, Va. Video shot on May 30, 2009.

By Kevin Ambrose  | June 3, 2009; 10:45 AM ET
Categories:  Photography  
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As a former wetlands ecologist in NoVa, I came across many beaver dams all across the area. It's amazing how quickly they are built. And, as you suggest, they are dam strong.

I promise you it's not going anywhere unless abandoned for several years or physically removed. Notwithstanding the damage they can cause, beavers are pretty interesting to watch. Be careful if you venture out on the dam, though -- several times I've been soaked by annoyed beavers trying to scare me off by slapping their tails on the water.

Posted by: ParkerGP | June 3, 2009 11:37 AM | Report abuse

A note on beavers...they eat the tender inner bark of trees as well as small branches and leafy twigs. They also use their flat tails to slap on the water, warning neighbors [beavers, that is!] of the presence of predators [humans included!] in the area. They DO NOT use their tails to pat down mud into their dams and lodges, as we sometimes see in the cartoons!

Perhaps many of you remember the family of beavers who moved into the Tidal Basin a few years back. They didn't need to buid a dam but took up residence in prefabricated Tidal Basin digs [at taxpayer expense???]; however their apparent taste for Japanese cuisine got them into trouble when the National Park Service noticed that a few of their recently-planted cherry trees began disappearing overnight. Anyway, the eager beavers soon found themselves trapped and relocated to a suitable habitat in the Catoctins where they have plenty of food, but no more cherry teriyaki, and must construct their own dams and lodges rather than living in Government facilities...Wonder if they were trying to apply for subsidized housing at the National Zoo...

There's a nice beaver colony in the ponds below the Fanconia/Springfield Metro station; you can see the lodges and sometimes evidence that they have harvested the trees that landscapers have planted at the Metro station. Also the Japanese cherries are ripening and, contrary to some posts, the fruits are edible...but they taste rather like a Wisconsin chokecherry. I'm surprised the birds haven't planted Japanese cherries all over the countryside, as they haven't taken over like the highly-invasive "volunteer" Callery pears resulting from the dissemination of fruits from Bradford and other cultivars.

Posted by: Bombo47jea | June 3, 2009 1:02 PM | Report abuse

I live in North Laurel near Hammond Park. There is a small creek that runs through this park and it is quite remote. I walk my dogs along a trail near the creek. There were three different Beaver dams along the creek. my dogs loved to watch the beaver work. One day, the dams were broken and the beaver were gone. So much for enjoying nature. Seems the park service or whoever set their conibear traps and killed all the beavers. Yes there was a struggle by their dens in the creek banks. These dams would create no flooding for they were just the width of the creek, which is about 15 ft wide. I am pissed at the wanton disregard of life and nature. How could i find out who was responsible? Nothing I can really do, I just want a debate with these killers.

Posted by: DIMMY | June 3, 2009 1:14 PM | Report abuse

Interesting report, Kevin. And great choice of music for the video!

Posted by: NoVaSnow | June 3, 2009 1:35 PM | Report abuse

Thanks for posting.

Similar to last Saturday night, I thought we would miss out on rain when I went to bed last night. But there must've been a shower overnight because we picked up a bit of rain.

In other news, we finally ran the air for the first time this year last night. We probably could've gotten by w/o (it was 59.9F this morning), but my wife's allergies have been acting up so I didn't want to open out.

Also, after the winter months, we've started occasionally seeing bears again.

Current conditions: 80.8F, partly sunny
Thunder observed at 3:00 in the Blue Ridge Mtns east of Front Royal.

Posted by: spgass1 | June 3, 2009 3:17 PM | Report abuse

Where in Dumfries is this trail / pond?

Posted by: charlierb3 | June 3, 2009 5:16 PM | Report abuse

About 3 years ago the Park Service moved a section of the Mt. Vernon trail between the airport and Old Town so that it was slightly higher in elevation and less prone to flooding. Since then, it appears the Park Service has allowed the beaver dams under the boardwalk section to remain. I love seeing the beavers out there when I pass by.

Posted by: mmurphy70 | June 3, 2009 6:09 PM | Report abuse

Thanks for the responses. The pond/trail is located near a large subdivision that is just north of Dumfries and east of Rt 1. The trails are fairly rugged and are a bit overgrown with weeds now. There are several older beaver dams in the area.

Posted by: Kevin-CapitalWeatherGang | June 3, 2009 11:08 PM | Report abuse

You know, it's funny: I was driving up Route 7 towards Leesburg last week and I saw TWO beavers near the road. Two. And I'm used to seeing groundhogs, or nutrea, or whatever -- but you can't mistake that tail. They were in very different places (and opposite sides) of Route 7, but I did think to myself suddenly about all the runs, creek, washes, and other small bodies of water that road crosses. And that soon there were going to be some serious dams around Route 7.

Posted by: BadMommy1 | June 4, 2009 7:24 AM | Report abuse

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