This week marks one year since a 500-year flood hit the small town of Alstead.
In one day, the course of the Cold River changed a process that normally would have taken hundreds of years.
The flood also sent homes, cars, debris and contaminants into the river.
New Hampshire Public Radio’s Amy Quinton reports on the environmental changes the flood caused.
Warren Brook Bridge, seen before the floods (top) and after. (Courtesy Mike Heidorn)
"This whole area was just covered 40 feet deep in logs."
Alstead Town Selectman Matt Saxton walks down to Millet Green, remembering in detail what the town’s park looked like one year ago.
This is where crews dumped debris from the Cold River, creating piles almost as high as the trees.
In the following weeks, crews pulled 36-thousand 500 tons of debris out of the river.
"There were 12 houses in the river, there were pieces of 36 houses in the river, and all the cars that went with them, there were two different businesses there’s a used car lot, there was a repair garage up the road that was surrounded by cars, there was a second repair garage surrounded by cars and trucks and all of that ended up in the river."
The waters moved with such force, that it picked up a four-foot tall boulder and moved it at a speed of 25 miles an hour.
Saxton was amazed by how cars were either ripped apart or completely changed by the strength of the water.
"There was one car that particularly fascinated me up there because it was a metal ball and all you could tell was that it contained enough metal to have been a car and that it was red, but it was spherical this car, which I guess had just rolled along the rocks long enough to become spherical."
Gasoline, transmission fluid, oil and sewage from septic tanks created a toxic stench.
But all those contaminants were either cleaned up quickly, or had only a short term effect on the river, says Department of Environmental Services water quality specialist Ted Walsh.
"They flushed down the river, flushed into the Connecticut River and from there moved on, a lot of things like volatile organic compounds, by their very name, they’re volitalized, as they are mixed up into the river they dissipate into the air."
The bigger hit: the transformation of the entire river habitat.
"There was just the absolute devastation of the river system"
Steve Couture is Rivers Coordinator at DES.
He says the flood expanded the channels of the Cold River and nearby Warren Brook, and now their paths are too wide.
Alstead Village Bridge, seen before the floods (top) and after. (Courtesy Mike Heidorn)
Couture says that makes the banks of the river unstable and leads to too much erosion and sediment falling into the river.
"You see examples of that throughout Warren Brook and the Cold where the river is trying to find its balance, where it’s eating away at banks and certain locations where it needs more sediment, so its finding it, then in other areas you’ll see deposition, where it starts to drop it off."
Erosion directly effects water quality.
DES water quality specialist Ted Walsh says the river’s water was in the worst condition right after the flood.
"The Cold River is normally, the water is about as clear as you can get, it’s a very clean river, when we went there right after the flood, the water was completely brown, you could not see the bottom, you saw debris, but mostly it looked like chocolate milk, it was that filled with sediment."
"We try to get it where the water is running" (sound of splash)
Hydro-geologist Mike Heidorn throws a long rope with a bucket attached to it, over the Alstead bridge.
He’s testing a water sample for the Cold River Local Advisory Committee.
Heidorn says while it no longer looks like chocolate milk, every time it rains the turbidity, or murkiness, rises.
He sticks a long tube-like apparatus in the bucket and a computer collects data.
"That’s it, the turbidity is four today, four NTU’s is the scale of measurement, that’s good, that’s relatively low... a couple of days ago it was a 97 because it rained, it wasn’t a heavy rain, it was moderate, so it doesn’t take much to pop it up."
Heidorn says before the flood, the highest turbidity level he ever saw on this stretch of the Cold River was a 10.
When it hits 97, fish and other aquatic life can have a difficult time surviving.
John Magee, Fish Habitat Biologist with DES, says after the flood the fish habitat was wiped out in parts of Warren Brook.
"We went back in late April early March of this year, 2006, and just as an example the area closest to the Cold River in Warren Brook, I think they only caught five fish, and the same area we sampled in July 2005, it was 170 fish, a much larger number like that."
Not only could turbidity have been hurting the fish, but Magee says the trees that once provided a canopy over the river came down during the flood.
Trees play an important role in the ecology of Warren Brook and the Cold River.
"They provide shade, and so cold water species like Slimy Sculpin or Brook Trout they absolutely require cold water, trees provide that shade, the other thing they provide is literally insects falling off of them and into the water..."
Many fish feed on those insects.
DES biologist David Neils says those insects – or macro-invertebrates - also took a hit immediately after the flood.
"You go down below where the major damage was near the confluence with the Cold River you find very few individuals if any at all and a major reduction in diversity of the community, in fact we found three to four different species of aquatic macro-invertebrates there whereas the previous sample that was done in 1999 we found up to about 20 different species."
Trees and other vegetation also act as a filter for storm water runoff.
Nutrient levels, from fertilizers, septic systems, and agricultural runoff, increased after the flood, although that’s now tapered off.
Scientists are seeing other hopeful signs.
In the most recent samplings – biologists found a much larger and more diverse insect population than shortly after the flood.
And where only five fish were spotted after the flood, a year later they’ve found more than 200.
That could be a sign of nature’s resilience.
The Natural Resource Conservation Service has awarded the state 9.8 million dollars to help restore and stabilize the rivers damaged by last year’s floods.
Environmental officials are hoping that effort will help the Cold River recover completely.
For NHPR News, I’m Amy Quinton.
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