River Scientists Offer New Way to Prevent Flooding

150 :26 squish, squish, squish

Nicolas Miller walks down the Ammonoosuc River in Littleton wearing hip-waders and carrying a small computer.

Miller, with Field Geology Services, is digitally mapping the physical features of the river.

152 :49 what are the banks like, are they eroding, are they stable, what are they composed of, how high are they.

As he enters data into the computer, Miller points to the river’s banks.

136 3:10 Along the base there, there used to be some large stone rip rap but it’s kind of failed and been washed away and that bank is still eroding up there.

Rip rap is usually blasted rock that’s dumped on the river’s edge to protect the bank from erosion – particularly during heavy storms.

Miller says the technique has been used for decades…but it doesn’t work.

136 4:28 it’s not a good idea, it’s a very bad idea and the reason is, though that’s the traditional bank protection and armoring technique, it doesn’t do anything to dissipate the erosive force, the energy of the streams.

In fact, Miller says it can make bank erosion worse.

136 5:07 a river wants to erode a little bit everywhere and if it can’t erode because you’ve rip rapped your bank, then all that energy will be taken out as soon as there isn’t rip rap, the downstream end or upstream end, and you’ll take a big bite out of the stream bank.

Miller says rivers want to meander.

But for centuries, man has used rip rap as a technique to straighten rivers.
John Field, with Field Geology Services, says straightened rivers provided a huge convenience in the 1800’s.

2:55 a lot of that straightening was probably associated with log drives, the construction of railroads, the draining of flood plains so they would be appropriate for agriculture etc.

And Field says there’s evidence of river straightening all over New England.

3:37 seven years ago I might not have realized how much the rivers were straightened the more and more I look the more and more obvious it is that almost every river in NH was straightened, I’m to the point now where you have to prove to me the river wasn’t straightened rather than me prove to you that it was straightened.

Field says the focus of river management- even for much of the 20th century - involved straightening rivers, building berms and levees to keep water out of the flood plain.

But Field says a river constrained by structures adjusts by incising, or digging down into the stream bed, and that exacerbates flooding problems.

“13:16 these straightened rivers are steeper, move quicker, so when waters get out of the straightened channel, it gets out of the channel with force, and actually has enough force to carve a new channel or carve a new meander on the flood plain.”

Both Field and Nicolas Miller advocate using fluvial geomorphology, a river science that looks at how water moves earth, to help prevent flooding.

Field says the goal is to allow rivers access to its floodplain, instead of building levees or dams.

25:05 this mentality often referred to as the dyke it, dredge it, dam it mentality of managing rivers that approach..people are beginning to realize the problems with it.

The debate is playing itself out on the Suncook River in Epsom.
During the floods of 2006, the River formed a new channel.

Since then, the river’s path continues to move east, eroding land, threatening roads and homes and sending massive amounts of sediment downstream.

New Hampshire’s Department of Environmental Services wants to use some fluvial geomorphology techniques to stabilize the Suncook River in its current path.

But they’re still looking for federal funds to pay for the project.

At a recent meeting on the issue, downstream resident Tom Beaumeister argued that a dam should be built to put the Suncook back in its original path.

113 2:40 You’ve never ever applied for one penny to put the river back, everything has been concerning leaving through the sandpits in its new channel…is that correct?

Richard Verville with New Hampshire’s Homeland Security and Emergency Management Department answered him.

“There are no federal funds available to put the river back in its original channel, the FEMA grants will not fund any kinds of levees, dams or anything like that…the only thing we can do is dam removals.”

Verville says FEMA wants long-term solutions for flood control.

And it’s beginning to realize large flood control projects like dams can create more problems than they solve.

Verville says a solution using fluvial geomorphology on the Suncook might include removing old railroad beds along the river, to restore existing floodplains.

Of course restoring a river’s flood plain can’t happen everywhere.

(nat sound walking)

Back on the Ammonusuc, Nicolas Miller walks out to the middle of the river, where sediment has created a large sandbar.

138 :45 “Sediment deposition is a natural thing but you can see here it’s just gotten really crazy with the steep bar faces on the downstream end of all these mid-channel bars, and part of the reason for that is the stream can’t access its floodplain, and that’s one of the human-caused problems.

Miller says this is part of the Ammonusuc was straightened.

The data he’s collecting will be used to create so-called fluvial erosion hazard maps.

It will allow communities to know where flooding might occur and where lands could be conserved to allow the river room to flood.