Spring Flooding Potential

[Blue Thunder]

I wanted to start this thread so our resident prognosticators could weigh in the the overwhelming potential that must be there with such a large and deep snowpack not just in New Hampshire but all of western and northern Maine. How can this widespread deep snowpack possibly melt with out serious flooding? CLA, B2B, Rose?

Blue Thunder

[trfour]

and mild days, Not Hot, and cold nights, and all of the dam operators.

[SIKSUKR]

We'll have a good start with todays warm temps and tonites heavy rain.I'm a little worried were going to get too much rain in this one event.Should be lots of street ponding tonite and tommorrow.

[Lakegeezer]

I heard from an excavator that the ground (where unpacked) is already pretty much thawed. Lots of the melt-water should be absorbed, as long as it doesn't melt too fast. Its going to be an interesting spring.

[wifi]

I would think the septic tank pumping business will be quite busy, until the land dries out some.

[Resident 2B]

BT,

Great idea with this thread.

After clearing snow and ice from our roof and decks yesterday, I can say there is a lot of water being held in the snow pack around the lake. CLA has some solid data in another thread that more accurately states the situation with the snowpack. It is very wet, especially at the bottom.

Personally, I have huge concerns about the flood potential this spring. This applies to rivers and to lakes. I am not well versed in hydrology, but I know this water heavy snow plus any additional precip we get in the next month or so has to get into the lakes and rivers and find its way to the sea. As BT said, the heavy snowpack is everywhere in our region, it increases dramatically from the Mass/NH boarder northward.

Here is a link to the NOAA AHPS web site where you can monitor rivier and lake levels and river flows: http://newweb.erh.noaa.gov/ahps2/index.php?wfo=gyx

We need warm days that can melt the snow, cool nights that can slow down the melt and most of all dry weather for the next month. We are warming up, but I continue to see wetter weather in our future. It it gets warm too soon, or if it stays cold too long, we are in big trouble. If it all melts in a ten day period with rain, it will be something to remember.

I have the highest regard for the folks at the dam. They may not be able to say much about the situation officially, but it would be great to hear from them about what they are thinking.

FEMA has advised for all residents to purchase flood insurance now. It takes 30 days for it to become effective, so if you buy it today, it becomes effective April 3rd. We have our flood insurance, purchased two years ago, and it helps us sleep at night in the spring.

Let us all hope for an orderly melt!

R2B

[CanisLupusArctos]

While we are all in the middle of roof-shoveling concerns, there is another thing that many of us *need* to take care of right away, and that is flood insurance.

Like R2B I'm not well-versed in hydrology but I did have some of it in college and what's happening around the lakes and White Mountains now reminds me of the stuff that was in our textbooks.

At this point I will say 'never mind science; common sense rules'. Imagine this question on an exam: We have a snowpack of historic size and water content, and spring is just around the corner--What is most likely to happen next?

I say 'most likely' because the weather has been doing crazy things lately and so it's not totally out of the question that we could suddenly have a drought, but that's not something I'm betting on.

Here are some things to consider as we transition into spring from where we are right now:

1) According to an article in yesterday's Union Leader, the Army Corps of Engineers and NH-DES just measured the amount of water in our existing snowcover and found it to be at 250% (Two hundred fifty percent) of normal. This was evident yesterday as my family and I shoveled off the 3 feet of snow from the roof, and the resulting enormous pile allowed me to walk right up to the top of it without packing it down first. Very, very dense snow chock-full of water.

2) While I'm not surprised that Lakegeezer's excavator friend says the ground is thawing (it never had a chance to freeze before the big white blanket came and stopped the process) the ground is *not* accessible to water right now. The bottom layer of our snowpack (which fell in December) has long ago turned to ice. In order to accurately measure the snow depth yesterday (42 inches) I used a san angelo bar (normally used for prying big rocks.) The pointed end went through the ice layer and found the ground... but when water hits this layer it *can't* get through to the ground. So it runs off. That's why your roof's snow load gets heavier with each storm: Meltwater and rainwater are not able to drain like water usually does from a roof. The same thing is happening on the ground.

3) By my estimate, The lakes region has enough saturated snow in its immediate vicinity to put the lake at or slightly above full.

4) The rivers are pre-loaded downstream of the lakes region... In a flood situation that means a dam operator can't allow 100% flow without causing a flood downstream or making an existing flood worse. Usually there are more people living downstream, so protecting them takes first priority. Concord's snowpack is just as deep as the lakes region's, and that will be feeding the Merrimack which originates in the lakes region. The rivers to the southeast of the lake (Alton to Portsmouth) will likely be overloaded with snow melt from central Maine (Fryeburg-eastward) where the snow depth is the greatest in all New England. Massachusetts hasn't had epic snow this winter but they've still had above-normal snow, and a flood watch is now in effect for the Boston area because of the 50-degree temps and rain expected there today and tonight.

5) The rivers are pre-loaded from upstream, too. In the last couple days I had an eye-opening experience when I checked the snow conditions from the AMC huts. Most are reporting snow depths between 50 and 60 inches. Hermit Lake Shelter in Tuckerman Ravine has 85 inches (There's a LOT more in the bowl itself... probably in excess of 100 feet) and the USFS Snow Rangers reported that "Every slope" avalanched on its own. They reported that there are now many places avalanching that don't normally avalanche, because snowfields have grown in size and have completely covered the usual holds (like trees.) Two of my climber-friends came back from a hike up Mt. Moosilauke (Franconia area) this weekend and reported the trail signs to be "at foot level" due to the deep snow. That area drains into the Pemigewassett and Connecticut Rivers. When this melts, it has to find the ocean.

6) Development around New England has grown a lot since the last time we had this much snow/water content on the ground in spring. The equation is simple: Paved ground doesn't absorb water, grass lawns don't absorb water like forest does, and foundations block the underground flow of water when they're located where they shouldn't be. Over the years many laws have been designed to protect the natural flow of water (and us, in turn) but the laws were never perfect and in some cases have been totally ineffective. Conclusion: New England's drainage isn't as good as it was the last time we had this much of a spring flood potential. Will this be the year that tests it all? No one can say for sure.

It's possible that some fluke of nature could render this discussion pointless, but it's probably better to get flood insurance now. If you live in a flood-prone area, it might be good to start preparing. Visit http://www.floodsmart.gov for details.

What happens next? Keep watching out the window and have your camera ready just in case.

[SIKSUKR]

I am monitoring the river levels very nervously right now having been flooded by 100 year floods on the Merrimack the last two years.I have a mill building right on the river in Downtown Manchester and suffered heavy losses 2 years ago.This could be the 3rd 100 year flood in 3 years.Even with all the upstream flood control work done by the Army Corps of Engineers in the 1940's it was not enough to save property that has been existing since the 1800's.I have a friend still rebuilding his house from last years flood.There is potential for another catstrophic flood in this area.
Here is the National Weather Service hydraulic site I use for the Merrimack.It shows levels and trends.It forecasts my river to rise 1 1/2feet in 2 days.Other stations can be found on this site.Cross your fingers.
http://newweb.erh.noaa.gov/ahps2/hyd...ew=1,1,1,1,1,1

[Seaplane Pilot]

In anticipation of tonight's impending rain/ice storm, the New Hampshire Division of Economic Development and New Hampshire Homeland Security and Emergency Management have joined forces to release the following message:


To All New Hampshire Commercial Building Owners and Property Managers:
New Hampshire has experienced near-record breaking snowfall this winter and as we move into spring, the accumulated snow and ice on building roofs is causing serious safety hazards in most regions of the state.

If you own or manage a commercial building, you should immediately assess the snow load on your roof and examine the building for signs of structural stress. You may wish to seek the advice of a professional engineer and should consider having snow and ice removed. Also, ensure that roof drains are cleared to allow for the drainage of water. Snow removed from roofs should not be allowed to block building fire exits.

Numerous building collapses have already been reported in the state due to the weight of accumulated snow and ice. That problem will be compounded by heavy rain and freezing rain that is predicted to move into the state beginning tonight (Tuesday).

Building owners and property managers with questions on snow loading issues should call their local code enforcement officer, fire department, a structural engineer or the state fire marshal's office (271-3294). If a building appears to be in imminent danger of collapse, evacuate the building and call 911.

Please note additional information provided by the Concord Fire Department at this link. You might also want to view a report compiled by the U.S. Army Corps of Engineers Cold Regions Research Laboratory in Hanover at the following web address: http://www.senh.org/committee%20reports/tr02-6.pdf.

Sincerely,

Christopher M. Pope, Director Michael Vlacich, Director
NH Homeland Security NH Division of Economic Development
and Emergency Management

[xltRod]

Originally Posted by SIKSUKR

I am monitoring the river levels very nervously right now having been flooded by 100 year floods on the Merrimack the last two years.I have a mill building right on the river in Downtown Manchester and suffered heavy losses 2 years ago.This could be the 3rd 100 year flood in 3 years.Even with all the upstream flood control work done by the Army Corps of Engineers in the 1940's it was not enough to save property that has been existing since the 1800's.I have a friend still rebuilding his house from last years flood.There is potential for another catstrophic flood in this area.
Here is the National Weather Service hydraulic site I use for the Merrimack.It shows levels and trends.It forecasts my river to rise 1 1/2feet in 2 days.Other stations can be found on this site.Cross your fingers.
http://newweb.erh.noaa.gov/ahps2/hyd...ew=1,1,1,1,1,1

I'm no expert, but I'd be buying boots. Not to make lite of your situation, I think the tide will be up over what is normal.

[CanisLupusArctos]

Originally Posted by Seaplane Pilot

.

If you own or manage a commercial building, you should immediately assess the snow load on your roof and examine the building for signs of structural stress. You may wish to seek the advice of a professional engineer and should consider having snow and ice removed. Also, ensure that roof drains are cleared to allow for the drainage of water. Snow removed from roofs should not be allowed to block building fire exits.


Sincerely,

Christopher M. Pope, Director Michael Vlacich, Director
NH Homeland Security NH Division of Economic Development
and Emergency Management

Ensure that roof drains are clear?

This is more like it: First find the locations of the roof drains. Then chip through the ice at the bottom of the snow load, in order to access the drains. Then make sure the drains aren't jam-clogged with ice.

Yesterday when we cleared the snow off a 20 x 20' section of relatively flat roof on the house, it took us 2 hours. The roof rake almost wasn't strong enough to cut it. The first few inches scraped right off, and then we were down to lower layers gradually more solid as we worked our way down past Indian arrowheads... a woolly mammoth or two... then dinosaur bones... and finally fossils of early life...

[Weirs guy]

Originally Posted by CanisLupusArctos

Ensure that roof drains are clear?

I enjoyed that part too. Shouldn't be too hard to tell a frozen over roof drain from a frozen over everything else.

[CanisLupusArctos]

According to WCSH-TV 6 in Portland, Maine just conducted a survey of the water content in its snowpack and not surprisingly determined it's way above normal. Emergency management officials there are comparing western Maine's current flood potential to that which existed prior to the 1987 floods there.

Some of western Maine's water ends up in the river system that runs along the Maine/NH border and flows through Milton, Rochester and Dover. The southeast outflow of Lake Winnipesaukee at Alton also heads in that direction.

Snow depth in the Fryeburg/North Conway area is among the greatest in New England, as shown by NOAA/NERFC imagery.

[mcdude]

Originally Posted by CanisLupusArctos

The southeast outflow of Lake Winnipesaukee at Alton also heads in that direction.

The Cocheco River flows in a southeasterly direction through New Durham, Farmington etc. but does not "drain" the big lake. Alton Bay (formerly known as Merrymeeting Bay) receives an inflow from the Merrymeeting Marsh and Merrymeeting Lake.

[SIKSUKR]

Originally Posted by CanisLupusArctos

The southeast outflow of Lake Winnipesaukee at Alton also heads in that direction.
.

There is no outflow at Alton.The only outflow of Winni is at Lakeport and that flows into the Merrimack for it's final journey to the sea.

[CanisLupusArctos]

Oops.

I didn't mean to imply that the rivers SE of Alton help drain the lake. I was trying to make a point I obviously didn't word correctly and now 24 hours later I can't remember what it was. Must remember to sleep more and multi-task less!

I got the whole process backwards, though. Upon checking around I learned the Merrymeeting River actually flows into Lake Winnipesaukee. Sorry 'bout that.

[mcdude]

Actually it is theorized that many moons ago, Winnipesaukee's outlet was at the southestern end, being drained by the "mcdude" river

See THIS THREAD for a map and more info.

[KBoater]

And here I thought it was the McDude River.

[Weirs guy]

Originally Posted by SIKSUKR

There is no outflow at Alton.The only outflow of Winni is at Lakeport and that flows into the Merrimack for it's final journey to the sea.

And just wait till you see how much we've got ready to send you soon SIKSUKR! My sympathies in advance. I thank God I'm uphill from the lake, but I'd still be willing to bet my basement gets wet.

[SIKSUKR]

Your sending me water?Gee thanks Weirs guy.Actually I'll be sending myself plenty from my place in Franconia.The Merrimack actually starts at Cannon,though under a different name.

[CanisLupusArctos]

To provide an idea of what will be flowing downstream in the coming weeks, here are snow depths as reported by the Appalachian Mountain Club today:

Tuckerman Ravine (Hermit Lake Shelter/Mount Washington): 76 inches

Lonesome Lake (Franconia area): 71 inches

Zealand Falls Hut (Crawford Notch area): 58 inches

Carter Notch Hut (Pinkham Notch area): 55 inches

Highland Center Lodge (Crawford Notch/Rt 302): 37.5 inches

Cardigan Lodge (Bristol area): 32 inches

This information is updated once daily at http://www.outdoors.org/recreation/t...ry-weather.cfm

[SIKSUKR]

Good info CLA With the exception of Lonesome lake and Cardigan lodge which will flow down the Merrimack,the other meltwater will end up headed towards Maine via the Saco or Androscoggin.

[CanisLupusArctos]

Originally Posted by SIKSUKR

Good info CLA With the exception of Lonesome lake and Cardigan lodge which will flow down the Merrimack,the other meltwater will end up headed towards Maine via the Saco or Androscoggin.

I didn't say where they would flow... only their general location, for those who aren't familiar with stuff that can't be seen from the road.

The idea is to provide those living 'further south' an idea of what's coming from 'up north'. I realized this need twice in the past week when I attended an event in the Portsmouth area and saw some friends from Northeastern MA before that. They were generally unaware of the flood threat, and those who were aware think we've already dodged the threat because the snow outside their houses isn't really there anymore. They were very surprised when I told them what's up north.

[Weirs guy]

Originally Posted by SIKSUKR

Your sending me water?Gee thanks Weirs guy.Actually I'll be sending myself plenty from my place in Franconia.The Merrimack actually starts at Cannon,though under a different name.

Ah yes, the Pemi I presume? It meets up with the Winnipesaukee river behind my old high school in Franklin. Thats always been Franklins claim to fame.

And yes, thats its only claim to fame.