What is a 100 year flood paln and a 500

[Tom]

I am in a 500 year flood paln are what does that mean? I am bordered by a 100 year plan.

Thanks in advance,

Tom

[Mr T]

From my understanding of it, it means that the stats are for that area that it is likley to flood once in every 500 or 100 years. (the 100year is a higher risk). Check for flood insurance requirements in the 100Year zone.

Around here they call it Flood class A, B, C (A means if a dog lifts his leg nearby, you got a flood coming, insurance required. B means Chance of frequent flooding, insurance highly suggested. C means little to no chance of a flood, insurance not needed. ) I live in a Flood class C here.

[Speedy Petey]

We just had the 100 year flood here in the Hudson Valley, NY. Not a fun thing I must say. Damage beyond belief in the flood areas. Places you would never think water would get to got flooded.
Lots and LOTS of folks lost everything due to no flood insurance. Who'd a thought they'd need it. :(

[Mr T]

We recently had some pretty moderate flooding around here. 2 Local towns had to get sand bag birgades going. It was probably the same system that got Speedy's area (was it late janurary/feb?)

I re-read that you border 100Y zones. I would do your homework in the area. It sounds as if you are on higher ground. Got a basement? Does it have a sump pump? GOt a backup plan for if you loose power?

Got a friend in the area, who bought a house about 3 years ago. He looked at a house 2 blocks away, in A class flood zone (insurance required, high chance of flood). His is in C (lowest class, little chance of flood). He has lost power in major storms. One day he spent 30-45 min nonstop running from the basement to outside with buckets of water. The sump hole filled as fast as he could drain it. He has had to rush home in other big storms when the power goes out, or is likley to. He now has 2 sump pumps in the hole, one is a battery backup one (home made with a car battery, power inverter, and a battery charger....(all was sitting around unused)...cheapscape :) )

THe point? Even if you are in a area that wont flood, make sure your prepared. Being near a flood zone may be all you need for flooding. I think flood zones are determined in part by ground level... your basement is 6-8 feet below ground. If you are near a riskier area...your basement may be part of that riskier area.

[Wgoodrich]

You have four classifications.

Floodway being normal flooding when river gets out of banks always floods and is normally a current flood area being on the sides of a river or creek not much higher than normal pool level. This area takes a special permit to build in most often no building is allowed in this area.

Floodway fringe is two of the other classifications

A floodway fringe is 100 year flood. FEMA used the army corp of engineers to survey your area and declare that area likely to flood within 100 years. This an area where you may build but per Federal law requires you to build your home at least with the first floor of the house including basement and garage to be above that flood protection grade [aka datum plain] {aka declared water level elevation the flood can reach in 100 years} This area requires flood insurance per FEMA and most lending institutions.

B floodway fringe is 500 year flood. FEMA declares this in their FEMA maps same as the A zone only in the 500 year flood plain your are not limited in building a home.

C is a non controlled nonflooding area. No concern for building.

Now as for basements you are not allowed to build a basement in a flood controlled area zone A.

The flooding on the surface water usually has little to do with the flooding of basements leaking in through your sump pit. Flooding during or after a storm that flood basements whether along the walls where the walls of a basement meets the floor is called by surface water that has perked through the earth but is trapped subsurface by a clay nonperk type soil. This water is called subsurface water. The amount of subsurface water is dicated that attacks a basement by how deep fast perk soil accepts water then hits nonperk soil creating an underground swimming pool with the water unable to continue perking down. Once this subsurface water hits an underground mass the water still wants to flow somewhere and only choice is horizontally towards your basement walls, perimeter drain etc. Example is say gravel type soil for a 7' deep basement with the gravel reaching 6' deep then a layer of nonperk clay mass stops the downward perk. Gravel soil is a very fast perk soil with the clay same as the concrete bottom of a pool of water. The subsurface water then flows rapidly right at your basement.

If you designed a basment with a perimeter drain that runs two 4" hoses into the sump pit inside your basement you just made a welcome mat inside your basement to flood your basement seeking the same water level as the trapped subsurface water level outside in teh soil.

To solve this flooding of a basement through your perimeter drain you should find a level of land that that perimeter drain can gravity drain to daylight then plug those inlets to your inside sump pump.

Remember a masonry basement is not even required to have a sump pit at all.

If you are lucky enough to have a soil type called a class A subsurface soil you have gravel way deeper than your basement is and the water perks right on by your basement never threatening your basement at all. No perimeter drain is required for a masonry basement at all if with deep class A subsurface soil.

Hope this helps

Wg