2019 Mississippi River

[Cajun90]

I'm lucky enough to be in that 20-25 feet number you listed. The roadways might be impassable to the house, but the house should be OK.

What I think I saw in the last flooding event in the Youngsville area was related to all the new subdivisions disrupting the previous slopes that led to the drainage systems in place. Could I maybe be right on that?

Much of the development has done a pretty good job of accounting for retention ponds etc. but that is a small part of the issue. A lot of the primary drainage channels haven't been adequately maintained which is a bigger problem. Climate change is another concern. Manmade or not there is plenty of evidence for changes in our recorded history to know that extreme events are on the rise and exceed the design standards that are probably 30-50 years old at this point.

I really believe it is time to change how we (U.S. government) publish data regarding flood risk. With computer based systems in place this should not be that difficult of a task.

[zephyr]

In another thread the talk of flood insurance came up and thought I would post a few things here.

The majority of homes flooded in the U.S. are NOT in a 100 yr. flood plain. It is important to understand your risk. Unfortunately realtors, builders, and our government aren't very good at doing this. They simple tell you.... "you aren't in a flood zone and don't have to have flood insurance". The truth is much more complicated. IF your property is a foot above base flood elevation then hey your good right? Not exactly; and a lot of property in the Lafayette area is like that. Many developers built up their property to that height. It is like walking a tight rope.

Bottom line is look up the flood maps online and see what your TRUE risk is for flooding. If you are one of those who isn't far above the base flood you should be concerned. IF you are say 20-25 feet above base flood then maybe your risk isn't that big of a deal. With that said flood insurance for most people outside of the 100 yr. plan isn't very expensive.

The problem is that we are in South Louisiana and even for properties not in a flood zone, we are close to the BFE. I've never seen a property here that is 20-25 above the BFE. There's risk in anything we do here. The simple fact is that you can't predict catastrophic storms and where their reach will go. You can monitor things like development trends and see what their impact on your property could be like. Cue Youngsville and the impact that years of development had on old farm land that was not homesites.

[CajunAmos]

The problem is that we are in South Louisiana and even for properties not in a flood zone, we are close to the BFE. I've never seen a property here that is 20-25 above the BFE. There's risk in anything we do here. The simple fact is that you can't predict catastrophic storms and where their reach will go. You can monitor things like development trends and see what their impact on your property could be like. Cue Youngsville and the impact that years of development had on old farm land that was not homesites.

The map says I'm 22-1/2' in between Youngsville & Milton.

[zephyr]

The map says I'm 22-1/2' in between Youngsville & Milton.

what is your ground elevation?

[BananaHammock]

I think they need to understand the significance of salt water intrusion up the Mississippi River up to Baton rouge (Possibly). This should not be underestimated as the amount of coastal erosion would be extreme. The salt water would kill all, what is now, native vegetation and result in bare soil that would easily erode. Also, the cities that rely on the Mississippi for drinking water would have to modify their water treatment plants to remove salt from the water.

But couldn't they let the river take over the Atchafalaya and do diversion projects towards Baton Rouge and NOLA? I understand the significance of impact the river change would have to BR and NOLA but how long can we go without planning for the inevitable?

[HelmutVII]

All properties in the US are in a flood zone. The difference is if you are in a regulated or unregulated flood zone. A regulated flood zone is either Zone AE (studied flood zone) or Zone A Unstudied flood zone. The difference being Zone AE has been modeled and Zone A has not been modeled. The BFE is published on the flood maps and the Flood Insurance Study in Zone AE while the BFE in Zone A is community determined. There are instances where the model does not pick up local inconsistencies in the ground elevation that puts it above the computed BFE. FEMA recognizes this issue and that is why it is best to have a Flood Elevation Certificate when you are located in Zone A or AE. While it is probably wise to have Flood insurance in many cases In my case the BFE on the Vermilion River nearest my home is 15. The BFE on the St. John Coulee is 25 while my lot is at elevation 38 and the floor is at 40.5. I am not buying flood insurance. If my home floods flooding is not my problem, staying alive is what I need to worry about.

IF I lived an an area south and west of Ambassador Caffery Parkway I would have flood insurance for sure. Scott is not too good either. Once you get west of Scott the land gets flat as a pancake and the drainage basins tend to communicate with each other during high rainfall events.

If you are looking at a piece of property and you see crawfish chimneys on the lot I would avoid it. That crawfish (first cousin to a roach) is trying to tell you something. You just need to be smart enough to understand what they are saying.

[ZoomZoom]

All properties in the US are in a flood zone. The difference is if you are in a regulated or unregulated flood zone. A regulated flood zone is either Zone AE (studied flood zone) or Zone A Unstudied flood zone. The difference being Zone AE has been modeled and Zone A has not been modeled. The BFE is published on the flood maps and the Flood Insurance Study in Zone AE while the BFE in Zone A is community determined. There are instances where the model does not pick up local inconsistencies in the ground elevation that puts it above the computed BFE. FEMA recognizes this issue and that is why it is best to have a Flood Elevation Certificate when you are located in Zone A or AE. While it is probably wise to have Flood insurance in many cases In my case the BFE on the Vermilion River nearest my home is 15. The BFE on the St. John Coulee is 25 while my lot is at elevation 38 and the floor is at 40.5. I am not buying flood insurance. If my home floods flooding is not my problem, staying alive is what I need to worry about.

IF I lived an an area south and west of Ambassador Caffery Parkway I would have flood insurance for sure. Scott is not too good either. Once you get west of Scott the land gets flat as a pancake and the drainage basins tend to communicate with each other during high rainfall events.

If you are looking at a piece of property and you see crawfish chimneys on the lot I would avoid it. That crawfish (first cousin to a roach) is trying to tell you something. You just need to be smart enough to understand what they are saying.

Been hoping you’d post something like this. Thanks.

[HelmutVII]

Much of the development has done a pretty good job of accounting for retention ponds etc. but that is a small part of the issue. A lot of the primary drainage channels haven't been adequately maintained which is a bigger problem. Climate change is another concern. Manmade or not there is plenty of evidence for changes in our recorded history to know that extreme events are on the rise and exceed the design standards that are probably 30-50 years old at this point.

I really believe it is time to change how we (U.S. government) publish data regarding flood risk. With computer based systems in place this should not be that difficult of a task.

Retention ponds are typically designed on a 10 or 25 year event. Flood zones are 100 year events. Most ponds I design are innundated in a 100 year model. As return periods jump from 25 to 100 year events the rainfall rates reduce but the ground conditions change because there is more water on the ground. One inch of rain falling on land is different than one inch of rain falling on water (runoff rates for water is 100%). While retention ponds are very effective for more frequent events, they are basically useless for 100 year events.

[Cajun90]

The problem is that we are in South Louisiana and even for properties not in a flood zone, we are close to the BFE. I've never seen a property here that is 20-25 above the BFE. There's risk in anything we do here. The simple fact is that you can't predict catastrophic storms and where their reach will go. You can monitor things like development trends and see what their impact on your property could be like. Cue Youngsville and the impact that years of development had on old farm land that was not homesites.

You are missing the point. There is significant difference in elevation in Lafayette parish when it comes to flooding concerns. Flood maps have historically done a very poor job of showing this.

The August 2016 storm is a prime example. Being one foot above BFE versus three feet above BFE could easily have been the difference in flooding or not flooding your home. For most people it is very difficult for them to fully understand that risk. All they are told is that "they don't have to have flood insurance" because they aren't in a special risk area.

And yes there is certainly property in South La. at 20-25 feet above BFE but that is an outlier. More important is for those that are right at that 1 ft. BFE and have this false sense of security.

[HelmutVII]

Go here if you want to get information on your property

http://maps.lsuagcenter.com/floodmaps/

(I know its LSU but it is what it is)

Click continue, select your parish, click continue and zoom into your location. If you know your lat/long then enter that.

Once you get to your location then click little ID icon and click on the map. It will give you the information for that location and an estimated ground elevation

ELEVATIONS ARE FEET AND TENTHS NOT FEET AND INCHES!!!!!!


If you live in Lafayette Parish

Go here

https://lcg.maps.arcgis.com/apps/web...360876caec2046

Enter your address and it should zoom to the location. New flood maps were adopted in December of 2018.


AGAIN ELEVATIONS ARE FEET AND TENTHS NOT FEET AND INCHES!!!!!!

[Cajun90]

Retention ponds are typically designed on a 10 or 25 year event. Flood zones are 100 year events. Most ponds I design are innundated in a 100 year model. As return periods jump from 25 to 100 year events the rainfall rates reduce but the ground conditions change because there is more water on the ground. One inch of rain falling on land is different than one inch of rain falling on water (runoff rates for water is 100%). While retention ponds are very effective for more frequent events, they are basically useless for 100 year events.

Agreed. Was trying to give a quick answer to the question about "slope". My point being that individual developments have gotten better about not contributing to the issue of adding to offsite flooding. Still could be improved but there are larger concerns. Some we can control and some we cannot.

It is interesting how water rules the world to a large extent. Some, such as us, often have too much while others have too little. Out West there have been discussions on the legality of rain collection systems on private property. The argument being that they are capturing a "public" water source for private usage.

Many don't understand the political power of water around the world either. In many countries those that control the water have the power. Especially if we are talking clean drinking water. Water is one of the biggest weapons utilized in third world countries.

[HelmutVII]

Agreed. Was trying to give a quick answer to the question about "slope". My point being that individual developments have gotten better about not contributing to the issue of adding to offsite flooding. Still could be improved but there are larger concerns. Some we can control and some we cannot.

It is interesting how water rules the world to a large extent. Some, such as us, often have too much while others have too little. Out West there have been discussions on the legality of rain collection systems on private property. The argument being that they are capturing a "public" water source for private usage.

Many don't understand the political power of water around the world either. In many countries those that control the water have the power. Especially if we are talking clean drinking water. Water is one of the biggest weapons utilized in third world countries.

The number one characteristic of a developed nation is the adequate supply of safe drinking water. The number two characteristic of a developed country is the adequate collection and treatment of waste water. The number one vector for disease is contaminated water. Go to a third world country and what is the first thing you smell?......... Sewage.

[HelmutVII]

Oh yeah I forgot, If you live in a parish or county that is adjacent to the Gulf of Mexico, I would buy flood insurance. Almost every drainage channel adjacent to the gulf is influenced by tides. If it is influenced by tides then it is probably subject to storm surge. Even some portions of extreme south Lafayette Parish could be subject to storm surge.

[zephyr]

You are missing the point. There is significant difference in elevation in Lafayette parish when it comes to flooding concerns. Flood maps have historically done a very poor job of showing this.

The August 2016 storm is a prime example. Being one foot above BFE versus three feet above BFE could easily have been the difference in flooding or not flooding your home. For most people it is very difficult for them to fully understand that risk. All they are told is that "they don't have to have flood insurance" because they aren't in a special risk area.

And yes there is certainly property in South La. at 20-25 feet above BFE but that is an outlier. More important is for those that are right at that 1 ft. BFE and have this false sense of security.

I will certainly have to ask Helmut for that info on being 20-25 feet above BFE. Like he mentioned, BFE is identified in areas of higher risk such as Flood Zone A & AE. BFE's change throughout the floodplain. It just seems odd to be in a flood plain to all of a sudden 25 feet above it. If you go to the LSUagcenter website and look at the floodplain, there are different BFE's throughout depending on the topography.

Also, in times of flooding I've seen properties identified as being in Flood Zone X to have flooded and properties in Flood Zone A not getting anything. I agree with you that flood insurance coverage should not be determined by a line on a map as I think you are suggesting because of these differences and the maps were never perfect to say the least.

[CajunVic]

I will certainly have to ask Helmut for that info on being 20-25 feet above BFE. Like he mentioned, BFE is identified in areas of higher risk such as Flood Zone A & AE. BFE's change throughout the floodplain. It just seems odd to be in a flood plain to all of a sudden 25 feet above it. If you go to the LSUagcenter website and look at the floodplain, there are different BFE's throughout depending on the topography.

Also, in times of flooding I've seen properties identified as being in Flood Zone X to have flooded and properties in Flood Zone A not getting anything. I agree with you that flood insurance coverage should not be determined by a line on a map as I think you are suggesting because of these differences and the maps were never perfect to say the least.

This is pretty Phucing funny.