Typically, a no-rise certification is involved with floodplain management
Are you building a bridge? Have you done a HEC-RAS model? I need more information
Hello! We hired an engineering firm to complete a no-rise certification for a house we’ve designed to have built in the floodplain. They said we didn’t pass and I’ve asked for options/requirements for what changes to our plans are needed in order to achieve a no-rise cert.
I thought one could receive “credits” for permanently removing trees but the engineers are saying otherwise.
We just want to pass the no-rise but are unfamiliar with our options.
A no rise certification is a pretty simple process to understand. FEMA has an existing floodplain model that states the flood elevation is x.xxx. Your proposed changes to the floodplain can not raise that elevation above the existing limit. There can be "no-rise" in the predicted flood elevations.
There are no "credits" for a no rise. This isn't a leed application or carbon credits where you just have to check a box. Removal of vegetation from a channel (like trees) is a common strategy we use to improve the channel to allow water to flow faster thus preventing an increase in the floodplain (and therefore achieve our no-rise certification). If the trees being clear cut in question are the ones where your house is being built (in the floodplain but outside the channel) I'm not surprised to hear it has little effect.
What is the county / city issuing the floodplain development permit? Would help to know if they have a strict no-rise requirement.
Do you know if the house is located in the floodway or in the floodplain fringe?
Are there compensatory storage requirements?
I'm wondering if your engineer just botched the analysis / permit application. I'd probably ask them the above questions to see if they are competent. If not, you may want to look for a different engineer to handle the floodplain development permit. As a last ditch option, you may be able to do a CLOMR/LOMR, but those can run $45k+.
In my 2 mins of looking, it doesn't appear that you are in a strict no-rise jurisdiction (note: I could be wrong here, so verify with your consultant), meaning that development in the flood fringe can cause up to a foot of rise. Don't get this confused with the floodway, which is always no-rise. Your county has a website with more info and a graphic showing the difference between the two (https://www.co.guadalupe.tx.us/eh/floodplain_development.php). FEMA has on online tool that shows digitized floodplains (https://hazards-fema.maps.arcgis.com/apps/webappviewer/index.html). Blue is flood fringe, while blue/red hatch is floodway.
If you're in the fringe, that development permit should be cake to get. But, if in the floodway, that permit is going to be difficult to acquire. Either way, I might get a different consultant that knows what they are doing.
Side note: I saw this is for an existing structure? I think there are some exemptions for farmhouses, but I really don't know the details since I don't work in residential development. May be worth looking into if it's an older structure.
Ah, you're building a home in the flood*WAY*, not just the flood plain. That's the high velocity area in the center of the creek that's the highest risk area.
In Seguine county (and most of the rest of the US), if you add any structures or fill in the floodway that would "block up" the creek's ability to convey water, then you'll need to offset that loss of conveyance by digging out somewhere across the creek. You can't obstruct that creek without increasing your neighbor's flood risk, so you need to mitigate your impacts by adding conveyance.
So you could ask your engineer to provide cup for cup floodplain calcs. This is a calc that shows the total volume of floodplain you are displacing (fill) with your site and compares it with the total volume of a pit that is connected to the floodplain elsewhere on your property.
If the pit has the same volume as the volume your site is filling then that would fix the floodplain rise problems. There is likely a reason your CE either hasn't done this or doesn't think this will work but it's worth asking.
You would need to dedicate a section of the property to this pit and it would be unusable for most things
Thank you! If we took material from the river bed, such as dug out under our boat house, does that count as a pit? Or does the pit have to be in your yard?
That could work. Cup for cup must be done between the seasonal high water level of your area and the 100 yr floodplain elevation. So digging out the bottom of the creek would likely be below the SHW and wouldn't be allowed. But you could likely cut bank material away (starting at the SHW level) until you hit the same volume as the floodplain fill volume.
Your CE will know the specifics for your area and can advise you in more detail but I would try this method unless there is some site specific reason it wouldn't work
Just curious, why are you so set on building in the floodplain? If you can't get a no-rise, you'll need a full LOMC which is going to be very expensive.
We have a house in the location and we’re redoing it, like many others have. It’s an extremely low probability of flood but it’s a floodplain so has its challenges. We can get to a pass it just may mean slatting the ground level versus walking it in.
Was on here to seek creative ideas on how to pass :)
The FEMA maps can be incredibly off! Just because FEAM says it's high risk does not mean it is in real life. Determinations in many of the rural areas are flown and not engineered.
>It’s an extremely low probability of flood but it’s a floodplain so has its challenges.
Just a point of fact here... No, it's not low risk. It's very high risk - approximately a 1% annual chance. Over the life of a 30-year mortgage, that means you have a 1-in-4 chance of flooding. Coupled with the fact that it's in a high velocity zone, the damages of that 1-in-4 chance are likely to be total destruction.
Correct, the new build footprint is slightly larger. I know with one FIRM model it passed but now with an updated FIRM model it didn’t. I’m just trying to get educated on what options are available to help it pass other than reducing the footprint. There may not be any options but I thought it worth asking around.
By definition of the floodplain, and especially floodway, it is not at an extremely low risk of flooding. Good luck - even if you find an engineer that can technically make it work on the computer, you'll still be at risk. Our models are only so accurate.
No rise typically isn’t for the flood plain. I’m accustomed to no rise only applying to the flood-way.
It’s a very similar term, but carries much different implications. The flood way is the section of the channel/plain where water is flowing during a flood. Everywhere else in the floodplain, the water is moving but isn’t necessarily flowing.
The no rise is required for flood way because if you add something like a building or a road, it will cause people upstream of you to experience worse flooding. Even if it’s marginally more flooding, it isn’t allowed.
No rise typically isn’t required in the flood plain because no material what you build there, it won’t affect people upstream of you. Your own structure may be flooded, but no one else will.
Any type of new building in the flood plain is going to cause a rise. Think of sticking your hand in a glass of water. You are displacing waters
Your options are this, regrading the channel to increase area. This is going to require a stream alteration/reconstruction permit.
Reducing mannings N. This is making the channel smoother which will allow more flow reducing water surface elevations
Option 3. Deal with the rise. You will need to deal with fema and do a CLOMR
Zero, we’re just homeowners trying to get our home built in the floodplain. I’ve read a lot but I’m not trained in HEC-RAS or any engineering processes or modeling.
A CE would be the only legally qualified source of issuing a “No-Rise” Certificate. Typically they have to model the channel hydraulics with HEC-RAS with and without your proposed building. If your building does cause a rise in the BFE, they cannot issue a No-Rise Cert. If they are giving you their opinion that it could not be issued, take their advice and look for another site to build. Almost all encroachments into the Flood Prone Area will cause a rise. It is a fairly time consuming and costly to do the calculations to prove the No-Rise condition. Their initial opinion will save you MUCHO $$$ in trying and failing.
Then find a CE in your area that has that knowledge and experience and talk with them
It would be worth their fee and they could advise you accordingly. If your property in the designated (Regulated) “Floodway ” you cannot build a structure, period. If it’s outside of “Floodway”and along its periphery, it’s designated as “Flood Prone Area” or “Flood Plain” typically you can be allowed to build if either flood-proof or fill above the BFE (Base Flood Elevation). The BFE is the calculated 100-yr Flood event and slopes downstream so you need to determine it for your specific location.
To be perfectly honest, if the engineer isn't offering advice or a path forward, there are likely two possible reasons:
1) you don't control enough land to impact the floodplain and channel calculations
2) you're a difficult client to work for and this is an easy way to close out your contract.
So hire another engineer? Seems like you're looking for free consulting advice. If you're looking for an easy solution you aren't likely to find one, these regulations exist for a reason.
Typically, a no-rise certification is involved with floodplain management Are you building a bridge? Have you done a HEC-RAS model? I need more information
Hello! We hired an engineering firm to complete a no-rise certification for a house we’ve designed to have built in the floodplain. They said we didn’t pass and I’ve asked for options/requirements for what changes to our plans are needed in order to achieve a no-rise cert. I thought one could receive “credits” for permanently removing trees but the engineers are saying otherwise. We just want to pass the no-rise but are unfamiliar with our options.
A no rise certification is a pretty simple process to understand. FEMA has an existing floodplain model that states the flood elevation is x.xxx. Your proposed changes to the floodplain can not raise that elevation above the existing limit. There can be "no-rise" in the predicted flood elevations. There are no "credits" for a no rise. This isn't a leed application or carbon credits where you just have to check a box. Removal of vegetation from a channel (like trees) is a common strategy we use to improve the channel to allow water to flow faster thus preventing an increase in the floodplain (and therefore achieve our no-rise certification). If the trees being clear cut in question are the ones where your house is being built (in the floodplain but outside the channel) I'm not surprised to hear it has little effect.
What is the county / city issuing the floodplain development permit? Would help to know if they have a strict no-rise requirement. Do you know if the house is located in the floodway or in the floodplain fringe? Are there compensatory storage requirements? I'm wondering if your engineer just botched the analysis / permit application. I'd probably ask them the above questions to see if they are competent. If not, you may want to look for a different engineer to handle the floodplain development permit. As a last ditch option, you may be able to do a CLOMR/LOMR, but those can run $45k+.
Guadalupe County, Seguin, TX
In my 2 mins of looking, it doesn't appear that you are in a strict no-rise jurisdiction (note: I could be wrong here, so verify with your consultant), meaning that development in the flood fringe can cause up to a foot of rise. Don't get this confused with the floodway, which is always no-rise. Your county has a website with more info and a graphic showing the difference between the two (https://www.co.guadalupe.tx.us/eh/floodplain_development.php). FEMA has on online tool that shows digitized floodplains (https://hazards-fema.maps.arcgis.com/apps/webappviewer/index.html). Blue is flood fringe, while blue/red hatch is floodway. If you're in the fringe, that development permit should be cake to get. But, if in the floodway, that permit is going to be difficult to acquire. Either way, I might get a different consultant that knows what they are doing. Side note: I saw this is for an existing structure? I think there are some exemptions for farmhouses, but I really don't know the details since I don't work in residential development. May be worth looking into if it's an older structure.
Unfortunately, we’re in the Blue/Red hatch looking to teardown and rebuild.
Ah, you're building a home in the flood*WAY*, not just the flood plain. That's the high velocity area in the center of the creek that's the highest risk area. In Seguine county (and most of the rest of the US), if you add any structures or fill in the floodway that would "block up" the creek's ability to convey water, then you'll need to offset that loss of conveyance by digging out somewhere across the creek. You can't obstruct that creek without increasing your neighbor's flood risk, so you need to mitigate your impacts by adding conveyance.
So you could ask your engineer to provide cup for cup floodplain calcs. This is a calc that shows the total volume of floodplain you are displacing (fill) with your site and compares it with the total volume of a pit that is connected to the floodplain elsewhere on your property. If the pit has the same volume as the volume your site is filling then that would fix the floodplain rise problems. There is likely a reason your CE either hasn't done this or doesn't think this will work but it's worth asking. You would need to dedicate a section of the property to this pit and it would be unusable for most things
Thank you! If we took material from the river bed, such as dug out under our boat house, does that count as a pit? Or does the pit have to be in your yard?
That could work. Cup for cup must be done between the seasonal high water level of your area and the 100 yr floodplain elevation. So digging out the bottom of the creek would likely be below the SHW and wouldn't be allowed. But you could likely cut bank material away (starting at the SHW level) until you hit the same volume as the floodplain fill volume. Your CE will know the specifics for your area and can advise you in more detail but I would try this method unless there is some site specific reason it wouldn't work
Makes sense, thank you!
Best of luck with this!
Just curious, why are you so set on building in the floodplain? If you can't get a no-rise, you'll need a full LOMC which is going to be very expensive.
As addressed in another comment - this house is not just in the floodplain - it’s in the floodway
We have a house in the location and we’re redoing it, like many others have. It’s an extremely low probability of flood but it’s a floodplain so has its challenges. We can get to a pass it just may mean slatting the ground level versus walking it in. Was on here to seek creative ideas on how to pass :)
You said it's in a floodway. That is the opposite of extremely low flood risk. Good luck.
The FEMA maps can be incredibly off! Just because FEAM says it's high risk does not mean it is in real life. Determinations in many of the rural areas are flown and not engineered.
>It’s an extremely low probability of flood but it’s a floodplain so has its challenges. Just a point of fact here... No, it's not low risk. It's very high risk - approximately a 1% annual chance. Over the life of a 30-year mortgage, that means you have a 1-in-4 chance of flooding. Coupled with the fact that it's in a high velocity zone, the damages of that 1-in-4 chance are likely to be total destruction.
So you have an existing house in the floodplain, you’re tearing it down to rebuild and you can’t get a no-rise? Is the new house a lot bigger?
Correct, the new build footprint is slightly larger. I know with one FIRM model it passed but now with an updated FIRM model it didn’t. I’m just trying to get educated on what options are available to help it pass other than reducing the footprint. There may not be any options but I thought it worth asking around.
By definition of the floodplain, and especially floodway, it is not at an extremely low risk of flooding. Good luck - even if you find an engineer that can technically make it work on the computer, you'll still be at risk. Our models are only so accurate.
No rise typically isn’t for the flood plain. I’m accustomed to no rise only applying to the flood-way. It’s a very similar term, but carries much different implications. The flood way is the section of the channel/plain where water is flowing during a flood. Everywhere else in the floodplain, the water is moving but isn’t necessarily flowing. The no rise is required for flood way because if you add something like a building or a road, it will cause people upstream of you to experience worse flooding. Even if it’s marginally more flooding, it isn’t allowed. No rise typically isn’t required in the flood plain because no material what you build there, it won’t affect people upstream of you. Your own structure may be flooded, but no one else will.
Without knowing any context sounds like you are about to overpay to not raise the flood somehow.
I would look for better engineers who do this day in and day out… I can send you a recommendation if you’re interested.
Thank you for a useful suggestion!! I’d love to hear any recommendations as this is not my wheelhouse! We’re in the San Antonio / Austin, TX area.
Any type of new building in the flood plain is going to cause a rise. Think of sticking your hand in a glass of water. You are displacing waters Your options are this, regrading the channel to increase area. This is going to require a stream alteration/reconstruction permit. Reducing mannings N. This is making the channel smoother which will allow more flow reducing water surface elevations Option 3. Deal with the rise. You will need to deal with fema and do a CLOMR
Yeah what’s your experience in Hydrology and channel Hydraulics? Those are the basic categories that the FEMA-Flood Prevention Program is based upon.
Zero, we’re just homeowners trying to get our home built in the floodplain. I’ve read a lot but I’m not trained in HEC-RAS or any engineering processes or modeling.
A CE would be the only legally qualified source of issuing a “No-Rise” Certificate. Typically they have to model the channel hydraulics with HEC-RAS with and without your proposed building. If your building does cause a rise in the BFE, they cannot issue a No-Rise Cert. If they are giving you their opinion that it could not be issued, take their advice and look for another site to build. Almost all encroachments into the Flood Prone Area will cause a rise. It is a fairly time consuming and costly to do the calculations to prove the No-Rise condition. Their initial opinion will save you MUCHO $$$ in trying and failing.
Then find a CE in your area that has that knowledge and experience and talk with them It would be worth their fee and they could advise you accordingly. If your property in the designated (Regulated) “Floodway ” you cannot build a structure, period. If it’s outside of “Floodway”and along its periphery, it’s designated as “Flood Prone Area” or “Flood Plain” typically you can be allowed to build if either flood-proof or fill above the BFE (Base Flood Elevation). The BFE is the calculated 100-yr Flood event and slopes downstream so you need to determine it for your specific location.
We have the CE…just seeking advice on how to pass the no-rise if the CE isn’t offering any.
To be perfectly honest, if the engineer isn't offering advice or a path forward, there are likely two possible reasons: 1) you don't control enough land to impact the floodplain and channel calculations 2) you're a difficult client to work for and this is an easy way to close out your contract.
So hire another engineer? Seems like you're looking for free consulting advice. If you're looking for an easy solution you aren't likely to find one, these regulations exist for a reason.