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No-Rise Certification Question

No-Rise Certification Question

(OP)
I have a client who is planning to add on to his dock. The property is located in Northampton County, NC.  The addition will include 4 – 4x4 posts to be in constructed in the lake.  The county is requiring that our client get a No-Rise Certification before they issue a building permit.   Are there any guidelines/methods for correctly modeling the effect of the dock posts in the lake and floodway?  Any guidance would be appreciated.   

RE: No-Rise Certification Question

Is the lake within a floodway or floodplain?

RE: No-Rise Certification Question

(OP)
The reservoir is dam controlled and the dock location is in the floodway.

RE: No-Rise Certification Question

Can you post a FIRMette or tell us where this place is so we can look one up?  I'm having a hard time visualizing a lake in a floodway.   

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: No-Rise Certification Question

(OP)
If there is any problem opening the firmette let me know.   

RE: No-Rise Certification Question

Just thinking out loud but trying to calculate the rise in water elevation for instaling 4- 4x4 posts...in a lake? Are they serious? It's like a drop in a bucket.

I don't have much exertise in this area, however just trying to rationalize the request. I look forward to see other posts from the forum.

RE: No-Rise Certification Question

Yeah, I might be going out on a limb here, but to heck with it.  

The only way a bureaucrat can lose his job is if he actually makes a judgment call.  That's just the nature of the regulatory environment.  Following the rules ad-absurdum not only ensures you don't lose your job, it positions you well for promotion.  I suspect you have run into one of these people.  They're quite common, in truth.

So the natural thing to do is to rant and rave about how stupid their request is, but the better thing to do is try to see the issue from their point of view.  They're a bureaucrat looking after their job security, so they want you to provide them some sort of documentation they can point to that shows they followed the "no rise rules" in your design review.

So here's what I would do.  First I'd try to get a hold of the hydrology study for the lake, presuming there was one.  That study probably had a stage storage table in it somewhere, just subtract the volume of the posts from the lake storage, show the reviewer that the stage storage didn't change due to roundoff error, and submit a 'compliance study' with them that acts as an amendment to the approved hydro study on file.  If such a study doesn't exist, then compensate for the volume of the posts by digging a few wheelbarrows full of dirt out of the shore somewhere to compensate.

If the reviewer wants HEC-RAS for this, then make a painstakingly detailed effort to explain to your client how unreasonable the reviewer is being and ask him what approach he'd like to take.  If it gets that far, then it might not be an engineering issue at all.  The whole thing could be political, and may need to involve his boss.

The two most likely scenarios I see are either A) you ran unto Ultimate Bureaucrat and just need to work it out with him somehow, or B) the owner pissed off local government and the issue isn't the dock at all, it's something else.

This sort of thing is what makes engineering fun, right?  :)

 

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: No-Rise Certification Question

(OP)
Is the rise in water elevation due to the additional volume or from restricted flow due to the obstruction.  If it is merely a volume issue then just removing the volume of the posts from the bank would be the simplest fix.  If it is from having a restriction in flow then it would require some analysis to prove that the restriction in flow doesn't cause the water elevation to rise.  In our case would be negligible.   

RE: No-Rise Certification Question

In theory, rise in elevation could be from either decrease in lake storage or increase in flow obstruction.  In practice, there will be no rise because your dock is a drop in the bucket.  Your reviewer is being nitpicky, but apparently needs something on file saying there's no rise due to your dock.  

Talk to the reviewer, try to handle this with a conformance letter, or an addendum to whatever hydrology study was performed for the lake, based on volume.  Avoid HEC-RAS if possible.    

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: No-Rise Certification Question

Additionnal volume from the posts vs estimated actual lake volume.

In %.

That could be a killer.  

RE: No-Rise Certification Question

(OP)
The contact at FEMA said that the rise in water elevation needed to be evaluated from a voloume and restriction of flow standpoint.  FYI   

RE: No-Rise Certification Question

Does the 100 year flood top the dam?

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: No-Rise Certification Question

(OP)
The normal pool is 132' and 100 yr flood is 133' and the top of the dam is 142.  They have the right to flood the lake up to 133'
 

RE: No-Rise Certification Question

Then there is no "restriction" because there is no flow to restrict.  Say that explicitly in your conformance letter.   

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: No-Rise Certification Question

How can someone at the FEMA says that it has to be evaluated from a restriction of flow standpoint?!

4 4x4 posts in a reservoir...

Is there something else we should konow?  

RE: No-Rise Certification Question

I'm having a hard time believing this is classified as floodway instead of floodplain.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: No-Rise Certification Question

(OP)
The planner at the County is requiring the no-rise cert.  The southern part of Roanoke Rapids lake in in Halifax county and they don't require anything but the northern area is in Northampton county.  We have done a no-rise cert for a small dock in creek several years ago where we actually surveyed cross sections of the creek; however, it isn't very practical to do that on the reservoir.  We are planning getting data from FEMA and using HEC-Ras, for what its worth on this small project, to prove the elevation rise is negligible.  I hate to have to go though using HEC-Ras but the planner wants to see some technical data.  
I do have a question concerning HEC-Ras.  I have little experience with the software but upon looking at it the information for the dock would be input into the pier tab on the bridge scour window, correct?  

RE: No-Rise Certification Question

Is the lake even in the RAS model at all?  There's no flow in the lake.   

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: No-Rise Certification Question

Using HEC RAS for this problem is an overkill.

In the Geometric Data/bridge Culvert Data, you add the dock as a bridge deck/roadway between 2 cross sections and then you add piers.    

RE: No-Rise Certification Question

But then as beej67 pointed out, how will you define the flow data between those 2 cross section?

Boundary conditions and flow rate.  

RE: No-Rise Certification Question

It may be worth asking the planner what they are looking for. For example, as beej67 suggested is it a simple volume comparison or are they looking for a HEC-Ras model? I agree with SMIAH a Ras model for this is overkill.

Another option to consider.....just my two cents but I wonder if it's worh speaking to someone higher up the ladder to see if this is really necessary. Is it the engineer or the planner that is requesting the no-rise? I'm all for doing things the right way but for something like this I would wonder if a "no-rise" calculation would be required for boats entering the lake and or swimmers. By comparison, I would think that even a 14' aluminum boat would displace more water than 4-4x4 posts.

Again, just my two cents, but I think this request from the planner is unreasonable. For a creek it may be worth a look into but not a reservior.  

RE: No-Rise Certification Question

Yeah, go back and reread my "out on a limb" post near the top.

This sounds to me like a reviewer who doesn't fully understand the science trying to cover his rear, and he probably just needs something to stick in his file that says the words "No Rise" on it with some math somewhere and a PE stamp.  Just explain that there's no flow in the lake, and the volume change is minimal.  For the 'math' portion of the conformance letter, show him a pre/post stage storage table.  

If you do happen to run into an existing HEC-RAS model for this river, and it has the lake right there smack dab in the middle of the reach, please post it here.  I'd like to take a look at it.

 

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: No-Rise Certification Question

Not that is much consolation, Builder, but the owner of that dam has been through this no-rise ordinance with the county recently for a simple structure downstream.  I was not the (lucky?) consultant, but I have heard the stories about the process!  Yuck!  Unfortunately I don't know what the resolution was.

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