No-Rise Certification Question

[Builder604]

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.

 

[SMIAH]

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

Boundary conditions and flow rate.

 

[Ryb01]

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.

 

[beej67]

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

 

[DMcGrath]

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.