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re: How years of storm water pond construction are causing issues in Baton Rouge metro area
Posted on 9/14/21 at 10:11 am to BottomlandBrew
Posted on 9/14/21 at 10:11 am to BottomlandBrew
quote:
TP-40, which had a publication date in 1961.
TP-40 actually has slightly higher rain rates, except for 100 yr, than the current NOAA Atlas 14 so that argument is moot also. Looking at 24 hr rates for Baton Rouge:
Atlas 14: 10 yr (7.4"), 25 yr (9.1"), 100 yr (12.2")
TP-40: 10 yr (8.2"), 25 yr (10.6"), 100 yr (12.0")
1
Posted on 9/14/21 at 10:11 am to lsu13lsu
I’m not sure. Ask the developer, which I am not.
Posted on 9/14/21 at 10:12 am to LSUengr
quote:
You guys keep repeating this and it is still wrong. It doesn't matter what happens below the water surface.
He's actually right, and you're misunderstanding the point. He's talking about detention basins where there is no "below the water surface." That dry storage makes full use of the excavated or impounded area.
Wet storage, or retention ponds, have some maintenance benefits in regards to woody vegetation, but the bigger part of it that developers are abusing is that digging deeper allows them to use more fill claiming "no net fill." Then they add aeration and stock it with bass and sell buyers on a lake.
Posted on 9/14/21 at 10:14 am to lsu13lsu
quote:
Then why don't they put it in the budget/reserves and have Dues priced accordingly?
they don't want that bc it would hurt their home sales.
Exactly. It's why they also fight against energy efficiency codes. The only economics these developers and their builders seem to acknowledge are $/sf.
Posted on 9/14/21 at 10:15 am to Galactic Inquisitor
Dig a hole in the ground and see how quickly you hit water 
Posted on 9/14/21 at 10:15 am to LSUengr
quote:
TP-40 actually has slightly higher rain rates, except for 100 yr, than the current NOAA Atlas 14 so that argument is moot also
TIL. Thanks. I got out of the field prior to Atlas 14, so I've never used that data.
Posted on 9/14/21 at 10:18 am to jimbeam
quote:
Dig a hole in the ground and see how quickly you hit water
Which is exactly why on-site fill should not be excluded from no net fill ordinances, but the developers are making too much money to let that change.
Posted on 9/14/21 at 10:20 am to Galactic Inquisitor
quote:
They also use the soil that was removed from the bottom of the pond to build up the land around the pond to meet base flood requirements. This meets "no net fill" ordinances, but reduces net storage volume by that exact same volume below the water surface.
Wrong. You must replace air for air. So the dirt below the water surface is not allowed to be counted for fill mitigation. Only above the static water surface.
There is no voodoo. Downstream capacity must be analyzed to see how it affects your site and the detention being provided. Ponds and sites aren't designed in a vacuum.
Everyone just wants something to blame when flooding happens and new development is an easy target. However, it plays a miniscule part.
If you want to make an argument that older development (pre 1990) that didn't provide detention, fill mitigation or requirements for houses to be built above the flood elevation are more of the problem, then I'll agree with you. New development is not the issue.
Posted on 9/14/21 at 10:23 am to LSUengr
quote:
There is no voodoo.
Muh Saint-Venant equation
Posted on 9/14/21 at 10:24 am to Galactic Inquisitor
quote:
He's actually right, and you're misunderstanding the point.
Not misunderstanding the point. When dry detention silts up, it does impact storage. So building dry detention creates more of a maintenance issue. When you have wet retention, silt building up below the water surface doesn't impact storage. Dry detention requires more frequent maintenance to maintain the proper storage volume.
Posted on 9/14/21 at 10:30 am to LSUengr
quote:
When you have wet retention, silt building up below the water surface doesn't impact storage. Dry detention requires more frequent maintenance to maintain the proper storage volume.
The silting is usually before the developer even leaves and shows how messy they are and that they probably did a lot of other crappy work in regards to drainage build.
Posted on 9/14/21 at 10:30 am to jimbeam
quote:
I’m sure an engineer and a contractor would love to have a maintenance contract with an HOA but then all those stay at home mom’s will bitch about how expensive it is.
I've started or completed drawings for several weirs, bulkheads, and retaining walls for HOAs in the past decade. Only one of the projects was built.
Posted on 9/14/21 at 10:31 am to LSUengr
quote:
There is no voodoo. Downstream capacity must be analyzed to see how it affects your site and the detention being provided. Ponds and sites aren't designed in a vacuum.
Are engineers using maps to design ponds and sites or is there any actual on the ground study of actual runoff, downstream flow etc.?
Posted on 9/14/21 at 10:34 am to LSUengr
quote:
There is no voodoo.
quote:
You must replace air for air.
And the likes of Tommy Spinosa would never stray from that....
Posted on 9/14/21 at 10:34 am to lsu13lsu
quote:In my professional experience
actual on the ground study of actual runoff, downstream flow etc
Posted on 9/14/21 at 10:36 am to Galactic Inquisitor
quote:
And the likes of Tommy Spinosa would never stray from that....
The same people who are reviewing retention ponds and other drainage for regular maintenance are reviewing sites to make sure they were built as designed/properly.
It is all a big mess and it is so much of a mess that everyone can just blame everyone else or say "you just don't understand engineering!"
Posted on 9/14/21 at 10:36 am to lsu13lsu
quote:
Are engineers using maps to design ponds and sites or is there any actual on the ground study of actual runoff, downstream flow etc.?
They use maps (topos) and design storms usually. Not many of them are using "actual runoff" to validate and calibrate. Frankly, that data isn't available for most locations.
Posted on 9/14/21 at 10:43 am to lsu13lsu
quote:well you buy a house than needs painting and ac filter change, ac maintenance ,etc. but this isnt completely spelled out in your home owners agreement.
This is one problem. But, Developers are turning this over to stay at home moms with no engineering or maintenance experience. it isn't in the Developers reserves or accounting or budgets
IMO i do think HOAs need to plant for this BUT i do not agree the blame for not, should be passed to the engineers and or developer.
Posted on 9/14/21 at 10:44 am to Galactic Inquisitor
quote:thats just not true.
Firms often do extremely inadequate validation and calibration of their models, as they are more interested in giving their client, the developer, the answer they need for approval than giving them the correct answer.
Posted on 9/14/21 at 10:46 am to lsu13lsu
quote:
Are engineers using maps to design ponds and sites or is there any actual on the ground study of actual runoff, downstream flow etc.?
On the ground survey data of the site and downstream facilities is being used as the basis for design. Capacity of downstream facilities is calculated from that on the ground survey. Flows from the site and surrounding areas contributing to the flow in the downstream facilities is based on design storms. Major streams that have USGS gauge and flow data can be used to confirm capacity and flow.
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