We specify +/- .05' on our parking lots.
But in most cases you'll get much larger fluctuations.
The paving contractor has to spend time looking at your plans trying to find your drainage intent based on the few spot grades you give. And I guarantee no one puts as many spot grades as a...
You'll never be able to design the pond to drain below 72 hours and meet your release rate. Your wetland pond should be planted with wetland style plants which will be water tolerant to a point.
But even if that point is reached the wetland style plants will establish a "seed bank" which will...
Assuming full-flow would not be good, there are too many scenarios that could invalidate your bypass drainage calcs.
For example, what if the upstream development used overtopping of a roadway as part of the natural flow path. Your pipe flow would be totally insufficient.
Look at USGS contour...
Short answer is "Yes"
The rational method is a "peak" method since it doesnt use a distribution.
Just make sure that you add the bypass and release rates for each individual storm duration. Do not mix durations.
ie.
2-hr storm duration Bypass + 2hr storm release rate = Post develop rate for...
Kingpawn,
Using your example, as long as you arent devleoping the bypass area:
Bypass flow = CI*[10 ac. (not trib.)]
Detainable flow = CI*[10 ac. (Developable area)]
Storage = (Detainable flow - Release Rate)*t/12
Post Develop Rate = Bypass flow + Release Rate
Kingpawn:
Is there another stormwater management guy in your office?
Please ask him for some instruction. I dont know the project specifics, but I will guarantee your pond, in real life, will not see more than a few centimeters of water in it (ever!!) if you design with a 30cfs discharge...
Shallow up your inlets.
Connect shallower pipes downstream to a deeper (external or internal) "drop" manhole (similar to a sanitary drop manhole). The drop manhole is expensive but you may save money depending on how many inlets you can shallow up.
With the drop manhole you wont have the...
Bring an experienced Pavement Engineer with you to mark out where the Full-Depth Patches are needed. Most of these types of jobs are financially constrained and the more patches you do the more it'll cost you. An experienced field guy/engineer will tell you which areas are of concern.
Heres a...
You peaked my curiosity, so a quick google search found these links.
http://www.flow3d.com/
http://www.usbr.gov/pmts/sediment/kb/SpanStructs/reports/TSC%20Overview%20-%20Modeling%20Three-Dimensional%20Hydraulics%20of%20Rock%20Weirs.pdf
Looks quite expensive, and far beyond a HEC-RAS analysis...
Holy Smokes...120 cfs for "several commercial sites"? Even with detention basins? My last sanitary lift station was for less than 2 cfs peak and it cost $1.0 million with the forcemain.
Reread all the above posts (especially RWF's), calculate your peak gpm and if it even comes close to 120 cfs...
Be careful when using a "per person/day" calculation in non-residential applications. Usage "can" change over time and a lower initial rate can cause problems down the road.
Theres a huge difference in the differing types of offices
(ie call center versus your office).
Ive run into a situation...
Anyone seen a digital planimeter that can calculate the geometric center of an irregular object?
While the ACAD "region" command would be nice and simple to use, the irregular shapes I am calculating are all on paper.
While I could digitize the shapes, my company needs to buy a nice planimeter...
Haestad Software (aka Bentley) is definitely not free!!
Although if you wanted to spend a small fortune, StormCad is really nice. I have found no free software with a graphical interface. Your only "free" solution is a spreadsheet like gbam said. SWMM wasnt meant for your typical storm sewer design.
Im going to assume that your HSG info is from a State Soils Survey. HSG is a generic source for types of soils in your area, sort of like the USGS 10' contours.
In Illinois the State Soils Maps seem to be pretty accurate but there are always discrepancies.If you have a geotech report, borings...
It doesnt matter what you use as long as your shape area is substantiated by your flow calculations. It sounds like you are using an external weir with multiple control points. If they Cast in Place, they can form any shape that you want.
Just remember the poor guys that have to construct the...
In conjunction with what CVS said..
Illinois Urban Manual:
ftp://ftp-fc.sc.egov.usda.gov/IL/urbanmnl/drawings/IL-630A.pdf
ftp://ftp-fc.sc.egov.usda.gov/IL/urbanmnl/drawings/IL-630B.pdf
I agree with RWF7437, additional survey is required.
However you may have enough data already available to you.
Take a look at the floodplain maps and USGS 10' contour data and extend out your cross sections farther out.
Your current model cannot handle the given historical flows because your...
