storm water managment calcs

[blimkie.k]

I need some help dealing with storm water. I'm trying to get a site plan approved and the township engineer wants to see "calculations in the form of a storm water management brief to indicate how post development floes will be managed such that they do not exceed pre development flows for a 100 year event."

The building is 50x60 feet and the new aspalt parking area will be 500 sq metres. I have allready set slopes off the building to be 2% as well as 2% on the asphalt to the sides and ditch at the front of the lot.

A Civil Engineer wants 3,000 dollars to do a site grading and storm water managment plan. Thats too much the owner of the property is not happy because the same company allready charged him 3,000 for a topo plan.

Anyways just wondering if anyone could provide me with a link or point me in the right direction on how i could attempt these calcs.

Thanks.

[infsup]

Focus on the downrange variables:

1) Hydrographic Survey can get you elevation data in combination to depth gradients for your area, small one time fee.

"I'm trying to get a site plan approved and the township engineer wants to see "calculations in the form of a storm water management brief to indicate how post development floes will be managed such that they do not exceed pre development flows for a 100 year event.""

2) Input,Output
Rough Calculations can track the average/mean flow based on median measurements, this follows the law of large numbers, given 50/50 percentile distribution over longer ranges all distributions converge to an average. Ran this calculation for a client to predict mean values over an unknown duration sampling only the past ten median values of a boundary layer function (with no calculus or trigonometry!), for all future values predicted the mean value at 99% accuracy.

In short this requires a xy(actual), xz(actual),xz(target), and w=error |xz(actual)-xz(target)| usually a root mean squared error. Then plot (xz,w) for future, with and w/o building. Rough total of six plots, add a diagram of an input-output plant control model w=theta, et cetra. (X=Years Y=Min/Max/Median Z=Avg(Median,X+years))

"The building is 50x60 feet and the new aspalt parking area will be 500 sq metres. I have allready set slopes off the building to be 2% as well as 2% on the asphalt to the sides and ditch at the front of the lot."

Add this to the above calculations in the new output model, using the existing topo plan , min/max values can be acquired for a small one time fee. We are roughly subtracting the area and indicating on an overhead of the new site the input-output based on the new elevations.

I could set-up a draft proposal for your township's approval, with all pseudo-charts, calculations, and hydrographic flow maps for past and present. Once approved we can talk details, send me an e-mail clearlineofsight@gmail.com to discuss this at your connivence.

[CarlAK]

I'm a Civil Enginer and have no idea what the previous responder was saying.

We would have charged you more than $3000 + $3000 to do a topo survey, produce a drawing, then a site grading plan, & stormwater calculations. To "manage" flows and not exceed pre-development, a pond or chamber along with flow controls would need to be included in the design as well. Agencies usually require these plans & calcs be performed under the direction of a qualified (licensed) individual. My advice, leave it to the professionals.