Detention Pond Volume 3

[bank]

Can someone give me an equation I can plug into excell to calculate the volume/capacity of an irregular shaped detention pond with sloped sides, assuming the top and bottom areas are known?

 

[cvg]

see page 45 of the attached HEC-1 manual

 

[amb2002]

You could take the average area times the depth of storage:
0.5 * (Upper Area + Lower Area) * (Upper Elevation - Lower Elevation).

 

[bank]

Thanks cvg. This is the equation I have been using for a long time, but was recently told by people smarter than me that I should be using something different.

Thanks also amb2002. I compared the two equations, and the results were almost identical.

 

[psmart]

It depends on the geometry of the pond. The "average area" method gives a precise answer if the sections are prismatic: That is, they have four flat sides, with 0, 1, or two (opposing) sides being sloped, and the other sides being vertical. Using conic sections (as in HEC-1) is more accurate for natural ponds with sloping sides all around. However, the difference may not be significant, especially if you use small enough slices. When in doubt, compare both procedures.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[chicopee]

If you know the geometry of the irregular shaped pond, you could calculate the volume by adding incremental volumes along the depth of the pond or if possible using calculus if you can approximate the pond wall profile into an equation.

 

[TGLG]

The average end method that AMB2002 described is good for a rough calculation, particularly if your basin has a regular shape.

If the shape of the basin is irregular, you can get closer to the actual number by measuring the area at various elevations and performing additional computations.

The smaller your vertical increment is, the more computations you'll do, and the more accurate the final number will be.

 

[thatdamengineer]

I performed this calculaton for 30 years while managing the dam safety program for the state of Ok. We used the average end area method when we could find contour maps. Yoyu have to remember that your survey or your input data will determine the accuracy of your study. In the early days of the inventory of dams when we were trying to determine the size of a lake or pond, we would take the depth at the dam, usually the top of the dam because we were trying to clculate max storage times the surface area at the top of the dam and then divide by 3. This turned out to be very accurate when compared to both Federal and state dam projects in Oklahoma. In fact it was prescribed in the early days of the inventory by the Army Corps of Engineers.

I used to perform dam breach analsyses and predicted 2 such later events within .5 ft of the actual flood level. Luckily my calculations were .5 ft higher than the occurrence.

Always remember we engineers work on averages, head in the oven, feet in the freezer, crotch is warm....

Also, you are measuring this with a micrometer, but cutting it with a chainsaw!!!!! Just because we have 5 digits right of the decimal does not mean we have to look further than the first one.





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