## Hydrocad Storage

## Hydrocad Storage

(OP)

I am finding conflicting results in calculating prismatic storage volumes in Hydro cad.

I have a basin which is 129 ft wide and 355 ft long with 3:1 side slopes. The basin depth is 4.83 ft. Based on these dimensions I would expect the total basin storage to be around 266,000 CF. When I enter the same dimensions in Hydro cad the total storage volume is reported around 256,000 cf. Not sure why there is a discrepancy. Our routings are scrutinize by the reviewing municipal engineer and I am not sure how to explain this off as just rounding errors. Any insight? I would think the total volume should be the same, nothing irregular about the basin shape.

I have a basin which is 129 ft wide and 355 ft long with 3:1 side slopes. The basin depth is 4.83 ft. Based on these dimensions I would expect the total basin storage to be around 266,000 CF. When I enter the same dimensions in Hydro cad the total storage volume is reported around 256,000 cf. Not sure why there is a discrepancy. Our routings are scrutinize by the reviewing municipal engineer and I am not sure how to explain this off as just rounding errors. Any insight? I would think the total volume should be the same, nothing irregular about the basin shape.

## RE: Hydrocad Storage

Peter Smart

HydroCAD Software

www.hydrocad.net

## RE: Hydrocad Storage

V = Y/6 (A1 + 4A2 + A3)

where:

A1 = L1 W1 (area of base)

A2 = L2 W2 (area at half-height Y/2)

A3 = L3 W3 (area of top surface)

L2 = ½ (L1+L3) (length at half-height Y/2)

W2 = ½ (W1+W3) (width at half-height Y/2)

L3 = L1 + 2 Y Z (length of top surface)

W3 = W1 + 2 Y Z (width of top surface)

Peter Smart

HydroCAD Software

www.hydrocad.net

## RE: Hydrocad Storage

Peter Smart

HydroCAD Software

www.hydrocad.net

## RE: Hydrocad Storage

Thanks for the additional background.

I was basing my volume on 1/2(a+b)x h x l (top length), where a and b are the bottom and top width.

My approximation is accordingly different.

## RE: Hydrocad Storage

The HydroCAD procedure uses four equally sloping sides. Your equation (which is basically the average-area method) would apply if you have two opposite sloping sides.

Peter Smart

HydroCAD Software

www.hydrocad.net