MATH HELP: Culvert pipe capacity in gpm | Page 5 | Construction and DIY projects | Forums

KVR said
Have you looked into licensing requirements to do this?

earthenstead said
Do you mean permits?

KVR said
yes, permits

I have now.

In the county there are no permits required for residential construction. I will need a permit to connect my driveway to the road and am required to install a culvert. That part I was going to do anyway, but they need to inspect and specify which culvert type and size.

For the stream crossing, that is handled by the Army Corps of Engineers. It is a federal level "Nationwide Permit" and no action is required for it. As the ACoE guy explained, "Its something you already have and just don't know you have it." I do have the option of getting them to issue me something in writing if I so desire. Might as well. Better to have it and not need it, then need it and not have it, right?

For clearing the land, there is a Department of Environmental Quality. They are concerned with sedimentary storm water run off. I will only be clearing 0.975 acres so they were really not concerned. They sent an email with appropriate links to best management practices by the EPA and to some forms that I am to print, fill out, and post at the entry of the property prior to beginning any construction.

There would also be a temporary disturbance permission issued by the Department of Environmental Quality if the culvert and fill work was done while the stream was running, but again, its not something I'd need to pay for, and I won't need it since I'm waiting for the stream to go dry. They also said its at my discretion anyway.

So there it is. Only 1 permit to pay for. Connecting the driveway to the road. A whole $15 for the permit + the specified culvert (which I was buying anyways).

UPDATE

I measured the actual drop of the pipe which turned out to be much more than I had calculated for in an earlier post. I have edited that post to reflect the correction which is a drop of 1 foot for every 24 feet of distance.

After much consideration and many calculations and permutations, I've abandoned the idea of retaining walls. The best price quote I got for Ready-mix concrete was $80 per yard. That makes retaining walls or a bridge too expensive. I decided it would also be too complex and time consuming. Instead, I am returning to using clay dirt fill from the pond excavation to create a land bridge and bring it to elevation with the rest of the driveway. As planned I will lay gravel and then rip-rap at the inlet for erosion control. Then eventually when I can afford it, I can pour concrete into the empty space of the rip-rap which should create some very dependable and durable erosion control. I may need to use stainless steel anchors to secure the concrete pour to the clay dirt fill.

A 2:1 slope will make the mound of clay dirt fill 44 feet wide from toe to toe which means 48 feet of pipe. Since I must double the length of pipe, I cannot have 2 lengths of equal diameter pipe. To compensate for the lost capacity, I decided to increase the diameter of the single pipe to 54 inches which is 1 to 2 sizes above the recommended pipe diameter. All it takes is 1 major flood event to overwhelm and destroy the stream crossing. Even though I am not in a flood plain, the stream crossing is too important. I would rather pay more now to have too much capacity than risk the potentially bank breaking expense of a wash out in the future.

Here are the new calculations...

With

• Roughness = 100
• Pipe Length = 48 feet
• Drop = 24 inches

For 42 inch pipe I get

• Capacity = 94,031.5 gallons per minute
• Velocity = 21.7758 feet per second
• Pipe Slope = 4.16667%

For 48 inch pipe I get

• Capacity = 133,596 gallons per minute
• Velocity = 23.6869 feet per second
• Pipe Slope = 4.16667%

For 54 inch pipe I get

• Capacity = 182,106 gallons per minute
• Velocity = 25.5114 feet per second
• Pipe Slope = 4.16667%

Two lengths of 42 inch pipe would move 188,063 gallons per minute versus the 182,106 gallons per minute of a single length of 54 inch pipe. I will also add a second run of 12 inch diameter pipe to catch the smaller branch and prevent pooling or damming.

With

• Roughness = 100
• Pipe Length = 48 feet
• Drop = 24 inches

For 12 inch pipe I get

• Capacity = 3,486.38 gallons per minute
• Velocity = 9.89032 feet per second
• Pipe Slope = 4.16667%

That brings the new total to 185,592.38 gallons per minute combined (54 inch pipe + 12 inch pipe) versus the 188,063 gallons per minute of two lengths of 42 inch pipe.