Rip rap calculator for Nebraska

A ton of riprap will cover roughly 17 square feet. That is correct. Since armor stone is installed in layers of 12 inches or more, each ton reaches about one tenth the area of landscape rock. The pile can seem small until you consider the bank depth it must cover. This calculator uses layer thickness and a density of 3,100 lb per cubic yard for rock commonly sized 4 to 12 inches and larger.

How to measure an armored bank

1. Take the slope measurement along its face rather than across the level ground, then multiply it by the shoreline or channel length.
2. For effective erosion control, use no less than 12 inches. Set total layer depth at 1.5 to 2 times the size of the largest rock.
3. Find cubic yards by dividing cubic feet by 27, then multiply by 1.55 for tons.

Tons of coverage

Stone placement basics

• Put fabric or bedding below the rock: use non-woven geotextile, or place 3-4 inches of #4 stone. Bare soil can look stable for a season, then the bank beneath the riprap erodes and the rock settles.
• Bury the toe row beneath the waterline or expected scour depth. Since riprap problems start low on the bank, this anchors the bottom first.
• Bring the slope to 2:1 or flatter before placing rock. A steeper slope calls for engineering, not simply extra stone.
• Use equipment or hand placement on the exposed upper course, fitting stones together instead of letting them stay where they land.
• Extend the apron 4-6 pipe diameters beyond a culvert outlet. Flow can scour the ground in that stretch.

Example: 50 feet of pond shoreline

For 50 feet of shoreline with a 6-foot slope face, you have 300 square feet to cover. At 18-inch thickness, calculate 300 x 1.5 = 450 cubic feet = 16.7 cubic yards. That works out to about 26 tons of riprap, or 27 allowing a little extra. Put down a roll of geotextile, or use about 4 tons of #4 stone as a rock bed instead. Before placing an order, check the truck path. The final 20 feet by a pond can trap a loaded truck, and moving stone again means paying twice.

Once the first major storm passes

After water along the Platte recedes, walk the bank and inspect the base of the slope for moved stone, exposed soil, or visible fabric. Put shifted rock back in place, use reserve material to fill sparse areas, and look over the outfall apron for erosion. Spending Ten minutes on this check two times a year is all the upkeep riprap needs: the stone protects the bank without ongoing work from you.

A quick guide to size classes

Choose the rock size for the water force. Four to eight inch riprap works for pond edges, downspout outlets, and gentle streams. Eight to twelve is suited to shorelines with boat wake and faster channels, including areas along the Platte River. Highway and spillway work has specified classes and layer depths, so follow the project drawing instead of this guide. If deciding between sizes, select the larger rock and use a deeper layer; added weight provides more tolerance.

Riprap sizing, quantities, and placement

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