Rip rap calculator for West Virginia

A ton of riprap covers roughly 17 square feet. That amount can seem surprising. Armor stone is installed at 12 inches or greater, so a ton covers about one tenth as much area as landscape rock. This calculator figures depth by layer, using 3,100 lb per cubic yard for rip rap generally sized 4 to 12 inches and up.

Measure an armored bank

1. Run your tape along the slope face instead of measuring level ground, then multiply that distance by the shoreline or channel length.
2. Set the stone layer at 1.5 to 2 times the largest rock dimension. Use at least 12 inches for erosion control.
3. Divide cubic feet by 27 for cubic yards, then multiply by 1.55 for tons.

Per-ton coverage

How to place stone so it holds

• Start with fabric or bedding: install non-woven geotextile beneath the stone, or use 3-4 inches of #4 stone. Riprap laid directly on soil can look sound for one season before the underlying bank erodes and the rock settles.
• Start with the toe. Install the lowest stones below the waterline or expected scour depth since riprap can unravel from the bottom.
• Before placing stone, cut the slope to 2:1 or flatter. A steeper bank needs engineering rather than more stone.
• Use equipment or hand placement on the exposed upper course to lock stones together rather than leaving them where they land.
• For culvert outlets, extend the apron 4-6 pipe diameters downstream. Water scours there.

Example: 50 feet of pond bank

For 50 feet of shoreline with a 6-foot slope face, the area is 300 square feet. With an 18-inch layer: 300 x 1.5 = 450 cubic feet = 16.7 cubic yards, or about 26 tons of riprap and 27 with the small allowance. Use a roll of geotextile, or about 4 tons of #4 stone for a rock bed. Check the truck route before you order. The final 20 feet at a pond edge can trap a loaded truck, and moving stone twice costs twice.

Following the first heavy rain

After water recedes, walk the creek bank. Check the toe for displaced rock, exposed soil in the gaps, visible fabric, and any scour at the outfall apron. Put shifted stone back in place and use reserve material to cover sparse areas. A brief check a couple of times each year is the full upkeep plan. Riprap is meant to carry the load with little work from you.

Stone sizes at a glance

Choose stone for the water force. Riprap from four to eight inches works for pond edges, downspout outlets and gentle streams. Eight to twelve fits lake banks with boat wake and quicker channels. Engineered projects such as highways and spillways have specified stone classes and layer depths, so use the plans rather than this guide. If deciding between sizes, choose larger stone and a deeper layer. More weight gives better tolerance.

Riprap amounts, sizing and placement

Other calculators