Costs and Installation Tips When Building a Riprap

It is recommended to install a gravel layer between the filter and the rocks

Lake Michigan Shireline in Evanston with distant Chicago
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Riprap is a commonly used method to protect soil from erosion in areas of concentrated runoff. Riprap is a layer of very large stones interlocked together acting as a barrier on slopes that are unstable because of seepage problems or areas that are receiving a large concentrated flow.

Where to Use Ripraps

Ripraps can be used to stabilize cut and fill slopes preventing erosion and other stabilization problems. Other areas that can be stabilized with ripraps are:

  • Channel Sides and Slopes
  • Culverts inlets and outlets
  • Bridges
  • Slopes
  • Drainage Structures
  • Grade stabilization structures 
  • Storm drains
  • Streambanks

Riprap Construction Tips

When building a riprap wall be sure to follow these helpful tips:

  • Use only well-graded mixture or rock sizes and avoid using the same rock size. By using different rock sizes, will allow the rocks to create a perfect interlocking system.
  • The rock type shall be durable enough to withstand freeze and thaw cycles, for instance granite-type rocks. An average size of 2 inches to 24 inches in diameter is recommended.
  • It is recommended to use blocky and angular shaped rocks. Be sure to select rocks that have similar dimensions in all sides and must have sharp clean edges.
  • To ensure that the riprap is anchored to the soil, be sure to make the riprap at least two times as thick as the maximum stone diameter.
  • Before installing the first layer of stones, apply a synthetic geotextile membrane to prevent the soil from moving through the riprap.
  • Extend your riprap all the way to the top of the bank or to the design water level so it can control erosion more efficiently
  • Ensure that riprap extends to five times the bottom width upstream and downstream of the beginning and ending of the curve and the entire curved section.
  • Consider using chain link fencing or wire mesh to secure riprap installations, especially on steep slopes or in high flow areas. You can use galvanized wire mesh for better efficiency and durability.

Things to Consider During the Installation

During the installation process, you will need to be careful and refrain from using this method when the slope if greater than 2:1. Slopes greater than 2:1 can cause the riprap to fall down due to erosion and sliding caused by water flow. If not used correctly, it can actually worsen the condition and increase the amount of erosion. If you are also considering using grouted riprap, a smaller rock might be used, but they will be interlocked with the grout and cement. Grouted riprap must be securely protected against toe scour or undermining and it cannot be self-repair like the ordinary installation.

After every storm or major runoff event, the system needs to be inspected and maintained. If the wire mesh or the stone has been damaged or altered, be sure to repair it immediately to prevent a cascade effect with the whole system.  Also, you might need to control weed and brush growth in some locations.

Erosion Control Costs

The cost of riprap varies depending on location and the type of material selected. A cost of $35 to $50 per square yard of nongrouted riprap can be used as a basic quote, while grouted riprap ranges from $45 to $60 per square yard. These costs will depend on the availability of resources, accessibility and total area to be covered.