Logging Requirements
Through this EarthCache you will have a chance to learn about waterway restoration and techniques for preventing erosion. To claim credit, please send answers to the questions listed below. You will need to read the write-up below and make observations at the posted coordinates to find the answers.
1. Name at least one benefit of using gabion baskets to prevent stream bank erosion, and at least one benefit of using riprap to prevent erosion.
2. Observe the repairs completed to the sides of the Wilde Lake Channel. Why do you believe that imbricated riprap was used to make the repairs and not gabion baskets?
3. While on the bridge at the posted coordinates, take a photo of yourself or a personal item with the Wilde Lake Dam in the background, and post it to your “Found” log.
Wilde Lake Channel Repair and Erosion Prevention
Wilde Lake was built in 1967 by the Columbia Association. This 22-acre lake was originally a low-lying meadow with a small stream running through it. This changed, however, when the 15-foot tall and 200-foot wide dam was erected to form the lake itself. Logs from the area were used to give the face of the dam its embedded look and evoke a more natural view as water cascaded down the dam face and into the channel. The water from Wilde Lake would eventually travel south along this channel and empty into Lake Kittamaqundi.
The sides of the Wilde Lake Channel were originally created using gabion baskets. In fact, from the bridge on which you are standing, look to the southeast side of the channel and you can still see a few of the original baskets remain.
The word gabion is Italian, meaning “large cage.” This is a very fitting description, as gabion baskets are wire cages that can be filled with stones. More environmentally friendly approaches to using these baskets would be to fill them with leftover building materials such as broken concrete or even use native stones. An environmental benefit of these baskets is that they are permeable. This means water can easily flow through them and help soil stability, and their installation can allow for roots of local trees and plants to weave throughout. However, while gabion baskets are useful in many situations, a downside to using these materials for erosion prevention is that they require more upkeep and maintenance compared with riprap. See the picture below for images of gabion baskets and riprap.
Unlike gabion baskets, using riprap to prevent erosion consists of stacking large rocks such as boulders and cobbles in a specific manner to stabilize the sides or edges of waterways. Here a “footer” stone is embedded at the bottom of the waterway and used as a stable base for which the large stones can be stacked upon. Given the size of the stones used, a benefit of riprap is that it’s useful along waterways where water has a chance of flowing at a more intense or faster speed. Riprap also requires less upkeep and maintenance compared to gabion baskets. It’s also argued that the rocks used in riprap are more aesthetically pleasing to look at as opposed to the wiring used with gabion baskets.
A downside of riprap is that with its large stones, it lacks the permeability found with gabion baskets. Soil from the sides of the waterway can erode through the gaps in the stone. Therefore, additional material is needed to prevent this erosion and riprap must be “imbricated.” This means a granular material (such as a layer of smaller stones) or a geotextile material (such as a polypropylene fabric) needs to be layered between the large riprap stones the earth. In doing so, the construction now has the stability of the large riprap stones, without the chance of the soil eroding through the gaps in these stones.
Imbricated riprap is the technique that was used here in repairs to the Wilde Lake Channel. The picture below gives some details on construction used to repair the walls of the channel.
Now that you have read the description, take some time to make observations of the Wilde Lake Channel and its repaired walls. Using both your observations and the information in the description, please send answers to the questions listed above to claim credit for this cache.
Hope you enjoyed your time at Wilde Lake, and also learned a little bit too!
References
Aird, Janet. 2017. Preventing Erosion With Riprap and Gabion Walls. Erosion Control; May 30.
Columbia Assocation. 2024. Wilde Lake Channel Repair. CA Project & Access Dashboard; November 18.
Wyzykowski, Mike. 2024. Understanding the Difference Between Riprap and Gabions. Erosion Management Services Incorporated Blog; December 13.
Stormwater Manager's Resource Center. n.d. Stream Restoration: Bank Protection Practices.