Construction is still going strong on the Cold Spring Creek Debris Flow Mitigation Project and in the past few weeks a great deal has been accomplished. The concrete outlet structure has been completed and the steel beams – known as the grillage – have been installed in the opening. The grillage will capture sediment and debris while allowing water to pass through. The permanent diversion has been completed and the creek is now flowing through the outlet structure. Another important part of the project that was completed before the creek could flow through the outlet is the erosion protection downstream of the outlet structure. The erosion protection limits damage to the downstream toe during high flows and consists of the grade control structure, a grouted riprap channel, and riprap aprons.

The barrier itself is being constructed of roller compacted concrete (RCC). Roller compacted concrete is a concrete mixture that is placed in lifts and compacted. It is a commonly used material for dam construction and was selected for this project because of its construction cost, durability (lower maintenance costs) and strength. In late August, Mackay completed a large scale RCC trial placement to demonstrate the methods that they will use in the construction. Once the trial was completed, they were able to begin construction on the RCC components of the project starting with the grade structure mentioned above. In later September, construction of the large RCC barrier commenced (referred to on site as “the main show”!).

This phase of the project is intricately tied to weather conditions as there are strict guidelines on the RCC placement conditions. The working window each day gets shorter as our days get shorter and the colder temperatures settle in. There is a large volume of RCC to be placed (approximately 10,000 cubic meters) and everyone on the project team is working together towards the goal of completing the RCC barrier this fall.

While substantial completion was originally planned for the end of September, as with any construction project, and certainly one of this complexity and magnitude, estimated completion dates are subject to change as the project progresses. That is the case with this project. While our contractor is making good progress, there are a number of factors that are continuing to impact the construction timeline. Once the substantial completion is complete, there will still be work remaining, for example, some work cannot be done until the RCC is fully cured, so the construction will truly be complete in 2025; however, we will continue to keep the community advised as we edge closer to being able to better estimate completion dates.