Branch Creek Armored Stream Crossing

Project abstract:

Branch Creek enters North Fork Toppenish Creek at river mile 3.2, and drains a 23-square-mile watershed. Mid-Columbia River steelhead use the stream for spawning and rearing. Two locations on Branch Creek were identified as suitable for culvert removal and replacement by armored stream fords. One is located at RM 1.1 and the other at RM 1.4. The project is located in the NW1/4, NE1/4, Township 9 North, Range 14 East, Section 1, on tribal trust land in the closed area of the Yakama Reservation.

Yakama Reservation Watershed Project (YRWP) staff proposed to remove both culverts and replace them with armored stream fords. The uppermost culvert was a complete loss because the stream had undermined the footing, and was flowing outside of the culvert on the left side bank. The lower culvert was still functional, although the stream had undermined a small portion of the right side on the downstream end. We used a professional engineer during the planning phases of this project to produce a set of construction plans. In addition to the fish and stream benefits, this project will serve as an example to show Tribal and BIA road engineers how armored stream crossings can be used in place of culverts. Armored stream crossings are often a much better choice for stream crossings, and with the success of this project, we expect to see their increased use, where appropriate.

Project goals:

Replace failing culverts.
Keep the road open for emergency vehicles
Demonstrate the greater efficiency of armored stream crossings.

Project plan:

Culvert removal included: excavation of excess road fill, installation of rock grade control structure to stabilize the ford, and armoring or roughening of the ford. Both culverts were removed using a 300 series tracked excavator. The culvert fill was removed until the culvert’s structural bolts and concrete footing were exposed. The culvert was removed in pieces in a manner tol allow it to be used again. Care was taken at all times to prevent sedimentation of the stream. Once the culverts were removed, construction of the new road approaches began. The crossings had to be constructed to allow use by wild land firefighting vehicles. The existing road approaches were sloped back to create an incline that large vehicles can climb out of under a load. After the approaches were set, the final task of constructing the armored ford began with hauling 844 cubic yards of 2’x3’ columnar basalt from a quarry approximately two miles away. The existing streambed was excavated to a depth of approximately 2’ and the basalt was placed so that the surface was flush with the surrounding stream bed grade (the ford cannot impound water.)

Project progress:

The Branch Creek project was successfully completed. There were two issues that came up during construction that are worth further discussion. The first was our discovery of a small, ephemeral spring that had been hidden by the culvert fill. The spring was a problem because it discharged directly onto the new road surface, making it very soft. Our solution was to excavate more of the soil from the roadway and replace it with large rock. This allowed the spring water to infiltrate the interstitial spaces around the large rock, below the surface grade of the road. The final step was to cover the rock with crushed top-course rock to create a smoother finished road surface.

The second issue we encountered had to do with the size of the rock armor. Once the crossing furthest upstream was completed, it became apparent that the spaces around the armor rocks were too wide, causing the stream flow to go subsurfacect for about 20 ft. The solution was simple; a load of crushed rock was brought to the site and mixed into the interstitial spaces around the larger rock. This forced the stream to flow over the armored crossing instead of under it.