Heernett Foundation Projects
Crawford Creek Tributary
Collapsed Earthen Bridge
Improvements were completed in 2000
Issue:
The mass of dirt, fill, and debris that created a dam and fish blockage within this tributary system needed to be removed to enhance the functioning aspects of the stream system. Substantial volumes of water flow from the headwaters of Crawford Mountain throughout fall, winter, and spring months. These flows would be stopped and slowed by the blockage, allowing the system to deposit voluminous amounts of silt and fine sediments. Concealing any aquatic wildlife (including macroinvertebrates and microorganisms) in the system. Over a period of time, the large flows began to scour the upstream banks behind the blockage causing the stream channel to expand wider, killing the trees and shrubs that were once on the banks edge. This further erosion delivered additional sediment into the system, continuing to change the ecosystem and diversity that once thrived there. The habitat and diversity on the downstream side of the blockage was still in tact. Juvenile salmon have been present in the system for several years and have used this as a rearing habitat. Once the blockage was corrected the juvenile salmon could continue further upstream, having better mobility within the system to find food sources and to develop critical life long survival behavior tactics.
Plan:
Removing the dirt, fill and debris was going to be the easy part of this project. The difficult aspect was going to be salvaging the two, well used (birds have made good use of drilling holes throughout both trees), old snags that we needed to make every effort to leave in tact. The second issue was all the sediment stored behind the blockage. The difference in elevation between the upstream and downstream sides was quite substantial, about three feet. How were we going to manage the potential delivery? It was decided to remove as much as possible without injuring any more of the trees left in the system and allow the stream to flush itself over the next two years. Returning then to readdress the system and plan for possible log weirs and rock placement to help with the water velocities. Once everything stabilized, we would then place spawning gravel in the streambed and along the banks for potential recruitment, thereby diverting more sediment delivery. Lastly, plant native shrubs and trees for bank stability.
