Assessment, Design, and Some Lessons Learned From Application of Natural Channel Design Principles in Conversion of a Multiple Thread to Single Thread Channel on an Alluvial Fan

摘要

McCallum Creek crosses the Trans Alaska Pipeline in the Central Alaska Range near Paxson, Alaska. It was converted from a braided channel on an alluvial fan to a stable single thread channel at the pipeline crossing. Objectives included controlling the position of the channel at the pipeline crossing and minimizing aufeis accumulations through the converted reach. A natural channel design methodology was used, which involves determining the dimension, pattern, and profile of a stable reference reach for the associated valley type and stream type and emulating those characteristics in the design reach. A failure mode analysis was conducted. Mitigative measures were incorporated into the design for each potential failure mode. The channel was lowered to reduce surface energy loss and associated winter aufeis accumulations. The site has been subjected to at least one bankfull flow event since construction was completed in May 2000. Performance has been good during the 2000 and 2001 summer seasons. Aufeis accumulations have not recurred since the channel conversion. Lessons learned are presented from this and several similar projects constructed along TAPS in 2000 and 2001.