Abstract: Session F  1:30 pm (Back to Session F)
High Sediment Load Systems – Get Comfortable with Being Uncomfortable

Lucas Babbitt, PE, CFM
WaterVation, PLLC
Salida, Colorado

If the idea of working in a small gravel-bed system with a drainage area of 530 square miles and bankfull flow of 1,700 cubic feet per second keeps you up at night, this presentation might be for you.  Working in high-sediment load systems can be unnerving and requires spending more time with assessment and design tasks to better understand how the stream system could function under various flow events along with identifying potential modes of failure.  Working in high sediment load systems not only requires a thorough understanding of the immediate project site, but also an understanding of the larger geologic and geographic context of the watershed to help identify major sediment transport tendencies in addition to sediment routing that occurs during bankfull flows.  Designing stream restoration projects in these systems requires special attention to the natural boundary conditions and in-stream features that provide stability and habitat because history has shown that introducing materials out of context of the watershed setting within these systems results in devastating failures.  Most high sediment load systems exist within unconfined alluvial valleys where large woody debris (LWD) is an important element of floodplain stability and can be very beneficial to these projects when design and placed properly.

This presentation will examine two projects that were recently designed and constructed, both of which have massive sediment loads.  This presentation will emphasize the following elements as it relates to designing stream restoration projects in high sediment load systems:

  • Stream assessments

  • Applying 2-dimensional hydraulic models to bracket modes of failure

  • Applying various sediment transport models to limit uncertainty

  • Importance of geologic and geographic context

  • Design strategies

  • Detailed LWD design and placement

  • Expectation setting