Nooksack geomorphology

Problem

Flood hazard management in the lower Nooksack River is inherently intertwined with the dynamics of sediment transport and deposition. These issues have become particularly salient near Everson, WA, where the 2021 floods caused immense damage to communities in both Washington and SW British Columbia and reflect, in part, the loss of channel conveyance due to sediment deposition. Understanding how channel geometry has changed historically, the underlying causes of those changes, and how channels may adjust in the future all inform management decision-making. Regular monitoring of local channel change is also critical for understanding evolving flood risks year to year, or even flood-event to flood-event.

Objectives

The primary goal of this work is to finalize and expand existing channel change analyses for the lower Nooksack River, largely based on analyses of repeat topographic surveys. Observed changes will be reported and, in combination with other existing data, used to improve conceptual and quantitative understanding of sediment transport dynamics through the Everson Reach. Secondary goals include minor collection of additional grain size data. 

Relevance and Benefits

This work will support active flood-management decision-making in the lower Nooksack River, with emphasis on the Everson Reach. Local stakeholders will receive timely and relevant synthesis of complex data.

Approach

This work primarily involves differencing of high-resolution topographic datasets to document channel change, with the larger goal of improving understanding of the transport, erosion, and deposition of coarse (sand and gravel) sediment through the lower Nooksack River. The scope of this proposal is primarily to extend and finalize preliminary results; synthesize observations in an interpretive publication; and help integrate results into concurrent sediment transport modeling efforts, flood management discussions, and general public understanding. There is a minor additional task of collecting river channel grain size distribution in collaboration with Northwest Hydraulic Consultants (NHC) to support sediment transport modeling.