Layer-wise Application of River Habitat Enhancement Features Yields
Significant Ecological Functionality and Physical Sustainability
Abstract
Physical habitat losses for Pacific salmonids in California’s Central
Valley motivate stream restoration. Considerable river morphodynamics
affect the sustainability of habitat enhancing interventions. In
addition, the presence of large dams in many river catchments causes low
sediment supply. This study revises existing stream restoration
techniques for their ecologically efficient and physically stable
embedding in a 36-km testbed river. Ecological efficiency is evaluated
in terms of a commonly used hydraulic habitat suitability index.
Physical stability results from 2D hydrodynamic modelling of bed shear
stress during steady flows of different flood frequencies. We
differentiate between terraforming, stabilizing and maintaining stream
restoration techniques, which constitute three feature layers. The first
layer, terraforming, includes artificial terrain modifications such as
grading or backwater creation to generate new habitat. These features
require stabilization, which is provided by the second feature layer.
The stabilization (layer two) is achieved by bioengineering such as
placement of streamwood, angular boulders and vegetation plantings. The
third feature layer has the purpose to maintain newly created habitat,
e.g., through artificial gravel injections. We illustrate the
application of the three-layer-approach at one major restoration site of
the lower Yuba River using a self-written Python package. Ecohydraulic
2D modeling was applied to designs with incremental layer additions to
evaluate newly created spawning habitat and feature sustainability. This
procedure represents a pertinent way for stream restoration planning,
which avoids non-sustainable habitat enhancement features and implements
ecologically as well as physically sustainable features only.