Physics Precedes Biology – Fish Habitat Restoration
A central theme of the symposium, workshops and fieldwork of the Society of Ecological Restoration Northwest and Great Basin Conference held in Redmond, Oregon was “Physics Precedes Biology”.
Attending instructors and professionals presented papers unanimously in favor of the reintroduction of wood into streams of the Northwest and elsewhere.
The imperative is to geomorphically plan and design systems that remove erosive stress from banks and to create deep holding pools and riffles that are important to salmon and steelhead survival.
This includes an analysis of the hydraulic geometry to entrain and transport total sediment loads.
When planners and designers say, “no such bedload transport analysis is needed”, is an indication of the lack of understanding, or negligence, as the necessity for any design to accommodate loads coming through the reach where wood structures, or others are planned for construction.
If resting or adult holding pools located near redds are to be maintained in the high bedload streams of the glacial fluvial through valleys of the
West Cascade Mountain range, then an analysis of load transport needs to be analyzed and calculated, relative to any design—wood or other.
Wood structures haphazardly placed in a cross-section of a river with high loads, creates highly accelerated streambank erosion.
Wood placement used exclusively as art and not integrated to physics, is a disservice to the lotic system.
Natural streambank erosion is good and essential to the health and natural geomorphic adjustment processes of all rivers and streams.
Accelerated erosion exacerbated by randomly placed log structures can cause extreme streambed erosion rates, sometimes an order of magnitude beyond pre-construction streambank conditions.
It is essential to plan both streambank stability and load transport capabilities of any proposed in-channel log structure.
The manifestation of a geomorphically healthy river system is the combination of physics and biological attributes. The simple introduction of biological attributes preceding physical morphology of dimension, plan-form, longitudinal profile, associated hydraulics and hydrology, disregards the central tendency for rivers and is working outside the range of natural variability of the specific waterway.
Summary of Presentations given at “Society for Ecological Restoration Conference” Oct. 6-10, Redmond Oregon, 2014.