Abstract: Opening Plenary Session 2:15 pm (BACK)

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Evaluating Aquatic Habitat Quality using Geomorphic Criteria

Dave Rosgen, PhD
Wildland Hydrology
Fort Collins Colorado

Matt Kondratieff
Colorado Parks and Wildlife
Fort Collins, CO

Improving aquatic habitat is a prominent goal in the natural channel design approach to river restoration.  Prior to developing a restoration plan, assessments are necessary to identify the limiting factors related to aquatic habitat.  Traditionally, aquatic habitat assessments are stratified primarily by ecoregion, which makes population variance difficult to explain.  Within the same ecoregion, a variety of fluvial landscapes, stream types, and stability conditions exist; however, habitat evaluations seldom integrate geomorphic characteristics and processes.

A framework is presented to evaluate aquatic habitat quality using geomorphic criteria to compare impaired river systems to their physical and biological potential using reference reaches (stratified by landscape type, potential stream type, flow and sediment regimes).  Seven critical habitat components that drive aquatic species populations and support various life stages in natural river systems are evaluated, including:

  1. Salmonid forage production areas (includes aquatic and terrestrial sources)
  2. High flow refugia
  3. Low flow and winter refugia
  4. Overhead cover
  5. Instream cover
  6. Spawning habitat
  7. Rearing habitat

The purposes of the habitat quality evaluations are to 1) identify the limiting factors and variables responsible for the ratings, and 2) direct the restoration design to establish a functioning biological system that is compatible with the physical system.

The quality of each habitat component is evaluated using criteria that integrates the geomorphic assessment associated with channel stability characteristics and river processes (Figure 1); habitat quality is rated as Excellent, Acceptable, Marginal, or Poor.  Geomorphic criteria include stream types, riparian vegetation, instream wood, baseflow to bankfull discharge, pool quality and frequency, instream fine sediment, and bed compaction.  Additionally, stream stability metrics including aggradation, degradation, and streambank erosion are factored into the evaluations because of their adverse consequences to aquatic habitat quality and ecological functioning.

A spatial and temporal hierarchical view of the habitat quality evaluations is used to understand impairments related to the limiting factors and to incorporate critical habitat components into a watershed-based restoration plan.  Potential limitations to aquatic habitat and ecological functioning must be investigated at a larger spatial scale, including water quality, streamflow, and hydrological connectivity (longitudinal, lateral, vertical, and temporal).