Abstract
ABSTRACTA geomorphic assessment of the Middle Fork John Day Watershed, Oregon, USA, was used to generate a hierarchical, map-based understanding of watershed impairments and potential opportunities for improvements. Specifically, we (1) assessed river diversity (character and behavior) and patterns of reach types (and their controls); (2) evaluated the geomorphic condition of the streams; (3) interpreted their geomorphic recovery potential; and (4) synthesized the above into a hypothetical, strategic management plan. Collectively, these maps can set bounds and provide realistic guidance for river rehabilitation, design and implementation efforts. Fifteen distinct reach types were identified, two-thirds of which are found along perennial streams. On the basis of a variety of geo-indicators, approximately two-thirds of all perennial stream reaches were found to be in ‘good’ geomorphic condition, whereas one-third had departed to ‘moderate’ and ‘poor’ condition. Departures from ‘good’ condition were primarily related to riparian vegetation removal, conversion of floodplain to agricultural land uses (farming and grazing), logging, and channel bed dredge mining for gold. Encouragingly, the majority of reaches classified as being in moderate geomorphic condition were found to have high recovery potential. While our geomorphic assessment has practical utility for informing physically realistic expectation management for efforts like salmonid habitat restoration, the maps themselves are the key vehicle for communicating and visualizing among stakeholders.
Highlights
Geomorphic mapping of channel patterns and reach types over entire drainage networks sets the stage for restoration and conservation planning (Beechie & Imaki, 2014)
Using the results of reach types, geomorphic condition, and recovery potential, we developed a watershedframed strategic plan wherein realistic goals for river rehabilitation and restoration occurring over a timeframe of 50–100 years are defined
Our study presents a series of maps for the MFJD Watershed in northeast Oregon, which help set physically realistic, geomorphic bounds on what might be possible for managers to achieve through restoration and conservation actions
Summary
Geomorphic mapping of channel patterns and reach types over entire drainage networks sets the stage for restoration and conservation planning (Beechie & Imaki, 2014). Lithology and rock strength, stream power and drainage basin area are all important controls on river character and behavior (Church, 1992; Schumm, 1977) Interactions among these factors shape channels and their floodplains forming reaches of relatively distinctive structure and function (Buffington & Montgomery, 2013; Kellerhals, Church, & Bray, 1976). A reach break is the physical transition between different adjacent reach types with characteristic valley setting, planform, bed material, and geomorphic unit assemblages In this study, such process-based reach types are synonymous with distinct river styles (cf Brierley & Fryirs, 2005). Links between the physical environment and aquatic ecosystems, support efforts to move beyond site or reach-specific management applications to procedures that work with watershedspecific process relationships This is especially important for fish protection (Fausch et al, 2002). We use the Middle Fork John Day Watershed in Oregon, USA as a case study
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