Demonstration Flow Assessment: Judgment and Visual Observation in Instream Flow Studies

Abstract

The Demonstration Flow Assessment (DFA) method evaluates instream flow benefits using expert judgment and direct observation of habitat during several flows. Early DFA applications were low‐effort, qualitative, and vulnerable to well‐known biases. We describe a higher‐effort, more quantitative DFA (or expert habitat mapping) approach that uses techniques from the judgment‐based decision analysis literature to increase objectivity and reproducibility. Specific metrics—habitat types to be quantified visually during flow observations—are designed from appropriate conceptual models of how flow affects target resources. During field observations, patches of each habitat type are delineated by consensus and marked on maps for digital analysis. A case study illustrates these procedures applied to instream flows for salmon spawning and rearing.

Demonstration Flow Assessment and 2‐D Modeling: Perspectives Based on Instream Flow Studies and Evaluation of Restoration Projects

“…ABSTRACT: Railsback and Kadvany (2008) make a compelling case for the use of demonstration flow assessments (DFA) for instream flow assessments as a more robust method than traditional one-dimensional habitat simulation techniques, such as the Physical Habitat Simulation System. But, based on experience with DFAs used for instream flow assessments and evaluation of stream restoration projects, the methods presented by Railsback and Kadvany (2008) may not give reproducible results, and DFAs have significant drawbacks relative to two-dimensional (2-D) hydraulic and habitat modeling.…”

“…But, based on experience with DFAs used for instream flow assessments and evaluation of stream restoration projects, the methods presented by Railsback and Kadvany (2008) may not give reproducible results, and DFAs have significant drawbacks relative to two-dimensional (2-D) hydraulic and habitat modeling. Application of the DFA methodology presented in Railsback and Kadvany (2008) to assess a stream restoration project on the Trinity River, California, did not give reproducible results, with substantial disparity between replicate surveys in the total quantity and spatial distribution of habitat. As an empirical two-dimensional habitat modeling method, DFAs have several drawbacks.…”

“…Further, 2-D modeling offers significant benefits over DFA in the context of adaptive management. Advantages of DFAs cited by Railsback and Kadvany (2008), namely the feasibility of assessing habitat with complex hydraulics, the ease in using mechanistic and theoretical conceptual models, and the ability to assess long reaches, also apply to 2-D models. Modification of the DFA methods presented in Railsback and Kadvany (2008) to give reproducible results may increase the cost of DFAs or reduce the length of stream that can be assessed with DFAs to the point where 2-D modeling may be a more cost-effective technique than DFAs.…”

“…Notably, Railsback and Kadvany (2008) cite many advantages of DFAs versus traditional onedimensional habitat modeling, such as the Physical Habitat Simulation (PHABSIM) System. The terminology for DFAs is still in flux and relate to a variety of habitat evaluation techniques; DFAs are sometimes referred to as "expert habitat mapping," "judgment based habitat mapping," or "habitat criteria mapping."…”

“…Recent DFAs in California have been used for instream flow assessments on the Pit (R 2 Resources Consultants, Inc. 2003), Lower McCloud (Pacific Gas and Electric Company 2007) and Upper Tuolumne (McBain and Trush, Inc. 2007) rivers, and for evaluation of stream restoration projects on the Trinity River (the subject of this article). These studies illustrate three important aspects of DFAs that should be considered: (1) the ability of the procedure outlined in Railsback and Kadvany (2008) to produce a credible, legally defensible, and reproducible result; (2) the relative performance of two-dimensional (2-D) hydraulic and habitat modeling (Gard 2006) versus DFAs; and (3) the range of flows and actual effort needed for DFAs. Previous applications of judgment-based habitat evaluation techniques have received criticism for their potential lack of reproducibility (Arthington and Zalucki 1998;Young et al 2004).…”