The IFIM is meant to be implemented in five sequential phases: problem identification, study planning, study implementation, alternatives analysis, and problem resolution (see figure below).
Overview of Instream Flow Incremental Methodology:
1. Start of the IFIM process
2. Legal and Institutional Analysis Model (LIAM)
3. Strategy Design
4. Technical Scoping
5. Micro and Macro-habitat Models
6. Formulate Alternatives Using Total Habitat Model, Network Habitat Model
7. If Alternative is not feasible, step back to (6) and re-Formulate Alternatives.
8. Negotiate issue resolution with stakeholders. If negotiation concludes
further analysis is required, re-enter the analysis cycle at step (2).
If a negotiated resolution is achieved, stop.
After a proposed change in the water management system becomes known, the first phase of an IFIM assessment begins. This phase has two parts, a legal-institutional analysis, and a physical analysis. The interagency group should perform the legal and institutional analysis. This analysis identifies all affected or interested parties, their concerns, information needs, and relative influence or power, as well as the likely decision process. Thus, phase one will result in a better understanding of the proposed project, the likely impacts, and the objectives of all interested parties.
In the second part of phase one, the physical analysis determines:
1. The physical location and geographic extent of probable physical and chemical changes to the system.
2. The aquatic resources of greatest concern, along with their respective management objectives.
Problem identification is often accomplished with a scoping meeting involving the management and regulatory agencies likely to be involved with the decision. A preferred alternative may be identified by the project proponent, and the consequences of this alternative are translated into a hydrologic time series that assumes the project is in place and operating as proposed. The group should also jointly develop a baseline hydrologic time series representing either the status quo or another baseline that is mutually acceptable. The two hydrologic time series, in a preliminary sense, establish the basis for the next phase -- study planning.
Carefully planning the course of an IFIM assessment is critical. The focus of this phase is to identify what information is needed to address the concerns of each group, what information already exists, and what new information must be obtained. Study planning details should dominate the discussions and result in a concise, written plan documenting who is going to do what, when, where, how, and for how much money. The study plan must be feasible, given the decision schedule and the human and financial resources available.
The planning team must build on the objectives and information needs of each party. The team should not try to predict the outcome of a study but focus on data collection and the methods to be used. Proper planning will lead to the identification of :
1. The temporal and spatial scale of evaluations.
2. The important variables for which information is needed.
3. How information will be obtained if it does not exist.
The planning group must also agree on methods of quantifying the effects of each alternative.
The hydrologic information chosen to represent the baseline or reference condition should be reexamined in detail at this point. All parties must understand and agree on one or more hydrologic time series that will be used for comparison. The baseline hydrologic time series serves as a reference for judging potential impacts. Often the baseline condition is not the actual historical hydrology used in problem identification, but a synthetic time series representing present water uses, operational procedures, and waste loads superimposed on the variability found in the historical hydrologic records.
The resource agency responsible for fisheries must describe the biological reference or benchmark conditions. Identifying the geographic distribution and important times of the year is critical in evaluating different life history phases of the fish populations. A population benchmark may be constructed using historical habitat conditions and 'backcasting' to identify critical events that populations may have experienced due to physical or chemical limitations.
A written study plan should:
1. Determine when data collection must be completed in
the field.
2. Synchronize the collection of data needed for model input, calibration,
and testing.
3. Estimate the labor, equipment, travel, and other costs required to
produce the needed information by the agreed study deadline.
An interdisciplinary planning effort representing all the major interest groups can result in considerable savings of time and effort during the conflict resolution phase.
From the field biologists' perspective, the implementation phase is often the most interesting and scientifically challenging. This phase consists of several sequential activities: data collection, model calibration, predictive simulation, and synthesis of results. Proper implementation of the study is critical and can bring biological credibility to the decision process but will not, by itself, result in good decisions.
During implementation, sampling locations are selected for collecting data used in predictive models. Data collected can include temperature, pH, dissolved oxygen, biological parameters, and measures of flow such as velocity, depth, and cover. These variables are used in describing the relation between stream flow and stream habitat utility. IFIM relies heavily on models because they can be used to evaluate new projects or new operations of existing projects. Model calibration and quality assurance are keys during this phase and, when performed carefully, lead to reliable estimates of the total habitat within the study area during simulation of the alternative flow regimes. Total habitat is synthesized by integrating large-scale macrohabitat variables with small-scale microhabitat variable (see figure below). An important intermediate product from this phase is the baseline habitat time series. This analysis determines how much habitat in total would be available for each life stage of each species over time. The baseline habitat time series provides the base from which rational judgments can be made about proposed alternative management schemes.
Total habitat combines elements of macrohabitat and microhabitat:
In the macrohabitat, discharge affects temperature, water quality and channel structure. Temperature and discharge affect water quality, which yields miles of useable stream(1).
In the microhabitat, discharge and channel structure affect depth, velocity, and substrate structure. These in turn give us the yield of habitat area per mile of stream(2).
The product of miles of useable stream(1) and habitat area per mile of stream(2) is the Total Habitat.
Some site-specific empirical evidence should be collected to ensure validity when applying instream flow models. Site-specific data helps reduce uncertainty in understanding how biological systems work and reduces the imprecision of the small samples used to represent a dynamic stream system. Site-specific data also fosters communication among the diverse disciplines of engineering, law, ecology, and economics. Just as grab sample measurements of temperature, water quality, depths, and velocities are routinely used to calibrate physical and chemical models, samples of the aquatic organisms and their habitat use must be used to 'calibrate' the habitat simulations used in IFIM alternatives analyses.
Phase three results in estimates of the relation between flow and total habitat, as well as measures of the amount of habitat available under the chosen baseline conditions and the various with-project alternatives. This habitat quantification leads naturally into the next phase that will compare and evaluate the alternatives. Before discussing the next phase, however, it would be best to make specific mention of PHABSIM.
Many people confuse IFIM with the Physical HABitat SIMulation System (PHABSIM). Where IFIM is a general problem solving approach employing systems analysis techniques, PHABSIM is a specific model designed to calculate an index to the amount of microhabitat available for different life stages at different flow levels. PHABSIM has two major analytical components: stream hydraulics and life stage-specific habitat requirements (see figure below)
Conceptualization of how PHABSIM calculates habitat values as a function of discharge. (A) First, depth (Di), velocity (Vi), cover conditions (Ci), and area (Ai) are measured or simulated for a given discharge. (B) Suitability index (SI) criteria are used to weight the area of each cell for the discharge. The habitat values for all cells in the study reach are summed to obtain a single habitat value for the discharge. The procedure is repeated through a range of discharges to obtain the graph (C).
The stream hydraulic component predicts depths and water velocities at specific locations on a cross section of a stream. Field measurements of depth, velocity, substrate material, and cover at specific sampling points on a cross section are taken at different flows. Hydraulic measurements, such as water surface elevations, are also collected during the field inventory. These data are used to calibrate the hydraulic models and then predict depths and velocities at flows different from those measured.
The hydraulic models have two major steps. The first is to calculate the water surface elevation for a specified flow, thus predicting the depth. The second is to simulate the velocities across the cross section. Each of these two steps can use techniques based on theory or on empirical regression techniques, depending on the circumstances. The empirical techniques require much supporting data; the theoretical techniques much less. Most applications involve a mix of hydraulic sub-models to characterize a variety of hydraulic conditions at various simulated flows.
The habitat component weights each stream cell using indices that assign a relative value between 0 and 1 for each habitat attribute indicating how suitable that attribute is for the life stage under consideration. These attribute indices are usually termed habitat suitability indices and are developed using direct observations of the attributes used most often by a life stage, by expert opinion about what the life requisites are, or by a combination. Various approaches are taken to factor assorted biases out of this suitability data, but they remain indices that are used as weights of suitability. In the last step of the habitat component, the hydraulic estimates of depth and velocity at different flow levels are combined with the suitability values for those attributes to weight the area of each cell at the simulated flows. The weighted values for all cells are summed -- thus the term weighted usable area (WUA).
There are many variations on the basic approach outlined above, with specific analyses tailored for different water management phenomena, or for special habitat needs. However, the fundamentals of hydraulic and habitat modeling remain the same, resulting in a WUA versus discharge function. This function should be combined with water availability to develop an idea of what life stages are impacted by a loss or gain of available habitat at what time of the year. Time series analysis plays this role, and also factors in any physical and institutional constraints on water management so that alternatives can be evaluated.
Several things must be remembered about PHABSIM. First, it provides an index to the microhabitat availability; it is not a measure of the habitat actually used by aquatic organisms. It can only be used if the species under consideration exhibit documented preferences for depth, velocity, substrate material/cover, or other predictable microhabitat attributes in a specific environment of competition and predation. The typical application of PHABSIM assumes relatively steady flow conditions such that depths and velocities are comparably stable for the chosen time step. PHABSIM does not predict the effects of flow on channel change. Finally, the field data and computer analysis requirements can be relatively large.
Back to the phases of IFIM.
The water project proponent will usually have a preferred alternative, but other alternatives must be identified for comparison. Other parties to the decision process should propose alternatives. The alternatives analysis phase compares all alternatives with the baseline condition to facilitate an understanding of potential impacts and to begin negotiating and creating new alternatives more compatible with the multiple objectives of the many parties. When properly completed, simulation modeling using IFIM allows for straightforward comparison of many alternatives, each of which is examined for:
1. Effectiveness -- Are the objectives
of all parties sustainable? Is no net loss of habitat possible on a sustainable
basis? What are the habitat costs and benefits of each alternative?
2. Physical feasibility -- Do reservoirs dry up? Are
priority water rights not met? Will flooding occur? Is enough water available?
3. Risk -- How often does an alternative lead to failure
or collapse of the biological system? Is a failure reversible? Can contingency
plans be developed?
4. Economics -- What are the costs and benefits of each
alternative?
Probably the biggest mistake the interagency group could make at this point is to choose one alternative from a group of poor alternatives. It is far better to create new alternatives, learning as you go. When complete, this phase results in a comprehensive array of alternatives, each quantitatively described.
Given several alternatives that have been thoroughly evaluated, the choice should be obvious, right? Usually, this is not the case; the IFIM does not guarantee a single, best solution. The optimum solution can rarely be identified because:
1. Biological and economic values are never truly commensurate.
2. Data and models are never complete or perfect.
3. Rational people can reach different conclusions.
4. Uncertainty about the future is ever-present. IFIM was designed to aid in formulating and evaluating alternatives; however, it still relies heavily on professional judgment by interdisciplinary teams.
The teams must integrate their knowledge and understanding of a problem with their professional judgments about the biological resources and social needs to reach a negotiated solution implying some kind of balance among conflicting social values. The methodology is not fixed. It is open-ended and imaginative. Flexible, mutually beneficial, negotiated solutions are encouraged.
Though an IFIM assessment concludes with the Problem Resolution phase, many projects offer the opportunity for continued learning by all parties. Because our models and judgments are by their nature incomplete and imperfect, our predictions are likewise incomplete and imperfect. Post-project monitoring and evaluation, with the intent of developing into adaptive management, should be considered when appropriate. The more we understand, the better we can assess and manage the next project. Ultimately, IFIM's goal is ensuring the preservation or enhancement of our fish and wildlife resources.
For more detailed coverage of IFIM, download Stream Habitat Analysis using the IFIM.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://www.fort.usgs.gov/Products/Software/ifim/5phases.asp
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