PROCEDURES FOR INSTREAM FLOW STUDIES: WETTED PERIMETER (WP) AND INSTREAM FLOW INCREMENTAL METHODOLOGY (IFIM)

Prepared August, 1988, by Jim Mead, DWR, and revised December 1998

• TWO VARIABLE MODEL
• FOUR VARIABLE MODEL

1. Optional field study may be done if developer does not accept desktop recommendation.
2. Field study may be required if:
   • controversy or trade-offs anticipated;
   • low water availability for multiple uses, etc.;
   • high quality habitat is affected;
   • hydropower peaking project - need to evaluate effects over a range of flows.

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1. Wetted Perimeter or Incremental Wetted Perimeter Method:
   • habitat is not of high quality or quantity;
   • a single flow will be recommended, e.g. a continuous minimum release to a diversion.
2. Instream Flow Incremental Methodology (IFIM):
   • controversy or trade-offs anticipated;
   • high quality or quantity habitat;
   • need to evaluate effects over a range of changing flows, e.g. a peaking project.

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REMAINDER OF THIS OUTLINE PERTAINS TO IFIM

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1. Examine affected portion of stream under moderately low flows.
2. Choose area that encompasses all major habitat types.
3. Multiple sites may be needed to represent changing character of different reaches of the stream.
4. Multiple sites may also be needed above and below major tributaries to reflect effects of flow from intervening drainage.

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1. Examine available data and possibly conduct sampling at sites.
2. Also decide on seasonal presence/absence of different life stages of each species chosen.

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1. Examine literature and consider suggestions from consultant or agencies.
2. Consult with Instream Flow Group, USGS (U.S. Geological Survey), Ft. Collins, Colorado if necessary.
3. If available information is not satisfactory, on-site studies to develop HSI's may be needed.

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1. Some other relevant needs or issues that may have to be considered are:
   • Canoeing, whitewater rafting or other recreational needs;
   • Water quality;
   • Aesthetics;
   • reservoir level considerations for fish spawning or recreation and during what time of year;
   • conveying water for downstream withdrawals, although not an instream flow need, may also be a factor.
2. Decide on methods and criteria for evaluating these other uses.

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1. Examine available stream gage records and select record of flows for natural, baseline conditions at study site.
2. Conversion from gage location to study site may be necessary.
3. If no gaging data, other simulation techniques may be needed.
4. A flow record for "with-project" conditions will also be needed, possibly for several scenarios.
5. Decide on time-step to be used, e.g. monthly median, monthly average, or daily flows.

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1. Determine at least 3 flow targets for data sets based on:
   • adequate range to allow simulation of minimum and maximum flows for time series analysis;
   • intervals sufficient for good stage/discharge relationship;
   • a particular range of interest, e.g. an earlier desktop recommendation or project operating characteristics.

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1. Expand written outline to include details as to site(s), species and HSI's, flows, and other instream flow needs.
2. Include schedule and roles.
3. Include specifics on techniques for interpreting results of habitat modeling and criteria for agency recommendations.
4. Include methods/criteria for evaluating other instream uses and lake levels.

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1. Agency responsibilities
   • initial data set:
     • map habitat at site to weight transects;
     • select transects for habitat and hydraulic modeling;
     • select verticals during survey of transect profiles;
     • assign cover/substrate code to each vertical.
2. Consultant responsibilities
   • initial and subsequent data sets:
     • participate in habitat mapping etc. listed above;
     • surveying, velocity and discharge measurements;
     • photographs of each transect at different flows.

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1. Agency Responsibilities:
   • provide reach length and weighting factors for each transect;
   • provide list of flows for which habitat will be modeled;
   • suggest methods for simulating water surface elevations;
   • provide HSI's selected earlier.
2. Consultant Responsibilities:
   • construct and calibrate hydraulic model;
   • merge hydraulic output with habitat model to yield habitat versus discharge relationship for each species/life stage chosen.

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1. Describe study design, methods, calibration of IFIM model, habitat versus flow relationships, and evaluation of other instream uses and lake levels.
2. The following are needed for initial review of IFIM modeling:
   • copies of field notes;
   • any spread sheets or other calculations used for data compilation;
   • labeled photographs or slides;
   • final production run IFG4 model, on diskette;
   • key to substrate/cover code used in IFG4 model;
   • table of HSI values for each species/life stage.
3. Details needed to review water surface elevation (WSL) simulation:
   • table of WSL's for all transects at all calibration flows, with a column for each of the following: target WSL's based on field measurements, simulated WSL's using IFG4 and any other approaches tried (WSP, MANSQ, arithmetic plots, HEC-5, etc.);
   • rationale for final selection of WSL simulation method(s);
   • provide production run models if WSP or MANSQ is used for any transects. Similarly, provide any arithmetic plots used.
4. Details needed to review velocity simulation:
   • Output from RIFG4 final calibration run, showing velocities and roughnesses at each vertical, on diskette. Note: Calibration flows should be equal to the discharges of the different data sets.
   • Output file of velocity adjustment factors (from production run) versus discharge, at each transect, on diskette.
   • Explanation of any IFG4 modifications for velocity simulation, e.g. BMAX, NMAX, manually entered roughnesses.

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1. After habitat versus discharge relationships are accepted by DWR, WRC, and USFWS, convert baseline natural flow record into a time series of habitat.
2. Determine Index C value under natural flow conditions for species/life stage. This is the arithmetic average of all habitat occurrences between the 50% and 100% exceedence values.
3. Evaluate the effects of with-project scenarios on habitat:
   • Calculate the Index C value for habitat occurring under each flow scenario.
   • What is the percentage change in Index C for each species/life stage? This is calculated as ((natural - project) / natural).
4. Develop proposed operating conditions to meet criteria for aquatic habitat.

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1. Based on criteria agreed upon earlier.
2. Network analysis of multiple sites and target flows or operating recommendations.
3. Fisheries management decisions to reconcile differing requirements for different species/life stages.

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Please send questions or comments to the Instream Flow Unit, which created and maintains this site.