Understanding Instream Flow Incremental Methodology (IFIM) Joey Kleiner

IFIM: Instream Flow Incremental Methodology The goal of an IFIM study is to show the relationship between stream flows and available aquatic habitat This Flow:Habitat relationship is necessary for assessing potential downstream impacts on habitat resulting from upstream flow alterations A main product of an IFIM study is the Weighted Usable Area (WUA) table- an index showing habitat suitability for a given species over a range of flows

Steps in the IFIM Process 1)Habitat identification 2)Transect selection 3)Species selection, habitat suitability criteria (HSC) compilation 4)Collection of field hydraulic and habitat data 5)Physical Habitat Simulation System (PHABSIM) model 6)PHABSIM output of “Weighted Usable Area” (WUA)

The Formation of Fish Habitat Fish habitat is dependent on: Depth Velocity River bottom conditions (substrate/cover) Depth and velocity conditions change with increasing flow Example: Riffles, runs, pools

The Mapping of Fish Habitat The first step in an IFIM study is the identification of aquatic habitats within the study area The stream is divided into “study reaches” at points where significant changes in channel morphology or flow occur The primary types of mesohabitats within these reaches need to be identified to facilitate transect site selection

The Mapping of Fish Habitat (cont.) Habitat mapping is achieved through the use of existing institutional knowledge, aerial photographs, GIS, GPS, and site-specific data obtained through “float trips”

Transect Locations Once the river reaches and habitat types are identified and mapped, transect locations for the collection of field hydraulic data are determined Transects are located in areas representative of the hydraulic/habitat conditions observed in that reach

Field Data Collection Physical Habitat Simulation (PHABSIM) software is used to simulate the relationship between streamflow and habitat for various species and life stages of fish Data collected in the field at each transect location is used to calibrate PHABSIM for the study reach of interest Data is collected at sampling stations/cells equally spaced along each transect Data collected at each cell include: Water surface elevation (WSE) Water velocity Substrate/cover

Field Data Collection (Cont.) WSE and velocity data are typically collected at each transect under 3 different “target flows” (low flow, medium flow, high flow) The target flows observed at the transects are achieved by altering dam releases upstream Example of target flows: 50, 150, and 300 cfs (measured by a USGS gage within the study reach) By entering the measurements taken at 3 flows, PHABSIM is able to interpolate WSE and velocity values for flows other than the 3 observed in the field

Field Data Collection (Cont.) Cover/substrate measurements are taken during the lowest target flow Codes for cover/substrate are assigned to each cell along a transect

Species Selection and HSC A set of fish species needs to be selected for Flow:Habitat analysis The species selected must be present within the study reach The species chosen are usually the ones most affected by changes in flow Each species has corresponding Habitat Suitability Criteria (HSC) that can be gathered from existing sources HSC quantify habitat quality for each species/life stage based on flow velocity, depth of the water column and substrate/cover HSC utilize a preference index ranging from 0 (least preferred) to 1 (most preferred)

PHABSIM Development A hydraulic model within PHABSIM is created for each study transect The hydraulic model consists of a water surface model and a velocity model The water surface and velocity models are developed and calibrated using the 3 data sets obtained in the field (1 data set from each of the 3 target flows) The calibrated hydraulic model is able to simulate WSE and velocity values at each cell along the transect for any flow value The hydraulic model at each transect is combined with the HSC to produce a WUA table showing the Flow:Habitat relationship at that transect

PHABSIM Development (Cont.) HSC for water depths, water velocities and substrate/cover are used to rank the suitability of each model cell in a transect This uses a multiplicative approach where suitability indexes (on a scale from 0.0 to 1.0) for a single cell in a transect are multiplied together (depth*velocity*substrate) to produce a composite suitability score for that cell (0.0 to 1.0) The suitability score of a cell is used to weight the area of that cell to produce a “Weighted usable area” (WUA) value for that cell The weighted values for all cells in a transect are summed to produce a total WUA for that transect WUA = suitability-weighted samples of area WUA is an index to the microhabitat availability

WUA Development within PHABSIM By repeating this process for multiple species/lifestages over an entire range of flows, a WUA table can be produced for each transect displaying the flow:habitat relationship for each species/lifestage of interest The WUA tables from each transect in a reach can be averaged together using weighting factors to produce a single WUA table representative of the entire reach WUA tables from each transect are weighted so that each transect's contribution to the reach-WUA is indicative of the amount of each habitat type (% area) present in the reach Area weighting factors are determined during the development of the habitat maps

WUA Development within PHABSIM (Cont.) Weighting transect-WUAs to produce a single reach-WUA table: % of each habitat type present in a single reach Weighting factors for each transect in the reach

WUA Example

Sources: Appomattox River Instream Flow (IFIM) Study: George F. Brasfield Dam to Harvell Dam, Final Report. Hunt Valley, MD: EA Engineering, Science, and Technology, Inc., Averett et. al. Stream Habitat Modeling to Support Water Management Decisions for the North Fork Shenandoah River, Virginia, Final Report. Blacksburg, VA: Virginia Tech Dept. of Fisheries & Wildlife Sciences, Bovee, K. D. et al. Stream Habitat Analysis Using the Instream Flow Incremental Methodology. Fort Collins, CO: U.S. Geological Survey, Instream Flow Incremental Methodology (IFIM) Studies on the North Anna and Pamunkey Rivers, Virginia, Final Report. Sparks, MD: EA Engineering, Science, and Technology, Inc., Krstolic, J.L., and Ramey, R.C. South Fork Shenandoah River habitat-flow modeling to determine ecological and recreational characteristics during low-flow periods: U.S. Geological Survey Scientific Investigations Report 2012–5081, 64 p Payne, T. et. al. Appalachian Power Company Claytor Hydroelectric Project No , Instream Flow Needs Study, Final Report. Arcata, California: Thomas R. Payne & Associates, pdf 08.pdf Schreiner et. al. Habitat Assessment of the Potomac River From Little Falls to Seneca Pool, Final Report. Columbia, MD: Versar, Inc., Stalnaker, C. et al. The Instream Flow Incremental Methodology, A Primer for IFIM. U.S. Dept. of the Interior Report 29,