Instream Flow Incremental Methodology (IFIM) for Modelling Fish Habitat.
The concept of instream flow criteria was first defined in the 1940's, and has since developed into a major component of water resources management (Doerksen, 1991). However, defining instream flow standards has been often criticized because of the costs associated with the determinations and maintenance of the chosen flow regime (Smith, 1990), and because of the ambiguity associated with instream flow criteria, because standards have not been clearly defined by regulatory agencies (Beecher, 1990). But even critics contend that there is a need to effectively manage water resources, including the need to establish instream flow criteria.
There are a variety of instream flow methods available to determine the impact of water flow on aquatic biota (Wesche and Rechard, 1980), but the use of the Instream Flow Incremental Methodology (IFIM) has become one of the predominant methods for establishing instream flow criteria. Some states use a hierarchical approach for selecting the methodology for determining instream flows, with IFIM selected for the most complex projects that: 1) are expected to have significant impacts on the aquatic biota, 2) impact a valuable fishery, 3) are peaking facilities, and 4) involve complex negotiations (Reed and Mead, 1990). In Michigan, the Michigan Department of Natural Resources (MDNR) requires that IFIM studies be conducted on projects that do not operate as runof-river (flow into impoundment equals outflow from turbines). One major drawback to using IFIM is that this approach is the most costly and time consuming of the most frequently used instream flow methodologies (Reed and Mead, 1990).
The IFIM was developed in the late 1970's (Bovee and Milhous, 1978) and has continually been refined amid constructive criticism (Orth, 1987; Nestler et al., 1989). The methodology is based on habitat quality, as dictated by stream hydraulics, and the relationship between incremental changes in water flow as it affects available habitat (area that is suitable for a particular organism). Available habitat is based on the quality of microhabitat variables (water velocity, water depth, substrate and cover) and macrohabitat variables (water temperature, dissolved oxygen, and other water quality variables), depending on an individual organism's preference for these variables. The methodology can be used to determine available habitat for fish and wildlife, as well as determine suitability for recreational uses such as canoeing.
Annear and Conder (1984) contend that the ideal instream flow determination method should have the following attributes: 1) it should be based on biological data, 2) provide defensible results, and 3) provide for trade-offs in negotiation. The IFIM process incorporates all three attributes by using biological as well as physical data, while also providing the opportunity for intelligent interpretation of the data. Cavendish and Duncan (1986) also felt that the IFIM technique was the preferable approach because it is a good negotiating tool which allows for compromises based on alternate flow evaluations and the perceived trade-offs between flow volume (= cost) and habitat suitability. Because of these attributes, IFIM appears to be the preferable approach for resolving complex/controversial instream flow issues.
A survey of U.S. Fish and Wildlife Service field users of IFIM conducted by Armour and Taylor (1991) revealed that the methodology incorporated assumptions that are technically too simplistic but yet the methods are too complex to apply. Technical simplicity of assumptions is an inherent characteristic of the methodology (and most models). However, literature and training are available to teach all aspects of IFIM to the uninitiated, so complexity of application should not be an insurmountable problem. Armour and Taylor (1991) also reported a need for further research on the development of habitat suitability index (HIS - index that measures suitability of habitat based on preference for microhabitat variables) curves; the relationship between weighted usable area (VXA - square feet of suitable habitat for 1000 feet of river) and fish responses; and the need for monitoring studies to determine the adequacy of the recommended flows. There have been studies conducted to fill some of the above research needs. Tyus (1992), Modde and Hardy (1992), and Lenard and Orth (1985) have dealt with fundamental concepts behind HIS curve development and their application, while numerous other studies have been conducted on habitat suitability of individual species and life stages. The relationship between available habitat and standing crop has been addressed by Conder and Annear (1987) and Moyte and Baltz (1985). However, it is likely that the lack of validation or monitoring studies to determine the adequacy of agency recommended flows will continue until follow-up studies are mandated by regulations (Armour and Taylor, 1991).
The Thunder Bay Power Company (TBPCO) owns and operates a series of hydroelectric facilities and water storage impoundments on the Thunder Bay River, located in northern Michigan. Because the water storage impoundments that we studied are not operated as run-of-river, MDNR requested that the TBPCO conduct an IFIM study as part of the Federal Energy Regulatory Commission (FERC) hydroelectric relicensing process. This study was conducted by the Great Lakes Environmental Center (GLEC) to determine the effect of various flow regimes on the WUA (available habitat) of four life stages (spawning adult, fry, juvenile, and adult) of smallmouth bass (Micropterus dolomieut), northern pike (Esox lucius), and white sucker (Calostomus commersoni) below the two water storage impoundments. Smallmouth bass and northern pike were selected because they are important game species and are representative of many other game species in the Thunder Bay River system while white sucker was selected because of their importance as a prey species. The objective of this study was to determine the effects of proposed minimum water release flows below these impoundments on the Thunder Bay River in northern Michigan.
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