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<br />UUI0GG <br /> <br />e <br /> <br />e <br /> <br />availabili~y or suitability of the habitat ~ <br /> <br />2. Flow Timing: The timing of particular flow conditions ~ determine whether <br />certain lith cycle requirements are met, or influence the degree of stress or <br />mortality associated with extreme events such as floods or droughts. <br /> <br />3. Flow Frf!quency: The frequency of occurrence of specific flow conditions such as <br />floods or droughts may be tied to reproduction or mortality events, thereby <br />influenclllg population dynamics. <br /> <br />4. Flow DUJ'ation: The length of time over which a specific flow condition exists may <br />determin.: whether a particular life cycle phase can be completed or the degree to <br />which stn:ssful effects such as inundation or desiccation can accumulate. <br /> <br />S. Flow Ra,~e of Change: The rate of change in flow conditions may be tied to the <br />stranding of certain organisms in ponded depressions or along the water's edge. <br /> <br />The 33 biologic"Jly-relevant hydrologic at1ributes comprising the ilIA method are divided <br />into five major groups for purposes of analysis. These groups are: <br /> <br />1. IHA Gr(,lup #1; Magnitude o/Monthly Flow Conditions: This group includes 12 <br />attributes I the mean (or median) flow value for each calendar month. <br /> <br />2. IRA Group #2; Magnitude and Duration of Annual Extreme Water Conditions: <br />This grOl;.p is comprised of 12 attributes, including the 1-,3-, 7-, 30-, and 90-day <br />annual flow minima and maxima. <br /> <br />3. IRA Group #3; Timing of Annual Extreme Water Conditions: This group includes <br />2 at1ributes, the Julian date of the I-day annual minimum flow condition and the <br />Julian dfde of the I-day annual maximum flow condition. <br /> <br />4. IRA Gr.Jup #4; Frequency and Duration of High and Low Flow Pulses: The 4 <br />attribute~ in this group include two which measure the number of annual <br />occurreIll-::es during which the flow magnitude exceeds an upper threshold or remains <br />below a lower threshold, respectively, and two which measure the mean duration of <br />such high and low flow pulses. Pulses are defined as those periods within a year in <br />which th;l mean daily flow rises above the 7SLh percentile (high pulse) or drops <br />below the 25th percentile (low pulse) of all daily values for the pre-impact time <br />period. <br /> <br />4 <br /> <br />E09-~ BlO/lOO"d 99;-1 <br /> <br />-WOJ~ wdll:IO EO-BO-l'O <br />