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In order to evaluate the changes in the flow regime resulting from the constn~ction of McPhee <br />Dam, hydrologic data from the Bedrock gage and the gage near Cisco, UT on the Dolores River <br />were analyzed using the hidicators of Hydrologic Alteration (IHA) software (Richter el al., <br />1996). The analysis was performed by David Graf at CDOW (2005). IHA evaluates changes in <br />flow regime by comparing pre-impact mean daily flows with post-impact mean daily flows. <br />Results of the analysis include 32 parameters that statistically characterize the flow regime and <br />differences between the pre-impact and post-impact periods. The summary statistics can be used <br />to understand changes in geomorphically important hydrologic processes along the Dolores <br />River as a result of McPhee Dam. Of the 32 parameters summarized by the IHA software, the <br />most geomorphically important are the magnitude and duration of annual maximum flows and <br />the frequency and duration of high pulses (high flows that are less than the annual maxima). At <br />the Bedrock gage, the parameters exhibiting the greatest impact by the dam are the annual <br />maximum flows (36 to 41% decrease) and the duration of the high pulse (60% decrease) (Table <br />1). The Cisco gage is below the input of the San Miguel River, the largest tributary to the lower <br />Dolores River. The impacts of the dam on the flows at the Cisco gage are not as significant as at <br />the Bedrock gage (Table 2). The greatest change is in the one and three day maximum flows <br />(13% decrease). <br />Table 1- IHA Results for the Dolores River at Bedrock gage. <br />Pre-Impact Period: 1918-1983 (18 years) <br />Post-Impact Period: 1984-2003 (20 years) <br />fu~~~ n f~~ n f~1.~~r7 ir. u ~f~ ~ '~~ ~ 1717 <br />'~~{~I fir ~{~It•I~ f~l~ ~I~f~r~lti~ I~~~~~~~ f~~ <br />~I~- ~~~t- ~tX'~ 17 I}p`~ ~~ I~~ I} {}fit- <br />Iml}•~~t Iml~~~~:t "I111~019: imf~~~t <br />~~lir~~ P~li~~a il~~i.~~vt I~ritl I~~ri~~l <br />~~il - ITr€~~11 m~~ntf71~ flew ff;i 1 ~1 ~ -~~~ - <br />I'~~~ - m0311 m~lltflf~ fig' 1~~8i ~1 ~~ 1 ~B~ -7~~ ~ <br />Jlal~ - main ~'~rrtf7fl{ fionw' f~:f~1 1~ ~a ~ -a ~~ -~~ <br />~~~ - m~~n m~arrtf7h~ #f~n} i"~~~! ~ 1 ~a -1 ~? ~3 <br />1~~~ m~€Iml~m I~fB`I ~~11 ~~~ -1~1~ ~ <br />~~r3~f m~:x:imum 1~5•I ~~1 ~11~~ -1 ~~1 - <br />a ~~~ m~?€ Imam (+~#~~I ~ 1 ~ 1 ~~ 1 ~ -1 1 ~~ -~ <br />~~ ~j m~~im um d~:f a 23`~~~ 1 ~ -°~ ~~ -~ <br />~I~ ~j m.~{:IPTm um I~f~~ a 1 ~~i ~~~ 1 -~~~ ~ 1 <br />Hi~f7 ~ul:~` dur~ti~n f~i31 1~ -1 1 ~a <br />'Tl~ f7i~f7 ~uf3~ ~~;~I n~ 15{~~ ~~f im~.3n,~f ~r~-~ri~a~ ~~tf7 ~r~nti~ f{a~'I <br />26 <br />