Dolores River Core Science Report

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T~'ihle ? - [H,~ ~e~ults F+nr [l~ol~o~es [~i~er at ~'i~c~a, [.;T ~~~g. ~f~-Illl~lry"t ~l~ll~~t - 1 ~y., - 1 ,~ ~~Li k'$~I`.°,;I ~ie~:at-II"~},~i:m:t ~121I~i;l- '~~~- ~? ~~v X~nl~~; M~~~n ~~9~t~n F~~[~f11kLJtl~ ~t ~~ ~It~r~t~e "~t~l~ fol~ '~~~Ik~ fc~r ~l~fer~ltice I~~k~~~+en ~} ~r~- r~$t- It1~f~r1 ~}I'~ t91ti(# ~IC~St- ~f7li}~~t ~nlilt'~Ct .~rlEll}0"k- IRil3~`iCt ~~Il~[r' p211C[C II1i }~9ut 1~I10f~ I~rIG[l~ I - rr'~~3 n rr~~~ nCt~ ky ~~'~' 9~ ~ I 1 °~~~~ ~~v 11 ~ 1 ~ bA.3'y - rr~.3n m~nti~iy fay' I,dsl ~~'1 ~@s1~~ ~5 Jung - rrraan rrr~nth f6~' B:~fsl ~~a ~ 1 ~~5 -3;~ -1 Jwfy - ma:3n m~r~[hl'y fk~' i'~s! ~4~3 5a °3 -~ ~ -11 1 ~~~ m~ximl~m ~~~I 5~38~ ~~a ~ -75~ -13 ~~lay~ m~cimum fcfse 5~~'3 4a~4~ -~~~ -13 '~i.~y rr~3xirnurn f~#s1 ~1?.5~ ~~~ -~1' -~ ~s~~j: mimwm f~f3j ~5'~ ~~45 -~~°~ -~ ~~~j m,3xlml~m f~~f~~~l X451 ~'~7~ -14~ -~ Hi~~h pulsa` ~iur.3[i~a7 ~,~~'~ ~i 1 a ~+~ ~ ~1 `Tha high ~ul~$ 4a;~1 is ~°3~~ ~.f, I:maan ~f p~r$~ari~~d ~~th ~-ar~enti~ fl~'I Channel-forming discharge The channel-forming discharge or the flow that maintains the channel morphology and planform are typically estimated in various ways. One estimation method is to determine the flow that fills the available channel cross section, referred to as the bankfull discharge (Wolman and Leopold, 1957). Another method is to determine the flow that carries the most sediment, which is called the effective discharge (Wolman and Miller, 1960). Another way to estimate the channel- fornung discharge is to determine what discharge is necessary to mobilize the sediment particles comprising the bed material of the chaiulel. A correlation between both the banlcfull and effective discharge and the 1-2 year recurrence interval flood has been found in many rivers, particularly those in humid, temperate areas (Wolman and Leopold, 1957, Wolman and Miller, 1960). The designation of the 1-2 year flow as the channel-forming discharge is an versimplification in many respects, because channel form is product of a range of discharges (which may include the bai~lcfull discharge) rather than a single formative discharge and of the temporal sequence of high-flow events (Knighton, 1998). In river segments where the channel boundary is controlled by bedrock or other highly resistant material, high-magnitude, low frequency floods (»1-2 year) may represent the channel-forming discharge (Knighton, 1998). This caveat is particularly relevant to bedrock-controlled segments of canyon reaches of the Dolores River, where floodplains are largely absent and the canyon walls comprise the channel boundaries. k7 1990, BLM performed an assessment of the pre- and post-dam flow regimes of the Dolores River and the impacts of changes in the flow regime on channel morphology (USDI BLM, 1990). 27