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~~~~rv <br />Uva - -I - r r -I r r r r r - ~- r r 7 I 1 I 1 <br />I I I I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I I I <br />~'~~'+°~ I I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I <br />~4! J of <br />I I I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I I <br />~`} ry c,g~.h. I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I I <br />~~~~ I I I I I I I I I I I I I I 1 11 <br />.~' I I I I I I I I I I I I I I I I <br />~~ ryC I I I I I I I I I I I I I I I I I <br />C J~.~i .~t I I I I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I I I <br />ry,.4,V ~ I I I I I I I I I I I I I I I I <br />~ C I I I I I I I I I I I I I I I I <br />ryw I I I I I I I I I I I I I I I I <br />4 15u <br />I I I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I I <br />1 ~_ryw I I I I I I I I I I I I I I I I <br />i+a I I I I I I I I I I I I I I I I I <br />Cry I I I I I I I I I I I I I I I I I <br />`~ °~ I I I I I I I I I I I I I I I I <br />I I I I I I I I I I I I I I I I I <br />1.a 1u.u„ 1~u'~.~~,' <br />FCec~arr~r~c~ litireral~l 61r~e:~rsi <br />+ P~ . F ~.tiw FPS ~ rK~yf <br />F i~~rs• ti - I"r~~k I° I~pn~ I~'rca~~ n~c~ 1lcllr5s .llsl`hcc R~,x n €Ilr ? 19?i6 - 3UU3 i - {'~tl~K~lrla I~ti~'1# ~ain~, S lik tirlo,~~xl <br />bti I:~aYS ill (:ruE, ~t'INg~~', ~IfiFS i <br />BLM (1990) also estimated the flows necessary to mobilize the bed material between Bradfield <br />Bridge and Bedrock. This report suggested that a flow of 2,000 cfs is required to move the <br />median bed material size (D50), and that a flow of 7,000 cfs is necessary to move most of the <br />bed materials (USDI BLM, 1990). These results suggest that prior to constn~ction of McPhee <br />Dam, the median size bed material moved on the average every 1 to 2 years, and the larger bed <br />material sizes moved about once every 5 to 10 years (USDI BLM, 1990). Recent estimates of <br />banlcfull discharge have been developed for the Dolores River in Big Gypsum Valley (Figure 7) <br />(Richard and Anderson, Preliminary Results) using HEC-RAS river modeling software to <br />determine at the discharge associated with floodplain inundation. Twenty five cross sections <br />were established throughout a 1.9-mile reach (Figure 8). Preliminary results suggest that flows of <br />at least 2,000 cfs are necessary to inundate the floodplains and that 1,000 cfs does not flow onto <br />the floodplain surfaces. Further calibration and validation of the model are necessary to further <br />refine the banlcfull discharge estimates. The results correlate well with BLM's (1990) estimate of <br />2,200 cfs banlcfi~ll discharge below Disappointment Creek. Cross sections BG19 and BG20 (BG <br />= Big Gypsum, see Figure 9 and Figure 10) provide an example of the modeled floodplain <br />inundation. Flows of 1,000, 2,000 and 3,000 cfs were modeled in HEC-RAS as well as a <br />calibration flow of 60 cfs (Figure ll and Figure 12). The model results were combined with a <br />digital elevation model of the channel and adjacent topography to show areas inundated at <br />different flow rates (Figure 13, Figure 14 and Figure 15). The resulting inundated areas show <br />that 1,000 cfs does not inundate the floodplain. Similar results were obtained in other areas of the <br />Big Gypsum reach, for example at cross sections BG16 and BG17 (Figure 16 and Figure 17). <br />29 <br />