|
<br />3.6
<br />
<br />Mussetter Engineering, Inc.
<br />
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />I
<br />
<br />gradeline elevations at equivalent points along the bar were similar in both models at high flows, indicating
<br />that the amount of cross flow will be relatively minor, The modeling approach used at the high flows is
<br />therefore believed to be reasonable. Similar to the previous analysis of the Cleopatras Couch hydraulics
<br />(Harvey, et aI., 1993), the energy gradeline profiles indicate that the riffles and tertiary bars are very
<br />pronounced at low discharges, but are drowned out at higher discharges (Figures 3.4 and 3.5), Mean
<br />velocities in the left branch channel (Cross Sections 1 through 5), vary from about 1 fps at Cross Section
<br />2 at 500 cfs to over 14 fps in the riffle at Cross Section 1,5 at 32,300 cfs (Figure 3.6). Velocities in the
<br />right branch channel vary from about 1 fps at Cross Section 2 at 500 cfs to about 11 fps in the riffle at
<br />Cross Section 5 at 32,300 cfs (Figure 3.7), In the pool upstream of the primary bar (Cross Section 6 and
<br />7), velocities range from 0.4 fps at 500 cfs to about 8,2 fps at 32,300 cfs.
<br />
<br />able 3.1. Sunimal)'offl()WspHtsfordischargesrangingfr()1ll301cfsto32,~QObfs,Y~rnp~r
<br />> ~. . ... . ..... .....r'....,.,..h ..... ... .... ... ." ......... ....... .... .....
<br />> .... ... ...............
<br /> ..LeftBr~hchiOischar9~ Right..I3ra\'lchDts$t\~rge ChuteChahl"lel
<br /> . (Cfs)1 (cf$)t DiScharge (cfs)
<br /> ............... ...................
<br /> 301 1 59 142 0
<br /> 51 6 2 289 2 227 2 0
<br /> 1 ,000 600 400 1 3
<br /> 1 ,208 71 9 489 27
<br /> 2,000 1 , 1 30 870 89
<br /> 5,000 2,880 2,120 505
<br /> 1 0,000 6, 1 80 3,820 1 ,950
<br /> 1 5,000 8, 145 6,855 n/a, see text
<br /> 20,000 1 0,820 9, 1 80 n/a, see text
<br /> 25,000 1 3,475 1 1 ,525 n/a, see text
<br /> 32 300 17 41 0 14 890 n/a see text
<br />
<br />1 Discharge in each branch upstream of the chute channel.
<br />2Measured discharges on August 25, 1995 were 292 cfs (left branch) and 224 cfs (right branch).
<br />
<br />It is important to note that the hydraulic analysis performed at this site for this study is based on
<br />a one-dimensional solution to a multi-dimensional problem, and as such, local velocities and shear
<br />stresses can vary significantly from the cross-section averages predicted by the HEC-2 model. However,
<br />the present analysis clearly defines the variation in hydraulic energy that occurs over a range of
<br />discharges at various locations at the site.
<br />3.2. Incipient Motion Analysis at Cleopatras Couch (RM 16.5)
<br />
<br />An incipient motion analysis was performed to evaluate the range of flow conditions necessary
<br />to mobilize the bed material at critical locations around the spawning bar. The analysis was performed
<br />by comparing the critical shear stress (rc , shear stress required to initiate motion) for the median particle
<br />size with the bed shear stress due to grain resistance (r') for the range of discharges up to and including
<br />the maximum recorded discharge of 32,300 cfs.
<br />
|