Legend
690
Legend
WSW1565600 fss
S 100 ccf
Mill Road
WSW313170fcfs
S 70c s
WS 2000 cfs
680
WS 2000 cfs
WS 783 cfs
WS 78ounds
3 cf
Gr
Obsound 83 cfs
Gr WS 7
670
Obs bsS S 800cfcfs
OWW 723 0 s
Obs WS 3170cfs
Obs WS 2000 cfs
Obs WS 15600 cfs
Leydecker
Obs WS 3170cfs
Road
660
Obs WS 15600 cfs
650
Figure 17. Open-water calibration of HEC-RAS
model without ICS (Plan 61). The vertical line farthest
640
to the left is the location of Mill Road, and the other is
Leydecker Road.
630
620
-3000
0
3000
6000
9000
12000
15000
18000
Main Channel Distance (ft)
644
Legegend
Lend
WS 5800 cfs
WS 5800 cfs
WS 2900 cfs
WS 2900 cfs
WS 1550 cfs
WGround50 cfs
S 15
642
Obs WS r580ndfs
G ou0 c
Obs WS 2900 cfs
Obs WS 5800 cfs
Obs WS 1550 cfs
Obs WS 2900 cfs
640
Obs WS 1550 cfs
638
636
Figure 18. Open-water calibration of HEC-RAS
model with ICS (Plan 60). Observed WSE's are from
physical model. Channel distance is relative to location
634
of ICS (positive upstream).
632
-500
0
500
1000
1500
2000
Main Channel Distance (ft)
has not been an area of concern during past events. The
all the tests, however, the jams were grounded at the
ice run through the reach in 1985 caused 5- to 6-ft-high
ICS, a feature that cannot be modeled directly with
shear walls upstream of both Mill Road and Leydecker
HEC-RAS. Instead, we matched the measured WSE's
Road (Predmore 1985), although these probably reflect
by setting 6-ft-thick ice covers along the first 50 ft
very dynamic jam formation and collapse processes at
upstream of the ICS (Fig. 19). We selected a conserva-
the onset of the event (say, 20004000 cfs). Also, local
tive value of 0.08 for Manning's n of the underside of
residents (J. Durand and J. Brady) noted that ice runs
the ice jam and used this for all the final ice-jam runs.
have caused below-flood-stage elevations at and up-
Runs conducted with variable Manning's n (i.e., n
stream of Winspear Road, but they differed in opinion
dependent on jam thickness) yielded similar results.
about whether stationary jams formed.
Also, runs with the ice jam toe at Mill Road converged
The physical model provided WSE data with the ICS
with these results about 1000 ft upstream of the ICS,
for many different ice-jam conditions. We selected three
indicating that river geometry governs ice-jam thick-
data sets (2000, 6000, and 6100 cfs) that offered fairly
ness except near the structure. At ice-jam discharges of
long, steady-state ice jams upstream of the ICS. As with
900012,000 cfs, we thickened the jam toe to 8 ft and
17
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