ETL 1110-2-367
31 Mar 95
g. Seepage. Seepage curves for each interior ponding area
hydrographs at each flank levee outlet site. With HEC-IFH,
one can enter a family of curves with the tributary discharge
were supplied by geotechnical personnel to estimate seepage
and Meramec backwater elevation to determine the
inflow during blocked outlet conditions. These relationships are
corresponding elevation at the tributary gravity outlet site.
shown in Table E-4.
Figures E-3 and E-4 illustrate this procedure. Consequently,
h. Auxiliary outflows. One diversion was incorporated to
blocked outlets from either the Meramec or from the
tributary could be included. Grand Glaize and Fishpot
transfer inflow from the upper subarea for the Highway 141
Creek parameters are shown in Table E-5.
basin to the Fishpot subarea during blocked outlet conditions
at the Highway 141 site. Figure E-1 shows the diversion
E-5.
Minimum Facility
location.
i. Flank levee exterior elevations. Because some gravity
A minimum facility was evaluated at each of the five
subareas using both the HEA and the CSA techniques.
outlet structures discharge into Fishpot and Grand Glaize
Creeks, exterior river elevations for these structures can
a.
HEA. HEA was performed for both blocked and
change rapidly during local rainfall events independent of
unblocked outlet conditions, using hypothetical storm rainfall,
the Meramec elevations. Consequently, the blocked outlets
subarea runoff, available interior storage, and a minimum
at these sites could be caused by either Meramec River
gravity outlet diameter. Stage-frequency relationships for both
backwater, by Fishpot or Grand Glaize Creek flows, or a
blocked and unblocked conditions were determined. Larger
combination of the two. Water surface profile analyses were
gravity outlets were evaluated, but essentially no improvement
performed for a variety of tributary discharges coincident with
in interior peak stages was noted, due to the ponding storage
the full range of Meramec River backwater elevations. Unit
available at each site.
hydrographs and runoff coefficients were used to generate
Table E-4
Seepage Curves for Ponding Areas
Fishpot
I-141
Glass Plant
Simpson Lake
Grand Glaize
Head
Seepage
Head
Seepage
Head
Seepage
Head
Seepage
Head
Seepage
(ft)
(cfs)
(ft)
(cfs)
(ft)
(cfs)
(ft)
(cfs)
(ft)
(cfs)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
24.1
1.0
24.1
0.8
1.0
0.8
1.0
0.6
24.0
0.8
26.1
1.1
26.1
1.0
2.0
1.5
3.0
1.8
26.7
1.0
29.7
1.2
29.7
1.1
3.0
2.3
4.0
2.4
29.7
1.1
36.2
1.3
36.2
1.2
5.0
3.8
5.0
3.0
36.2
1.2
10.0
7.5
10.0
6.0
15.0
11.3
15.0
9.0
20.0
15.0
20.0
12.0
25.0
18.8
30.0
18.0
30.0
22.5
Table E-5
Exterior Unit Hydrograph Parameters
Runoff
SCS
Exterior
Area
Coefficient
T(Lag)
Location
(sq mi)
(percent)
(hr)
Fishpot Creek
10.1
85
.90
Grand Glaize Creek
23.7
85
1.58
E-5
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