FLOOD01055

• County: Phillips
• Community: Haxtun
• Stream Name: North Fork Frenchman Creek
• Title: Floodplain Study and Master Drainage Plan
• Date: 1/1/1987
• Prepared For: Haxtun
• Prepared By: Simons Li & Associates Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

9

10

Table 2. Sumary of Rainfall Depth ~nd Distribution Data
In-Town Drainage Basins.

o
5
10
15
20
25
30
J5
40
45
50
55
60
65
70
75
80
85
90
95
100
105
ilO
il5
120

0.000
0.020
0.057
0.139
0.289
0.539
0.659
0.715
0.758
0.796
0.828
0.860
0.892
0.924
0.956
0.988
1.013
1.032
1.051
1.070
1.089
1.108
1.127
1.144
1.154

0.000
0.010
0.040
0.086
0.166
0.306
0.556
0.696
0.776
0.838
0.888
0.928
0,968
1.008
1.028
1.048
1.060
1.072
1.084
1.096
1.108
1.120
1.132
1.144
1.156

Results
Contolined in the Technical Addendl.JIll to this report. are the multiple SCS
CCl11puter outputs for the major basins. Hydrologicdatawascompiledineach
of the major basins for the 10- andlOO-yearfrequenc1es, using theZ-, 6-.
and24-hourstonndurations. Basin characteristiCS and hydrologic lnputpara-
meters arc presented in Table 3. Using this data peak flow rates were
generated for eachbas1n. The results are presented in Table 4 for each of
key design points, shown on Figure 1.
Asd1scussedabove. the occurrence of a 24-hour storm prnducingthepeak
flows presented in Table 4 Is unlikely. Therefore, to provide more conser.
vati~e major basin peak flow estimates, the 6-hour, 10. and lOO-year fl ows
shown 1nTable 4werellsed in the hydrau11c analys1s portion of this study.
Hydrographs were generated using the $CSmodel for major basins 1 through 3,
and were used in combination with the SWMf'.ll1lodelllng of the In.Town basins.
the SWMM model allows for the input of a singular hydrograph art/where into the
system, thereby allowing for the effects of runoff from both In-Town and off-
site basins. Flows generated wi thin Town will be con~eyed almost instan-
taneously to the storm sewer system, and the Offslte flows will lag behind.
Thl s is expected to be the case In t.~e Haxtun area, because of the agri-
cultural and urban land uses whlch are present. These flow hydrcgraphs
generatedhy the SCSmethodology were input at the approoriatedesi qnpoints.
and routed through the existing street and channel syste<lls lnHaxtun, to pro-
duce flOOd hydrographs at key design polnts.
Presented In Table 5 are the peak discharges generated by the S'~MM COl'l-
puterlllodel at key design polntsthroughouttheTown. for basin A through F.
Figure 2. prevlously presented ShOWS the basin delineatlon and flow net syst~n
developed for this study. Contained in the TeChnical Addendum is the computer
output for th<:' 10. and lOO-year frequencles, as well as a chart showing ti1e
flw net Input into the $'.lMMmodel.

Incremental Time
{min.}

lO.Year
Percent of
Total Ralnfal1

100-Year
Percent of
Total Ra1nfall

Total Depth = 2.6"

Total Depth =3.5"

Source: Urban Drainage and Flood Control District Storm Drainage Criteria
Manua. l~evi seJ 1185)

Oiscussion
Presented in Figures 3 and 4 are the floodhydrograplJs for the 10- and
lOO-year frequencies. at several key design points within the study are~. The
hydrographs shrM a double peak,whiCh reflects the lagging of thei n-townand