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**Unformatted text preview: **Flood Finding Inc.
517 Ball Drive
Hanover, IN 47243 November 20, 2013
Iohn Smith 1234 Wabash Lane
Wabash, IN 46992 Dear Mr. Smith; We at Flood Finding Inc. have been working hard and are very pleased to present to
you our ﬁndings of the 75-minute quadrangle ofthe Wabash River at Wabash,
Indiana. Enclosed please ﬁnd the following items: Table 1 consists ofthe data for the
maximum annual ﬂow for the USGS stream gaging station on the Wabash River at
Wabash, Indiana; Table 2 consists of a spreadsheet showing the year, the stage,
discharge (QM-ix], rank, recurrence interval, exceedence probability, and LOG QM;
Figure 1 is the rating curve for the Wabash River at Wabash, Indiana; Figure 2 is the
ﬂood frequency curve for the Wabash River at Wabash, Indiana; and Figure 3
consists of the map showing the extent of the 100-year ﬂood zone in the Wabash River at Wabash, Indiana USGS 75-minute quadrangle. W
The IOU-year ﬂood is not the ﬂood that occurs every one hundred years. Rather, it is that in any given year, there is a one in one hundred chance, or one percent chance, that the maximum ﬂow for that year will exceed the ﬂow of the IOU-year ﬂood. In other words, the exceedence probability of that year is one over one hundred. The recurrence interval is one hundred years. O-Y rFlo dM 1 To ﬁnd the 100-year flood level ofthe Wabash River at Wabash, lndiana for any given year, the one percent mark had to ﬁrst be found on the ﬂood frequency curve,
Figure 2, on the x-axis. Then, where 1.00% met the line on the graph of Figure 2
would correspond to the number on the y-axis. The y-axis represented the QM
(cubic feet squared). The number that corresponded with 1.00% on the ﬂood
frequency curve is 45,400 cubic feet squared. This shows that there is a one percent
chance that the water discharge will be at 45,400 cubic feet squared. Next, the rating
curve, Figure 1, was looked at. Qmax is on the x-axis. 45,400 cubic feet squared on the
x-axis corresponded to match the stage, measured in feet above the datum, on the y-
axis, based on the curved line in the graph. lt corresponded with 24 feet above
datum. Meaning that the water discharge would surpass the datum, which is the
ﬁxed started point at the gaging station, by 24 feet Then, on the USGS website for
the gaging system on the Wabash River at Wabash, Indiana, Table 1, the gage datum
is 642.66 feet about sea level, which is added to the 24 feet above datum to calculate
how high up the water level would rise from sea level. The addition of the two
numbers equals about 666 feet above sea level, which the 100-year ﬂood model. This can be seen in Figure 3, which is the map of the 75-minute quadrangle of the Wabash River at Wabash, Indiana. Colored in blue is the area that would be affected by this ﬂooding. Becgmmﬂldaﬂmlﬁ We recommend that you do not build anywhere within the blue shaded area of
Figure 3 to avoid water and ﬂood damage. Though there may be ways to prevent the
ﬂooding waters, such as an artiﬁcial levee. But with an artiﬁcial levee, ifbroken,
could cause signiﬁcantly more damage than if it had not been there. Another
alternate could be channel straightening, which would increase the gradient of the
stream channel, but would also increase potential ﬂooding of areas downstream. We highly recommend that you look into building on an upland shoulder slope instead to ensure that ﬂood damage is avoided. Best Regards, ...

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