Alexander Ct-CS0804072010) Ken Griffin - Re: Lot 11 elevations Page 1
From:
Mike Boyd <mboyd @ndmce.com>
To:
Ken Griffin <kgriffin @ci.coppell.tx.us>
CC:
Rhonda Adloo <RADLOO @ci.coppell.tx.us>
Date:
4/7/2008 12:46 PM
Subject:
Re: Lot 11 elevations
Attachments:
20080407123943. pdf
Ken, Attached is the output summary that I am using. At the two cross sections of concern the computer
does not assume any critical depth. Thanks
Mike Boyd, P.E.
Nathan D. Maier Consulting Engineers, Inc.
214 - 739 -4741 214 - 739 -5961 (fax)
- - - -- Original Message - - - --
From: "Ken Griffin" <kgriffin @ci.coppell.tx.us>
To: "Mike Boyd" <mboyd @ndmce.com>
Cc: "Rhonda Adloo" <RADLOO @ci.coppell.tx.us>
Sent: Monday, April 7, 2008 11:42:12 AM GMT -06:00 US /Canada Central
Subject: Re: Lot 11 elevations
Thanks for the info. I had used the same methodology, but arrived at different numbers. The south lot line
of Lot 11 is actually only about 100' from cross section 27400 and there is about 350' from cross section
27400 to cross section 27050. This means that the south lot line is about 30% of the way from section
27400 to section 27050. This would calculate to an existing 100 year water surface of 492.05 (492.83 -
490.22 = 2.61'& 30% of 2.61 = .78'& 492.83 -.78 = 492.05). Using the same approach for the ultimate
100 year water surface calculate to a an ultimate water surface of 493.39. Using this approach yields a
minimum finish floor of 494.39 for Lot 11.
The question I have concerning the computer runs is whether or not the critical depth was assumed by the
computer runs or if the program was actually able to calculate it. If the critical depth was assumed, then
the minimum finish floor is calculated using the energy grade line not the water surface. Using the
methodology above, with the critical depth assumed, yields a minimum finish floor of 495.06(ultimate
controls: 494.28 - 493.56 = .72'/ 30% of .72 = .22'/ 494.28 -.22 = 494.06).
know this doesn't appear to be much of a difference, but worst case there could be a difference of 1.02
feet (495.06 - 494.04 = 1.02'). If critical depth was not assumed, then the minimum finish floor for Lot 11 is
494.39.
Let me know as soon as possible so we can wrap up this item before the plat goes to P & Z.
Thanks,
Ken Griffin, P. E.
Director of Engineering & Public Works
972 - 304 -3686
kgriffin@ci.coppell.tx.us
>>> Mike Boyd <mboyd @ndmce.com> 4/7/2008 10:45 AM >>>
have looked at the recent FIRM mapping. It shows that lot 11 would be between the BFE of 491 and 493.
Looking at the computer runs and the floodplain work map two cross sections in the vicinity have the south
lot line midway between them. Cross sections 27050 and 27400 (lot 11 south line midway between) have
2010) Ken Griffin - Re: Lot 11 elevations Page 2
FEMA elevations of 490.22 and 492.83 (average 491.53) and ult elevations of 492.19 and 493.90
(average 493.04). Two feet above FEMA will set the finish floor at 493.53 and 1 -foot above ult is 494.04.
If you have any questions or need further information please call /email.
Thank you,
Mike Boyd, P.E.
Nathan D. Maier Consulting Engineers, Inc.
214 - 739 -4741 214 - 739 -5961 (fax)
Page 1 of 2
Ken Griffin - Re: Lot 11 elevations
From:
Ken Griffin
To:
Mike Boyd
Date:
4/7/2008 11:42 AM
Subject:
Re: Lot 11 elevations
CC:
Rhonda Adloo
Thanks for the info. I had used the same methodology, but arrived at different numbers. The south lot
line of Lot 11 is actually only about 100' from cross section 27400 and there is about 350' from cross
section 27400 to cross section 27050. This means that the south lot line is about 30% of the way from
section 27400 to section 27050. This would calculate to an existing 100 year water surface of 492.05
(492.83 - 490.22 = 2.61'& 30% of 2.61 =.78'& 492.83 -.78 = 492.05). Using the same approach for
the ultimate 100 year water surface calculate to a an ultimate water surface of 493.3 9. Using this
approach yields a minimum finish floor of 494.39 for Lot 11.
The question I have concerning the computer runs is whether or not the critical depth was assumed by
the computer runs or if the program was actually able to calculate it. If the critical depth was assumed,
then the minimum finish floor is calculated using the energy grade line not the water surface. Using
the methodology above, with the critical depth assumed, yields a minimum finish floor of 495.06
(ultimate controls: 494.28 - 493.56 = .72' / 30% of .72 = .22' / 494.28 - .22 = 494.06).
I know this doesn't appear to be much of a difference, but worst case there could be a difference of 1.02
feet (495.06 - 494.04 = 1.02'). If critical depth was not assumed, then the minimum finish floor for Lot
11 is 494.3 9.
Let me know as soon as possible so we can wrap up this item before the plat goes to P & Z .
Thanks,
Ken Griffin, P. E.
Director of Engineering &Public Works
972- 304 -3686
kgriffin @ci. coppel1. tx.us
»> Mike Boyd <mboyd @ndmce.com> 4/7/2008 10:45 AM »>
I have looked at the recent FIRM mapping. It shows that lot 11 would be between the BFE of 491 and
493. Looking at the computer runs and the floodplain work map two cross sections in the vicinity have
the south lot line midway between them. Cross sections 27050 and 27400 (lot 11 south line midway
between) have FEMA elevations of 490.22 and 492.83 (average 491.53) and ult elevations of 492.19
and 493.90 (average 493.04). Two feet above FEMA will set the finish floor at 493.53 and 1 -foot
above ult is 494.04.
If you have any questions or need further information please call /email.
file: HC: \Documents and Settings \radloo \Local Settings\ Temp \XPgrpwise \47FA0895City_... 2/19/2010
Page 2 of 2
Thank you,
Mike Boyd, P.E.
Nathan D. Maier Consulting Engineers, Inc.
214-739-4741214-739-5961 (fax)
file: HC: \Documents and Settings \radloo \Local Settings\ Temp \XPgrpwise \47FA0895City_... 2/19/2010
HEC -RAS Plan: Plan 12 River: RIVER -1 Reach: Reach -1 Profile- Natural
Reach
River Sta
Profile
Q Total
Min Ch El
W.S. Elev
Crit W.S.
E.G. Elev
E.G. Slope
Vel Chnl
Flow Area
Top Width
Froude # Chi
(cfs)
{ft}
(ft)
(ft)
[ ft /ft)
- -IF
(ft/s)
(sa ft)
(f )
Reach -1
23900
Natural
15500.00
463.00
482.511
478.21
483.43
0002619
7.97
2376.90
366.31
0.43
Reach -1
Reach -1
2 4100
24500
Natural
I Natural
155
15500.00
464.00
468.00
484.01
484.52 _
484.77
485.79
0.001490
0.003513
7.10
9288
2401.81
2104.98
254.79
266.25
0.34
0.51
Reach -1
25370 Natural
W
15500.00
472.00
485.86
487.58
0.005124
10.55
1469.70
150.00
0.59
Reach -1
25470
Natural
15500.00
470.00
487.36
478.86
488.10
0.001216
6.97
2315.51
179.04
0.31
Reach -1
25485
Bridge
Reach -1 25500 Nat
15500.00
15500.00
470.00
470.00
487.66
487.34
478.86
488.37
488.65
0.001138
0.003422
6.83
9.19
a 2364.40
1714.00
180.04
201.00
0.30
0.49
Reach -1 25550
Natural
Reach -1
25685
Natural
15500.00
470.00
487.43
488.87
0.003893
9.65
1646.77
217.83
0.53
Reach -1
25725
Natural
15500.00
472.00
487.92
489.03. 0.002679
8.53
1981.39
267.77
0,45
Reach -1
125820
Natural
15500.00
470.00
488.98
48
0.000853
0.001975
5.03
7.87
3869.66
2392.14
416.14
326.78
0.25
0.39
Reach -1
26170 '
Natural
14450.00
472.00
489.021
489.89
Reach -1
Reach -1
26300
26700
Natural
Natural
14450.00
14450.00
470.00
474.00
489.25
489.93
490.24
491.82
0.002399
0.006625
, 0.004271
8.19
11.11
11.36
2131.64
1407.64
1489.96
331.60
250.94
259.70
0.421
0.67
0.55
Reach -1
26880
Natural
14450.00
474.00
491.05
492.99
Reach -1
27050
Natural
11250.00
474.00
492.19
493.56
0.003378
10.20
9691.01
2727.37
354.27'
331.13
0.48
0.29
Reach -1
27400
Natural
11250.00
476.00
493.90
494.27
0.001154
5.76
Reach -1
27540
Natural
11250.00
475.00
493.12
490.31
495.69
0.006419
12.86
874.94
315 .69
0.66
Reach -1
27555
Bridae
Reach -1
27570
Natural
11250.00
475.20
494.48
490.54
49 6.60 0.004682
11.70
8.80
8.22
961.82
167439
1406.42
456.79
345.97
147.02
0.58
0.45
0.41
Reach -1
27620
Natural
11250.00
476.00
495.84
496 ;
0.003070
Reach -1
27900
Natural
11250.00
480.00
497.19
498.23'1
504.1
0.002310
Reach -1 130130
Natural 1
11250.00
483.70
502.881
11.21
1627.80
279.88
0.52