HomeMy WebLinkAboutSite Certifications - 05/11/1999May 11, 1999
Basil Hamdan.
The City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, CO. 80521
RE: Drainage Certification
Pedersen Auto Plaza
Project Number: 9915.00
Dear Basil:
We have completed our review of the as -built drainage and grading at the above referenced
project. This certification is intended to verify compliance of the drainage facilities with the
approved plans entitled "Utility Plans for Pedersen Auto Plaza" (Plans).
A field survey of the site was conducted by Ayres and Associates and has been used in the
evaluation of the drainage facilities. There are two onsite detention ponds, Pond 1 and Pond 2,
both of which have emergency overflow weirs and a discharge restricting orifice.
Pond 1 was required to have a maximum storage volume of 9153.49 cu-ft at an elevation of
5039.23 (which is the maximum 100yr water surface elevation) and an allowable 100yr release of
0.36 cfs. Based on the survey data, Pond 1 has a volume of 8312.87 cu-ft at the same elevation,
which is a difference of 840.62 cu-ft. A new stage -discharge rating was developed for Pond 1
based on the survey stage -storage information (see page Al). The 100yr inflow hydrograph was
routed thru the pond using the Modified Puls method, as was done in the design. The new peak
discharge is 0.36 cfs with a maximum water surface elevation of 5039.28 (see page A2). The
water surface increased by 0.05' (roughly 5/8"). The notch elevation in the emergency overflow
weir (as surveyed by Ayres) is 5039.27, which will be adequate.
Pond 2 was required to have a maximum storage volume of 8917.59 cu-ft at an elevation of
5038.69 (which is the maximum 100-yr water surface elevation) and an allowable 100yr release of
1.42 cfs. Based on the survey data, Pond 2 has a volume of 7589.83 cu-ft at the same elevation,
which is a difference of 1327.76 cu-ft. A new stage -discharge rating was developed for Pond 2
based on the survey stage -storage information (see page A3). The 100yr inflow hydrograph was
routed thru the pond using the Modified Puls method. The new peak discharge is 1.46 cfs with a
maximum water surface elevation of 5038.80 (seepage A4). The water surface increased by 0.11'
(roughly 1-3/8"). The notch elevation in the emergency overflow weir (as surveyed by Ayres) is
5038.70.
The finished floor elevation of the building is 5040.00, as furnished by Ayres Associates. This is
D.\Projects\Ped\CERT4-99.LTR.wpd
420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221 -4 159
Pedersen Auto Plaza
Drainage Certification
May 11, 1999
Northern Engineering Services, Inc.
0.72-feet and 1.20-feet above the 100yr water surface elevations of Pond 1 and Pond 2
respectively.
The emergency overflow weir for Pond 2 will require modification. The notch elevation will need
to be raised from 5038.70 to a minimum elevation of 5038.80, based on the new surveyed pond
routing. The contractor (Sinnett Builders) was notified of this change on April 28, 1999. The
_work is expected to be completed the week of May 10'b and will be field verified by Northern
Engineering.
Enclosed are the surveyed, pond stage -storage ratings for both ponds, along with the routing of
each. A red -lined blueprint has also been provided to document the surveyed finished grades.
To the best of my knowledge, belief; and opinion, the finished grading and detention facilities are
in substantial compliance with the design intent of the approved drainage report and construction
drawings. If you require additional information or analysis regarding this project please contact
me at 221-4158.
Sincerely,
NORTHERN
Mary B. Woln
cc: David Stolte - Sinnett Builders
Encl.
D:\Projects\Ped\CERT4-99.LT .wpd
INC.
Elevation
5037.700
5037.800
5037.900
5038.000
5038.100
5038.200
5038.300
5038.400
5038.500
5038.600
5038.700
5038.800
5038.900
5039.000
5039.100
5039.200.__
5039.300
5039.400
5039.500
5039.600
5039.700
5039.800
5039.900
5040.000
Area (sf)
0.000
0.765
1.860
5.398
1083.283
1634.826
2205.477
2844.827
3659.444
6505.269
7619.384
8790.259
10007.993
11251.978
13517.860
T_ 14863.429..
17141.466
18425.788
19813.525
21266.109
22735.190
24227.111
25714.162
27587.948
Average Area
0.000
0.382
1.312
3.629
544.340
1359.055
1920.152
2525.152
3252.135
5082.357
7062.326
8204.821
9399.126
10629.985
12384.919
14190.644.
16002.447
17783.627
19119.656
20539.817
22000.650
23481.151
24970.636
26651.055
Volume (cu-ft)
0.000
0.034
0.129
0.260
83.878
135.221
192.290
250.835
324.071
595.744
705.773
820.473
939.574
1062.549
1289.303
1417.943.
1649.327
1778.478
1910.700
2053.531
2199.396
2349.467
2496.838
2644.969
Cum. Volume (cu-ft)
0.000
0.034
0.163
0.423
84.301
219.521
411.811
662.646
986.717
1582.461
2288.234
3108.707
4048.281
.5110.830
6400.133
7818.076
9467.403
11245.881
13156.581
15210.112
17409.508
19758.975
22255.813
24900.782
Cum. Volume (ac-ft)
0.000
0.000
0.000
0.000
0.002
0.005
0.009
0.015
0.023
0.036
0.053
0.071
0.093
0.117
0.147
0.1.79
0.217
0.258
0.302
0.349
0.400
0.454
0.511
0.572
Pond 1- Surveyed
✓- �3iL . e`7
1
4/26/99 Page 1 L
HYDROGRAPH REPORT
RECORD NUMBER : 9
TYPE : RESER MOD. PULS
DESCRIPTION : Pond 1: 100-yr Routing
- Surveyed
[HYDROGRAPH INFORMATION]
Peak Discharge ............................ =
0.36
(cfs)
Volume .................................... _
0.07
(acft)
Time Interval ............................. _
0.10
(min)
Time to Peak .............................. =
28.80
(min)
Time of Base .............................. =
144.00
(min)
Peak Elevation ............................ =
5039.28
(ft)
[RESERVOIR STRUCTURE INFORMATION)
Reservoir 0 ............................... = 5
Description ............................... = Pond 1 - Surveyed
Storage type .............................. = MAN STAGE/STOR
Max storage ............................... = 24900.78 Cuft
Discharge type ............................ = COMP STAGE/DIS
Max discharge ............................. 0.44 As
[RESERVOIR INFORMATION)
Reservoir #............................ 5
Reservoir Description ..................... Pond 1 - Surveyed
[INFLOW HYDROGRAPH INFORMATION]
Hydrograph#.............................. = 1
Hydrograph Description .................... = Basin 1
D:\Projects\Ped\Pondl.rou
�A3
Elevation
Area (sf)
Average Area
Volume (cu-ft)
Cum. Volume (cu-ft)
Cum. Volume (ac-. t) Pond 2 - Surveyed
5036.760
0.000
0.000
0.000
0.000
0.000
5036.860
39.853
19.927
1.336
1.336
0.000
5036.960
149.968
94.910
9.013
10.349
0.000
5037.060
356.040
253.004
24.128
34.477
0.001
5037.160
613.940
484.990
48.338
82.815
0.002
5037.260
890.089
752.014
75.032
157.848
0.004
5037.360
1231.848
1060.969
105.377
263.224
0.006
5037.460
1679.465
1455.657
145.201
408.426
0.009
5037.560
2158.205
1918.835
191.486
599.912
0.014
5037.660
2717.198
2437.701
242.795
842.707
0.019
5037.760
3341.153
3029.175
302.835
1145.542
0.026
5037.860
4003.903
3672.528
366.876
1512.418
0.035
5037.960
4689.397
4346.650
434.477
1946.896
0.045
5038.060
5392.484
5040.941
503.631
2450.527
0.056
5038.160
6207.408
5799.946
578.655
3029.181
0.070
5038.260
7032.668
6620.038
661.987
3691.168
0.085 _
5038.360
7954.666
7493.667
749.013
4440.181
0.102
5038.460
8882.768
8418.717
841.577
5281.758
0.121
5038.560
9822.932
9352.850
934.988
6216.746
0.143
5038.660
10834.427,
10328.679-._____.__1031_1267247.872
0.166 19"
5038.760
11935.748
11385.088
1139.857
8387.729
0.193
5038.860
13004.979
12470.364
1246.470
9634.199
.0.221
5038.960
14100.489
13552.734
1354.950
10989.149
0.252
5039.060
15226.237
14663.363
1465.978
12455.127
0.286
5039.160
16322.778
15774.508
1577.003
14032.130
0.322
5039.260
17218.278
16770.528
1678.779
15710.908
0.361
5039.360
18061.022
17639.650
1764.089
17474.997
0.401
5039.460
18847.041
18454.031
1845.880
19320.877
0.444
5039.560
19522.478
19184.759
1919.532
21240.409
0.488
5039.660
20043.713
19783.095
1979.283
23219.691
0.533
5039.760
20488.493
20266.103
2027.579
25247.271
0.580
5039.860
20881.206
20684.849
2068.556
27315.827
0.627
5039.960
21255.539
21068.372
2106.908
29422.735
0.675
5040.060
21608.512
21432.025
2143.284
31566.019
0.725
5040.160
21914.074
21761.293
2176.695
33742.714
0.775
5040.260
22160.655
22037.365
2204.439
35947.153
0.825
5040.360
22367.172
22263.914
2226.688
38173.841
0.876
5040.460
22522.352
22444.762
2244.817
40418.658
0.928
5040.560
22632.494
22577.423
2257.966
42676.623
0.980
5040.660
22709.446
22670.970
2267.470
44944.093
1.032
5040.760
22750.813
22730.129
2273.242
47217.335
1.084
5040.860
22774.924
22762.869
2276.407
49493.742
1.136
5040.960
22782.924
22778.924
2278.023
51771.766
1.189
4/25/99 Page 1 A 4
HYDROGRAPH REPORT
RECORD NUMBER : 8
TYPE : RESER MOD. PULS
DESCRIPTION : Pond 2: 100-yr Routing
- Surveyed
[HYDROGRAPH INFORMATION]
ischarge............................ =
Peak Discharge.. *** .......................
1.46
(cfs)
Volume .................................... =
0.26
(acft)
Time Interval ............................. =
1.00
(min)
Time to Peak ............................... =
27.00
(min)
Time of Base .............................. =
167.00
(min)
Peak Elevation ............................ =
5038.80
(ft)
[RESERVOIR STRUCTURE INFORMATION]
Reservoir II ............................... - 4
Description ............. :................. = Pond 2 - Surveyed
Storage type .............................. = MAN STAGE/STOR
Max storage ................................ - 11.575.54 Cuft
Discharge type ............................ - COMP STAGE/DIS
Max discharge ............................. = 1.53 cfs
[RESERVOIR INFORMATION]
Reservoir # ............................... _ .4
Reservoir. Descri.pti.on..................... Pond 2 - Surveyed
[INFLOW HYDROGRAPH INFORMATION]
Hydrograph #.............................. = 6
Hydrograph Descripl:ion..................... = Combine Basin 01
and Basin 2
D:\Projects\Ped\Pond2.rou