HomeMy WebLinkAboutDrainage Reports - 02/24/1995 (2)`IIWASTE
February 24, 1995
Mr. Basil Hamdan
City of Fort Collins
Utility Services Stormwater
235 Mathews
Fort Collins, Colorado 80522
2629 Redwing Rd. Suite 200, Fort Collins, Colorado 80526-2879
(303)226-3535
fax (303) 226-6475
RE: VALUE PLASTICS - FINAL DRAINAGE AND EROSION CONTROL REPORT - POND
DRAIN TAILWATER ANALYSIS
Dear Mr. Hamdan:
I am writing in response to your question regarding the carrying capacity of a 15" RCP when
the water in the pond is full at elevation 41.0 and the tailwater is at elevation 40.0. As you
can see from the enclosed calculation sheet, it is 12.5cfs, less than the 18cfs used for a
release rate in the pond analyses. Since the 15" carries 18cfs when the pond is full and there
is no tailwater, we felt the system was practical. The RBD study done in conjunction with
the new fire station determined that runoff from a 100 year event, using all assumptions that
we complied with in designing the Value Plastics system, would pond in Vermont Drive, and
in the swale the 15" drains to, to elevation 41.5. Therefore the analysis of a tailwater at 40.0
becomes somewhat academic as under that condition flooding is occurring in the low area of
the site. We felt as long as the pond drain restricted the flow after the tailwater subsided we
had satisfied the intent of the detention. We have also enclosed the calculation sheet for an
18" RCP under tailwater conditions which indicates too high a release rate (21cfs). An
alternative would be to install an orifice designed for a specific set of conditions. We did not
feel this was warranted.
If .you have any questions please call me.
Thank you.
Sincerely,
WATER, WASTE & LAND,. IN .
Ma rice H. Lutkin, P.E.
Manager, Civil Engineering Division
Consulting Engineers and Scientists
� Pressure Pipe Analysis & Design�
Circular Pipe
Worksheet Name: VALUE PLASTICS
Comment: PIPE DISCHARGE 1�T TA�LWATE�
Solve For Discharge
Given Input Data:
� Elevation @ 1...." 39.40 ft `
Pressure @ I.,.... 0.67 psi
_ - Elevation @ 2..... 39.00 ft
Pressure @ 2....,. 0.43,psi �
Diameter.,.,...... 15.00 in
Lengtb..°~°....,.. 55°00 ft `
Hazen -Williams C°. 150°00
Computed Results: `
�� «�
Discharge ........ 5859.16 gpm �� o~'*��-` ��� -
Velocity.......~". 10.64 fps
Readloss.......... 0.95 ft
Energy Grade @ 1.. 42.70 ft
Energy Grade @ 2.. 41.75 ft
Friction Slope.... 17.340 ft/1000 ft
Open Channel Flow Module, Version 3.41 (c) 1991
Haestad Methods, Inc. * 3� Brookside Rd * Waterbury, Ct 06703
Pressure Pipe Analysis at Design
Circular Pipe
Worksheet Name: VALUE PLASTICS
Comment: PIPE DISCHARGE iFT TAILWATER
Solve For Discharge
Given Input Data:
'Elevation @ 1..... 39.40 fit
Pressure @ 1...... 0.67 psi
Elevation @ 2..... 39.00 ft
Pressure @ 2...... 0.43 psi
Diameter.......... 18.00 in Length ............ 55.00 fit
Hazen -Williams C.. 150.00 .
Computed Results: -
Discharge......... 9464.16 gpm
fps
Headloss.......... ,-, 0.95_ft ,
Energy Grade @ 1.. 43.16 ft
Energy Grade @ 2.. 42.21 fit
Friction Slope... 17.340 ft/100O.ft
Open Channel Flow Module, Versic-n 3.41 (r_) 1901
Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct 06708