HomeMy WebLinkAboutDetention Pond As-Built SummaryGENERAL
Emergency Outfall:
Spillway Length:
Side slopes:
Spillway Elev.:
Top of Berm Elev.:
Cross slope:
Manning 's n:
HEC-HMS Analysis Summary
Detention Pond As-Built Summary
The Barracks Subdivision -Phase 2
March,2009
This addendum is issued to address the as-built condition of the completed
detention pond at the Barracks Subdivision. The detention pond was constructed
larger than the ori ginal des ign in order to provide additional fill for the streets and
building lots in Phase 1. However, the pond side slopes were steeper than the
original design and the surface material was hard clay which made it difficult to
establish vegetation. As part of Phase 2, fill material was placed in the pond to
reduce the steepness of the side slopes and improve soil characteristics so that
vegetation can be established . The final grading of the pond is shown on Sheet 6
of the construction drawings. A private sidewalk was constructed on top of the
pond berm around the entire pond . Also, 4 concrete flumes were constructed at
locations with concentrated runoff from the adjacent development to help control
erosion of the side slop es.
The pond was surveyed upon completion and the volume of the pond calculated .
The as-built pond vo lum e is very similar to the original design.
The emergency spillway fo r the pond was modified from its original design to
allow for flatter side slopes tb accommodate the private sidewalk. The dimensions
of the spi I I way are as foll ows.
92.4 ft .
40H:1V
31 2.55 ft
31 3.4 ft
0.50%
0.025 (short gra ss) and 0.012 (concrete sidewalk)
The final pond volume and the spillway parameters were input into the
HEC-HMS computer model and a summary of the results is as follows:
Condition _
2 Y'_~L2_s*--: 100 ci_ '""s:;,~~OC: !
___ --·--+--c_fs [ cfs ! cfs cfs cfs i cfs !
Pre-Dev. 55.3" . 114.1 J 144.-8 I 180.5 / i l0.2 l •
Post-Dev. 54.I 110.6 137.5 ; 166.5 ! 184.9 ! .._ ____ _
i
Pond WSF.:L 309.9 'l l0.7 3111 I 311.7 312.3 31 2.9
Emergency Spillway Elev.= 312. 55 ft
Top of Berm Elevation = 313.4 Ji
Available Freebocrd = 0. 5 ft.
As shown abo ve, the post development project discharge is less than the
pre-development discharge for all storm events.
Page I of 2
CONCLUSION
The detention pond in The Barracks Subdivision as constructed will function as
originally designed.
E GINEERING ATTESTATION:
Joseph P. Schultz
Licensed Professional En gineer
State o f Texas No. 65889
Page 2 0 12
HARLE ENGINEERING COMPANY
flRM#4538
WATER SYSTEM FIRE HYDRANT FLOW TEST REPORT
Date: 2-9-10
Water System Owner: _W~e_ll_bo_r_n_S_U_D ___________________ _
Development Project: The Barracks Subdivision -Phase 2 -College Station, Texas
Flow Test location: FH 3 in Phase 2 near the intersection of Sergeant and Lt. Avenue
Nozzle size (in.): 2.5
Pitot Reading (psi): 52
Flowrate (gpm): 1,210
Pressure Gauge Location: FH 1 on General Parkway
Static Pressure (psi): 75
Residual Pressure (psi): 56
Discharge Coeff: (c) = 0.90
Flowrate Formula: Q=29.84cd2p112
c = discharge coeff.
d = orifice size (in)
P = pitot pressure (psi)
Computed Discharge at 20 psi Residual Pressure: QR=_ 2.148 gpm
Note: The flow test and report were prepared in accordance with NFPA 291.
Report Prepared by: Joseph P. Schultz
Others Present: Stephen Cast -Wellborn SUD
Wallace Phillips ____ _
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