NC Central University P3 - Chidley South - Chidley Drainage Report (2)

Dewberry
Drainage Systems
Calculation Report
Chidley South Residence Hall
NC Central University
Dewberry Project Number: 50104803
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December 12, 2018
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SUBMITTED BY: SUBMITTED TO.
Dewberry Engineers Inc.
2610 Wycliff Road
Suite 410
Raleigh NC 27607
919.881.9939
NC License No.- F-0929
City of Durham
101 City Hall Plaza
Durham, NC 27701

TABLE OF CONTENTS
Drainage System Calculations Narrative
Appendix A Drainage Area Maps
Appendix B Hydraulic Grade Line Calculations

Drainage Systems Calculation Narrative
A. Project Description
The Chidley Residence Hall project is a proposed residence hall on the campus of North Carolina
Central University (NCCU). This project will be completed approximately concurrently with another
residence hall project on Campus — George Street Residence Hall. The project area is within a 3.62-
acre parcel on with a PIN of o830-05-19-1226 and a 48.51-acre parcel with a PIN of o830-05-09-
1658. Both parcels are on NCCU campus. For the purposes of project permitting a project area has
been delineated that is contiguous with the limit of disturbance. The project is located at 1400 Alston
Avenue. The site is in the Jordan Lake basin.
The existing impervious area within the project area is 1.04 acres and the impervious area as of 1997
and 2009 is 1.o6 acres. The proposed impervious area is 1.71 acres. The area of disturbance is 142,079
square feet. There is no watershed protection overlay.
The current use of the project area is a mowed lawn, two service drives, and an unoccupied dorm (Old
Chidley). The 1994 aerial indicates that a small dorm, called Lathan Residence Hall, a small parking
lot, and an unidentified building occupied the southern half of the project area. These areas of
impervious were demolished in 2011 when the Nursing Building to the south of the project was built.
A new residence hall is proposed for the site. The project also consists of the demolition of the
unoccupied dorm to the north. The demolition of Old Chidley would occur prior to the completion of
the new Chidley Residence Hall.
Chidley Residence Hall will be an approximately 164,000 square foot dorm and retail dining with 404
beds. It will be 6 stories tall. The retail dining portion on the lower floor will be about 7,500 square
feet.
The project also consists of the construction of a patio and new sidewalks, regrading of the service
streets, and construction of ADA parking.
B. Runoff Calculations
The Rational Method was used to compute the peak runoff for the proposed systems within the
project area. The Intensity -Duration -Frequency table was taken from NOAA Atlas 14 data for
Durham. The time of concentration to each inlet was set to five minutes. Delineation of each inlet
basin was completed using proposed grading.
Hydraflow software was utilized to compute the hydraulic grade line in the drainage system.
Hydraflow uses travel time to determine the time of concentration and, consequently, the intensity for
the peak flow calculations at each node.
Rational " C values" were obtained from Section 8.0 of the City of Durham "Reference Guide for
Devleopment".
';� Dewberry Drainage System Reports I NCCU Chidley 11

The minimum pipe diameter of 15 inches was maintained in the proposed storm sewer systems,
except for roof or yard inlet pipes and the 6" outlet from the proposed sand filter.
Velocities were calculated using Hydraflow for the 3 inches/hour storm to establish velocities meet
minimum requirements of 2.5 feet/second for pipes flatter than 1%. This calculation was labelled the
"scour" model.
';� Dewberry Drainage System Reports I NCCU Chidley 12

APPENDIX A - DRAINAGE AREA MAPS

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