Untitled Kimley>>>Horn
TECHNICAL MEMORANDUM
To: Hamid Fard, P.E. —City of Dallas
From: Brad Moss, P.E. —Kimley-Horn and Associates, Inc.
Cc: Jacob Reinig, P.E., ENV SP—Kimley-Horn and Associates, Inc.
Brad Pickering, P.E., CFM—Kimley-Horn and Associates, Inc
Date: February 4, 2015
Subject: Drainage Analysis—Channel E -Cypress Waters Development
Billingsley Company proposes to construct the first phase of Olympus Boulevard improvements from
Belt Line Road to approximately 3,600 LF southeast to the future Town Center and a 1,100 LF
extension of Cypress Waters Boulevard from the Multi-Family Phase 1 site to north to tie in with
Olympus Boulevard at the future Town Center. Olympus Boulevard is proposed to consist of a
combined 4-lane divided and 4-lane undivided street section. The purpose of this drainage analysis is
to describe the methodology and design of a proposed channel ("Channel E")and culvert("Culvert E")
intended to convey flow generated by areas west of Belt Line Road and within the Cypress Waters
development to North Lake.
The following technical memorandum summarizes the hydrologic and hydraulic modeling used for this
analysis.
HYDROLOGIC MODELING
Kimley-Horn prepared one hydrologic model for the watershed draining to Culvert El as shown on the
attached Drainage Area Map. The model represents fully developed watershed conditions.
HEC-HMS 3.5 was used to calculate the peak flow rates generated by the watershed for the 1-, 2-, 5-,
and 100-year storm events. The NRCS Unit Hydrograph Method was used in accordance with City of
Dallas criteria.
Fully developed times of concentration were calculated in accordance with the methodology described
in Technical Release 55 (NRCS, 1986) and the City of Dallas Drainage Design Manual. Curve
Numbers for fully developed watershed conditions are based on anticipated fully developed land uses
and soil type.Anticipated fully developed land uses are based on the Conditional Letter of Map Revision
for North Lake prepared by Kimley-Horn and Associates, Inc., dated September 2012. Soil types were
found to consist of predominantly Type D soils based on the NRCS Web Soil Survey (NRCS, 2014).
Drainage area boundaries within the watershed were determined using aerial and on-ground
topographic information, record plans provided by the City of Dallas and Coppell, and site observations.
kimley-horn.com 12750 Merit Drive, Suite 1000, Dallas, TX 75251 972-770-1300
Kim ey>>>Horn Page 2
The watershed contributing flow to the subject reach is approximately 280 acres and is shown on the
attached Drainage Area Map.
Fully developed condition peak flow in the 1-, 2-, 5-, and 100-year storm events are shown in Table 1.
Table 1: Existing Peak Flow Summary
Location Qi (cfs) Q2 (cfs) Q5 (cfs) Qum (cfs)
El 737 937 1213 2176
E2 377 484 633 1149
E3 114 146 189 340
HYDRAULIC MODELING
Two channels are proposed to convey flow from Belt Line Road to North Lake. A new culvert is also
proposed at the Olympus Boulevard crossing of the channel. The U.S Army Corp of Engineers HEC-
RAS version 4.1.0 hydraulic modeling software was used for hydraulic modeling of the project under
fully developed conditions.
Design flows summarized in Table 1 were used in the development of the HEC-RAS model. The
proposed channel consists of trapezoidal sections with a 40' bottom width and 4:1 side slopes. Four
vertical drops are proposed to flatten the channel slope and maintain non-erosive flow velocity. Erosion
protection is also proposed in areas of the channel where flow velocity exceeds 8 feet per second. The
work map used to generate cross-sections for the HEC-RAS model is included in Appendix C. Refer to
Appendix D for the HEC-RAS profiles, cross-section plots, and the output tables from the various
models. Culvert E, as shown on the Drainage Area Map and Hydraulic Workmap, is located
approximately 850 feet east of Belt Line Road. The crossing is sized to convey the fully developed peak
flow generated by the watershed in general accordance with City of Dallas Drainage Design Criteria.
The crossing will consist of 6-10' x 6' pre-cast reinforced concrete box culverts.
Attachments
A- Channel E - Drainage Area Map
B - Proposed Condition Hydrologic Model Output
C- Hydraulic Workmap
D - HEC-RAS Output
E - Digital Files
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