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mit DRAINAGE REPORT
FOR
N
INDIAN LAKES SUBDIVISION
PHASE VII
ARIN
COLLEGE STATION TEXAS
4-
May 2005
SUBMITTED BY:
McCLURE & BROWNE ENGINEERING /SURVEYING, INC.
tAgi
1008 Woodcreek Drive, Suite 103 • College Station, Texas 77845
CERTIFICATION
I, Jeffery L. Robertson, Registered Professional Engineer No. 94745, State of Texas, certify
that the drainage report, for INDIAN LAKES SUBDIVISION, PHASE VII, were prepared by me
in accordance with the provisions of the City of College Station Drainage Policy and Design
Standards for the owners thereof.
�e_ OF TEk t �� ti
• * / / ROBERT SON L. R o rtson, P.E. No. 94745
JE ..... ... 94745 w i
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DRAINAGE REPORT i
Indian Lakes, Phase VII
Drainage Report
MBESI #1062 -0007
SUMMARY
This storm drainage report is intended to analyze the drainage infrastructure proposed for the development
of the Indian Lakes Subdivision, Phase VII. The existing and proposed conditions are included to show how the
design will achieve the desired drainage objectives of Brazos County and the City of College Station.
GENERAL INFORMATION
Area encompassed by this phase: 18.28 acres
Anticipated land use: Single family residential
Anticipated number of lots: 10 lots
Notes on surrounding development: The area surrounding the site is partially developed with existing phases of
Indian Lakes to the north and west, undeveloped phases of Indian Lakes to
the east and south.
FLOOD HAZARD INFORMATION
FEMA FIRM Map #: 48041CO215 C
Effective Date: July 2, 1992
Comments: No portion of the site is shown to be within the 100 -year floodplain, so it is not currently
regulated under the National Flood Insurance Program.
Applicable Exhibits: A — Excerpt of FEMA FIRM
DESCRIPTION OF DRAINAGE SYSTEMS
Primary System: The site is wooded with dense undergrowth. The topography slopes toward a tributary of
Peach Creek flows from the north to south through the property. Peach Creek flows to the
Navasota River.
Secondary System: Runoff from the residential lots will be captured in roadside ditches where it will be
conveyed to the natural streams that flow through the site. Corrugated metal pipes will be
used as culverts at road crossings.
Applicable Exhibits: B — Drainage Area Map
SECONDARY STORM DRAIN DESIGN
Design Storm: 10 -yr Return Period (Ditches)
100 -yr Return Period (Culverts)
Design Methodology
Hydrology: Rational Formula (Culverts)
SCS Runoff (Overall Runoff from Site)
Software Model: Excel Spreadsheet (Rational Method)
HEC -1 (SCS Method)
Time of Concentration: 10 min.
Runoff Coefficients: 0.40 - Undeveloped area
0.55 - Residential areas
0.90 - Paved areas
Curve Numbers: 80 — Undeveloped Areas
94 — Paved Areas
Drainage Report Page 1 of 2
Indian Lakes, Phase VII
Hydraulics: Manning's Equation
Software Model: Excel Spreadsheet
Manning's N: 0.024 (corrugated metal)
Applicable Exhibits: C -1 Rational Formula Drainage Area Calculations
D -1 HEC -1 Analysis
E -1 Anasazi Bluff Drive Culvert Analysis
E -2 Toltec Trail Culvert Analysis
F -1 Drainage Area Parameters
G -1 HEC -RAS Analysis of Peach Creek Tributary
DETENTION REQUIREMENTS
General Note: A summary of the pre - developed and post - developed runoff rates and water surface
elevations are shown in the table below:
Table 1— Summary of Runoff
Storm Event Existing Runoff Proposed Runoff
5yr 201cfs 211cfs
10yr 257cfs 267cfs
25yr 322cfs 332cfs
100 yr 426 cfs 435 cfs
100 yr W.S.E. 234.74' 234.76'
Summary: When considered as a single development, the proposed runoff rates and the 100 -yr
water surface elevation from Phase 7 are slightly higher than pre- development
conditions. However, when considered in conjunction with the previous phases and
the over - detention provided by Lake Arapaho, the runoff rates are far below pre -
development runoff rates (approximately 1300 cfs less for the 100 -year event as
noted in the Drainage Report for Phases 2 & 5). Therefore, no additional detention
is necessary with this phase of the subdivision.
EROSION AND SEDIMENTATION CONTROLS
Control Measures: Silt fence
Hydromulch seeding
Rock Filter Dams
Straw Bale Barriers
Construction entrance /exit
SWPPP: The contractor shall be responsible for establishing and maintaining the SWPPP in
accordance with TCEQ requirements.
Drainage Report Page 2 of 2
Indian Lakes, Phase VII
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Flood Insurance Rate Map Excerpt
Brazos County, Texas
and Incorporated Areas
Map Numbers: 48041CO215C
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N.T.S. Effective Date: July 2, 1992
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