storm water drainage report - 7bdev.com

P A G E | 1

STORM WATER DRAINAGE REPORT

for

Dale Shine Xpress Car Wash Located at

2301 U.S. Highway 83 Business

City of McAllen, Hidalgo County, Texas

Issue Date: April 10, 2020

Prepared by:

Burkhardt Engineering

28 N. Cherry Street

Germantown, Ohio 45327

(937) 388-0060 By:____________________________________________

Ryan J. Morrissey, P.E. Date

4/10/2020

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TABLE OF CONTENTS

TITLE PAGE……………………………………………………..…………….…….………...1

TABLE OF CONTENTS………………………………………..………….….…………....2

DRAINAGE NARRATIVE…..….…………….…………………………......…………....3

HYDRAULIC CALCULATIONS…………………………………………………..………..4

METHODOLOGY & EQUATIONS……………………………………......……...4

EXISITNG CONDITIONS SUMMARY………………....………….…..…..…...5

PROPOSED CONDITIONS SUMMARY………………………………………....6

REQUIRED DETENTION VOLUME SUMMARY……………………..………7

DRAINAGE SYSTEM PERFORMANCE SUMMARY…………..…….….…..7

APPENDIX – EXHIBITS……………………………………….…………..……….………..8

- Vicinity Map

- USGS Topo Map

- FEMA Floodplain Map

- USDA Soils Map

- Existing Site Map

- Proposed Site Map

- Detention Basin Grading

- Outlet Structure Detail

P A G E | 3

DRAINAGE NARRATIVE

The Proposed Dale Shine Xpress Car Wash (2301 U.S. Highway 83) will be developed on an 0.963 acre

tract, Being a combination of Lots 1-6, Block 1, John J. Young Subdivision. This land will be platted as

part of this development in order to create one 0.963 acre lot.

This development is located in Flood Zone “C” on FEMA’s Flood Insurance Rate Map, Community Panel

No. 480343 0005 C, dated November 2, 1982. Zone “C” is defined as “Areas of minimal flooding”.

The soils in this area mostly sandy clay as seen from and USDA, NRCS Web Soil Survey – Urban Land

(Map Unit Symbol dbml) – Hydraulic Soil Group D, which have low infiltration rates.

The existing 0.963 acre site is a developed lot and is generally flat with two apparent drainage areas,

North (0.418 acres) and South (0.546). The North drainage area drains towards South 23rd Street to an

existing curb inlet and the South drainage area drains towards Austin Avenue to an existing curb inlet.

The existing 10-year discharge for the North Drainage area is 3.28 cfs, being the maximum allowable

discharge in proposed conditions to the North. The existing 10-year discharge for the South Drainage

area is 2.72 cfs, being the maximum allowable discharge in proposed conditions to the South. The

proposed development will maintain the split drainage areas to the North and South. The North

drainage area peak 50-year flow does not exceed existing conditions 10-year peak flow and therefore

will not require storm water detention. The South drainage area 50-year peak flow exceeds existing

conditions 10-year peak flow and therefore will require storm water detention to limit the proposed site

discharge. Required volume was determined by checking multiple storm durations to locate the critical

event (Modified Rational Method).

The proposed 0.963 acre site will consist of a new Dale Shine Car Wash with onsite storm water

collection system for the Southern Drainage area (0.570 acres) which has been designed to collect the

proposed 50-year site discharge of 4.63 cfs and drain into a detention basin sized to store the required

volume for the 50-year storm event (1,140 cu-ft) and discharge at a maximum rate of less than the

existing 10-year storm event (2.72 cfs). The proposed detention basin will store 1,268 cu-ft while

discharging a maximum of 2.69 cfs (8” orifice control) to the catch basin located on Austin Avenue. On-

site storm structures (catch basins and curb cuts) and the site outlet (12” pipe) have been sized to

convey storm water using the 100-year design storm.

The proposed detention basin has been designed to limit storm water runoff to predeveloped 10-year

flow or better for the post developed 50-year storm event. There will be no adverse effect to

surrounding properties or public right-of-way due to site development.

The Rational Method was used to calculate storm discharge and volume values, see Site Development

Plans for additional details of this property development.

*See Appendix – Exhibits for applicable tables, diagrams, etc.

4/10/2020

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HYDRAULIC CALCULATIONS

METHODOLOGY & EQUATIONS:

Rational Method using the 50 year frequency design storm were used to show

runoff rate and volume control with development design.

Q = CiA (Rational Method)

where,

Q = runoff rate (cfs)

C = runoff coefficient (0.90 impervious / 0.20 pervious)

i = rainfall intensity (in/hr)

A = watershed area (acres)

Rainfall Intensity per TxDOT Bridge Division Hydraulic Manual - Hidalgo County.

i = b / (Tc+d)^e

where,

i = storm intensity (in/hr)

Tc = time of concentration (min)

Orifice Equation was used to calculate basin discharge at given depths.

Q = C*A*(2gh)^0.5

where,

Q = discharge (cfs)

C = orifice coefficient (0.60)

A = orifice cross sectional area (sq-ft)

g = gravitational constant (32.2 ft/sec/sec)

h = distance between water surface and orifice centroid (ft)

Manning’s Equation was used to check overflow pipe capacity for the 100-year frequency design storm.

Q = 1.49/n *A*R^2/3*S^1/2

where,

Q = capacity (cfs)

n = roughness coefficient (0.012 storm pipe)

R = A/P = hydraulic radius (ft)

A = cross sectional area (sq-ft)

P = wetted perimeter (ft)

S = slope (ft/ft)

Storm Event 10 50 100

b = 87 99 103

d = 9.2 9.2 9.6

e = 0.778 0.749 0.74

4/10/2020

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EXISTING CONDITIONS SUMMARY:

The existing 0.963 acre site is pre-developed lot and is generally flat with two apparent drainage areas,

North and South. The North 10-year site peak discharge is 3.28 cfs. The existing drainage area to the

South 10-year site peak discharge is 2.72 cfs, being the maximum allowable discharges in proposed

conditions.


North Drainage Area

Area = 0.418 acres

C = 0.90 (100% impervious)

Tc = 10 min

Q10 = 3.28 cfs ← ALLOWABLE PEAK DISCHARGE

Q50 = 4.07 cfs

Q100 = 4.28 cfs

South Drainage Area

Area = 0.546 acres (53% impervious)

C = 0.57

Tc = 10 min

Q10 = 2.72 cfs ← ALLOWABLE PEAK DISCHARGE

Q50 = 3.37 cfs

Q100 = 3.54 cfs

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PROPOSED CONDITIONS SUMMARY:

The proposed 0.963 acre site will consist of a new Dale Shine Car Wash with onsite storm water

collection system for the Southern Drainage area (0.570 acres) which has been designed to collect the

proposed 50-year site discharge of 4.63 cfs and drain into a detention basin sized to store the required

volume for the 50-year storm event (1,255 cu-ft) and discharge at a maximum rate of less than the

existing 10-year storm event (2.72 cfs). The North Drainage area (0.393 acres) will discharge directly into

the existing catch basin on 23rd Street at a rate less than the existing 10-year storm event (3.28 cfs).


North Drainage Area


C = 0.71

Tc = 10 min

Q10 = 2.44 cfs

Q50 = 3.02 cfs ← LESS THAN ALLOWABLE PEAK DISCHARGE

Q100 = 3.18 cfs

South Drainage Area


C = 0.75

Tc = 10 min

Q10 = 3.73 cfs

Q50 = 4.63 cfs ← EXCEEDS ALLOWABLE PEAK DISCHARGE

Q100 = 4.87 cfs

The proposed development will increase discharge rates due to increasing impervious area and

therefore requires storm water detention to limit the proposed 50-year site discharge to existing 10-

year flow or better for the Southern Drainage area. The Northern Drainage area will not increase

discharge to the existing catch basin on 23rd Street for the 50-year storm event above the allowable

release rate of the existing 10-year storm event.

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REQUIRED DETENTION VOLUME SUMMARY:

Duration Tc i-50 Q-50 Q-Allow Inflow Outflow

Req.

Storage

(min) (min) (in/hr) (cfs) (cfs) (cu-ft) (cu-ft) (cu-ft)

20 10 10.83 4.62 2.72 2,772 1,632 1,140

30 15 9.10 3.87 2.72 3,483 2,450 1,033

40 20 7.91 3.36 2.72 4,035 3,267 768

50 25 7.03 2.99 2.72 4,481 4,083 397

60 30 6.34 2.70 2.72 4,855 4,900 -46

50-year Critical Storm: Duration = 20 minutes / Minimum Required Storage Volume = 1,140 cu-ft

DRAINAGE SYSTEM PERFORMANCE SUMMARY The proposed detention basin will store a maximum of 1,268 cu-ft while discharging 2.69 cfs for the 50-year storm

event to a catch basin located along the north side of Austin Avenue.

On-site storm structures (catch basins & curb cuts) and the site outlet (12” pipe) have been sized to convey storm

water using the 100-year design storm.

The proposed detention basin has been designed to limit storm water runoff to predeveloped 10-year flow or

better for up to the 50-year storm event. There will be no adverse effect to surrounding properties or public right-

of-way due to site development.

*Average End Area Method used to calculate storage volume.

*Emergency overflow through outlet structure grate @ 124.80.

*Maximum storage volume provided (1,268 cu-ft) exceeds 50-year required volume (1,140 cu-ft).

50-year Storm Event / Critical Duration of 20 minutes: High Water Surface Elevation = 124.80 Basin Peak Discharge @ 124.80 = 2.64 cfs (less than allowable of 2.71 cfs

Site Overflow Check:

In an emergency condition the detention basin would overflow through the grate of the outlet structure and

through the 12” pipe draining to catch basin on Austin Ave. Proposed Q-100 = 4.87 cfs

12" Storm Pipe @ 1.00% slope Capacity = 10.96 cfs (exceeds overflow discharge of 4.87 cfs)


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APPENDIX - EXHIBITS

Vicinity Map

USGS Topo Map

FEMA Floodplain Map

USDA Soils Map

Existing Site Map

Proposed Site Map

Detention Basin Grading

Outlet Structure Detail

STORM WATER REPORT EXHIBIT FOR

TBPE Firm No.: 16636

28 North Cherry Street | Germantown, Ohio 45327 | Phone: 937-388-0060 | BURKHARDTINC.COM

CIVIL ENGINEERING | LAND SURVEYING | NATIONAL RETAIL SITE DEVELOPMENT

VICINITY MAP

2301 U.S. HIGHWAY 83 BUSINESS

CITY OF MCALLEN, HIDALGO COUNTY, TEXAS

CAR WASHXPRESS

N

N

23rd S

t.

N

B

icentennial B

lvd.

S

29th S

t.

S

23rd S

t.

SITE

83

BUSINESS

2

83

83

BUSINESS




USGS TOPO MAP

N

U.S. Department of the Interior

U.S. Geological Survey

MISSION / PHARR QUADRANGLE

Texas - Hidalgo County

7.5-minute Series

SITE

CAR WASHXPRESS







FEMA FLOODPLAIN MAP

N

SITE

FIRM # 480343 0005 C, effective date: November 2, 1982

Zone "C" : Areas of minimal flooding.

CAR WASHXPRESS







USDA SOILS MAP

Urban Land:

Hydrologic Soil Group: D

Hidalgo-Urban Land

Complex:

Hydrologic Soil Group: B

Ksat: 0.57 to 1.98 in/hr

N


CAR WASHXPRESS






EXISTING SITE MAP

23

rd

S

tre

et

The existing 0.963 acre site is pre-developed lot and isgenerally flat with two apparent drainage areas, North (0.418acres) and South (0.546). The North drainage area drainstowards South 23rd Street to an existing catch basin and theSouth drainage area drains towards Austin Avenue to anexisting catch basin. The existing 10-year discharge for theNorth Drainage area is 3.28 cfs, being the maximum allowabledischarge in proposed conditions to the North. The existing10-year discharge for the South Drainage area is 2.72 cfs,being the maximum allowable discharge in proposedconditions to the South. The proposed development willmaintain the split drainage areas to the North and South. TheNorth drainage area will decrease impervious area andtherefore will not require storm water detention. The Southdrainage area will increase impervious area and therefore willrequire storm water detention to limit the proposed sitedischarge to existing conditions or better.

North Discharge AreaArea = 0.418 acres (100% pervious)C = 0.90Tc = 10 min

North Discharge Area 10-year Storm Event:Q = 3.28 cfs [0.90 x 8.73 in/hr x 0.418 ac]V = 1,968 cu-ft [3.41 cfs x 10 min x 60 sec/min]

South Discharge AreaArea = 0.546 acres (53% pervious)C = 0.57Tc = 10 min

South Discharge Area 10-year Storm Event:Q = 2.72 cfs [0.57 x 8.73 in/hr x 0.546 ac]V = 1,632 cu-ft [2.72 cfs x 10 min x 60 sec/min]

N


CAR WASHXPRESS

Austin Ave

U.S. Hwy 83

EX. CURB INLET

EX. CURB INLET

EX. BUILDING

EX. CURB INLET



NORTH DISCHARGE AREA

Q-10=3.41cfs

SOUTH DISCHARGE AREA

Q-10=2.71cfs




PROPOSED SITE MAP

The proposed 0.963 acre site will consist of a new Dale ShineCar Wash with onsite storm water collection system for theSouthern Drainage area (0.570 acres) which has been designedto collect the proposed 50-year site discharge of 4.63 cfs anddrain into a detention basin sized to store the required volumefor the 50-year storm event (1,140 cu-ft) and discharge at amaximum rate of less than the existing 10-year storm event(2.69 cfs).

North Discharge AreaArea = 0.393 acres (73% pervious)C = 0.71Tc = 10 min

North Discharge Area 50-year Storm Event:Q = 3.02 cfs [0.75 x 10.83 in/hr x 0.393 ac]V = 1,812 cu-ft [3.02 cfs x 10 min x 60 sec/min]

South Discharge AreaArea = 0.570 acres (78% pervious)C = 0.75Tc = 10 min

South Discharge Area 50-year Storm Event:Q = 4.63 cfs [0.75 x 10.83 in/hr x 0.570 ac]V = 2,778 cu-ft [4.63 cfs x 10 min x 60 sec/min]

PR

OP

OS

ED

C

AR

W

AS

H

Measured Impervious Area (Building, Pavement, Sidewalk, etc.) = 31,760 sq-ft (76% lot coverage)Measured Pervious Area (Lawn, Landscaping, etc) = 10,195 sq-ft (24% lot coverage)


N

CURB CUT

CAR WASHXPRESS

N

23

rd

S

tre

et

Austin Ave

U.S. Hwy 83

CURB CUT

OUTLET

CONTROL

12"@1.00%



EX. CURB INLET

EX. CURB INLET

EX. CURB INLET

NORTH DISCHARGE AREA

Q-50=3.02cfs

BASIN INFLOW

Q-50=4.63cfs

BASIN OUTFLOW

Q-50=2.71cfs

AUSTIN AVENUE




DETENTION BASIN GRADING


CAR WASHXPRESS



WESTERN STORAGE VOLUME:124.00 (invert) Contour Area = 212 sq-ft124.80 (overflow) Contour Area = 238 sq-ftStorage Volume = 180 cu-ft

SOUTHERN STORAGE:124.00 (invert) Contour Area = 762 sq-ft124.80 (overflow) Contour Area = 1,160 sq-ftStorage Volume = 769 cu-ft

EASTERN STORAGE AREA:124.00 (invert) Contour Area = 334 sq-ft124.80 (overflow) Contour Area = 464 sq-ftStorage Volume = 319 cu-ft

TOTAL SYSTEM STORAGE VOLUME = 1,268 cu-ft




OUTLET STRUCTURE DETAIL


CAR WASHXPRESS



OUTLET STUCTURE SECTION

NOT TO SCALE

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