9/12/2014

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City of Sugar Land – AMIL Gates

“Replacing some Interesting Gates”

TFMA Fall Conference

September 4, 2014

• Constructed in 1970’s by Fort Bend County LID No. 2

• City took ownership in Feb. 2007

• Gates are hydraulically activated (open from bottom)

• Main purpose is Flood Protection (not watertight)

• Partner w/ Gulf Coast Water Authority (GCWA) 2

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• Water storage from GCWA Shannon Plant & rainfall

• Floats off Dam #2 and Ditch “H” Extension Weir

• Diversion to Brazos River through Ditch “H”

• High efficiency as Flood Prevention

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Ditch “H” Extension

Dam #2

Dam #3

Dam #1

AMIL Gates

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• Flood Control Measures

• Water Surface Elevation

• Maintenance Cost

• GCWA Concerns (Bypass)

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• 100-yr FEMA BFE

• Normal Operating WSE

• Use of Most Current Model

• Maximum Utilization of

Ditch “H” Improvements

• Reduced Maintenance Costs

• Minimize Downstream Impacts

• Environmental Impacts

• Construction Cost

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• Unsteady HEC-RAS Model

(Originally prepared in 2011)

• Control Flows thru Brooks Lake Diversion (AMIL Gates)

• Minimize impacts to Oyster Creek (D/S)

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• Evaluate Multiple

Tailwater conditions

along Brazos (Ditch H)

– 100-yr in Oyster w/

10-yr Brazos

– 10-yr in Oyster w/

100-yr in Brazos

BLD

4896

4780

4480

4250

4140

3850

3664

3505

30562767246021491889

175015551270972

900

881

770

470412

400

313

128

Bro

ok

s L

ak

e D

ive

1405.1

1262.74*

1120.38*

978.02*

835.66*

693.3

653.42*

613.54*

573.66*

533.78*

493.9*

454.02*

414.139*

374.259*

334.379*

294.499*

254.619*

214.739*

21990

21498

20968

20872.6*

20777.3*

20682.*

20586.6*

20491.3*

20396

20331

20222

20153

19926

19726

89900

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• Non-Mechanical System

• Labyrinth Weir

– Length vs. Capacity

– Concrete vs. Steel

• Slide Gate (Future Flexibility)

• Existing Structure Footprint

• Amenity Features

– Pedestrian Bridge

• Constructability / Phasing

• WSE Impacts Downstream

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• Evaluated potential modifications to:

– Ditch H Overflow

– Dam’s 1, 2, & 3

– Various Bridge Structures / Restrictors

– 100-ft Weir within Existing AMIL Gate Structure

0 50 100 150 20066

68

70

72

74

76

78

BR_OC_BHB 2012(FT ) P lan: OC100-BRLOW 10/22/2012 Geom: BR_OC_BHB_PrePrj Flow:

River = Ditch H Reach = US-BLD RS = 24951.2 Just D/S of Weir

Station (ft)

Ele

va

tion

(ft)

Legend

Ground

Bank Sta

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• Bridges and Ditch H modifications had localized impacts

– No effective benefit for Brooks Lake Diversion (AMIL Gates)

• Not sufficient capacity with only 100-ft Weir conversion

• Considered Labyrinth Weir with varying length

0 1000 2000 3000 400067

68

69

70

71

72

73

RS: 881

Flow (cfs)

Sta

ge

(ft)

Legend

RC

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• Modeling a Variable Weir Length

– Change Length by varying Weir

Coefficient (100-ft to 1,000-ft)

• 100-ft Weir: ‘C’ = 3.3

• 200-ft Weir: ‘C’ = 6.6

• 300-ft Weir: ‘C’ = 9.9

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• Add Vertical Slide Gate

– Increase “Factor of Safety”

– Adjustable WSE Control

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Labyrinth Weir

Pedestrian Bridge

Slide Gate

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Labyrinth Weir

Pedestrian Bridge

Slide Gate

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Constructability / Cost

• Utilize Existing Structure

• Phased Construction

• Maintain Flow

• Within Current ROW

• Faster Nationwide Permitting

Pedestrian Bridge

2 ~ 15-ft x 4-ft Gates(Automated Controls &

Downward Opening)

2 ~ 65-ft Long x 20-ft Wide Weirs(12-ft Tall Structural ConcreteRetaining Walls w/ Depressed

Inside Edge for Low-Flow)

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Impacts noted along Oyster Creek approx. 5 mi. D/S & 3 mi. U/S

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Contained within Banks on City Owned Property

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Constructability / Cost

• Utilize Existing Structure

• Phased Construction

• Maintain Flow

• Within Current ROW

• Faster Nationwide Permitting

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Option Effective

Weir Length

Total Width of

4’ High Gates

Rise above

FEMA BFE1

Effectiveness Cost

Rating

(Low = Best)

Type of

Construction

Approx Cost, in

$1,000s2

1-conc. 200 0 0.32 3.68 Concrete $1,151

1-steel 200 0 0.32 4.93 Steel Piling $1,541

2-conc. 200 30 0.21 3.01 Concrete $1,434

2-steel 200 30 0.21 3.74 Steel Piling $1,779

3-conc. 300 0 0.24 3.44 Concrete $1,433

3-steel 300 0 0.24 4.70 Steel Piling $1,958

4-conc. 300 30 0.16 2.74 Concrete $1,715

4-steel 300 30 0.16 3.53 Steel Piling $2,204

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