The Woodlands

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BASIN and RIVER SYSTEMS
Divide
Dam at Lake Travis DEM of Trinity River
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Watershed Parameters
Divide

• Size
• Slope
• Shape
• Soil type
• Storage capacity

Reservoir
Natural stream
Urban
Concrete channel
3
Parameters that Affect Response in a Watershed
Floodplain
Divide

1. Rainfall intensity / duration
2. Size, Slope, Shape, Storage
3. Channel morphology
4. Location of Developments
5. Land use/land cover
6. Soil type
7. Percent impervious

Reservoir
Natural stream
Urban
Concrete channel
Floodplain
Q
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Urbanization Effect in a Watershed
Floodplain
Divide
Urban Effects Increase Peak Decrease timing
Confluence
Q
Channeliized stream
Natural
Urban
Concrete channel
T
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The Floodplain and Floodway
Top Width
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Watershed Hydraulics
Floodplain
Divide
D
QD
Tributary
C
Reservoir
Confluence
QC
Main Stream
B
QB
A
QA
Cross Sections
Cross Sections
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Watershed Topography
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Flood Control Methods - Structural

• Objectives
• Increase channel flow rate
• Decrease flood levels
• Means
• Earthen or concrete
• Swale clearing
• Gobi mats
• Gabions
• Rip-raps

9
Non-Structural - Buyouts

• Objectives
• Manage old and new structures
• Minimize future damages
• Means
• Relocate old structures
• Condemn frequently flooded structures
• Replace storage as areas develop

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Adding Useable Storage for Flood Control

• Objectives
• Runoff storage controls
• Decrease peak flows
• Means
• Retention/detention ponds
• Natural drainage system
• Runoff catchment areas
• Reservoirs
• Dikes and levees

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The Woodlands

• The Woodlands is a 30-year-old totally planned
  community north of Houston.
• Designed to minimize the floodplain and water
  quality impacts as development proceeds.

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USE of Storage Reservoirs
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Guidelines for Planning in an Urban Drainage Basin

• Maximize the distance of storm water travel
  from the site to a collection area or stream.
• Maximize the concentration time by slowing the
  rate of storm water runoff.
• Minimize the volume of overland flow per unit
  area of developed land.
• Utilize buffers such as forests and wetlands
  to protect collection areas and streams from
  urban impacts.
• Divert storm water away from critical features
  such as steep slopes, unstable soils, or valued
  habitats.

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Cochrans Crossing
Alden Bridge
College Park
Bear Branch Reservoir
Research Forest
Indian Springs
River Walk
Lake Woodlands
Town Center
Grogans Mill
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The Woodlands

• The Woodlands planners wanted to design the
  community to withstand a 100-year storm.
• In doing this, they would attempt to minimize any
  changes to the existing, undeveloped floodplain.

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The Woodlands

• The community was designed as if it were fully
  developed.
• Strict requirements were made about land use and
  drainage and storage volumes.

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Land Use

• More than 33 was designated as open space
• There are 3.5 lots per acre in residential
  areas, or about 20 impervious
• Extensive use of roadside ditches

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The Woodlands

• Designed detention ponds that are both
  effective and attractive.
• Incorporated these ponds into the fabric of
  communities and golf courses.
• Ponds were used to control the volume and
  quality of urban runoff into Panther Branch.

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Channel Design

• Most streams and ditches have been left in
  their natural state, thus increasing their
  Manning roughness coefficients and their storage
  capacities.
• This drainage system design minimizes the
  impact of urbanization on the peak runoff
  response.

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Flow and Erosion Control

• Another method of controlling the flow rate is
  placing energy dissipaters in the streambeds.
• These are commonly located directly near
  bridges due to steeper downward slopes.

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Bridge Designs

• Only channelized under the bridges in order to
  reduce erosion of the banks and the deterioration
  of bridge structures.
• Since this increases the flow rate, structures
  are built at each end to control velocities

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Urbanization

• Urban development designed to complement
  waterways.
• This reflection pool also serves as storage for
  runoff from local parking facilities.
• The concept is to allow for full urbanization
  but with a minimum environmental impact on the
  watershed.

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Detention Ponds - Amenities

• Ponds constructed so that amenities such as the
  golf course and other community centers could be
  built up around them.
• These ponds store and treat the runoff from such
  facilities and also add to the aesthetics of the
  overall development.

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Detention Ponds

• Community Center -
• One of the first ponds built in Texas - 1972

• Fountains added for aesthetic value and to
  increase circulation of air for water quality

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Roadside Drainage

• Culverts are used to move water under streets.
• An attempt is made to blend these culverts in
  with their natural surroundings.

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The Woodlands - a Major Test

• The hydrologic system at The Woodlands was
  severely tested during October 17-18, 1994, when
  a greater than 100-year event dropped heavy rains
  over the area.
• The design worked well, with only a few houses
  impacted.
• The same storm flooded 1000s in other
  watersheds.

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Amenities

• Hike-and-bike trails
• Wildlife and habitat
• Water quality benefits

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Conclusions

• Example of how to build an environmentally
  sound community
• 70,000 and will reach 150,000 population 2020
• Example of a sustainable watershed concept that
  has worked
• Concepts need to be studied and expanded to
  other areas

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Brays Bayou - Low Flow
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Brays Bayou High Flow
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Kissimee River - The Everglades
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Bull Creek, Austin - CEVE 412
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San Antonio River
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California - Temecula
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I-45 Bridge over Clear Creek - 1979
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T.S. Allison - Houston, June 9, 2001
Rice Blvd at Entrance 16 looking west
Jeep indicating high water mark - inlet to Harris
Gully
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Southwest Freeway (US 59) Detention storage
between Mandell and Hazard
Looking West
Looking East
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Flood Warning SystemsDowntown Houston

• Emergency
• Response
• Flood Doors
• Flood Gates
• Facility Entrances
• Communications
• Operations
• Training

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Brays Bayou-Typical Urban System

• Concrete-lined urban channel (200 million)
• Built in the 1960s
• Increase flow rates
• Capacity eroded with upstream development
• Current Federal Project will completely update
  the channel and add upstream storage areas - 450
  million rebuild by 2012

288 Crossing