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BASIN and RIVER SYSTEMS
Divide
Dam at Lake Travis DEM of Trinity River
Watershed Parameters
Size
Slope
Shape
Soil type
Storage capacity
Reservoir
Divide
Natural stream
Urban
Concrete channel
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
DivideFloodplain
Reservoir
Natural stream
Urban
Concrete channel
Parameters that Affect Response in a Watershed
Floodplain
Q
DivideFloodplain
Confluence
Channeliized stream
Urban
Concrete channel
Urbanization Effect in a Watershed
Urban EffectsIncrease PeakDecrease timing
Q
T
Natural
The Floodplain and Floodway
Top Width
Watershed Hydraulics
Reservoir
Floodplain
Divide
Main Stream
Confluence
Tributary
Cross Sections
Cross Sections
A
B
C
D
QA
QD
QC
QB
Watershed Topography
Flood Control Methods - Structural
Objectives
Increase channel flow rate
Decrease flood levels
Means
1. Earthen or concrete
2. Swale clearing
3. Gobi mats
4. Gabions
5. Rip-raps
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
1. Retention/detention ponds
2. Natural drainage system
3. Runoff catchment areas
4. Reservoirs
5. Dikes and levees
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.
The Woodlands
USE of Storage Reservoirs
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.
Grogan’s Mill
Indian Springs
Lake Woodlands Town
Center
Research Forest
Bear Branch Reservoir
College Park
Cochran’s Crossing
Alden Bridge
River Walk
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.
The Woodlands
The Woodlands
The community was designed as if it were fully developed.
Strict requirements were made about land use and drainage and storage volumes.
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
Land Use
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.
The Woodlands
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.
Channel Design
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.
Flow and Erosion Control
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
Bridge Designs
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.
Urbanization
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.
Detention PondsCommunity Center - One of the first ponds built in Texas - 1972
Fountains added for aesthetic value and to increase circulation of air for water quality
Culverts are used to move water under streets.
An attempt is made to blend these culverts in with their natural surroundings.
Roadside Drainage
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.
The Woodlands - a Major Test
Amenities
Hike-and-bike trails
Wildlife and habitat
Water quality benefits
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
Conclusions
Brays Bayou - Low FlowBrays Bayou - Low Flow
Brays Bayou High FlowBrays Bayou High Flow
Kissimee River - The EvergladesKissimee River - The Everglades
Bull Creek, Austin - CEVE 412Bull Creek, Austin - CEVE 412
San Antonio River
California - TemeculaCalifornia - Temecula
I-45 Bridge over Clear Creek - 1979I-45 Bridge over Clear Creek - 1979
Rice Blvd at Entrance 16 looking west
Jeep indicating high water mark - inlet to Harris Gully
T.S. Allison - Houston, June 9, 2001
Southwest Freeway (US 59)
Detention storage between Mandell and Hazard
Looking East
Looking West
Flood Warning SystemsDowntown Houston
EmergencyResponse
Flood Doors Flood Gates Facility Entrances Communications Operations Training
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