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BASIN and RIVER SYSTEMS

BASIN and RIVER SYSTEMS. Divide. Dam at Lake Travis DEM of Trinity River. Watershed Parameters. Divide. Size Slope Shape Soil type Storage capacity. Reservoir. Natural stream. Urban. Concrete channel. Parameters that Affect Response in a Watershed. Floodplain. Divide.

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BASIN and RIVER SYSTEMS

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  1. BASIN and RIVER SYSTEMS Divide Dam at Lake Travis DEM of Trinity River

  2. 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 Rainfall intensity / duration Size, Slope, Shape, Storage Channel morphology Location of Developments Land use/land cover Soil type Percent impervious Reservoir Natural stream Urban Concrete channel Floodplain Q

  4. Urbanization Effect in a Watershed Floodplain Divide Urban Effects Increase Peak Decrease timing Confluence Q Channeliized stream Natural Urban Concrete channel T

  5. The Floodplain and Floodway Top Width

  6. Watershed Hydraulics Floodplain Divide D QD Tributary C Reservoir Confluence QC Main Stream B QB A QA Cross Sections Cross Sections

  7. Watershed Topography

  8. 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

  10. 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

  11. 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.

  12. USE of Storage Reservoirs

  13. 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.

  14. Cochran’s Crossing Alden Bridge College Park Bear Branch Reservoir Research Forest Indian Springs River Walk Lake Woodlands Town Center Grogan’s Mill

  15. 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.

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

  17. 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

  18. 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.

  19. ChannelDesign • 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.

  20. 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.

  21. 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

  22. 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.

  23. 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.

  24. 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

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

  26. 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.

  27. Amenities • Hike-and-bike trails • Wildlife and habitat • Water quality benefits

  28. 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

  29. Brays Bayou - Low Flow

  30. Brays Bayou High Flow

  31. Kissimee River - The Everglades

  32. Bull Creek, Austin - CEVE 412

  33. San Antonio River

  34. California - Temecula

  35. I-45 Bridge over Clear Creek - 1979

  36. T.S. Allison - Houston, June 9, 2001 Rice Blvd at Entrance 16 looking west Jeep indicating high water mark - inlet to Harris Gully

  37. Southwest Freeway (US 59) Detention storage between Mandell and Hazard Looking West Looking East

  38. Flood Warning SystemsDowntown Houston Emergency Response • Flood Doors • Flood Gates • Facility Entrances • Communications • Operations • Training

  39. 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

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