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