Central Texas is often called "Flash Flood Alley" because of its frequent,
intense storms. The "big ones" seem to happen every decade. The major
floods of Austin described below have left a lasting impression in people's
memories and in the record books.
November 15, 2001
A slow-moving storm system
stalled over central Texas, west
of Austin, and waves of rain
and thunderstorms began to
sweep up the I-35 corridor.
Widespread rainfall totals
typically ranged from five to
eight inches, but radar based
estimates indicate that some
areas may have received 15
inches of rain. Much of this rain
fell within the space of six
hours.
There was one fatality and widespread flood damage both where the
drainage capacity of streets and storm drains was exceeded by rainfall and
where creeks overflowed their banks in floodplain areas. In total, 860
buildings were reported to have flood damage. Onion Creek suffered the
most significant damage, but home and businesses in the floodplains of
Slaughter Creek, South Boggy Creek, Williamson Creek, West Bouldin
Creek, East Bouldin Creek, Shoal Creek and Walnut Creek were also hard
hit. There was also some flood damage along other streams.
October 17, 1998
Twin hurricanes Madeline and
Lester on the west coast of
Mexico funneled continuous
waves of moisture inland
causing flooding in Central and
South Texas. Across the state
there were 31 deaths, 20
counties declared disaster
areas, and 7,000 people
evacuated from their homes.
Property damages and losses
reached almost $1 billion. In
Austin, 454 homes were damaged, with most of the damages incurred to
houses along along Onion Creek, Walnut Creek, and Williamson Creek.
December 20, 1991
Record peak discharges were
recorded at many creek gaging
stations across Central Texas. A
week of heavy rains contributed
to flooding in Lake Travis,
Shoal, Williamson, Bull, and
Walnut Creeks. An estimated
200 homes in Travis and
Bastrop counties were
completely under water.
Needless to say, this flood
ruined the holiday season for many people.
May 24, 1981
This storm event will always be
remembered as the "Memorial
Day Flood" which drowned 13
people and caused $36 million
in damages. This short-duration
storm with intense rainfall hit
many of Austin's urban creeks:
Shoal, Walnut, Little Walnut,
Bee, and Waller creeks. Shoal
Creek normally flows at 90
gallons per minute, but peaked
during this flood at 6 million gallons per minute! Some areas received over
10 inches of rain in four hours. More 1981 flood photos.
November 23, 1974
An evening cold front brought thunderstorms in a 40-mile wide line that
dropped between four and ten inches of rain in Central Texas. Stalled cars
were abandoned all over Austin and "every road in the county has people
stranded on the rooftops," said a Travis County sheriff's office spokesman.
A man and his 8-year-old daughter and 5-year-old son were swept into
West Bouldin Creek after driving past an off-duty firefighter as he tried to
stop traffic from crossing the area. Their car was immediately swept
downstream, drowning all three and bringing the death toll up to 13.
October 28, 1960
Similar to the 1974 flood, an evening cold front brought downpours in a 75-
mile radius around Austin. An Austin Statesman article described the
frightening evening: "Giant, swirling walls of water, spawned by torrential
rains of up to nine inches, snuffed out at least two lives, swept away
property valued at $2.3 million, and forced 200 people to flee their homes
before the flood in a nightmarish night of death and destruction in Austin.
Early Saturday, bleary-eyed police reported they had answered an
unprecendented 6,000 calls during the night." Several motorists were
washed away in their cars, bringing the final death toll to 11. Police claimed
the floodwaters from Boggy Creek rose to such a height and to such force
that "cars were being pushed around like floating beer cans" on Rosewood
Avenue.
April 24, 1957
Texans cheered when rains
came in early April to end the
seven-year drought. But on April
24, the Austin American
Statesman said, "when the
black, purple shrouded cloud
first appeared in the sky, Central
Texans knew something was
about to happen. It did. Up to 10
inches of rain fell within a few
minutes in a wide sweep of
middle Texas." April 24th was
labeled "The Day of the Big
Cloud," and "the worst day of floods, tornadoes and torrential rain and hail
Central Texas has ever seen." As if that wasn't bad enough, the rains kept
coming for a total of 32 days, causing flooding all across Austin and Central
Texas.
June 15, 1935
The flood of 1935 was one of
three major floods to hit the area
in the 1930's. Austin was hit
with 22 inches of rain in three
hours. Between 2,500 and
3,000 residents in East Austin
(near present-day IH-35 and the
river bank) were left virtually
homeless after the waters
receded. A Statesman article
described the situation: "Sloppy
silt was deposited to a depth of from six to 18 inches on the floors, over
furniture, bed clothing and in fact everything that the glue-like mud could
fasten itself upon, and only the most rugged articles of furniture could be
salvaged."
"South Congress Avenue between Barton Springs Road and the Texas
School for the Deaf was a crumpled mass of ruins, the street being littered
with broken sewer lines torn from business buildings that once stood in the
area, broken concrete, twisted water pipes, signs, trees, timbers, structural
steel, a number of the new concrete lamp posts erected a month ago by the
city and other debris. The street, the pride of Austin and of the state
highway department presented a wretched scene." The Montopolis and
Marble Falls bridges were also both destroyed.
September 8-10, 1921
This storm event,
known as "The Great
Thrall/Taylor Storm",
still stands in the record
books as the greatest
of all continental U.S.
rainstorms during 18
consecutive hours. The
storm entered Mexico
as a hurricane from the
Gulf and then drifted northward dropping six inches on Laredo before
unleashing on Central Texas. Like the storms of 1998, 1991, and 1981, this
storm followed a pattern that ran along the Balcones Escarpment, then
centered over Williamson and Travis Counties. At Taylor, 23.11 inches of
rain fell in 24 hours. Thrall reported approximately 36 inches in 18 hours and
40 inches of rain in total. There were 224 fatalities across the seven
counties that were affected.
Austin received 18.23 inches of rain in 24 hours. Miraculously, only six
fatalities were reported in Travis County, all on Onion Creek. Three steel
bridges washed out on Onion Creek at Moore's Crossing and Doyle's
Crossing and on Walnut Creek at Dessau Road.
Although less rain fell in Bexar County, the results were more disastrous. In
a paragraph titled "Less Warning Than War", the Austin American described
the terrifying night there: "Only in San Antonio the flood victims had less
warning than the booming of a distant cannon. The stories told by those
who fled before the flood waters seem to make it clear that the Alazan
Creek, usually a placid rivulet of water, became a rushing torrent in less
than half an hour. The water, it is said, rose eight feet in approximately
twenty minutes. So it was not long before the first of the houses near the
creek bed floated from their foundations and it was a barrage of these that
hurled themselves against the International & Great Northern trestle. By
midnight between forty and fifty houses that a few minutes before vomited
men, women and children in all stages of dress and undress, were being
churned into a shapeless mass of debris where they lodged against the
railroad bridge. Their tremendous weight and pressure against the trestle
soon cracked that structure in the middle, which pushed itself against a
second trestle that broke shortly after under the strain."
April 23, 1915
Flash floods killed 35 people,
most of whom lived near Waller
Creek. Many people drowned
from swirling water inside their
houses. Excerpts from a 1915
article in the Statesman says it
all: "Whole sections of the city
were submerged for hours.
Houses were washed away,
cows, horses, chickens and
other fowls were careening
down swelled Shoal and Waller Creeks to join the human corpses that had
gone swirling before them to the bosom of the Colorado... This morning
Austin presents a pitiable sight. There is not a section of the city traversed
by the treacherous little streams docile most months of the year, which has
not felt the finger of death." More 1915 flood photos.
April 7, 1900
The flood waters started from a two-day storm in the High Plains halfway
between Lubbock and Amarillo. The stormwater filled the Colorado, the
Brazos and the Guadalupe rivers, sending the torrent through unsuspecting
cities like Austin and Bastrop. This flood will always be remembered as "The
Day the Dam Broke." McDonald Dam on the Colorado River broke up,
sending a wall of water down the river which killed dozens of people, even
whole families. The river peaked at 60' high and a mile wide. The pride of
Austin at the time, "Ben Hur," the 181-foot long, triple-decker leisure
steamboat, was also destroyed
by the flood.
July 6, 1869
The dams and Town Lake did
not exist at this time, so the
Colorado River was normally
small as it ran through Austin
and was commonly called a
"stream". The month of July
started with rains at short
intervals causing the Colorado
River to rise gradually. On the
6th, a flood came down the river
in walls causing it to overflow at
an alarming rate. According to
Brown's Annals in the Austin History Center, "the mass of waters rushed
down from the narrow and confined channel between the mountains above,
to the wider one below, with such fearful velocity that the middle of the
stream was higher than the sides, and the aspect it presented was
appalling."
Floodplain Development Information for
Developers and Engineers
Projects proposing development in the 25-year and 100-year floodplains
have the potential for placing our citizens and their property at risk of
flooding and producing changes in floodplain elevations and plan view
extent. Both City of Austin regulations and National Flood Insurance
Program regulations apply.
Developers and engineers that are contemplating development in floodplain
areas should be especially familiar with the Land Development Code (LDC):

Chapter 25-7 Drainage

Chapter 25-12-3 "Local Amendments to the Building Code," Section
1612, Flood Loads

Chapter 25-12-3 "Local Amendments to the Building Code," Appendix
G, Flood Resistant Construction
The Building Code is contained within LDC Chapter 25-12 "Technical
Codes".
Additional ordinances and technical criteria are contained in:

LDC 25-5 "Site Plans"

LDC 25-8 "Environment"

Technical Manuals for Drainage Criteria and Environmental Criteria.
Major Issues
The following list summarizes the major issues of personal safety and
property protection associated with development within floodplain areas.
Each point is discussed in greater detail below. There are other issues
related to environmental integrity and preservation of the natural and
beneficial functions of floodplain areas that are not discussed in this
document.
1. 25-year floodplain - Encroachment of buildings and parking areas is
prohibited.
2. 100-year floodplain - Encroachment of buildings and parking areas is
restricted.
3. No adverse impact - Proposed development must not result in
additional identifiable adverse flooding on other property.
4. Site Plans - A site plan is required for all development proposed
within the 100-year floodplain.
5. Variances - Variances to allow development of the floodplain are
considered by the City Council. Variances must be requested in
writing.
6. Floodplain Mapping - Approval by Federal Emergency Management
Agency of changes to floodplain mapping may be required.
Discussion of Major Issues
25-Year Floodplain
LDC 25-7-92 (A) prohibits encroachment of buildings or parking areas within
the 25-year floodplain.
100-Year Floodplain
LDC 25-7-92 (B) prohibits encroachment of proposed building or parking
areas beyond the 25-year floodplain but within the 100-year floodplain with
certain specific exceptions:

LDC 25-7-93 General Exceptions sets forth conditions and
requirements to allow construction of parking areas less than 5,000
square feet, single family residential structures in a subdivision
recorded before September 25, 1983, buildings within certain
floodplain areas of the Colorado River, and certain boat docks.

LDC 25-7-94 Exceptions in the Central Business Area sets forth
conditions and requirements that apply within the area bounded by
IH-35, Riverside Drive, Barton Springs Road, Lamar Boulevard, and
15th Street.
o
The foundation floor slabs must be a minimum of two (2)
feet above the 100-year floodplain elevation.
o
Pedestrian and vehicular access to the proposed buildings
must be to areas above the regulatory flood datum, which is
equivalent to the 100-year floodplain elevation plus a
freeboard of one foot.
o
All development associated with the construction of
buildings must compensate for any floodplain volume
displaced by that construction.
o
The applicant must demonstrate by means of a study by a
Texas registered professional engineer that the
construction of the building and associated development
activities improve the drainage system by exceeding the
minimum requirements of Sections 25-7-2 (Obstruction of
Waterways Prohibited), 25-7-3 (Duty to Maintain
Unobstructed Waterways), and 25-7-4 (Standing Water
Declared a Nuisance).

LDC 25-7-95 Exceptions for Parking Areas provides additional
exceptions for parking areas.
LDC 25-12-3, "Local Amendments to the Building Code," Section 1612.4.1
requires that the foundation floor slabs must be a minimum of one foot
above the 100-year floodplain elevation.
LDC 25-12-3, "Local Amendments to the Building Code," Section 1612.4.3
requires that normal access to proposed buildings must be to areas a
minimum of one foot above the 100-year floodplain.
No Adverse Impact
LDC 25-7-61 (A) (5) requires that a final plat, subdivision construction plan,
or site plan may not be approved unless the proposed development will not
result in additional identifiable adverse flooding on other property and to the
greatest extent feasible, preserves the natural and traditional character of
the land and waterway.
LDC 25-7-151 (A) states that the owner or developer of property to be
developed is responsible for the conveyance of all stormwater flowing
through the property, including stormwater that is directed to the property by
other developed property or that naturally flows through the property
because of the topography.
Development within the floodplain may cause adverse impact to others by
obstructing the existing waterway or by placing fill in floodplain storage
areas.
Obstruction of the waterway reduces the cross sectional area of the channel
and typically creates identifiable adverse impacts of increased erosion and
scour at the obstruction and/or increased flood elevations upstream of the
obstruction. A proposed site plan should not decrease the conveyance
capacity of the channel and overbank areas. Hydraulic analysis is required
to demonstrate that the proposed development will not create any additional
identifiable adverse flooding on other property due to loss of conveyance.
Placement of fill in the floodplain reduces the natural capacity of the
floodplain to store floodwaters. Loss of floodplain storage typically causes
higher peak flows and additional identifiable adverse flooding on
downstream properties. A proposed site should not decrease the floodplain
storage volume of the channel and overbank areas. Accurate plans and
cut/fill calculations must be provided for any proposed development within
the floodplain to demonstrate that any proposed fill is offset by at least an
equal amount of excavation within the floodplain.
Excavation and fill of the floodplain and modification of the channel are
subject to requirements to preserve the natural and traditional character of
the land and waterway.
The contours of the channel bottom change continually due to natural
processes of deposition and scour. Temporary removal of sediments from
depositional areas may have unforeseen impacts on channel erosion, and is
not considered to affect calculations of cut and fill or conveyance.
Site Plans
LDC 15-12-3, Appendix G, Section 6104, requires that no structure or land
within the 100-year floodplain identified by the Federal Emergency
Management Agency and within the planning jurisdiction of the City of
Austin shall be located, altered, or have its use changed without submittal of
a site plan to ensure conformance with the floodplain management
regulations. Site plan applications must be submitted to the Watershed
Protection and Development Review Department at One Texas Center. The
Development Review Division will coordinate review of the site plan with the
Building Inspection Division and the Watershed Engineering Division as
may be necessary.
Variances
LDC 15-12-3, Appendix G, Section 6105, states the administrative
procedures and criteria that must be considered in evaluating standard
variances from the floodplain management regulations. Variances are
considered by the City Council and require two separate actions by Council:
first to set a time for a public hearing, and second to conduct the public
hearing and to render a decision to grant or deny the requested variance.
There is also an administrative variance process that can be used in certain
specialized cases. For more information on its requirements, see the Land
Development Code Section 25-7-92 (C). Requests for variances must be
submitted in writing to the Case Manager. The Watershed Protection and
Development Review Department can assist the applicant to identify the
variances that may be required.
Flowchart for Residential Building Permits in the Floodplain
Floodplain Mapping
The Drainage Criteria Manual, Section 1.2.6 "Flood Plain Delineations"
governs the delineation of floodplain boundaries and requirements to update
the effective floodplain maps when changes occur. Floodplain mapping that
is outdated may create unnecessary encumbrances (such as federal
requirements for flood insurance or building permit restrictions), or may
allow citizens to be placed at undue risk of flooding. Both the City of Austin
and the Federal Emergency Management Agency through its National Flood
Insurance Program have review and approval authority for floodplain
mapping within the City's jurisdiction.
Projects may change the 100-year floodplain with respect to either plan view
or elevation. The applicant may submit a more accurate analysis of predevelopment conditions to demonstrate that the site is less encumbered by
the floodplain. Alternatively, the applicant may propose structural
modifications to reduce the post-development floodplain. In either case,
floodplain maps must be updated to effectively manage the floodplain.
FEMA establishes formal processes for revisions of its Flood Insurance
Rate Maps (floodplain maps.) Revision of the pre-development floodplain
will require a Letter of Map Revision. Changes to the post-development
floodplain will require a Conditional Letter of Map Revision, i.e. the maps will
be revised on the condition that proposed improvements are constructed as
planned.
If the applicant proposes an encroachment on the floodplain that will result
in increases in flood elevations, then FEMA must approve a Conditional
Letter of Map Revision before the City of Austin will issue a development
permit. For all other proposed modifications to the Flood Insurance Rate
Maps, the applicant shall apply to the FEMA for a Conditional Letter of Map
Revision before the City of Austin will issue a development permit. The
Conditional Letter of Map Revision must be approved by FEMA before the
City of Austin will issue the final letter of acceptance for a subdivision or the
certificate of completion for a site plan.
The applicant is responsible to prepare the engineering analysis, to follow
FEMA's administrative procedures, and to pay any fees required by FEMA.
The Watershed Protection and Development Review Department is the
Community Representative to FEMA for the National Flood Insurance
Program. Therefore, the Watershed Protection and Development Review
Department must review and concur with the engineering analysis prior to
acceptance for review by FEMA. The Watershed Engineering Division can
assist applicants and their engineers to complete the process and to review
the engineering analyses.
Featured Project
Manor Circle Emergency Erosion Project
The November 2004 floods caused severe creek bank erosion along a bend
of Tannehill Branch. Two four-plex structures were located on the edge of
the creek. Heavy rains saturated the creek bank and storm flows scoured
away the base of the bank. The high bank failed and slid into the creek and
created an emergency situation. The foundation of one structure was
undermined and a second structure was threatened. Eight families could
have been displaced if bank conditions worsened. This emergency project
reconstructed the creek bank with limestone armor on the lower bank and
wrapped soil lifts on the upper bank. The entire upper section was seeded
with native grasses. The property was reclaimed, the four-plex structures
are protected and the natural creek setting is enhanced.
Heavy rains saturated the creek
bank and storm flows scoured
away the base of the bank. The
bank failed and slid into the
creek.
Armor section and wall
foundation construction begins.
The wall foundation
construction continues and geogrids are laid between lifts.
The lower bank armor section is
near complete.
The upper bank is reconstructed The project is complete, the
with a series of wrapped soil
property is reclaimed, the two
lifts.
structures are protected and the
natural creek setting is enhanced