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Severe flooding in parts of south-central Texas resulted from a

major storm during October 17–18, 1998. The flooding occurred

in parts of the major streams and tributaries of the San Jacinto,

San Benard, Colorado, Lavaca, Guadalupe, and San Antonio

River Basins. Peak gage height, peak streamflow, and documentation of the significance of the peaks were compiled for the

streamflow-gaging stations where the storm caused substantial

flooding. This information is available on the U.S. Geological

Survey (USGS) world-wide web site at http://tx.usgs.gov/alert/

oct_floods_98.html.

Most of the substantial rainfall and flooding occurred in the

Guadalupe and San Antonio River Basins. This report summarizes

rainfall and flood peaks in these two basins during October 1998.

Meteorology of the Storm

According to the National Weather Service (NWS) (John

Patton, written commun., 1999), the meteorologic conditions

that produced the storm rainfall were dominated by Hurricane

Madeline in the Eastern Pacific near the tip of Baja California, and

Hurricane Lester in the Eastern Pacific near Acapulco, Mexico.

The hurricanes, coupled with an atmospheric trough of low pressure over the western United States, forced a very deep layer of

air with high water-vapor content across Mexico and into Texas.

Meanwhile, an atmospheric ridge of high pressure to the east,

extending from the North Atlantic to the Yucatan Peninsula of

Mexico, confined the surface and mid-level water-vapor plumes to

south-central Texas.

During the morning of October 17, 1998, a strong low-level

inflow of moist air traveling 23 to 35 miles per hour flowed from

the Gulf of Mexico across Texas into Bexar County (

upper-level divergent wind pattern over south-central 

the extremely moist air mass from lower levels. Early 

storms slowly pushed eastward throughout the day in

prevailing moisture-rich flow.

In the early morning hours of October 17, extreme 

instability over western Bexar County extending nort

Kendall County caused rapid uplift of low-level moist

heavy thunderstorms. By 6 a.m., the area from weste

County to eastern Medina County had received 4 to 6 

rain. By 8 a.m., 6 to 10 inches had fallen; and by late m

area had received about 15 inches.

By late morning on October 17, the rains extended 

and Travis Counties. The NWS rain gage at Wimberl

County) indicated that intense rainfall began by 8 a.m

recorded 4.5 inches by 11 a.m., 6 inches by 1 p.m., 9 

4 p.m., and 11.25 inches by 8 p.m. At 11:30 p.m., the 

collector overflowed.

Finally, by mid-day October 18, the tropical plume 

rainfall shifted eastward to the upper Texas Coastal P

extended into Louisiana.

Storm Rainfall

A map of the total rainfall for the storm (fig. 1) wa

by the NWS (John Patton, written commun., 1999). T

equal rainfall (isohyetals) are based on total rainfall r

NWS rain gages and totals determined from a bucket 

coordinated by the NWS. The bucket survey identifie

rainfall from privately owned rain gages and rainfall 

Floods in the Guadalupe and San Antonio R

Basins in Texas, October 1998

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact S

View of structures inundated by the Guadalupe River at Victoria,

Tex. (From video by M.W. Sunvison, D.S. Brown, and B.L. Petri,

U.S. Geological Survey.)

USGS personnel measuring streamflow discharge for 

at streamflow-gaging station 08188500 San Antonio R

Goliad. (From video by M.W. Sunvison, D.S. Brown, a

U.S. Geological Survey.)
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collectors. Rainfall totals less than 8 inches were documented outside the area encompassed by the 8-inch isohyetal (fig. 1) but are

not discussed in this report.

The rainfall shown (fig. 1) represents total rainfall for October

17–18. However, as indicated previously, most of the rain fell in

less than 24 hours. The isohyetals show two main centers of rainfall. The largest documented rainfall was in southern Hays County

just south of San Marcos, where at least 30 inches was recorded.

A second center, with about 22 inches of rain, was documented at

a site in western Comal County. The isohyetals indicate that about

2,300 square miles in 12 counties received at least 12 inches of

rain, and about 5,000 square miles in 19 counties received at least

8 inches of rain. The NWS operates and sponsors many recording

rain gages in the area; however, many of the gages overflowed

during the storm, thus, incremental rainfall totals are not available

for much of the area with the greatest rainfall.

The available incremental rainfall data and the rainfall indicated by NEXRAD radar operated by the NWS indicate that the

storm was moving from northwest to southeast, the same direction

as the course of the streams in the area (John Patton, National

Weather Service, oral commun., 1999). This movement most

likely caused the flood peaks for some sites to be higher than if

the storm had been stationary or had moved in another direction.

The largest rainfall occurred in the Guadalupe River Basin, and

most of the basin received 8 or more inches of rainfall.

Peak Gage Heights and Streamflow

Substantial flood peaks were documented for 27 s

gaging stations operated by the USGS in the Guadalu

San Antonio River Basins (table 1). Table 1 lists the p

record, peak gage height, and peak streamflow for th

known flood prior to the October 1998 flood. Also in

the peak gage height and streamflow for the October 

along with the ratio of the October 1998 peak stream

maximum known peak streamflow prior to October 1

stations have ratios equal to or exceeding 1.0, indicat

October 1998 flood produced the highest known peak 

for those stations.

The largest ratio (6.5) is for site 8, Guadalupe Riv

Gonzales; however, only 20 years of data are availab

station (1978–present). Perhaps the most historically 

peaks occurred at site 10, Guadalupe River at Cuero, 

Guadalupe River at Victoria. The October 1998 peak 

was 2.6 times the previous maximum streamflow at t

station. The previous maximum streamflow had been 

since before 1833.

The recurrence period, in years, is indicated for th

where peak-flow frequency has been estimated (Asqu

Slade, 1997). For other stations, the October 1998 pe

cated as greater than the 100-year recurrence period w

Figure 1. Total rainfall depths for October 17–18, 1998, storm in Guadalupe and San Antonio River Basins.

TEXAS

Study area

San Antonio

LOCATION MAP Pedernales

River

River

River

Guadalupe

Blanco

River

Cibolo

Creek

Medina

River

San

Antonio

River

Lavaca

River

San Marcos

River

CANYON

 LAKE

CALAVERAS

 LAKE

Col orado

San Gabriel River

LAKE

 TRAVIS

BLANCO

TRAVIS

WILLIAMSON

LEE

BASTROP FAYETTE

MEDINA

KENDALL

COMAL

HAYS

BEXAR

CALDWELL

GUADALUPE

GONZALES

LAVACA

WILSON

KARNES

DEWITT

GOLIAD

VICTORIA

MILAM

98o

97o

31o

99o

30o

29o

0 20 40 60 MILES

Georgetown

Austin

Wimberley

Bastrop

Smithville Lockhart

San Marcos

New

 Braunfels

Selma

Victoria

Gonzales

Westhoff

Cuero

Goliad

Falls

 City

Elmendorf

Macdona

La Coste

Somerset

San

 Antonio

Luling

Helotes

Kyle

8

12

16

20

20

8

12

16

20

24

28

12 Line of equal rainfall—

 Interval 4 inches

Streamflow-gaging station—

 Number referenced in table 1

EXPLANATION

4 5 7

6

8

9

10

11

3

1

2

24 26

20 25

1215

17

18

13

16 14 21

19 22

23

20

27

Gulf of Mexico
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Table 1. Peak gage heights and streamflows during October 17–20, 1998, for selected stations in the Guadalupe and San Antonio River Bas

[mi2, square miles; ft, feet; ft3/s, cubic feet per second; (ft3/s)/mi2, cubic feet per second per square mile; --, no data; >, greater than]

1 Recurrence period for peak streamflow from Asquith and Slade (1997).2 100-year peak streamflow from Asquith and Slade (1997). Ratios not computed for peaks exceeding 100-year recurrence period for stations where peak stream

magnitude of peak large enough to indicate peak greater than that of 100-year recurrence period.

3 Historical peak data from land-owner account before systematic data collection.4 Station at different location 1.2 miles upstream with different gage-height datum in 1987.

Site

no.

(fig. 1)

Station

no.

Station name

Total

drainage

area

(mi2)

Previous known maximum peak data October 17–20, 19

Period of

 record for

peak data

Date

Gage

height

(ft)

Streamflow

(ft3/s)

Date

(month/

day)

Time

Gage

height

(ft)

Streamflow

(ft3/s)

Guadalupe River Basin

1 08168500 Guadalupe River above Comal River at

New Braunfels

1,518 1845–present 07/08/1869

12/1913

338338

----

10/17

--

1745

--

35.57

--

142,000

--

2 08169500 Guadalupe River at New Braunfels 1,652 1915–1927

1974–present

09/10/1921 28.60 56,600 10/17 -- 38.54 222,000 

3 08170500 San Marcos River at San Marcos 47 1996–present 06/21/1997 7.73 787 10/17 1600 21.29 21,500 4 08171000 Blanco River at Wimberley 355 1869–present 05/28/1929 33.30 113,000 10/17 1415 28.50 116,000 5 08171300 Blanco River near Kyle 412 1882–present 05/1929 340 139,000 10/17 1700 35.82 105,000 

6 08172000 San Marcos River at Luling 838 1859–present 1869 or 1870 340.4 -- 10/18 0615 41.85 206,000 7 08172400 Plum Creek at Lockhart 112 1905–present 06/1936 322 -- 10/18 0330 23.09 47,200 8 08173900 Guadalupe River at Gonzales 3,490 1978–present 06/05/1987 (4--) 52,000 10/18 2100 50.44 340,000 

9 08175000 Sandies Creek near Westhoff 549 1864–present 07/02/1936 33.1 92,700 10/19 2000 28.80 36,200 

10 08175800 Guadalupe River at Cuero 4,934 1900–present 07/02/1936 344.33 -- 10/20 0030 50.35 473,000 

11 08176500 Guadalupe River at Victoria 5,198 1833–present 07/03/1936 31.22 179,000 10/20 1400 34.04 466,000 

San Antonio River Basin

12 08177700 Olmos Creek at Dresden Dr., San Antonio 21.2 1935–present 04/05/1991 14.38 19,700 10/17 0930 14.01 18,600 13 08178050 San Antonio River at Mitchell St., San Antonio 42.4 1993–present 10/08/1994 7.98 5,090 10/17 1015 12.94 14,300 14 08178565 San Antonio River at Loop 410 at San Antonio 125 1987–present 07/15/1990 32.20 64,300 10/17 1600 32.57 79,400 15 08178700 Salado Creek (upper station), at San Antonio 137 1853–present 10/1913 323–24 -- 10/17 1600 22.40 64,400 

16 08178800 Salado Creek (lower station), at San Antonio 189 1941–present 09/27/1973 28.83 13,100 10/17 1300 34.07 47,800 17 08180640 Medina River at La Coste 805 1987–present 05/30/1987 24.05 24,600 10/18 1300 21.30 13,400 18 08180700 Medina River near Macdona 885 1982–present 05/30/1987 20.58 36,800 10/18 1945 17.39 16,300 19 08180800 Medina River near Somerset 967 1971–present 07/17/1973 29.39 30,500 10/18 1515 22.70 13,500 20 08181400 Helotes Creek at Helotes 15 1923–present 1927 313.7 -- 10/18 0115 15.21 12,600 

21 08181480 Leon Creek at IH–35, at San Antonio 219 1985–present 06/22/1997 24.60 27,900 10/18 1715 29.31 93,300 22 08181500 Medina River at San Antonio 1,317 1913–present 1913 355 -- 10/18 1600 49.45 30,000 23 08181800 San Antonio River near Elmendorf 1,743 1900–present 1946 361 -- 10/18 1200 64.20 75,000 24 08183500 San Antonio River near Falls City 2,113 1875–present 09/29/1946 33.80 47,400 10/20 0600 33.60 70,000 25 08185000 Cibolo Creek at Selma 274 1869–present 06/22/1997 29.73 69,600 10/17 1345 35.37 98,100 26 08186000 Cibolo Creek near Falls City 827 1890–present 10/1913 335 35,000 10/19 0700 39.86 47,500 27 08188500 San Antonio River at Goliad 3,921 1800–present 1869 3>53.0 -- 10/22 1230 51.78 59,200 
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large magnitude of the peak makes exceedance of the 100-year

recurrence period obvious (table 1). The recurrence period is

not estimated for the remaining stations because the peak streamflow might have been affected by reservoirs or flood-retarding

structures. The October 1998 peak streamflow equals or exceeds

the 100-year recurrence period for 13 stations in the two basins.

Flood Volume in Guadalupe River Basin

The volume of runoff for site 10, Guadalupe River at Cuero,

was computed for the period October 17–31, 1998, at about

1,840,000 acre-feet. Most of the runoff from the October 17–18

storm occurred at the station by the end of October. The total

outflow from Canyon Lake during October 18–31 was only about

2,600 acre-feet (Tommy Hill, Guadalupe-Blanco River Authority,

oral commun., 1999); thus, almost all runoff at the Cuero station

originated from the basin downstream of the reservoir.

The volume of rainfall associated with the runoff at the Cuero

station also was computed on the basis of the total rainfall (fig. 1).

The rainfall volume in the drainage basin upstream of the Cuero

station and downstream of Canyon Lake is about 2,580,000 acrefeet, which represents a mean depth of about 15.0 inches in that

area. The runoff accounts for about 10.7 inches or about 71 percent of the rainfall—most of the remaining 4.3 inches of rainfall

thus is attributed to depression storage (such as ponds and valleys)

and infiltration.

From October 17 to 31, the change in storage in Canyon Lake

was about 134,000 acre-feet, which, when added to the 2,600

acre-feet of outflow, approximates the runoff during that period

from the 1,432-square-mile basin upstream of the reservoir. The

maximum water elevation at Canyon Lake was about 923 feet,

which is about 20 feet lower than the spillway crest at the

reservoir.

Flooding in San Antonio River Basin

The largest rainfall in the San Antonio River Basin was in the

upstream areas (fig. 1). However, the flood peaks at the stations on

lower Cibolo Creek and the lower San Antonio River exceeded the

100-year recurrence period (table 1). Flood losses in the San

Antonio River Basin were less than in the Guadalupe River Basin

mostly because fewer urban areas were inundated.

Flood Losses

According to the Texas Department of Public Safety (written

commun., 1999), 31 people drowned during the floods, and total

property damage was estimated to be about $750 million. Fortythree counties in Texas received Presidential Disaster Declarations

and thus were eligible for compensation for financial losses from

the floods. Total compensation of about $188 million was provided for small businesses, individual-family grants, temporary

housing, public assistance, and unemployment assistance.

Reports on Major Storms and Floods in Texas

Many storms with rainfall depths similar to and even exceeding

those documented in this report have occurred throughout much of

Texas—some of these storms have produced world-record

rainfall rates. The USGS and other Federal and State agencies

have prepared many reports documenting specific storms and

floods in Texas. Two recent reports documented the June 1997

floods in south-central Texas (Raines and others, 1998) and the

October 1994 floods in southeast Texas (Liscum and East, 1995).

Lanning-Rush and others (1998) present references for reports

documenting major storms and floods in Texas. That report also

presents narratives for all known major storms and includes

analyses of the areal extent of extreme rainfall depths 

of Texas. A method to estimate rainfall depths for du

15 minutes to 7 days in Texas was prepared by Asqui

Many flood peaks that greatly exceed the 100-yea

period have occurred throughout Texas. A report pres

greatest documented peak streamflow at many sites i

prepared by Asquith and Slade (1995). That report al

method to estimate the maximum peak streamflow fo

sizes of drainage areas for 11 regions in Texas. Asqui

(1997) present a method to estimate peak streamflow

rence periods of 2 to 100 years for basins in Texas th

affected by urbanization or reservoirs.

Selected abstracts and references for some of thes

USGS reports are presented on-line at http://tx.usgs.g

also includes current and historic streamflow data and 

for gaging stations across the State (Water Data).

References

Asquith, W.H., 1998, Depth-duration frequency of pr

for Texas: U.S. Geological Survey Water-Resour

Investigations Report 98–4044, 107 p.

Asquith, W.H., and Slade, R.M., Jr., 1995, Document

potential extreme peak discharges and relation b

potential extreme peak discharges and probable 

flood peak discharges in Texas: U.S. Geological 

Water-Resources Investigations Report 95–4249

______1997, Regional equations for estimation of pe

streamflow frequency for natural basins in Texas

Geological Survey Water-Resources Investigatio

96–4307, 68 p.

Lanning-Rush, Jennifer, Asquith, W.H., and Slade, R

1998, Extreme precipitation depths for Texas, ex

Trans-Pecos region: U.S. Geological Survey Wat

Investigations Report 98–4099, 38 p.

Liscum, Fred, and East, J.W., 1995, Floods in southe

October 1994: U.S. Geological Survey Fact Shee

FS–94–073, 2 p.

Raines, T.H., Asquith, W.H., and Brown, D.S., 1998, 

south-central Texas, June 1997: U.S. Geological 

Sheet FS–053–98, 6 p.

—R.M. Slade, Jr. and Kristie Persky

Any use of trade, product, or firm names is for descri

purposes only and does not imply endorsement by the 

Government.

For more information, please contact:

District Surface-Water Specialist

U.S. Geological Survey

8027 Exchange Dr.

Austin, TX 78754–4733

Phone: (512) 927–3500

FAX: (512) 927–3590

World Wide Web: http://tx.usgs.gov