Summer 2007 Report

LCRA Water Services River Operations Center

NEXRAD image of the June 27 storm that triggered the Summer 2007 Flood Executive Summary Flood Facts:

The Summer 2007 Flood this event, as did relation- The Summer 2007 Flood Rainfall intensity near Marble Falls was unexpected, sudden, ships with other agencies did not break the severe (18 inches in 6 hours) was in ex- cess of a 500-year event, based on severe and a great test of that work with LCRA during drought of 2006. Actually, depth-duration-frequency analysis. LCRA assets, both in terms flood emergencies. the drought had ended of facilities and people. before then, thanks to The greatest intensity of Unit-peak discharge on Hamilton rains earlier that spring This event demonstrated rainfall was in the Marble Creek, 722 cubic feet per second which filled lakes Bu- the value of remote- Falls area. The peak flow (cfs) per square mile, exceeded the chanan and Travis. But historical record. Unit-peak flow controlled floodgates at on Hamilton Creek sur- public attention was riv- was even higher on Backbone Starcke , dedicated passed that of the previ- eted by the June 27 rain Creek in Marble Falls. floodgate hoists at Wirtz ously documented extreme event. The public became Dam, a refined computer peak discharge set in more aware of and reached its fifth highest simulation model to fore- 1936. The worst flooding droughts, and of the value level: 701.52 feet above mean sea cast flood conditions with occurred in Marble Falls of the Highland Lakes to level (msl). greater accuracy, a higher and the headwaters of the people of the lower state of readiness, and Lake Travis, qualifying the basin. LCRA received so many hits on its depth at key positions. area for federal disaster Flood Summary page on the LCRA Communications continued assistance. web site, that the method of gener- to improve as a result of ating graphics had to be changed to keep up with demand. Summer 2007 Flood Report Weather Pattern

The phenomenally heavy rich supply of moisture off counties. The storms en- rain event on June 27 was the . The trained a very warm, moist part of an unusually wet May to August period was flow of air off the Gulf of weather pattern that began one of the wettest on re- Mexico (low-level Jet). The After 18 months in May and lasted into cord. These rains filled the intersection of the Jet with early August. During that conservation pool of Lake outflow in the upper atmos- of drought, wet time, a trough of low pres- Travis. phere caused the storm sure in the middle and complex to stall. Rainfall On June 26, a complex of upper atmosphere over intensity increased as indi- weather in the thunderstorms developed was surrounded by vidual storms repeatedly in the unstable atmos- spring of 2007 ridges of high pressure to moved over the same ar- phere over Central Texas. the east and west. Atmos- eas. Heavy rain began to Late that night, the storms filled Lake Travis. pheric disturbances track- fall after midnight. reached Llano, Burnet and ing south from the Plains northwestern Williamson Then the flood hit states interacted with a in June 2007.

Hydromet Gauge Marble Falls 6 ENE Between 11 p.m. on June Rainfall continued at a rate Here, totals of 14 to 18 26 and 5 a.m. on June 27, of about 3 inches per hour inches were recorded. The the storms moved slowly for 6 hours. This amount highest total of rain meas- east across southern Bur- of rain in such a short time ured during the event was net County with heavy rain. ranks among some of the 19.06 inches at the Marble Between 12:45 a.m. and 2 highest rain rates ever Falls 6 ENE Hydromet sta- a.m., the rainfall intensity observed in Texas. The tion. Approximately 18 became extremely heavy very heavy rain around inches of rain fell in a six over southeastern Burnet Marble Falls began to re- hour period. That rate of County. An LCRA tipping- cede, with most of the rain rainfall intensity exceeded bucket rain gauge located ending around 5 a.m. the 500-year return fre- six miles east-northeast of quency for Central Texas. The core of the heaviest Marble Falls captured the rain occurred across south- For much of the region, the intensity of this extremely ern Burnet County near the summer of 2007 ended up heavy rain, at one point City of Marble Falls and being one of the wettest measuring nearly 2 inches areas just to the east. and coolest on record. of rain in 15 minutes.

Page 2 Rainfall Distribution LCRA Water Services

In the watersheds feeding three inches west of Mason, covers the area uniformly directly into the Highland from 3 to 5 inches between and fills the gaps between Lakes, the June 27 rainfall Mason and Llano, and from rainfall gauges, and the rain- totals were very impressive. 5 to 10.5 inches between fall gauges provide data that The storm reached its full Llano and Lake LBJ. The refines the map of rainfall intensity in the early morning pattern was higher rainfall at distribution. of June 27, with rainfall locations closer to the lakes. The following figure, showing rates as high as two inches The area around In the wa- the 24-hour rainfall accumu- in 15 minutes. The Marble tershed, there were lesser lation on June 27, can be Falls area received as much Marble Falls rainfall totals than the Llano compared to the gauge- as 18 inches of rain in six River watershed, from less adjusted radar rainfall distri- hours. Many gauges in received 18 than 0.5 to 4.5 inches. bution shown in the NEXRAD southern Burnet County, image on Page 1. This grid- inches of rain in north and south from the LCRA uses this rainfall data ded data is used as input to Colorado River, measured in two ways: as direct input LCRA’s flood simulation six hours. more than 8 inches of rain to estimates of runoff result- models. The models accu- on June 27. ing from heavy rainfall, and rately predict rates of flow in as an adjustment to radar In the Lake LBJ watershed, streams and rise of lake rainfall estimates. Radar rainfall totals were less than levels through time.

Page 3 Summer 2007 Flood Report Streamflow

Intense rainfall in southern Backbone Creek near Mar- land on Sycamore, Camp Burnet County caused tribu- ble Falls has a contributing and Hickory Creeks. taries in the area to rise watershed of 35 square Cow Creek near Lago Vista rapidly. Most of the runoff miles. The estimated peak entering the north side of experienced devastating flow on Backbone Creek was Lake Travis came from Ham- peak flows where the stream ilton Creek with a watershed 26,000 cfs. The flow on washed out FM 1431 on the north side of Lake Travis. Many bridges of 84 square miles. The Backbone Creek combined peak flow on Hamilton Creek with Whitman Branch and Cow Creek had a peak flow of approximately 25,000 cfs were washed out was approximately 56,000 caused extensive flood dam- cfs, exceeding the previously age in the City of Marble from a watershed of 46 square miles. There were documented peak discharge Falls. Many bridges were and many homes two fatalities attributed to that occurred in 1936 washed out, and many (USGS, WRI Report 96- the flood in that area. and businesses homes and businesses were 4072). Incredibly, the FM flooded. That water flowed Flood damages in southern 1431 bridge over Hamilton into , then Burnet County qualified for were flooded in Creek was undamaged by federal disaster assistance. the event despite massive into Lake Travis. Marble Falls. scouring in the floodway. Further east of Marble Falls That water entered the along FM 1431, there was headwaters of Lake Travis. significant flooding of ranch-

Tributaries upstream from Lake Travis - June 27, 2007

60000

50000 Hamilton Creek

Backbone Creek

40000 Cow Creek

Honey Creek

30000 Flow(cfs)

20000

10000

0 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00

Page 4 Streamflow (continued) LCRA Water Services

South of Marble Falls, tribu- To the east along the south taries to the Highland Lakes side of Lake Travis, Double also had high flows. In the Horn Creek experienced early morning hours on June similar conditions and washed out a county road 27, Little Flat Rock Creek crossing on the south side of quickly rose at State High- Lake Travis. way 71 and U.S. Highway 281, flowing over the high- Peak flow on the way at both crossings. There was about 69,000 cfs, which was a 12-foot rise on Flat was less than a 5-year flood magnitude (USGS WRI Re- Rock Creek at the Hydromet port 96-4307). The peak gauge at FM 2147. flow on the Pedernales River Flat Rock Creek came within at Johnson City reached a few feet of flooding the 18,000 cfs. These rivers are typically large contributors to Huber underground mine floods in the Texas Hill Coun- south of Marble Falls. Just try, but in this case most of downstream, the flood the water came from other caused damage to the tributaries. bridge crossing on the road leading to Starcke Dam.

Washout of FM 2147 at Double Horn Creek southeast of Marble Falls

Flat Rock Creek, June 27, 2007

1.4 882 Stream rise = 12 ft 1.2 880

1 878 Rain (in) Stage (ft) 0.8 876

0.6 874

Stage (ft) Stage Rainfall Rainfall (in)

0.4 872

0.2 870 Total rainfall = 10 in

0 868 20:56 1:56 6:56 11:56 16:56 21:56 2:56

Page 5 Summer 2007 Flood Report Streamflow (continued)

Prior to the flood in the Mar- again to a level of 4 feet storm in Marble Falls was ble Falls area on June 27, over the spillway on June 29. being passed into Lake rainfall totaling 7-10 inches The first event was short- Travis, LCRA staff was also also occurred in Brown lived, but the second event managing a flood upstream County in the preceding ten carried much more volume from , even- days. These heavy rains of water downstream on tually requiring four flood- Rainfall events caused discharge from Lake Pecan Bayou over several gates plus full generation to totaling 7-10 Brownwood, operated by weeks. Due to low stream pass flood waters through inches also Brown County Water Im- gradient in that area, inflows . That water provement District No. 1, into Lake Buchanan steadily was passed through inter- occurred in Brown into Pecan Bayou upstream increased to a peak of mediate into Lake County. from Lake Buchanan on two 31,000 cfs on July 1. The Travis. This operation was separate occasions. Lake inflows took several weeks done without worsening the Brownwood rose above the to recede as the level of damage in Marble Falls. level of the spillway on June Lake Buchanan rose. Just 17, receded and then rose when runoff from the major

Page 6 Streamflow (continued) LCRA Water Services

The following table shows charge of 542 cfs per the record of 434 cfs/sq.mi the calculation of unit-peak square mile (sq.mi.). By set in 1936. The unit-peak discharge, which is a meas- comparison, the highest discharge on Backbone ure of storm runoff intensity, intensity of runoff was in the Creek was even higher (867 as peak flow per square mile Marble Falls area. The June cfs/sq.mi), indicating the of contributing watershed. 2007 unit-peak discharge intensity of runoff that Cow Creek near Lago Vista on Hamilton Creek of 722 caused so much damage in had a high unit-peak dis- cfs/sq.mi surpassed that of Marble Falls.

June 2007 Unit-Peak Discharge Stream Gauge Location Peak Flow Rate Gauged Drainage Unit-Peak Discharge (cfs) Area (sq.mi.) (cfs/sq.mi.)

Llano River near Llano 69,000 4,197 16.4

Pederales River near Johnson City 18,389 901 20.4

Cow Creek near Lago Vista 24,939 46 542

Hamilton Creek near Marble Falls 55,954 77.5 722

Backbone Creek near Marble Falls 26,000 30 867

The following figure shows how the level of Lake Marble Falls responded to extremely high rates of inflow from Flat Rock Creek, Backbone Creek and Lake LBJ. The lake rose 7 feet despite full generation and all 10 floodgates being open.

Lake Marble Falls at Starcke Dam June 27, 2007

744 Peak stage = 743.81 ft msl

742

All 10 740 gates open

Elevation, ft Elevation, msl 1st gate 738 open

Normal operating range

736 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00

Page 7 Summer 2007 Flood Report Lake Operations

LCRA managed the flood Starcke Dam in the early Marble Falls rose above its that resulted from the June morning hours of June 27. upper operating level of 737 27 storm with a combination Operators had difficulty get- feet msl around 2:45 a.m.. of forecast modeling and ting to the dams because of Two floodgates at lake level control using hy- flooded roads and hazard- and all 10 floodgates at drogeneration and flood- ous driving conditions. Two Starcke Dam were open by gate operations, with consid- operators reached Starcke 3:00 a.m.. Four floodgates eration of downstream river Dam just before the access were open at Wirtz Dam by levels in accordance with road was damaged by flood- 3:07 a.m.. Lake Marble rules of the U.S. Army Corps ing on Flat Rock Creek (see Falls continued to rise and of Engineers. Discharge by photo upper left). peaked at 743.81 feet msl hydrogeneration was already at 5:00 a.m. and then began The first floodgate was in progress when the event to recede as the water was opened at Starcke Dam at began. The intensity of this passed into Lake Travis (see 1:40 a.m.. Floodgate opera- storm required floodgate graph below). Starcke Dam access road, damaged tions were initiated at Wirtz operations in the very early by flooding on Flat Rock Creek Dam at 2:14 a.m., and one The peak inflows into Lake hours of the event. floodgate was fully open by Travis on June 27 are shown The Hydro Operations Con- 2:28 a.m.. Due to the flash below. The graphic does not trol Center (HOCC) called out flooding on Backbone Creek reflect ungauged inflows. operators to Wirtz Dam and and Flat Rock Creek, Lake

Peak Inflows into Lake Travis The intensity of Hamilton Creek this storm 55,954 Cow Creek June 27, 2007 required 2:40AM 24,939 3:11 AM floodgate Starcke Releases operations in the 164,182 5:01 AM very early hours of the event.

18,389 9:25 AM

The total inflow volume to Lake Travis was estimated at 1.0 million acre-feet. All of that water was eventually passed downstream over several weeks because the conservation pool at Lake Travis was full. If did not exist, the estimated peak flow on the Colorado River through Austin would have been 269,000 cfs; instead it was 28,700 cfs. Just for reference, a flow of 269,000 cfs would inundate the City of Austin’s Hike and Bike Trail and raise to a level just below the Congress Avenue Bridge. Proper operation of Mansfield Dam kept that from happening. Page 8 Lake Travis Flood Management LCRA Water Services

U.S. Army Corps of Engineers field Dam in accordance the level of Lake Travis con- (USACE) rules govern the with USACE regulations. The tinued to rise as runoff from operation of Mansfield Dam second floodgate was the farther reaches of the at levels above the conser- opened at 7 a.m., the third basin and from additional vation pool, providing spe- floodgate at 9 a.m., and the rain storms continued to cific guidance on reservoir fourth and final floodgate at flow into the lake. Releases elevation and corresponding 11 a.m.. Floodgates at Tom from Mansfield Dam were at Releases from discharge during floods. Miller Dam were opened in the maximum allowed by combination with hydrogen- USACE regulations. Mansfield Dam At midnight on June 27, the eration to pass floodwaters level of Lake Travis was through . Re- Lake Travis crested July 6 at were at the barely in the flood pool at leases past the Austin gauge 701.52 feet msl, more than 681.13 feet msl, with hydro- were kept under 28,700 cfs 20 feet into the flood pool, maximum generation releases of in order to meet USACE con- with four floodgates open. 3,800 cfs. Heavy rain began trols on stage in the lower As the lake slowly receded, to fall about midnight. At 3 allowed by river. a.m., with a forecast of 685 the last floodgate at Mans- feet msl, hydrogeneration at The initial surge of inflows field Dam was closed on July USACE Mansfield Dam was in- from heavy rainfall on the 19. LCRA continued to re- creased to nearly 5,000 cfs areas around lakes LBJ, lease floodwaters from Lake regulations. in accordance with USACE Marble Falls and Travis Travis through hydrogenera- flood control regulations. At caused a rapid rise on Lake tion at Mansfield Dam. Lake 5 a.m., with a forecast that Travis from about 681 feet Travis was gradually brought Lake Travis would exceed msl to about 693 feet msl down to 681 feet msl by 685 feet msl, LCRA opened on the first day of the flood. August 14. the first floodgate at Mans- Over the next several days,

The following graph shows how the inflow to Lake Travis caused the lake level to rise to 701.52 feet msl, then recede to near 681 feet msl as water was released. The stair-step pattern of outflow indicates the four flood gates that LCRA opened at Mansfield Dam at the beginning of the flood, then closed one by one as the lake level receded.

LakeTravis Management

300,000 705 Inflow Outflow 700 250,000 Lake level 681 ft msl 695 200,000

690 150,000

Flow, cfs 685 Lake Travis flood pool 100,000 level, Lake msl ft Lake Travis conservation pool 680

50,000 675

0 670

7/1/07 7/3/07 7/5/07 7/7/07 7/9/07 6/27/07 6/29/07 7/11/07 7/13/07 7/15/07 7/17/07 7/19/07

Page 9 Summer 2007 Flood Report Upper Highland Lakes Management

LCRA conducts flood man- kept less than the rates of Lake LBJ rose to 825.88 agement on the upper High- inflow and did not exceed feet msl by 3:15 a.m. on land Lakes in accordance 22,000 cfs. Four floodgates June 27 before gate opera- with a 1990 agreement with and full hydrogeneration tions brought the lake level Four floodgates the Federal Emergency Man- were used to bring the lake under control and eventually agement Agency (FEMA). level down to elevation lowered the lake to a mini- were used at 1,018 feet msl, the conser- mum of 823.12 feet msl The first floodgate at Bu- vation pool level for that later the same day. Lake chanan Dam was opened on Buchanan Dam time of year as set in the LBJ was maintained slightly June 27 at 1:00 pm. The 1990 FEMA agreement. below its normal operating level of Lake Buchanan rose and Mansfield range throughout much of to 1019.47 feet msl on June The level of was the flood as large volumes of 28. Flows on the Colorado more than 1 foot over the Dam, leaving water from the Pecan Bayou River near San Saba peaked spillway from June 27 and Llano River watersheds both lakes full at at 31,800 cfs on June 30. through July 6 while gate continued to flow through Releases from Lake Bu- operations continued at the system. the end of the chanan were matched or Buchanan Dam. flood. Downstream Flood Management

It was necessary to adjust floodgate releases The following figure shows the measured from several times due to stage levels during the flood event and limits precipitation and runoff in the set by the USACE at control gauges down- watershed that would have otherwise ex- stream from Austin. As shown, releases ceeded the USACE control stages at Austin, from Lake Travis were kept in range of these Bastrop and Columbus. control stage levels.

Colorado River Downstream Gauges

40

Columbus control stage 35

30

Bastrop control stage 25

Austin control stage

20 Stage (ft) Stage

15 Colorado River at Austin stage (ft)

10 Colorado River at Bastrop stage (ft)

Colorado River at Columbus stage (ft) 5 Series4

0 Series5 6/27/07 7/2/07 7/7/07 7/12/07 7/17/07 7/22/07 7/27/07 Series6

Page 10 Magnitude of Record Floods LCRA Water Services

Volume Largest Flood Events, Measured by Volume At Mansfield Dam or Austin Dam (acre-feet) 1. The 1936 Flood (Sept. 15 to Oct. 20) Twenty days of rain (30 inches) swept away business and farms in West Texas. The Colorado River crested at 31.4 feet at Austin and remained in or near flood stage for three weeks, cutting the city in two. This flood occurred prior to completion of the Highland Lakes Dams. 3,258,000 2. The 1957 Flood (May 1 to June 30) A basin-wide series of floods broke the Drought of Record. LCRA opened floodgates at Mansfield Dam for the first time. It was also the first time that meteorologists used radar, adapted from World War II military equip- ment, to detect severe weather and warn residents. Lake Travis peak: 707.38 feet msl on May 18 – the second-highest peak. Floodgates open at Mansfield Dam: 6 (still a record). 2,700,000 3. The 1938 Flood (July 19 to Aug. 14) The first flood since LCRA completed Buchanan Dam. It confirmed the need to heighten Mansfield Dam (under construction), and resulted in what became LCRA’s Hydromet system of rain and streamflow gauges. Floodgates open at Buchanan Dam: 22. 2,028,000 4. The 1922 Flood (May 1 to 3) Runoff from basinwide storms resulted in floodwaters 5 to 10 miles wide in Wharton. 1,998,000 5. The 1935 Flood (June 12 to 20) Noted for the historic image of the houseboat going over the old Austin Dam, this basinwide flood caused re- cord rises on the Llano River as well as the Colorado River at Austin. 1,526,000 6. The Christmas Flood (Dec. 20, 1991, to Jan. 2, 1992) This was the first major flood for LCRA to make extensive use of its Hydromet electronic rainfall and stream- flow monitoring system. Several downstream communities had water levels that exceeded the 1935 Flood. Lake Travis peak: 710.44 feet msl on Dec. 25, 1991 – the all-time highest peak. Floodgates open at Mansfield Dam: 5. 1,172,000 7. The Fourth of July Flood (July 4 to 22, 2002) The bore the brunt of the storms, but the Highland Lakes received enough rain to trigger floodgate operations. Growth of hydrilla in Lake Austin complicated floodgate releases at Mansfield Dam. Lake Travis peak: 693.47 feet msl on July 7 – seventh all-time highest peak. Floodgates open at Mansfield Dam: 4. 1,118,081 8. The 1913 Flood (Dec. 1 to 13) Floodwaters caused the Colorado and Brazos rivers to merge 65 miles wide between Columbus and Bay City. 1,105,000 9. The Summer 2007 Flood (June 27 to July 13) Most likely to be remembered for the 19-inch “rain bomb” that hit Marble Falls – and the second time Lake Travis was closed to recreation over the July Fourth holiday in a decade (the lakes were closed for 17 days). Lake Travis peak: 701.52 feet msl on July 6 – 5th all-time highest peak. Floodgates open at Mansfield Dam: 4. 1,012,135 10. The 1952 Flood (Sept. 1 to 20) A respite in the middle of the Drought of Record, this flood was a workout for the recently completed Wirtz and Starcke Dams. One 15-inch storm resulted in a record 57-foot rise in Lake Travis within 14 hours. Lake Travis peak: 677.73 feet msl on Sept.11. Floodgates open at Mansfield Dam: 0. 934,000 11. (Honorable Mention): The Summer 1997 Flood (June 21 to 30) This flood was noted for raising Lake Travis to a near-record high, scouring a hole in the bed of Lake Marble Falls, and producing near-record flows on the Llano River. Lake Travis peak: 705.11 feet msl on June 26 – third all-time highest peak. Floodgates open at Mansfield Dam: 4. 832,000

Page 11 Summer 2007 Flood Report Summary

The rain event that began in Buchanan reached 1019.47 the early hours of Wednesday, feet msl on July 7. June 27 fell on wet soils and This event produced approxi- swollen lakes and streams mately 1.0 million acre-feet of causing heavy flooding in floodwater and ranked ninth southern Burnet County. Rain in terms of volume produced totals over 19 inches were for flood events since 1913. recorded near Marble Falls in This event mainly affected the the headwaters of Lake Mar- Highland Lakes region with ble Falls and Lake Travis. only trace amounts of rain Estimated peak flow on Ham- received in the lower basin. ilton Creek was 56,000 cfs on The rainfall experienced over June 27. Smaller streams the Hamilton Creek water- north and south of the Colo- shed was in excess of a 500- rado River also experienced year rainfall event for the high flows. By July 5, Lake area. This storm event will be Travis rose to a peak of Damage from flash flooding on Whitman Branch in remembered as the “rain 701.52 feet msl, its highest Marble Falls bomb” that hit Marble Falls. level since June 1997. Lake

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LCRA is a Texas conservation and reclamation district operating with no taxing authority. LOWER COLORADO RIVER AUTHORITY P.O. Box 220, Austin, Texas 78767-0220 1-800-776-5272 (512) 473-3200