Flood Guide lcra.org

Transcription

1 COLORADO RIVER Flood Guide lcra.org

2 Be prepared for weather and flood emergencies If you live along the Highland Lakes, the lower Colorado River or its tributaries, it s critically important to be prepared to protect yourself, your family and your property from a flood. LCRA prepared this guide to provide a better understanding of how LCRA manages floods along the Highland Lakes and the lower Colorado River. This guide also provides information and resources to help monitor weather and flood conditions. If you live on or near a lake, river or creek, stay alert to changing weather conditions: Buy and use a weather radio tuned to the NOAA Weather Radio All Hazards frequency nearest your location. Stay tuned to local radio and TV weathercasts, and listen for any flood watches or warnings the National Weather Service issues for your location. (A flood watch means conditions are favorable for flooding. A flood warning means flooding is imminent and you should move quickly to a place of safety.) LCRA rebroadcasts NOAA Weather Radio All Hazards broadcasts that include periodic updates on lake and river information. Tune to AM 1610 around the Highland Lakes and AM 1670 downstream of Austin to Matagorda Bay. You can monitor lake and river conditions though LCRA resources: LCRA.org provides the latest information on lake conditions and potential flooding. Hydromet.lcra.org provides real-time lake levels, streamflow and rain-gauge readings. Floodstatus.lcra.org provides information about flood operations. Sign up for LCRA s free Floodgate Operations Notification Service (FONS) at lcra.org. The service will call, text or when floodgate operations at the Highland Lakes dams are underway.

3 Flash Flood Alley The Colorado River flows through the Hill Country and Central Texas, an area the National Weather Service calls Flash Flood Alley. This region has one of the greatest risks for flash floods anywhere in the United States because the area has: A landscape with thin soils and steep slopes. Heavy rains can quickly saturate the thin, rocky soil. What the soil can t hold turns into runoff that cascades through steep hills and canyons, causing rapid rises on the creeks and tributaries that flow into the Colorado River. A large drainage area. The Hill Country watersheds of the Colorado River and its tributaries cover thousands of square miles. The Highland Lakes can receive storm runoff from many miles away. Intense rainfall. The Hill Country and Central Texas are at the crossroads of converging weather systems impacted by the uplift of the Balcones Escarpment, a fault that separates the Hill Country from the coastal plains of Texas. Moist air often flows from the Gulf of Mexico over the escarpment and as a result, this region holds many of the nation s extreme rainfall records. These factors can quickly transform heavy rains into walls of fast-moving water with great destructive potential. LCRA built Mansfield Dam and Lake Travis upstream of Austin to address the dangers Flash Flood Alley poses to Austin and other downstream communities. What s a Floodplain? Floodplains are areas along or near streams, rivers and lakes subject to periodic heavy flooding. Floodplain maps show areas that are most at risk of flooding. The Federal Emergency Management Agency (FEMA) uses floodplain maps to identify property needing flood insurance. Local officials use the maps to manage development in flood hazard areas. Floodplains change over time, especially in response to population growth and land development, placing more people at risk for floods. It s also important to note floods can happen outside of mapped floodplains. LCRA does not designate floodplains or control development of property in floodplain areas FEMA and local officials make those determinations. If you live in a floodplain, chances are good that at some point you will be flooded even if you live near a dam. Floods can and do kill people and damage property both in and out of floodplains. Are You in a Floodplain? Check with the floodplain administrator for your community and county to determine whether your property is in a designated floodplain. The Texas Colorado River Floodplain Coalition has a list of floodplain administrators at tcrfc.org. Flood Risks for Austin and Downstream Thanks to the Highland Lakes, Austin and other downstream communities along the Colorado River have not experienced the frequency of devastating floods that were typical of the 19th and early 20th centuries. Even so, this region still is at risk for floods, including those that result from heavy rains that fall downstream of Mansfield Dam and beyond the reach of the dam s flood management capabilities. Floods downstream of Austin may take hours or days to reach their peaks, as opposed to the sudden flash flooding that can occur in the Hill Country. Downstream floods can be widespread and cause significant damage.

4 Major Floods on the Colorado River More than 80 major floods have occurred in the lower Colorado River basin since the 1840s. Here are some examples: July 1869 In the worst flood on record, the Colorado crested at 51 feet at Austin and inundated Bastrop and La Grange. W00778 December 1913 Floodwaters joined the Colorado and Brazos rivers below Columbus, forming a lake 65 miles wide and flooding half a million acres. W00813 September 1952 Lake Travis rose 57 feet in about 14 hours in September 1952 in the middle of the decade-long Drought of Record. W00785 December 1991 The Christmas Flood raised Lake Travis to an all-time high of feet msl (less than 4 feet below the Mansfield Dam spillway). Downstream of Austin, the Colorado reached its highest stages since the completion of Mansfield Dam in W01013 June 2007 A 19-inch rain bomb in the Marble Falls area resulted in massive runoff into Lake Travis. But Mansfield Dam and Lake Travis captured the runoff, minimizing flooding in Austin and downstream communities. W00103 April 1900 Floods resulting from Hill Country storms destroyed the first Austin Dam, built in W s Heavy West Texas rains in 1935, 1936 and 1938 resulted in massive downstream flooding. In Austin during all three floods, a swollen Colorado River became impassable, cutting Austin in half. W00719 May 1981 During the Memorial Day weekend, rains of 10 inches in four hours in the Austin area downstream of Mansfield Dam flooded businesses and residential areas along Shoal Creek. W01010 October 1998 Rains centered in and downstream of Austin raised the Colorado River to its highest stages in many communities since the Christmas 1991 flood. Portions of Wharton s residential and downtown areas were inundated. All timeline photos: LCRA Corporate Archives

5 Protect Yourself from Floods Stay aware of changing weather conditions. Buy and use a weather radio. It can provide valuable lead time to prepare for or escape from an impending flood. LCRA and the National Weather Service provide NOAA Weather Radio All Hazards broadcasts throughout the lower Colorado River basin. NOAA Weather Radio All Hazards provides round-the-clock and up-to-the-minute weather information, including watches and warnings specific to each broadcast location. Tune your weather radio to the frequency serving the area nearest you. Monitor local media and heed warnings from your local officials. Determine an escape route to use if you need to evacuate. Plan and rehearse your route so you ll know how much time you ll need to reach safety. Don t drive through flooded roads. Even a small amount of rushing water can sweep your car off the road and out of your control. Damage to the road can be difficult to see, especially at night. Turn Around, Don t Drown. NOAA Weather Radio All Hazards Broadcast Tower Locations Stay clear of flooded creeks and streams. Don t let children play near fast-moving water. Swift currents only a few inches deep can knock most people off their feet. Stay away from areas near the Highland Lakes dams at all times especially during floods. Water may be released at any time with little or no warning, creating dangerous conditions, rapidly rising water and strong currents. Keep emergency supplies on hand. Canned food, bottled water, flashlights, battery-powered radios and a first aid kit are important to keep on hand. Sandbags and plastic sheeting may help protect property from water damage. Find a list of disaster supply items and other preparedness ideas at ready.gov. County Coleman San Saba Kimble Llano Kerr Travis Gonzales Fayette Wharton Matagorda Frequency MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz Managing Floodwaters Of the six Highland Lakes, only Lake Travis is designed to store and hold water that otherwise would flood Austin and downstream communities. The level of Lake Travis is usually within the lake s conservation pool. When Lake Travis reaches the maximum level of this pool or 681 feet above mean sea level (feet msl) the lake is considered full. The lake, formed by Mansfield Dam, is designed to hold additional water even above the level at which it is considered full. When heavy rains or floods push the level of Lake Travis above 681 feet msl, the lake enters its flood pool, where floodwaters are stored until LCRA can release them. The flood pool can hold about 787,000 acre-feet of additional water before reaching the spillway. Unlike Lake Travis, Lake Buchanan has no flood pool. It has very little additional capacity once it is full. The smaller, pass-through lakes Inks, LBJ, Marble Falls and Austin have no extra capacity for floodwaters. All the Highland Lakes dams except Inks Dam have floodgates. LCRA generally passes storm runoff through the hydroelectric power stations at the dams, gaining an additional benefit by generating electricity. When necessary, LCRA opens floodgates to pass additional water downstream.

6 Estimated Flow Times for Floodwaters This map illustrates the estimated time it takes for water to flow to Mansfield Dam from the upper basin locations, as well as the estimated time for water to reach downstream locations once LCRA releases it from Mansfield Dam. River flows and storm runoff originating upstream of Lake Buchanan can take two days or more to reach Mansfield Dam. When LCRA makes releases from Buchanan Dam, at the top of the Highland Lakes chain, the water may take up to nine hours to make the roughly 100-mile trip to Mansfield Dam, reaching Wirtz Dam in about six hours and Mansfield Dam in another three. In contrast, releases from Mansfield Dam take longer to flow downstream because the terrain is less steep along the 318-mile journey to the Gulf of Mexico. Floodwaters can reach Bastrop in about a day, Columbus in roughly three days and Bay City in about six days. Note: Flow times are estimates. Water travel times can be shorter during floods and longer during periods of low flow.

7 Key Things to Know The Hill Country and Central Texas are in Flash Flood Alley. This is one of the regions in the United States at greatest risk for flash floods. Lakes and rivers can flood quickly with little to no warning. The dams can reduce flood damages downstream of the Highland Lakes, but they can t prevent all floods. Key Elevations for Lake for Lake Travis Travis In managing floods, LCRA s first priority in operating the dams is to protect the integrity of the dams and communities downstream. This is particularly true for Mansfield Dam, which was designed to help protect Austin and downstream communities from Hill Country floods. None of the Highland Lakes are constant level. If storms pour more water into a lake than its dam can safely release, the lake will rise. The levels of lakes Buchanan and Travis fluctuate significantly as they capture water from heavy rains and floods and release water downstream. Even the smaller, pass-through lakes Inks, LBJ, Marble Falls and Austin can rise quickly as they pass floodwaters from tributaries and upstream lakes. Lake levels can vary even along the length of each lake. LCRA operates Lake Travis and Mansfield Dam during floods under U.S. Army Corps of Engineers (Corps) regulations and protocols. These protocols determine how much water LCRA may release depending on how much water is in the Lake Travis flood pool and downstream conditions. LCRA makes controlled releases of floodwaters through Mansfield Dam using any combination of three hydroelectric generating units and 24 floodgates. Water flows over the spillway of Mansfield Dam when Lake Travis rises above 714 feet above mean sea level (feet msl). Based on these Corps protocols, here are important trigger elevations that guide LCRA s flood-management operations: 750 feet msl Top of Dam 722 feet msl 714 feet msl Spillway Elevation 710 feet msl If Lake Travis rises above 722 feet msl, LCRA may release water as needed to maintain the safety of the dam. The release is not limited by downstream conditions. Water flows over the spillway of Mansfield Dam when Lake Travis rises above 714 feet msl. When Lake Travis is forecast to rise to between 714 feet msl and 722 feet msl, LCRA may release up to 90,000 cubic feet per second (cfs), including any flow over the spillway. Releases are not limited by downstream conditions. When Lake Travis is forecast to rise to between 710 feet msl and 714 feet msl, LCRA may release up to 50,000 cfs, as long as even with the releases, downstream conditions in the Colorado River at Austin, Bastrop and Columbus are below specified levels that may be near flood stage at some locations. Lake Travis highest level ever was feet msl on Dec. 25, When Lake Travis is forecast to rise to between 683 feet msl and 710 feet msl, LCRA may release 5,000 to 30,000 cfs, as long as even with the releases, downstream conditions in the Colorado River at Austin, Bastrop and Columbus are below specified levels that are below flood stage at all locations. Use available sources of information to keep you and your family safe. LCRA, NOAA Weather Radio All Hazards, local news media and local officials all provide valuable information during floods. Mansfield Dam 683 feet msl 681 feet msl Full Elevation When Lake Travis is forecast to rise to between 681 feet msl and 683 feet msl, LCRA may release 3,000 to 7,500 cfs, as long as even with the releases, downstream conditions in the Colorado River at Austin, Bastrop and Columbus are below specified levels intended to keep the river below flood stage at most locations. Know your flood risk and be prepared. It s your responsibility to stay alert to the dangers of floods and have an emergency plan for your family. Don t wait for someone to notify you. Lake Austin Lake Travis The level of Lake Travis usually is within the lake s conservation pool. When Lake Travis reaches the maximum elevation of this pool, 681 feet msl, the lake is considered full. When the level of Lake Travis rises above 681 feet msl, the lake enters its flood pool. The flood pool can hold about 787,000 acre-feet of additional water before reaching the spillway. LCRA may deviate from this general description of flood operations to respond to emergency incidents. LCRA operations will be conducted in a manner intended to minimize or avoid the risk of injury to life and property whenever reasonably possible.

8 Flood Management at Lake Travis As the Colorado River flows toward the Gulf of Mexico, it collects rainfall and storm runoff from Travis, Hays, Bastrop, Fayette, Colorado, Wharton and Matagorda counties. It s also important to remember that runoff from rainfall below Mansfield Dam can cause severe flooding downstream, even with no releases from Lake Travis. The Pedernales River, which flows into Lake Travis, collects runoff primarily from Gillespie and Blanco counties. This river can send a large amount of water into Lake Travis in a short time. Rainfall in Kimble, Mason, Llano and portions of other surrounding counties will send floodwaters through Lake LBJ. Floodwaters from Lake Buchanan also flow through Lake LBJ. This water is passed downstream into Lake Travis. Extreme weather anywhere in the upper Colorado River basin can affect Lake Buchanan. Heavy rains in Brown, Coleman, San Saba, Mills and portions of Lampasas, Burnet and Llano counties will reach Pecan Bayou and Lake Buchanan in a relatively short time. Lake Buchanan is filled primarily from this runoff. Lake Travis has a flood pool to store floodwaters until LCRA can safely release them downstream, as indicated in the Key Elevations for Lake Travis graphic. The four smaller lakes (Inks, LBJ, Marble Falls and Austin) pass releases from lakes Buchanan and Travis to manage floodwaters and meet water needs downstream. These smaller lakes are designed to allow water to pass through as opposed to being stored.

9 Lower Colorado River Watershed This map of the lower Colorado River basin shows the basin s major watersheds (designated by color), the Highland Lakes and dams, and locations of most of the LCRA Hydromet gauges (designated by numbered blue dots or red triangles) that monitor streamflow and weather conditions. Also included is information about each of the Highland Lakes and dams and river gauges at 19 major locations. For the Highland Lakes and dams, each listing includes the amount of water each dam could release during a flood if all its floodgates were opened and its hydroelectric power stations were at full generation. While the smaller dams have sometimes released water at maximum capacity, neither Buchanan nor Mansfield dams has opened all of its floodgates at the same time. The greatest number of gates opened simultaneously was 22 at Buchanan Dam in 1938 and six at Mansfield Dam in The gauge listings include stages (river depths) at which the river is bankfull and at flood stage, along with historic highs at each location. For gauges downstream of Mansfield Dam, the listings include historic highs before and after Mansfield Dam was completed in Some stream gauges have been relocated and datums have changed over time. Longhorn Dam and Lady Bird Lake, located just downstream of Tom Miller Dam and Lake Austin, are owned and operated by the City of Austin. A few notes about measurements: Elevations are in feet above mean sea level (feet msl). Lake volumes are measured in acre-feet; an acre-foot contains 325,851 gallons, or the amount of water needed to cover 1 acre 1 foot deep. Dam releases and river streamflows are measured in cubic feet per second (cfs); a flow rate of 100 cfs is equal to about 2.7 million gallons an hour or about 200 acre-feet a day. Elevations contained in this document, except for the 100-year flood elevations, are based on LCRA legacy or National Geodetic Vertical Datum of 1929 (NGVD29). The Federal Emergency Management Agency and the National Flood Insurance Program reference the North American Vertical Datum of 1988 (NAVD 88) to determine the 100-year flood elevations used in their floodplain maps and regulations. Lake levels reported by LCRA should not be used to determine first-floor elevations of buildings for compliance with floodplain regulations. Surveyors should refer to harn.lcra.org for information about LCRA GPS control marks and benchmarks. Buchanan Dam Lake Buchanan Inks Dam Inks Lake Buchanan Dam was originally designed to generate electricity and was completed in Lake Buchanan is one of LCRA s two major water-supply reservoirs. Inks Dam originally was designed to generate electricity and was completed in Inks Lake passes through releases from Buchanan Dam. Top of target range elevation: 1,020.0 feet msl Target range elevation: May through October: at or below 1,018.0 feet msl November through April: at or below 1,020.0 feet msl Top of dam: 1,025.0 feet msl Lake volume at 1,020.0 feet msl: 875,588 acre-feet 7 large floodgates at 18,800 cfs each 30 small floodgates at 7,000 cfs each 3 turbines at 2,000 cfs each Historic high: 1,021.4 feet msl (Dec. 20, 1991) River miles from Gulf of Mexico: 414 Top of target range elevation: feet msl Target range elevation: to feet msl Top of dam: feet msl Lake volume at feet msl: 13,668 acre-feet There are no floodgates at Inks Dam. 1 turbine at 3,200 cfs Historic high: feet msl (July 25, 1938) River miles from Gulf of Mexico: 409 Wirtz Dam Lake LBJ Starcke Dam Lake Marble Falls LCRA built Wirtz Dam to generate electricity and completed the dam in Lake LBJ passes through releases from upstream dams and inflows from the Llano River and Sandy Creek. LCRA built Starcke Dam to generate electricity and completed the dam in Lake Marble Falls passes through releases from upstream dams. Top of target range elevation: feet msl Target range elevation: to feet msl Top of dam: feet msl Lake volume at feet msl: 133,216 acre-feet 10 floodgates at 30,800 cfs each 2 turbines at 4,900 cfs each Historic high: feet msl (Sept. 11, 1952) River miles from Gulf of Mexico: 387 Discharge capabilities of the turbines, floodgates and spillways are approximate and will vary with lake levels at each dam. Top of target range elevation: feet msl Target range elevation: to feet msl Top of dam: feet msl Lake volume at feet msl: 7,186 acre-feet 10 floodgates at 10,100 cfs each 2 turbines at 4,600 cfs each Historic high: feet msl (Sept. 11, 1952) River miles from Gulf of Mexico: 382 Mansfield Dam Lake Travis LCRA built Mansfield Dam to manage floods, store water and generate electricity. It completed the dam in Lake Travis is one of LCRA s two major water storage reservoirs and has a designated flood pool for storing floodwaters. Top of target range elevation (top of conservation pool): feet msl Target range elevation: at or below feet msl Elevation of overflow spillway: feet msl Top of dam: feet msl Lake volume at feet msl: 1,134,956 acre-feet 23 floodgates at 5,250 cfs each 1 floodgate at 2,230 cfs 3 turbines at 2,500 cfs each Historic high: feet msl (Dec. 25, 1991) River miles from Gulf of Mexico: 318 Tom Miller Dam Lake Austin LCRA completed Tom Miller Dam in 1940 and operates it under an agreement with the City of Austin. Lake Austin passes through releases from upstream dams and inflows from local creeks. Top of target range elevation: feet msl Target range elevation: to feet msl Top of dam: feet msl Lake volume at feet msl: 24,644 acre-feet 4 large floodgates at 15,300 cfs each 5 small floodgates at 8,600 cfs each 2 turbines at 1,700 cfs each Historic high: feet msl (May 25, 1981) River miles from Gulf of Mexico: 298 LCRA s Hydromet monitors river, weather conditions LCRA s Hydromet system, a network of more than 270 gauges along the lower Colorado River and its tributaries, monitors river flow, rainfall and weather conditions throughout the river basin s 22,000 square miles. (Many of these locations are marked by red triangles on this map.) LCRA uses the data to manage its Highland Lakes and river operations more efficiently and, during heavy rains, anticipate floods. The National Weather Service also uses Hydromet data in forecasting flood conditions. You can view realtime data from any Hydromet gauge at hydromet.lcra.org. River Gauges Upstream from Austin Colorado River at Winchell Bankfull stage: 24.0 feet (1,288.9 feet msl) Flood stage: 26.0 feet (1,290.9 feet msl) Historic high: 62.2 feet (1,327.1 feet msl) Sept. 19, 1936 River miles from Gulf of Mexico: 561 Pecan Bayou near Mullin Bankfull stage: 20.0 feet (1,222.9 feet msl) Flood stage: 40.0 feet (1,242.9 feet msl) Historic high: 42.2 feet (1,245.5 feet msl) April 27, 1990 River miles from the Colorado River: 14 San Saba River at Menard Bankfull stage: 12.0 feet (1,875.0 feet msl) Flood stage: 18.0 feet (1,881.0 feet msl) Historic high: 23.3 feet (1,882.8 feet msl) June 6, 1899 River miles from the Colorado River: Llano River at Llano Bankfull stage: 10.0 feet (980.0 feet msl) Flood stage: 10.0 feet (980.0 feet msl) Historic high: 41.5 feet (1,011.5 feet msl) June 14, 1935 River miles from the Colorado River: 29 San Saba River near Brady Bankfull stage: 16.0 feet (1,547.0 feet msl) Flood stage: 30.0 feet (1,561.0 feet msl) Historic high: 33.8 feet (1,564.8 feet msl) July 23, 1938 River miles from the Colorado River: 73 Sandy Creek near Kingsland Bankfull stage: 8.0 feet (870.3 feet msl) Flood stage: 12.0 feet (874.3 feet msl) Historic high: 34.2 feet (896.5 feet msl) Sept. 11, 1952 River miles from the Colorado River: 7 San Saba River at San Saba Bankfull stage: 20.0 feet (1,182.2 feet msl) Flood stage: 24.0 feet (1,186.2 feet msl) Historic high: 39.3 feet (1,201.5 feet msl) July 23, 1938 River miles from the Colorado River: 17 Pedernales River near Fredericksburg Bankfull stage: 12.0 feet (1,577.0 feet msl) Flood stage: 22.0 feet (1,587.0 feet msl) Historic high: 41.6 feet (1,606.6 feet msl) Aug. 2, 1978 River miles from the Colorado River: 89 Colorado River near San Saba Bankfull stage: 25.0 feet (1,121.2 feet msl) Flood stage: 30.0 feet (1,126.2 feet msl) Historic high: 62.2 feet (1,158.4 feet msl) July 23, 1938 River miles from Gulf of Mexico: 474 Pedernales River near Johnson City Bankfull stage: 13.0 feet (1,109.7 feet msl) Flood stage: 14.0 feet (1,110.7 feet msl) Historic high: 42.5 feet (1,139.2 feet msl) Sept. 11, 1952 River miles from the Colorado River: 48 Llano River near Junction Bankfull stage: 12.0 feet (1, feet msl) Flood stage: 16.0 feet (1, feet msl) Historic high: 41.1 feet (1,689.4 feet msl) June 14, 1935 River miles from the Colorado River: Llano River near Mason Bankfull stage: 6.0 feet (1,236.4 feet msl) Flood stage: 13.0 feet (1,243.4 feet msl) Historic high: 46.0 feet (1,276.4 feet msl) June 14, 1935 River miles from the Colorado River: 61 River Gauges Downstream from Austin Colorado River at Austin Bankfull stage: 25.0 feet (417.0 feet msl) Flood stage: 33.0 feet (425.0 feet msl) Historic high before Mansfield Dam: 51.0 feet July 1869 Historic high after Mansfield Dam: 27.7 feet Sept. 8, 2010 River miles from Gulf of Mexico: 290 Colorado River at Bastrop Bankfull stage: 14.0 feet (321.4 feet msl) Flood stage: 23.0 feet (330.4 feet msl) Historic high before Mansfield Dam: 60.3 feet (367.7 feet msl) July 1869 Historic high after Mansfield Dam: 37.5 feet (344.9 feet msl) Dec. 22, 1991 River miles from Gulf of Mexico: 237 Colorado River at Smithville Bankfull stage: 10.0 feet (280.1 feet msl) Flood stage: 20.0 feet (290.1 feet msl) Historic high before Mansfield Dam: 47.4 feet (317.4 feet msl) Dec. 4, 1913 Historic high after Mansfield Dam: 34.8 feet (304.8 feet msl) Oct. 19, 1998 River miles from Gulf of Mexico: 212 Colorado River at La Grange Bankfull stage: 19.0 feet ( feet msl) Flood stage: 26.0 feet ( feet msl) Historic high before Mansfield Dam: 56.7 feet ( feet msl) July 1869 Historic high after Mansfield Dam: 45.5 feet (255.5 feet msl) Oct. 20, 1998 River miles from Gulf of Mexico: 177 Colorado River at Columbus Bankfull stage: 30.0 feet (175.5 feet msl) Flood stage: 34.0 feet (179.5 feet msl) Historic high before Mansfield Dam: 51.6 feet (197.1 feet msl) July 1869 and Dec. 6, 1913 Historic high after Mansfield Dam: 43.6 feet (189.1 feet msl) Oct. 21, 1998 River miles from Gulf of Mexico: 135 Colorado River at Wharton Bankfull stage: 20.0 feet (72.4 feet msl) Flood stage: 39.0 feet (91.4 feet msl) Historic high before Mansfield Dam: 51.9 feet (104.3 feet msl) July 1869, and Dec. 12, 1913 Historic high after Mansfield Dam: 48.7 feet (101.1 feet msl) Oct. 23, 1998 River miles from Gulf of Mexico: 67 Colorado River at Bay City Bankfull stage: 23.0 feet (23.0 feet msl) Flood stage: 44.0 feet (44.0 feet msl) Historic high before Mansfield Dam: 56.1 feet (56.1 feet msl) July 1869, and Dec. 10, 1913 Historic high after Mansfield Dam: 46.6 feet (46.6 feet msl) June 26, 1960 River miles from Gulf of Mexico: 33

10 ABOUT LCRA The Lower Colorado River Authority (LCRA) provides public services that help protect people, property and the environment in Texas. LCRA serves customers and communities in the region by managing the lower Colorado River, generating and selling electric power, ensuring a clean, reliable water supply, and operating parks. A nonprofit corporation created by LCRA also provides transmission services to help maintain electric reliability in Texas. LCRA, a nonprofit agency created by the Texas Legislature, cannot levy taxes or receive tax money. LOWER COLORADO RIVER AUTHORITY P.O. Box 220, Austin, TX lcra.org NOVEMBER 2014