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Mansfield Dam
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Mansfield Dam (formerly Marshall Ford Dam) is a dam located across a canyon at Marshall Ford on the Colorado River, 13 miles (21 km) northwest of Austin, Texas. The groundbreaking ceremony occurred on February 19, 1937, with United States Secretary of the Interior Harold L. Ickes attending. The dam was a joint project by the Lower Colorado River Authority (LCRA) and the United States Bureau of Reclamation, with partial funding provided by the Public Works Administration. Brown and Root, headed by James E. Walters, Sr., was the prime contractor.[1] The dam was completed in 1941. Originally called Marshall Ford Dam, the name was changed in 1941 in honor of United States Representative J.J. Mansfield. The reservoir behind Mansfield Dam is named Lake Travis. The dam is owned and operated by the LCRA.
Key Information
Mansfield Dam is 278 feet (85 m) high, 7,089 feet (2 km) long, and 213 feet (65 m) thick at the base. The concrete gravity dam with embankment wings and saddle dikes was designed to control flooding; to store 1.4 km3 (369 billion US gallons) of water; and to generate hydroelectric power (108 megawatts). The Spillway Elevation is 714 feet (218 m) above Mean Sea Level (MSL). LCRA begins to open floods gates when water reaches 681 feet above MSL. At 681 feet (208 m) above MSL, discharge capacity exceeds 130,000 cubic feet per second (3,700 m3/s) as the lake rises.
The two lanes of Mansfield Dam Road, formerly RM 620, traverse the top of the dam, but traffic other than service vehicles are now prohibited. 620 was rerouted in 1995 to a four-lane highway bridge on the downstream side of the dam built for increase in traffic due to the popularity in Austin of recreating at Lake Travis.[2]
Political History
[edit]Lyndon B. Johnson ran for his first elected office as United States Representative for Texas's 10th congressional district (where the Mansfield Dam was located). His campaign was backed by the dam's contractors, and his success in clearing funding and regulatory hurdles for the dam shortly after his election is considered a cornerstone of his future political career.[3]
See also
[edit]
References
[edit]- ^ "Guide to the Brown & Root / George R. Brown Executive Files, 1937-1978 MS 488". www.lib.utexas.edu. Retrieved March 22, 2017.
- ^ "Mansfield Dam Road (Formerly TX Ranch to Market Road 620) - Bridges and Tunnels". bridgestunnels.com. February 6, 2020. Retrieved June 8, 2022.
- ^ Caro, Robert (1982). The Years of Lyndon Johnson: The Path to Power. Alfred A. Knopf. pp. 648 and Chapters 20, 22, and 23. ISBN 978-0679729457.
External links
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Mansfield Dam
View on Grokipediafrom Grokipedia
Mansfield Dam is a concrete gravity dam spanning the Colorado River in Travis and Burnet counties, Texas, United States, about 13 miles northwest of Austin.[1]
Constructed jointly by the Lower Colorado River Authority (LCRA) and the U.S. Bureau of Reclamation from 1937 to 1942, following a redesign to increase its height after the 1938 flood, the dam stands 278 feet high and extends 7,089 feet in length.[1][2]
It impounds Lake Travis, the largest reservoir in the Highland Lakes chain, providing flood control for downstream areas including Austin, water storage for municipal and agricultural use, and hydroelectric power generation with a capacity of 108 megawatts.[1]
Originally named Marshall Ford Dam after its location at a historic river ford, it was renamed in 1941 at the suggestion of Lyndon B. Johnson to honor U.S. Representative J.J. Mansfield, who secured crucial federal appropriations for the project.[2][1]
History
Planning and Early Proposals
The planning for what became Mansfield Dam originated from longstanding flood threats to Austin, Texas, exacerbated by major inundations in the 1920s and 1930s, including severe events in 1935 and 1936 that prompted urgent calls for structural mitigation on the Colorado River.[2] The Lower Colorado River Authority (LCRA), established by the Texas Legislature in 1934 and operational from 1935, identified flood control as a core mandate, leading to evaluations of multiple sites along the river.[3] In summer 1936, LCRA selected the Marshall Ford site—a narrow canyon crossing historically used for river fording—for its geological suitability to impound large volumes of water efficiently.[4] Alvin Wirtz, LCRA's general counsel, advocated strongly for the project, framing it as essential for regional stability amid debates over federal versus state control of water resources.[2] Initial proposals envisioned a "low dam" approximately 190 feet high, designed primarily for flood detention with secondary benefits for water supply and power generation, in collaboration with the U.S. Bureau of Reclamation.[5] This two-stage construction approach allowed for phased development, starting with basic flood storage provisions while accommodating potential future expansion.[6] However, the catastrophic July 1938 flood, which overwhelmed preliminary works and caused extensive downstream damage, necessitated revisions to increase the dam height to 265 feet, enhancing storage capacity to over 1.1 million acre-feet for floodwaters.[7] These adjustments reflected empirical assessments of flood hydrology, prioritizing causal factors like upstream watershed runoff over optimistic low-storage assumptions.[8] The proposals faced early controversies, including disputes over funding allocation between flood control (non-reimbursable federal aid) and revenue-generating hydropower, with Wirtz leveraging political ties to secure Bureau of Reclamation involvement despite Army Corps of Engineers' competing interests in pure flood projects.[2] By late 1936, federal authorization enabled LCRA to advance site preparations, culminating in groundbreaking in March 1937, though full funding and design finalization hinged on integrating multi-purpose objectives verified through engineering reports.[3]Authorization and Political Involvement
The Lower Colorado River Authority (LCRA) was established by the Texas Legislature on November 10, 1934, during a fourth special legislative session called by Governor Miriam A. Ferguson, who signed the enabling legislation into law on November 13, 1934.[9][3] Drafted by attorney Alvin Wirtz and modeled on the Tennessee Valley Authority, the LCRA was created as a nonprofit conservation and reclamation district with authority to develop the Colorado River for flood control, hydroelectric power generation, irrigation, and water supply across ten counties in its jurisdiction.[9] This state-level authorization addressed the incomplete Buchanan Dam project, abandoned after the 1932 bankruptcy of the private Insull utility empire, and required a public entity to access federal funding opportunities.[3] The Mansfield Dam (originally Marshall Ford Dam) was authorized under the LCRA's statutory powers as its second major initiative, prioritized after floods in 1935 exposed vulnerabilities in the unregulated Colorado River, which threatened Austin and downstream areas.[3] Groundbreaking occurred in February 1937, establishing a joint federal-state partnership with the United States Bureau of Reclamation for design and operations, supplemented by Works Progress Administration labor and funding to mitigate Great Depression-era unemployment.[3] A 1938 Texas Senate investigation into regional flooding exonerated the LCRA's approach but recommended extending the dam's height by 78 feet for enhanced flood storage capacity, reinforcing legislative and executive support for the project.[3] Federal authorization hinged on intensive political lobbying, particularly by newly elected U.S. Congressman Lyndon B. Johnson, who in 1937 secured presidential backing from Franklin D. Roosevelt and a $10 million congressional appropriation despite the project's initial limbo without full land acquisition or prior approval.[10] Johnson, representing Texas's Tenth Congressional District, emphasized the dam's role in flood mitigation, rural electrification, and economic development, collaborating with LCRA General Manager Wirtz to navigate opposition from private utilities concerned about competition in power generation.[9][10] The construction contract awarded to Brown & Root proceeded preemptively on Wirtz's directive, with the firm's $5 million investment repaid through federal reimbursements facilitated by Johnson's influence, marking an early instance of intertwined business and political interests in Texas infrastructure projects.[10] In 1941, upon completion, Johnson proposed renaming the structure Mansfield Dam to honor U.S. Representative J.J. Mansfield of the Ninth District, who had supported river development efforts in Congress.[11]Construction Phase
Construction of Mansfield Dam commenced in February 1937 as a collaborative effort between the United States Bureau of Reclamation, which handled planning and design, and the Lower Colorado River Authority (LCRA), which supplied the land and financed the hydroelectric components.[6][2] The project adopted a two-stage approach to balance initial power generation with ultimate flood control needs: the first stage built a low dam reaching elevations of 640 feet at the spillway crest and 670 feet at the top, completed in August 1939, while the second stage raised the structure to a spillway crest of 714 feet and top of 750 feet, with work starting in September 1939 and finishing in May 1942.[6] Primary contractors included Brown and Root, Inc., and McKenzie Construction Company, employing concrete gravity methods augmented by earth and rockfill sections, diversion conduits for river flow during building, and 24 gated conduits plus three penstocks integrated into the design.[2] Deliberate impoundment of water for Lake Travis began in September 1940, enabling early reservoir formation, while the first hydroelectric power unit became operational in January 1941, supporting revenue generation amid construction.[6] The LCRA assumed direct oversight of construction following a 1941 contract transfer from federal entities.[6] Total expenditures for the dam, power plant, and associated facilities amounted to $28,709,948, with $5 million initially allocated for flood control under the Emergency Relief Appropriation Act of 1935.[6][12] Challenges during the process included 1938 flooding that overtopped temporary cofferdams, necessitating adaptive measures to maintain progress without compromising safety.[2] The conservation pool reached full intended levels by September 1942, marking effective completion of the reservoir's primary storage capacity ahead of final structural finalization.[6] This phased build-out prioritized functional hydropower early while ensuring the dam's 278-foot maximum height and 7,336-foot length could ultimately mitigate downstream flood risks from the Colorado River.[6][2]Location and Geography
Site Characteristics
The Mansfield Dam site lies on the Colorado River in Travis County, Texas, at river mile 322.2, approximately 12 miles northwest of Austin, spanning a narrow canyon at Marshall Ford.[13] This location within the North Central Plains features gently sloped to steep rolling hills transitioning into the rugged terrain of the Edwards Plateau, with a steep-sided valley that constricts the river flow.[13] Geologically, the site is underlain by Cretaceous-age limestone formations, including the Glen Rose Formation and Edwards Limestone, which exhibit karst characteristics such as dissolution cavities and high permeability typical of Central Texas limestone bedrock.[13] [14] Upstream areas overlie Paleozoic limestone and shale on Precambrian rock, while downstream exposures include sandstones, conglomerates, and shales interbedded with limestone.[13] The karstic nature of the Edwards Plateau limestone required extensive grouting and foundation drainage during site preparation to seal voids and manage seepage.[15] [16] The canyon's steep topography and limestone bedrock provided a stable yet challenging foundation, with the river's incision creating depths suitable for a high gravity dam structure.[13] The surrounding drainage area upstream of the dam encompasses approximately 15,300 square miles, contributing to the site's hydrological significance in flood-prone Central Texas.[17]Reservoir Formation
The reservoir known as Lake Travis began forming through staged impoundment of the Colorado River following the initial phases of Mansfield Dam's construction. A low dam, reaching an elevation of 670 feet, was completed in August 1939, enabling preliminary water retention behind the structure.[13] Deliberate impoundment for the primary reservoir commenced on September 9, 1940, as construction progressed on raising the dam to its full height of 278 feet to accommodate greater flood storage needs, a decision informed by severe flooding in July 1938 that prompted design modifications.[18][1] Impoundment continued amid ongoing high dam construction, which started in September 1939 and reached completion in May 1942, allowing the reservoir to gradually fill to its conservation pool capacity of approximately 1.1 million acre-feet at 681 feet mean sea level.[13][1] The process transformed a 65-mile stretch of the river valley into a deep reservoir with a surface area of 18,930 acres at full pool, primarily through natural inflows regulated by the dam's gates and spillways.[18] Early filling was influenced by seasonal Colorado River flows, with the structure's dual role in flood control ensuring controlled accumulation to prevent downstream inundation during wet periods.[13] Sedimentation surveys indicate that Lake Travis accumulated about 16,974 acre-feet of sediment by 2008 since impoundment began, reflecting gradual basin infilling from upstream erosion but not significantly impeding initial formation.[19] The reservoir's establishment supported the Lower Colorado River Authority's objectives of water storage and hydropower generation, with operational releases managed to balance filling against regional demands.[1]Design and Technical Specifications
Structural Features
Mansfield Dam features a central concrete gravity section flanked by zoned earthfill wing dams up to 100 feet tall, forming a composite structure that spans a narrow canyon on the Colorado River.[15] The gravity section relies on the weight of the concrete mass to resist water pressure, while the wing dams provide additional containment using compacted earth and rockfill materials.[17] The dam measures 278 feet in height from foundation to crest and extends 7,089 feet in total length, with the concrete gravity portion occupying the main channel and the wings extending along the abutments.[1] At its base, the structure thickens to 213 feet to enhance stability against hydrostatic forces.[20] Concrete was produced using local limestone aggregate, contributing to the dam's durability on a foundation of hard limestone bedrock with intermittent softer layers.[21] Key structural elements include an overflow spillway integrated into the crest, equipped with 24 double-gated ring-follower floodgates controlling 8.5-foot-diameter conduits at an invert elevation of 535.9 feet above mean sea level.[17] Internal features encompass over three miles of tunnels for drainage, construction access, and monitoring, supporting long-term integrity assessments.[22] The design incorporates provisions for uplift pressure mitigation, informed by geological evaluations of the limestone foundation.[15]
Hydropower Components
The hydroelectric power plant at Mansfield Dam consists of three turbine-generator units integrated into the dam's operations for electricity production. These units harness the potential energy of water released from Lake Travis, directing flow through penstocks to drive turbines that spin connected generators. The combined installed capacity of the plant is 108 megawatts, enabling generation during periods of sufficient reservoir inflow and release requirements.[23] Power output is primarily a secondary outcome of water management activities, including flood control releases and maintenance of downstream flows, rather than dedicated peaking or baseload service. The Lower Colorado River Authority (LCRA), which operates the facility, coordinates turbine discharges with overall river regulation to balance energy production against priorities like flood mitigation and water supply. Historical documentation indicates initial configurations with lower capacities, such as two 8,000-kilowatt units, but subsequent enhancements have achieved the current rating.[6][24] Key components include the turbines, likely vertical-shaft types suited to the dam's head of approximately 278 feet, and synchronous generators that feed into the regional grid via step-up transformers. Penstocks and draft tubes facilitate water passage, with operational flexibility allowing individual unit activation for flows ranging from minimal maintenance releases to higher-volume flood events. Annual generation varies with hydrological conditions, contributing a renewable but intermittent portion of LCRA's hydroelectric portfolio across the Highland Lakes chain.[1][17]Operations and Management
Flood Control Mechanisms
Mansfield Dam incorporates flood control through a combination of reservoir storage capacity in Lake Travis and controlled release structures. The reservoir's flood pool extends from an elevation of 681 feet mean sea level (msl), which marks the full level for water supply purposes, to 714 feet msl, providing approximately 776,062 acre-feet of dedicated flood storage space.[1][25] Above 714 feet msl, water flows uncontrolled over the main spillway, with the top of the dam at 754 feet msl.[24] The dam features a service spillway equipped with 24 gated outlets, each consisting of 8.5-foot diameter conduits controlled by double-gated ring-follower type gates with an invert elevation of 535.9 feet msl.[17] These gates, accessed via over three miles of service tunnels within the dam structure, enable precise regulation of outflows.[22] Releases are augmented by three hydroelectric generating units, allowing combined discharge capacities that escalate with rising lake levels: up to 7,500 cubic feet per second (cfs) between 681 and 683 feet msl, increasing to 30,000 cfs up to 710 feet msl, 50,000 cfs up to 714 feet msl, and 90,000 cfs or more above that threshold, incorporating spillway flow.[24] Flood management operations, conducted by the Lower Colorado River Authority (LCRA), adhere to the U.S. Army Corps of Engineers (USACE) Water Control Manual for Mansfield Dam and Lake Travis, supplemented by a Letter of Understanding and Water Control Agreement.[25][6] Decisions integrate real-time inflows, projected lake elevations, and downstream conditions, with releases curtailed if gauges at Austin (exceeding 33.0 feet or 30,000 cfs), Bastrop (27.2 feet or 45,000 cfs), or Columbus (35.5 feet or 50,000 cfs) indicate risks.[24] In emergencies impacting flood control, USACE may override with temporary real-time directives for storage regulation.[6] This system prioritizes attenuating peak flows from upstream tributaries while safeguarding downstream infrastructure along the Colorado River.[25]Water Supply and Allocation
Mansfield Dam creates Lake Travis, the uppermost major storage reservoir in the Lower Colorado River Authority's (LCRA) Highland Lakes chain dedicated primarily to water supply augmentation downstream, with a conservation pool capacity of 1,134,956 acre-feet below elevation 681 feet mean sea level (msl).[6] This storage supports releases to meet municipal, industrial, irrigation, and domestic demands in the lower basin, including replenishing Lake Austin and fulfilling direct diversions from the reservoir or the river immediately below the dam.[26] LCRA holds adjudicated water rights under Certificate of Adjudication 14-5482, authorizing annual appropriation of 1,398,000 acre-feet from the combined Highland Lakes for beneficial uses such as municipal supply, irrigation, and power generation, stemming from an original 1938 permit amended in 1976.[17] Allocation prioritizes firm contracts—typically for urban and industrial users with guaranteed deliveries at standard rates of around $165 per acre-foot—over interruptible agricultural contracts, which face proportional curtailments when combined Buchanan-Travis storage falls below thresholds outlined in LCRA's Water Management Plan (e.g., below 55% capacity triggering initial reductions).[27][28] Direct withdrawals from Lake Travis include smaller contracts, such as up to 840 acre-feet annually for specific recreational or municipal purposes, while broader system releases average hundreds of thousands of acre-feet yearly depending on inflows and demand, with 2024 use summaries showing overall Highland Lakes withdrawals declining 25% amid increased run-of-river availability.[29] Operations integrate environmental minimum flows and drought response tiers to sustain reliability, as combined storage reached 1,025,151 acre-feet (51% of capacity) on July 1, 2025.[26]Maintenance and Upgrades
The Lower Colorado River Authority (LCRA) is responsible for the ongoing maintenance, safety inspections, and operational upgrades of Mansfield Dam, including its floodgates, hoists, and hydroelectric components, in coordination with federal guidelines from the U.S. Army Corps of Engineers.[1][13] Routine activities encompass structural monitoring for corrosion, sediment management in Lake Travis, and testing of release mechanisms to ensure flood control efficacy, with the dam's 24 radial-arm floodgates—each weighing approximately 50,000 pounds—receiving particular attention due to age-related wear from their original installation between 1937 and 1942.[30][31] In late 2014, LCRA launched a multi-year rehabilitation project to address deterioration in the floodgates, involving the sequential removal, refurbishment, and reinstallation of each gate to preserve downstream flood protection while minimizing downtime; repairs occur primarily at LCRA facilities and take six to eight months per gate.[32][31] Initially budgeted at over $10 million with a projected 10- to 11-year timeline, the scope expanded to encompass hoists and ancillary facilities, resulting in a total investment of $51.1 million by project completion in 2021.[1][33] Post-rehabilitation efforts include functional testing of upgraded components, such as brief openings of refurbished floodgates to verify performance under controlled conditions, supporting the dam's role in water supply, hydropower generation (108 megawatts capacity), and flood mitigation.[1] No major structural failures or emergency repairs have been documented since the dam's commissioning, underscoring the effectiveness of LCRA's proactive maintenance regime.[1]Impacts and Benefits
Flood Mitigation Achievements
Since its completion in 1942, Mansfield Dam has significantly reduced flood risks for Austin and downstream communities by storing and controlled release of excess water from the Colorado River basin. The dam's flood storage capacity above the conservation pool elevation of 681 feet mean sea level totals approximately 776,000 acre-feet, allowing attenuation of peak inflows during heavy rainfall events. This infrastructure, operated by the Lower Colorado River Authority (LCRA) under U.S. Army Corps of Engineers guidelines, has prevented the recurrence of catastrophic urban flooding experienced prior to its construction, such as the 1935 event that inundated much of downtown Austin.[25][34] Notable achievements include the management of the 1957 floods, when spring and fall storms pushed Lake Travis above full pool, prompting the opening of up to six floodgates at Mansfield Dam—the maximum simultaneous openings at that time—to discharge water without overtopping or causing excessive downstream surges. The maximum discharge recorded since construction was 41,000 cubic feet per second during this event, far below pre-dam flood peaks that exceeded 200,000 cfs. Similarly, during the December 1991 flood, Lake Travis reached a record elevation of 710.44 feet, just four feet shy of the spillway crest, with five floodgates opened to manage inflows and avert potential overtopping while minimizing downstream impacts.[35][6][36] In more recent events, the coordinated operation of Mansfield Dam within the Highland Lakes system contributed to averting severe flooding in Austin during July 2025 heavy rains, where upstream reservoirs captured inflows that would otherwise have overwhelmed the Colorado River channel through the city. LCRA's releases were calibrated to avoid exacerbating local flash flooding while protecting infrastructure, demonstrating the dam's ongoing efficacy in a basin prone to intense precipitation. Although exact monetized damage prevention figures are not publicly quantified by LCRA or federal agencies, the absence of pre-dam scale disasters since 1942 underscores the structure's success in altering flood hydrology downstream.[37][38]Economic Contributions
The impoundment of Lake Travis by Mansfield Dam facilitates substantial recreational and tourism activity, driving direct and indirect economic outputs in Travis County and surrounding areas. In 2010, lake-related visitor spending reached $168.8 million from approximately 2.8 million visitor-days, primarily through boating, fishing, and park usage, while boat sales added $45.5 million, yielding a combined value added of $112.6 million.[39] These activities supported 1,916 jobs and $69.4 million in wages, with breakdowns including 1,607 jobs and $53.2 million in wages from tourism alone.[39] Fiscal revenues from Lake Travis bolster local and state budgets via taxes on property, sales, hospitality, and beverages. Property taxes from lakefront developments generated $158.4 million in 2010, reflecting an assessed value of $8.4 billion, including a $1.1 billion premium attributable to waterfront adjacency.[39] Sales taxes contributed $45.2 million, hotel occupancy taxes $1.3 million, and mixed beverage taxes $2.3 million, funding public services such as schools, emergency response, and infrastructure.[39] Mansfield Dam's hydropower generation provides renewable electricity as a byproduct of water management, integrated into the Lower Colorado River Authority's (LCRA) portfolio that funds regional operations without taxpayer subsidies. The facility contributes to LCRA's electric revenues, which comprised the majority of its $1.82 billion projected net revenues for fiscal year 2026, supporting broader economic stability through low-cost power transmission and development incentives.[40] Additionally, stored water from Lake Travis enables LCRA firm water supplies to 23 municipalities serving 650,000 residents and industrial/agricultural users, underpinning economic productivity in Central Texas by mitigating drought risks and enabling growth in water-dependent sectors.[39]Recreational and Tourism Role
Mansfield Dam impounds Lake Travis, a primary reservoir enabling diverse water-based recreation including boating, fishing, swimming, water skiing, sailing, and scuba diving.[41][42] The lake spans 18,929 acres with 271 miles of shoreline, drawing enthusiasts for these activities year-round, particularly during periods of adequate water levels.[41] Mansfield Dam Park, a 71-acre Travis County facility adjacent to the dam, serves as a key access point with the largest public boat ramp on Lake Travis featuring four lanes and a courtesy dock.[43] The park supports picnicking at covered shelters and tables with grills, playground use, horseshoe pits, chess tables, and paved multi-use trails for hiking and biking.[43][44] A designated no-wake swim cove and an underwater dive park with platforms, trails, and attractions cater to swimmers and divers.[43][42] These features position the area as a tourism hub near Austin, attracting families for outings and providing panoramic lake views from elevated vantage points.[44][45] Lake Travis supports 460,000 to 500,000 park visitor-days annually when water levels range from 660 to 680 feet above mean sea level.[39] Vehicle entry requires a $5 cash fee, with pavilion reservations available for groups up to 30.[46][43]