Volumetric and Sedimentation Survey of LAVON LAKE June – July 2011 Survey January 2013 Texas Water Development Board Billy R. Bradford Jr., Chairman Joe M. Crutcher, Vice Chairman Edward G. Vaughan, Member F.A. “Rick” Rylander, Member Lewis H. McMahan, Member Monte Cluck, Member Melanie Callahan, Executive Administrator Prepared for: U.S. Army Corps of Engineers, Fort Worth District Authorization for use or reproduction of any original material contained in this publication, i.e. not obtained from other sources, is freely granted. The Board would appreciate acknowledgement. This report was prepared by staff of the Surface Water Resources Division: Ruben S. Solis, Ph.D., P.E. Jason J. Kemp, Team Leader Tony Connell Holly Holmquist Tyler McEwen, E.I.T., C.F.M Nathan Brock Published and distributed by the P.O. Box 13231, Austin, TX 78711-3231 Executive summary In May, 2011, the Texas Water Development Board entered into agreement with the U.S. Army Corps of Engineers, Fort Worth District, to perform a volumetric and sedimentation survey of Lavon Lake. The U.S. Army Corps of Engineers, Fort Worth District, provided 100% of the funding for this survey through their Texas Water Allocation Assessment Program. Surveying was performed using a multi-frequency (200 kHz, 50 kHz, and 24 kHz), sub-bottom profiling depth sounder. In addition, sediment core samples were collected in select locations and correlated with the multi-frequency depth sounder signal returns to estimate sediment accumulation thicknesses and sedimentation rates. Lavon Dam and Lavon Lake are located on the East Fork of the Trinity River in Collin County, approximately 3 miles east of Wylie and 22 miles northeast of Dallas, Texas. The conservation pool elevation of Lavon Lake is 492.0 feet above mean sea level (NGVD29). TWDB collected bathymetric data for Lavon Lake between June 3, 2011, and July 21, 2011. The daily average water surface elevations during that time ranged between 486.50 and 489.95 feet above mean sea level (NGVD29). The 2011 TWDB volumetric survey indicates that Lavon Lake has a total reservoir capacity of 409,360 acre-feet and encompasses 20,559 acres at conservation pool elevation (492.0 feet above mean sea level, NGVD29). In 1970, the U.S. Army Corps of Engineers estimated a modified Lavon Lake encompassed 21,357 acres with a total reservoir capacity of 456,527 acre-feet. Based on comparison of the 2011 TWDB survey with the 1970 USACE survey and on direct measurements of sediment accumulation, Lavon Lake has lost between 1,212 and 1,310 acre-feet of capacity per year due to sedimentation since 1975. Sediment accumulation is found throughout the lake; however, the thickest deposits of sediment measured were north of U.S. Highway 380 and near the dam. TWDB recommends that a similar methodology be used to resurvey Lavon Lake in 10 years or after a major flood event. Table of Contents Introduction ........................................................................................................................... 1 Lavon Lake general information ......................................................................................... 1 Volumetric and sedimentation survey of Lavon Lake ...................................................... 3 Datum .................................................................................................................................. 3 TWDB bathymetric and sedimentation data collection ...................................................... 4 Data processing ..................................................................................................................... 5 Model boundaries ................................................................................................................ 5 Triangulated Irregular Network model ............................................................................... 7 Area, volume, and contour calculations .............................................................................. 7 Spatial interpolation of reservoir bathymetry .................................................................... 11 Analysis of sediment data from Lavon Lake .................................................................... 13 Survey results ...................................................................................................................... 18 Volumetric survey ............................................................................................................. 18 Sedimentation survey ........................................................................................................ 18 Recommendations ............................................................................................................... 20 TWDB contact information ............................................................................................... 20 References ............................................................................................................................ 21 List of Tables Table 1: Pertinent data for Lavon Dam and Lavon Lake Table 2: Sediment core sampling analysis data –Lavon Lake Table3: Capacity loss comparisons for Lavon Lake List of Figures Figure 1: Location of Lavon Lake Figure 2: Data collected during 2011 TWDB Lavon Lake survey Figure 3: Elevation relief map Figure 4: Depth ranges map Figure 5: 2-foot contour map Figure 6: Anisotropic spatial interpolation of Lavon Lake Figure 7: Sediment core sample L-1 from Lavon Lake Figure 8: Comparison of sediment core L-1 with acoustic signal returns Figure 9: Cross-sections of data collected during 2011 survey Figure 10: Sediment thicknesses throughout Lavon Lake Appendices Appendix A: Lavon Lake 2011 capacity table Appendix B: Lavon Lake 2011 area table Appendix C: Lavon Lake 2011 area and capacity curves Note: References to brand names throughout this report do not imply endorsement by the Texas Water Development Board Introduction The Hydrographic Survey Program of the Texas Water Development Board (TWDB) was authorized by the 72nd Texas State Legislature in 1991. The Texas Water Code authorizes TWDB to perform surveys to determine reservoir storage capacity, sedimentation levels, rates of sedimentation, and projected water supply availability. In May, 2011, TWDB entered into agreement with U.S. Army Corps of Engineers, Fort Worth District, to perform a volumetric and sedimentation survey of Lavon Lake. The U.S. Army Corps of Engineers, Fort Worth District, provided 100% of the funding for this survey through their Texas Water Allocation Assessment Program (TWDB, 2011). This report describes the methods used to conduct the volumetric and sedimentation survey, including data collection and processing techniques. This report serves as the final contract deliverable from TWDB to the U.S. Army Corps of Engineers, Fort Worth District and contains as deliverables: (1) an elevation-area-capacity table of the lake acceptable to the Texas Commission on Environmental Quality [Appendix A, B], (2) a bottom contour map [Figure 5], (3) a shaded relief plot of the lake bottom [Figure 3], and (4) an estimate of sediment accumulation and location [Figure 10]. Lavon Lake general information Lavon Dam and Lavon Lake are located on the East Fork of the Trinity River (Trinity River Basin) in Collin County, approximately three miles east of Wylie and 22 miles northeast of Dallas, Texas (Figure 1). Lavon Dam and Lavon Lake are owned by the U.S. Government and operated by the U.S. Army Corps of Engineers, Fort Worth District. Lavon Lake is primarily a water supply reservoir, storing water for the member cities of the North Texas Municipal Water District (USACE, 2012a). Lavon Lake also provides flood control to parts of Collin, Dallas, and Rockwall Counties (USACE, 2012a). In 1951, the Texas Legislature created the North Texas Municipal Water District as a conservation and reclamation district. The North Texas Municipal Water District is responsible for providing drinking water, wastewater treatment, and solid waste disposal to its member cities and customers, encompassing approximately 1.6 million people (NTMWD, 2011a, NTMWD, 2011b). Lavon Lake is the main raw water supply source of the North Texas Municipal Water District (NTMWD, 2011c). Other sources include Lake Texoma, Jim Chapman Lake, Lake Tawakoni, Lake Bonham, the Upper Sabine Basin Supply Project, and the East Fork Raw Water Supply Project (Wetland) (NTMWD, 2011b). 1 Construction on Lavon Dam began in January, 1948, and the dam was completed in September, 1953. Deliberate impoundment began on September 14, 1953 (TWDB, 1973). On May 15, 1970, construction began on a modification of Lavon Dam that increased the conservation storage pool from elevation 472.0 feet to the current elevation of 492.0 feet by raising the top of the dam 12 feet. The modification was completed and deliberate impoundment began December 1, 1975 (USACE, 2012b). Additional pertinent data about Lavon Dam and Lavon Lake can be found in Table 1. Water rights for Lavon Lake have been appropriated to the North Texas Municipal Water District through Certificate of Adjudication No. 08-2410 and amendments to Certificate of Adjudication Nos. 08-2410A, 08-2410B, 08-2410C, 08-2410D, 08-2410E, 08-2410F, and 08-2410G. The complete certificates are on file in the Information Resources Division of the Texas Commission on Environmental Quality. Figure 1. Location of Lavon Lake 2 Table 1. Pertinent data for Lavon Dam and Lavon Lake Owner The U.S. Government, operated by the