CHANNEL EVOLUTION OF THE TRINITY RIVER, DALLAS COUNTY TEXAS

A time line for channel evolution of the Dallas County reach of the Trinity River has been constructed. Four distinct channels dating 1890, 1909, 1918 and 1954 have been identified and compared to the river’s present location. Modern evolutionary history of the Trinity began in 1908 when it flooded most of Dallas in an event that exceeded all 19^th century records. This flood event had a gage reading of 52.6 feet and resulted in the Trinity River being approximately 2 miles wide. The memory of the 1908 flood spurred the development of the city of Dallas and construction of a levee system along the Trinity River. Construction of this levee system began in 1928 and included moving the confluence of the Elm and West Forks 3.5 miles to the west and construction of a straight channel 15 miles in length and located 0.5 miles west of the original channel. Also in 1928 two large water supply reservoirs were constructed in the headwaters of the Trinity. These reservoirs further altered the river’s flow regime by storing water and effectively reducing the flashiness of the River. After another significant flood in 1948, the levee reconstruction efforts included moving the southern Dallas reach of the channel and dredging the channel to increase its width and depth. In the later half of the 20^th century, the continued development of Dallas County caused an increase in urban runoff and thus the river’s flashiness. Also during this time, growth of the Great Trinity Forest in the downstream reach of the Trinity significantly reduced conveyance capacity. In conclusion, the modern Trinity River has been unable to evolve naturally due to anthropogenic regime changes made during the 20^th century and is in response, behaving as a geomorphologically young stream.