Seepage Analysis of Sardis Dam Under PMF Conditions

Sardis Dam is located in northwestern Mississippi on the Little Tallahatchie River, a tributary of the Yazoo River. Completed in 1940, it is one of four flood control dams in the Yazoo River Basin which lies almost entirely within the northwestern quarter of the state of Mississippi. Sardis Dam is approximately 10 miles southeast of the town of Sardis and 11 miles northwest of Batesville. It has a storage capacity of 1,461,900 acre-feet from a drainage basin of 1545 square miles. The main embankment is constructed predominantly of zoned hydraulic fill. The abutment dikes are rolled fill. The total length of the dam is approximately 15,300 feet with a crown width of 40 feet at Elevation 311.4 and a spillway crest at Elevation 281.4. The highest elevation of the dam above the stream bed is 177 feet. Following Periodic Inspection No. 6, August 1991, it was recommended that the Corrugated Metal Pipe (CMP) toe drainage system be abandoned and replaced where necessary. The CMP system is an original feature of the dam designed to intercept seepage during high lake pools. The pipe is now considered to be nonfunctional due to corrosion and clogging by iron precipitant and/or iron bacteria. The purpose of this study was to analyze the seepage pressures that could be developed during the Probable Maximum Flood (PMF) and to determine if additional pressure relief is required or if the CMP drain system may be abandoned.