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Lemon Dam

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Lemon Dam is a zoned earthfill structure with a structural height of 284 feet and a crest length of 1,360 feet. The dam embankment has a maximum base width of 1,170 feet, a crest width of 30 feet, and contains a volume of 3,042,000 cubic yards of earth and rock materials.

The spillway is on the right abutment of the dam and consists of an approach channel, concrete inlet structure, concrete ogee crest section, open concrete chute, concrete stilling basin, and outlet channel discharging into the Florida River. The design capacity of the spillway is 9,600 cubic feet per second.

The outlet works is also in the right abutment of the dam and consists of an approach channel, a concrete intake structure, and a concrete-lined tunnel gate chamber for two 2.25-foot-square high pressure gates. The 9-foot horseshoe-shaped tunnel has a design capacity of 910 cubic feet per second.

Lemon Reservoir is approximately 0.5 mile wide and 3 miles long with a surface area of 622 acres. The total capacity is 40,146 acre-feet, of which 39,030 acre-feet are active conservation.

Geology 

Lemon Dam is constructed on bedrock of the Cutler Formation (Lower Perian) consisting of red to gray calcareous siltstone, shale and sandstone with interbedded limestone.  The bedrock is highly fractured and fissile and the shale interbeds readily slack when exposed to air.  The dip of the bedrock beneath the dam is approximately 10 degrees to the south.  Reconstruction drill hole data indicates that some of the limestone intererbeds contain solution channels.  Foundation treatment consisted of a grout curtain, with a minimum depth of 160 feet across the valley floor and up both abutments, and a cutoff trench (1.5:1 side slopes) within the limits of the Zone 1 core and extending 5 feet into bedrock or to a minimum base depth of 30 feet.  The trench was excavated to a 10-foot width in siltstone below the old river channel at elevation 7,883.  The reservoir is in a narrow valley that is approximately half a mile wide and three miles long.  It has a maximum storage capacity of 40,146 acre-feet with a surface area of 622 acres at a water surface elevation of 8,148 feet.  The reservoir appears to be watertight since the siltstone and shale bedrock and randomly sorted glacial till are relatively impervious.  Several northwesterly trending normal faults, downdropped to the north have been identified around the edge of the reservoir.  There are no topographic of glomorphic indications that these faults are active.  Where observed, the fault planes are tight and filled with a clay gouge that restricts the movement of water from the reservoir.


Last updated: Mar 05, 2009