REPORT OF INVESTIGATIONS NO. 42


on these values the increased evaporation loss would be about 9
inches.

EVALUATION OF PROPOSED PLAN OF WATER CONTROL

 A comprehensive plan of improvements proposed by the U. S.
Corps of Engineers (1961) provides for diversion canals and
flood-control conservation reservoirs in the Green Swamp area, and
in the upper Oklawaha, Peace, Hillsborough, and Withlacoochee
River basins, shown in figure 54. Green Swamp Reservoir, largest
of those included in the plan of improvement, would be located in
the Withlocoochee River basin near the center of Green Swamp.
The proposed Green Swamp Reservoir would provide for a total of
460,000 acre-feet of storage (134,000 acre-feet at conservation pool
level of 100 feet above msl and 326,000 acre-feet above the
conservation pool for flood control at level of 107 feet above msl).
The surface area of the flood-control pool would be about 61,000
acres.
 The Southeastern Conservation Area (Johnson, 1961), also
designated the Lowery-Mattie Conservation Area (Corps of
Engineers, 1961), would be located in the southeast corner of the
Green Swamp area. This proposed water-conservation area would
cover about 46 square miles in three pools and provide for maximum
storage of about 72,000 acre-feet at pool levels ranging from 133.0
to 134.5 feet above msl.
 Also within the Green Swamp area and included in the
comprehensive plan of improvement are the Little Withlacoochee
Reservoir, the Upper Hillsborough Reservoir, Big Creek upper and
lower diversion canals, and Lowery Canal.

 REDUCTION OF FLOOD PEAKS IN THE
 HILLSBOROUGH RIVER

 The annual runoff to the Hillsborough River basin through the
 Withlacoochee-Hillsborough overflow was 104,000 acre-feet for
 1959 and 106,000 acre-feet in 1960. The flood-control pool of the
 proposed Green Swamp Reservoir is capable of impounding the
 total annual runoff contributed by the Green Swamp to the
 Hillsborough River basin. For the purpose of computing the
 effectiveness of the proposed Green Swamp Reservoir in reducing
 flood peaks of the Hillsborough River at Tampa, the flood of March
 1960 has been taken as a typical case. The maximum extent that


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