REPORT OF INVESTIGATIONS NO. 42


agriculture because of poor drainage. In spite of the many miles of
ditches, drainage is still inadequate. Even in the cleared areas that
are suitable for agriculture, few attempts have been made to
reclaim the many small, round, cypress swamps that dot the area.
 Cypress lumbering was once an important industry in the
western part of the area, particularly in the Withlacoochee River
Swamp where there were extensive stands of trees. The first access
roads to penetrate the interior of the swamp were trails and tram
roads built for cypress lumbering. Timber and pulpwood are now
produced from the pine flatwoods interspersed among the swamps.
 There is some development of the mineral resources of the area
 for the commercial market. Extensive phosphate deposits in Polk
 County lie just south of the Green Swamp area. Some phosphate
 is mined within the area but the amount is only a small percentage
 of that produced in southern Polk and eastern Hillsborough
 counties. Limerock, used in road construction and agriculture, is
 mined in the northwestern part of the area. Deposits of sand,
 suitable for building uses, are mined in many places in the eastern
 part of the area.

 CLIMATE

 The location of the Green Swamp area, well south in the
 Temperate Zone, and its proximity to large bodies of warm water
 produce a warm humid climate. Precipitation and temperature, the
 principal climatic elements that influence the hydrology of the
 Green Swamp area, are described separately.

 PRECIPITATION

 The study of precipitation in central Florida can be restricted
 to rainfall only, because snow and hail are virtually unknown. The
 normal or long-term average annual rainfall of the Green Swamp
 area is 52.7 inches. This normal is computed by the Thiessen
 method of weighting long-term rainfall records at each of the
 following U. S. Weather Bureau stations in or near the project area:
 Clermont 6 miles south, Lake Alfred Experiment Station, Lakeland,
 and St. Leo (figs. 2 and 5).
 The average rainfall for the station at St. Leo, west of the area,
 is slightly higher than that for the other three stations which are
 located farther inland. The average rainfall at the four stations
 ranges from a minimum of 50.1 inches at the Clermont station to