REPORT OF INVESTIGATIONS NO. 42


 The graph of mean monthly discharge for the Withlacoochee
River at Trilby (fig. 12) shows that runoff from the basin is lowest
for the months of November through June. The season of highest
runoff is the 4-month period, July through October. During these
months, 58 percent of the runoff from the basin occurs.

 CHEMICAL CHARACTERISTICS OF SURFACE WATER

 Waters of the Withlacoochee River in the eastern part of the
Green Swamp area are very low in mineral content (figure 13
a, b) acidic, and usually highly colored. Chloride is the principal
dissolved mineral constituent. The low mineral content is due to the
insolubility of the surface sands. The acidic condition of the water
in the southern area is probably due to decomposition of organic
matter and subsequent release of carbon dioxide and humic acids to
the water. The pH of surface water in this area ranged from 4.0
to 5.9 units. The presence of chloride as the principal dissolved
mineral constituent may be due to rain and wind-borne salt from
the coastal area. The chloride concentration is usually less than
12 ppm. High color is caused by organic matter in the water. The
color ranged from 90 to 600 units and was higher than 250 units
most of the time.
 The chemical characteristics of water in the Withlacoochee
 River near Eva (station 36) indicate no inflows from the Floridan
 aquifer to the stream. Between Eva and Dade City (station 40)
 the mineral content is higher during periods of low flow but is
 essentially the same as that above Eva during periods of high flow.
 The highest mineral content observed in this reach of the river
 was 302 ppm (see fig. 11). This high mineral content was present
 in the river just above the mouth of Gator Creek and is about the
 same as the mineral content of the water from the Floridan aquifer
 in this area. The hardness of the water at this point was 254 ppm
 and the color, 15 units. The principal dissolved mineral constituents
 were calcium and bicarbonate.
 During periods of low flow, the chemical characteristics of the
 water in the Withlacoochee River between Dade City (station 40)
 and Trilby (station 42) are similar to those of the water from the
 Pasco Packing Company Canal at Dade City. The source of water
 in this canal is from wells penetrating the Floridan aquifer. The
 mineral content of water in the canal ranged from 182 to 190 ppm.
 The color of water in the canal is low (usually less than 10 units),
 and the principal dissolved mineral constituents are calcium and