REPORT OF INVESTIGATIONS No. 40


 BLACKWATER RIVER BASIN

 OCCURRENCE OF WATER
 Blackwater River heads in southern Alabama, north of Bradley. The
river enters Florida north of Baker, flows across the northwestern corner
of Okaloosa County, and winds southward along the Santa Rosa-Okaloosa
county line for a distance of about 4 miles. At Bryant Bridge at the
county line, the river turns to the southwest and is joined by Big Juniper
Creek and Big Coldwater Creek, and then continues toward Milton. At
Milton it turns southward and flows into Blackwater Bay.
 The shape of the Blackwater River basin and the pattern of drainage
are similar to those of the Escambia River basin, in that the main chan-
nel parallels the eastern and southern edge of the basin and all major
tributaries enter from the north. The basin is well dissected by tortuous
stream channels that wind their way through a thick forest of pine and
juniper trees. Except during floods, the water is clear and flows in clean
channels of sand and gravel.
 The following discussion of streamflow is by tributary basins, pro-
ceeding upstream in the following order: Pond Creek, Big Coldwater
Creek, Big Juniper Creek, and upper Blackwater River.
 Pond Creek drains an area of 88 square miles, all within Santa Rosa
 County. The creek flows southward and empties into the Blackwater
 River just south of Milton. The basin has an elongated shape with rela-
 tively short tributaries that drain directly from the steep hills. The land
 along the basin divide is flat and is from 1 to 2 miles wide. From the
 flat divide, however, the land slopes steeply to the stream channel.
 Pond Creek has two channels within the lower three-fourths of its
 flood plain. One of these is the natural channel which is very crooked
 while the other is a straight channel dug many years ago for transporting
 logs. The valley slope is steep (fig. 29) with a total fall of about 200 feet
 from the headwaters to the mouth, a distance of 24 miles.
 The estimated unit runoff from Pond Creek is 1.4 cfs per square mile,
 which is equivalent to an average flow of 123 cfs from the basin. The
 minimum daily flow measured at the gaging station during a 4-year
 period ending 1961 was 43 cfs, or 0.7 cfs per square mile. About 75 per-
 cent of the total flow is derived from the ground as base flow and 25
 percent is direct runoff by overland flow.
 Big Coldwater Creek is the largest tributary feeding the Blackwater
 River. The total area drained by this tributary is 241 square miles, of
 which 228 square miles are in Santa Rosa County. All except the smallest