REPORT OF INVESTIGATIONS NO. 40


tion curve for Big Coldwater Creek in figure 16 shows some streamflow
characteristics at this point. Because of the rolling topography and steep
slope of the basin, flood waters drain rapidly. Ground-water seepage
sustains the base flows at rather high rates during dry weather.
 A useful arrangement of data is the group of low-flow frequency
curves given in figure 30. They show what the lowest daily flow is likely
to be and how often it is likely to occur. For example, the 1-day average
flow of 200 cfs (129 mgd) for Big Coldwater Creek has an average re-
currence interval of about 7 years.
 The seasonal distribution of runoff in Big Coldwater Creek basin
follows very closely the pattern of rainfall. The distribution of monthly
flows is given in figure 31. Heavy spring rains cause high runoff, thus
March and April have the highest average flows. High-intensity rain-
storms in July and August cause high peak flows. October is the month
of lowest flow.
 Big Juniper Creek, which joins the Blackwater River 5 miles up-
stream from Big Coldwater Creek, drains 146 square miles, of which 134
square miles are in Florida. The streambeds in this basin are composed
of loosely packed sand and gravel, and the banks are steep and heavily
wooded.
 The average flow from the Big Juniper Creek basin is estimated to
 be 260 cfs, or 1.8 cfs per square mile, of which about 240 cfs comes from
 the area within Florida. Flow was measured at the three sites within the
 basin: Big Juniper Creek at State Highway 4, near Munson; Sweetwater
 Creek at State Highway 4, near Munson; and Big Juniper Creek near
 Harold. Runoff characteristics are similar at these three sites. Slightly
 over one-half of the flow is base flow; the remaining is direct runoff
 from overland flow.
 The Blackwater River drains 580 square miles in Santa Rosa County
 and 280 square miles in surrounding areas. The streams in this basin
 bring 390 cfs into the county from surrounding areas, pick up 1,100 cfs
 within the county, and discharge an average of 1,490 cfs into Blackwater
 Bay.
 The main stem of Blackwater River brings in most of the flow from
 outside the county. The average flow at the Santa Rosa-Okaloosa county
 line near Holt is estimated to be 440 cfs. The flow-duration curve given
 in figure 16 is based on records collected at State Highway 4 near Baker
 in Okaloosa County. The drainage area above this point is 205 square
 miles. The daily flow has varied at this site from a low of 61 cfs to a
 high of 10,300 cfs. The average flow is 320 cfs. The flood of December