For development of minimum flows, the year is categorized into three distinct flow periods

or "blocks". Based on flow records for long-term United States Geological Survey (USGS) gage

sites at the Myakka River near Sarasota (USGS# 02298830), the Alafia River at Lithia (USGS#

02301500), the Peace River at Arcadia (USGS# 02296750), and the Hillsborough River at

Zephyrhills (USGS# 02303000, The Hillsborough River was used to develop the season block

for the region but is not otherwise discussed in this chapter), the seasonal blocks were

determined as periods corresponding to dates when specific exceedance flows occurred. On an

annual basis, a low-flow period, Block 1, was defined as beginning when the median daily-flow

fell below and stayed below the annual 75% exceedance flow. Block 1 was defined as ending

when the high-flow period, or Block 3, began. Block 3 was defined as beginning when the

median daily flow exceeded and stayed above the mean annual 50% exceedance flow and ending

when the flow fell below and stayed below the mean annual 50% exceedance flow. The

medium-flow period, Block 2, was defined as extending from the end of Block 3 to the

beginning of Block 1.

 Between these rivers, there was little difference in the dates that each defined flow period

began and ended (Table 3-1). Block 1 is defined as beginning on Julian day 110 (April 20 in

non-leap years) and ending on Julian day 175 (June 24). Block 3 is defined as beginning on

Julian day 176 (June 25) and ending on Julian day 300 (October 27). Block 2, the medium-flow

period, extends from Julian day 301 (October 28) to Julian day 109 (April 19) of the following

calendar year (Kelly et al. 2005a, b, c). Though the District has developed MFLs for all three

blocks, this paper focuses on the criteria for developing minimum flow standards for Block 3,

which runs from June 25 to October 27 of each year.