Alafia River Minimum Flows and Levels - Southwest Florida Water ...

Before discussing individual sub-basin land use changes, it is informative to
discuss the entire watershed of the Alafia River to get an appreciation of the
major land uses/covers and the changes that have occurred during the nearly 30
years for which land use maps are available. Land use / cover maps for 1972
and 1999 for the entire Alafia River watershed are shown in Figure 2-9. Note
that for mapping purposes, uplands were divided into two subgroups (rangeland
and upland forests) and wetlands were separated into wetland forests and
nonforested wetland subgroupings. Subgroupings were not maintained for
tabular analyses and plotting of land use changes (Table 2-2, Figure 2-10).
The total area of the Alafia River watershed is 269,986 acres or 422 square
miles. From inspection of acreage changes as shown in either Table 2-2 or
Figure 2-10, several land use/cover changes are readily apparent. There have
been noticeable increases in both urban land area and mined area. As of 1999,
almost 18% of the watershed area was urbanized. In 1972, urban land was 11%
of the watershed. Even more striking, however, is the increase in mined lands.
In 1972, approximately 11% of the watershed had been mined; by 1999 the
amount of mined land encompassed approximately 36% of the watershed,
equivalent to 105 square miles.
While the area of mined and urbanized lands increased markedly, upland and
agricultural land area decreased correspondingly. Total decreases in agricultural
land and uplands amounted to approximately 54 and 87 square miles,
respectively. Decreases in these two land use categories of 141 square miles
were almost offset by the 133 square mile increase in urbanized and mined
lands.
Of the eight large sub-basins delineated for this report, only four lie upstream of
the Alafia at Lithia gage. These are the North Prong, South Prong, Turkey Creek,
and Lithia Springs sub-basins. Based on land use maps prepared for this report
the total combined area of these four sub-basins is 218,073 acres or
approximately 341 square miles. The USGS reports that the area above the
Lithia gage is 335 square miles. Most of the mined land in the Alafia River
watershed can be found in these four sub-basins (96%) and most of this is in
either the North (32%) or South Prongs (57%).
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