Sweetwater Creek Watershed Mgmt. Plan 2007 Update--Part 2

CHAPTER 11
• LOS F, net load equal to or greater than 100% of untreated single family residential
areas. A LOS equal to F would indicate no treatment for sub-basin discharges, or the
presence of extensive areas of land uses producing larger pollution loads per unit area
than typical residential land uses.
11.2.1 Water Quality Level-of-Service Pollutant Load Calculations
Benchmark pollutant loads were calculated for each pollutant based on the assumption that 100%
of the watershed area was developed for low/medium residential land uses and no existing
stormwater treatment existed in any of the subbasins. Appendix 11-1 provides a summary of the
benchmark loads by subbasin for Sweetwater Creek watershed.
11.2.2 Water Quality Level-of-Service Scores
Based on the criteria described above, the treatment level of service designation were developed
for each parameter for each subbasin, which are summarized in the Appendix 11-2. As mentioned
earlier, the three most important parameters of concern in this watershed are total suspended
solids, total nitrogen, and total phosphorus. The observations on these three parameters are
discussed in detail in the following section.
Total Suspended Solids
Total suspended solids (TSS) LOS values tend to be the highest in areas dominated by existing
natural systems, such as wetlands, upland forests, and rangeland (Figure 11-1). These land uses
do not contribute any loads based on the model’s EMC value input dataset. However, Sweetwater
Creek watershed is characterized by densely developed areas. The majority of the watershed area
includes such land uses as high and medium/low density residential, commercial and services,
industrial, and highway/utilities. On an areal basis, a number of subbasin clusters with LOS scores
of C and higher are located in the northern and central portions of the watershed. These subbasins
include areas of undeveloped land, such as wetlands, small forested areas, and ponds. The area
to the north of the watershed includes Avila Golf and Country Club, while the area with higher TSS
LOS scores located closer to the center of the Sweetwater Creek watershed incorporates open
land and small areas of wetlands located to the east of the Citrus Park Lake. Overall, the
proportion of subbasins with high TSS LOS scores in the Sweetwater Creek watershed is
significantly lower when compared to the proportion of similar subbasins within other watersheds in
the Old Tampa Bay region (with exception of the Lower Sweetwater Creek watershed). The
Sweetwater Creek watershed is much heavier polluted than most watersheds in the northwest
Hillsborough County region.
The remaining subbasins are dominated by the scores of F and D and are primarily characterized
by high density residential, transportation and utilities, commercial and services, and industrial land
uses. Developed land uses are characterized by relatively large impervious surface area (such as
roads, buildings, parking lots, etc.), which have relatively high runoff coefficients and TSS loads.
11-3
Sweetwater Creek Watershed Management Plan