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Florida Lake Management Society Annual Conference, Naples, Florida, June 4 – 7, 2007

HYDROLOGIC AND WATER QUALITY MODELING OF THE LAKE JESUP WATERSHED USING HYDROLOGICAL SIMULATION PROGRAM – FORTRAN (HSPF)

Yanbing Jia, Ph.D. BCI Engineers & Scientists, Inc. Lakeland, FL

A Hydrological Simulation Program – Fortran (HSPF) model is developed in this study to simulate the hydrology and water quality in the Lake Jesup watershed, a high-urbanized watershed in central Florida. The HSPF model is calibrated for flow, water temperature, dissolved oxygen, sediment, and nutrients measured at several sites across the watershed for the simulation period from 10/1997 to 09/2003. The calibration results show a good agreement between the observed data and the simulated outputs. The average annual watershed loadings of TN and TP are 140.7 metric ton N/yr and 18.7 metric ton P/yr. There is significant variation between the watershed loadings in the three dry years (10/1998 – 09/2001) and those in the three wet years (10/1997 – 09/1998 and 10/2001 – 09/2003). The average dry year watershed loadings of flow, TN, and TP are 63,286.2 acre-ft water/yr, 95.5 metric ton N/yr, and 12.9 metric ton P/yr, respectively. The average wet year watershed loadings are 127,677.7 acre-ft water/yr, 185.8 metric ton N/yr, and 24.6 metric ton P/yr, which are approximately 2 times of the dry year watershed loadings. Using these loading estimates, a water and nutrient budget for Lake Jesup is developed.

The calibrated HSPF model is used to assess the impact of various management scenarios on the nutrient loadings to Lake Jesup. A general description of the simulated scenarios is given as follows:

  • 1.

    Current – current (1997 – 2003) conditions;

  • 2.

    Future – future land use with 100% Best Management Practice (BMP) implementation for future development (newly increased residential, industrial, and commercial areas);

  • 3.

    Future + 25% BMP – future conditions + 25% BMP implementation for current land uses without BMPs (excluding forest, water, and wetland);

  • 4.

    Future + 50% BMP – future conditions + 50% BMP implementation for current land uses without BMPs (excluding forest, water, and wetland);

  • 5.

    Future + 75% BMP – future conditions + 75% BMP implementation for current land uses without BMPs (excluding forest, water, and wetland);

  • 6.

    Pristine – all forested (except water and wetland) watershed.

Figure 1 compares the estimated TN and TP loadings to Lake Jesup under these six scenarios. The estimated TP loading under the future scenario is close to the current TP loading level, suggesting that the implementation of BMPs for all the future development and the decrease of the agriculture and pasture areas under the future conditions would effectively control the increase of TP loads. Because the removal efficiencies of BMPs for nitrogen are

Session 5A – Page 2

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