Estimated Phosphorus Load Reductions under Various Water Management Alternatives

To determine the detention volume (in terms of an equivalent runoff depth detained) that can provide a phosphorus load reduction of approximately 20% at the basin level, the Watershed Assessment Model (WAM) developed by the Soil and Water Technology, Inc. was applied to the four drainage basins that contribute high phosphorus loads to Lake Okeechobee. The typical land uses that are suitable to detain water on site include abandoned/closed dairy pasture, citrus groves, dairy pasture, field crop, low and medium density residential areas, improved pasture, unimproved pasture, woodland pasture, and row crops. Scenario one included a water detention depth of 0.25” runoff for all land uses mentioned above, and an estimated 9% load reduction was obtained. Scenario two increased the water detention depth to 0.50” for all land uses except for residential, citrus, field crop, and row crop, resulting in an estimated 18% phosphorus load reduction. Therefore, detention depths that range from 0.25” to 0.5” of runoff could be implemented to achieve a basin level of 18% phosphorus load reduction.