11-10-2003 Council Packet - Laserfiche WebLink

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Stubbs Bay Phosphorus Load Average Load |kg| Percent Internal Phosphorus Load 577 63 Atmospheric Phosphorus Load 61 7 External Phosphorus Load 270 30 Total Phosphorus Load 908 100 • Phosphorus profiles taken during 2003 indicate that phosphorus concentrations decrease along Classen Lake Creek as it flows toward Stubbs Bay from County Road 6. • Development within the Stubbs Bay watershed is expected to approximately double by 2020. Loads from the watershed can be expected to increase over the next 20 years. 1.3 Load Reduction Scenarios • Benchmark water and phosnhorus budgets were established for comparison of load reduction scenarios Average Year Benchmark Six-Year Average Conditions Average Internal Load 577 kg Atmospheric Load 61 kg Average External Load 270 kg Total Load 908 k Average Lake Outflow 1.06 m /yr • For benchmark loading conditions, the water quality response model predicts summer water quality as: Benchmark Water Quality Conditions _____(growing season average) Total phosphorus 57 ug/L Chlorophyll-a 38 ugL Secchi Depth 0.69 m • The benchmark chlorophyll-a concentration of 38 ug/L is significant in that severe nuisance algae blooms, defined as instantaneous chlorophyll-a exceeding 30 ug/L, will occur 85 percent of the growing season (approximately equal to the swimming season). In order to reduce this percentage to 30 percent, the average will have to be reduced to 27 ug/L; this corresponds to a load reduction of SO percent and total phosphorus concentration reduction to 42 ug/L and Secchi depth increase to 0.85 m. T Stubbf Bay Diagnostic Report