Secchi/Chlorophyll-a Model

Secchi Model 1 predicts transparency using the following model:

1 / SECCHI = ALPHA + BETA * CHL-A

where,

ALPHA = non-algal turbidity (1/m)

BETA = Secchi/Chlorophll-a Slope (m2/mg)

ALPHA represents non-algal turbidity, or the portion of light extinction that is due to factors other than algae (inorganic suspended solids, color). This typically ranges from 0.08 to >2 1/m.

I f Secchi Model 1, Chlorophyll-a Model 1 , and/or Chlorophyll-a Model 2 are used, the following considerations apply:

A positive non-algal turbidity must be specified for each segment on the Observed Water Quality tab of the Segments input screen.
If observed Chl-a and Secchi if both are specified, non-algal turbidity estimated from the above equation will be shown on the segment input screen. This provides an estimate that the user can specify in the turbidity input box (it is not automatically copied there).
If obseved Chl-a or Secchi data are not available, turbidity ) must be estimated independently (from adjacent segments or other regional data) and entered on the Observed WQ tab, otherwise an error message will be generated.

The BETA value applies to all model segments and is specified on the Model Coefficients input screen. The default value for BETA (= .025 m2/mg) has been calibrated to CE reservoir data. Experience in applying the model suggests that lower BETA values (.01 - .02 m2/mg) are typical of lakes and reservoirs which are dominated by flake-forming blugreen algae or other algal types with large cells. BETA values can be adjusted downward to account for this type of situation. Variations in BETA may also reflect differences in measurement procedures for Chl-a and transparency. BETA may be calibrated to site-specific Chl-a and transparency data.