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Analysis of Collected Data for Harbor Isle Lake

This is independent scientific analysis of Harbor Isle Lake regarding methods to aid in the reduction of toxic cyanobacteria and harmful blue green algae blooms.  This information comes from direct excerpts of e-mail communications sent directly to the City of St. Petersburg, and its public contractors, from a concerned citizen during the course of this city public project.  Additional analysis is the process of being added. Thank you for your patience.

Sent on July 15, 2022:

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2022-06-10 - Ignored Stormwater Contributions Analysis and Micro bubble Aeration Diffuser Locations
The partial information shown (below) is taken from a E-mail sent more than 2 years ago to Solitude Lake Management Staff and copied to the [St. Pete Public Works Administrator] Mr. Claude Tankersley and Departments under his Supervision.  The Subject was “Planned Harbor Isle Lake Micro-Bubble Aeration System Installation Suggestions”.  There was no reply, response or actions taken related to this information at that time or at any time after.  This information is repeated once again to aid in providing pertinent data for adding additional diffusers to optimize the existing micro bubble aeration system installed. The micro bubble bottom aeration system in Harbor Isle Lake, now running for two years, has reduced nutrients, but it’s undersized and not as effective as it could be.
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Supplemental Observations and Notes

  • Harbor Isle Lake has a very irregular shape with multiple relatively narrow lobes that can limit any continuous laminar circulation from diffusers if diffusers are only placed into more central lake locations.

  • Soft sediment covers the whole lake floor but extremely soft sediment is concentrated in certain lake lobes with high storm drain loading (see Figure 5 – Bottom Sediment Hardness Map and Important Notes)

  • The lake lobes have a characteristic of collecting and concentrating the wind fetch effects due to the relatively small enclosed concave shaped shorelines.

  • Uneven storm drain nutrient loading with several lake lobes having significantly higher contributions (see Figure 4 – Harbor Isle Storm Drain Property Contribution Diagram)

  • There is always an unavoidable reclaimed water runoff into the storm drains even with minimum water usage due to the significant grading of all Harbor Isle properties.

  • Less than 15% of the surface runoff flowing into the lake is from Harbor Isle lake front properties.  The remainder is from storm drains with every home in Harbor Isle contributing to runoff entering the lake.  This storm drain operation/function is by design and is common for all retention (detention) ponds.

Harbor Isle Lake Storm Drain Loading Analysis
Storm Drain Contributions Image.jpg

Symbol Key Definitions:

Symbol           =>        Description

_______________________________                                                                       

Solid Orange dots in lake => Optimized nutrient loading (14) Diffuser Locations

Small Red circles at shoreline => Storm drain outlets (14) into the lake

Color Areas => Runoff area/properties flowing into the lake via each storm drain outlet

Black Numbers => number of properties draining into lake from that storm drain

Thick Gray lines in lake => demarcation mark for the (6) lake lobes

Red Numbers in the lake => Total number of properties draining into that area of the lake

Important Notes:  

  1. The Southeast lake lobe has 3 storm drains vs. 1 for all other lake lobes.

  2. The Southeast lake lobe has 55 properties draining into it - the most of all lake lobes.

  3. The Northwest (27) and the North (24) lake lobes have the 2nd and 3rd most properties draining into them.

  4. The main lake area (not a lake lobe) drains (67) properties.

  5. Inspecting the storm drain loading for all areas of the lake shows that even with (3) diffusers in the Southeast Lobe it still has the highest property per diffuser loading ratio for the lake.  The largest main lake area (draining 67 properties) and having (4) diffusers has a smaller load ratio.  This arrangement of diffusers distributes the input loads for each diffuser for a more balanced and effective operation.  This also places oxygen capability with an emphasis in the lake lobes that have a trait of concentrating the negative algae effects due to prevailing wind fetch.

  6. Property Nutrient Load / Diffuser Ratios for each lake area:

Southeast lobe = 55/3 = 18.3      =>           Largest runoff Nutrient Loading per Diffuser

Northeast lobe = 18/1 = 18.0

Main Lake Area = 67/4 = 16.8

South lobe = 15/1 = 15.0

Southwest lobe = 15/1 = 15.0

Northwest lobe = 27/2 = 13.5

North lobe = 24/2 = 12.0               =>           Smallest runoff Nutrient Loading per diffuser

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