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Public Meeting Held on Five Island Watershed

By Staff | Mar 20, 2018

On Wednesday, March 7, FYRA engineering of Omaha, NE held a meeting for residents of Emmetsburg and the surrounding area concerning the Five Island Watershed. FYRA was prepared with a presentation to suggest ways to help clean up and protect the watershed.

Five Island Lake has 1,002 acres of surface area. The average depth is 5.7 feet with the northern end of the lake more shallow than the southern end. The maximum depth of the lake is 26.1 feet. The watershed area is 7,657 acres, which creates an 8:1 watershed: lake ratio.

Currently the phosphorus levels in Five Island Lake are too high which decreases clarity of the lake and increases the amount of algae. The purpose of the study is to reduce the algae and increase clarity, improve the ecological health of the lake, and evaluate the outlet structure of the lake.

According to the results, the northern-most part of the lake is responsible for the largest phosphorus load: 2,031 pounds per year to the northwest, and 1,869 pounds per year to the northeast. This land is mainly agricultural. According to the breakdown of the phosphorus load by source, cropland accounts for 78% of the load, urban sources make up 14%, and other sources account for 8%.

FYRA suggested ways that the Five Island Watershed can reduce the phosphorus load in the lake through three categories: watershed alternatives, near-lake alternatives, and in-lake alternatives.

Watershed alternatives was further broken down into five subcategories: Cropland Management Practices, Livestock Management Practices, Urban Land Practices, Septic System Repairs, and Construction Ordinances.

Cropland management practices include non-structural and structural alternatives. Non-structural alternatives include: conservation tillage and no-till farming, cover crops, extended crop rotations, fertilizer and manure managements, and CRP/WRP. Structural alternatives include: grassed waterways, riparian buffer strips, pothole wetland restoration, and iron-enhanced sand filters.

Livestock management practices include: CNMP development, Waste Storage Facilities, grazing management, and livestock exclusion.

Urban Land Practices are further divided into two categories: non-structural and structural. Non-structural practices include: no phosphorus fertilizer, pet waste management, and soil quality restoration. Structural practices include: rain gardens/ bioretention and bioswales.

Septic System repairs include: inspection of septic systems in watershed, repair/replace faulty systems, Palo Alto Gaming Development Corporation Grant set aside specific for failing systems.

Finally in the category of watershed alternatives, Construction Ordinances were suggested including: sediment and erosion control requirements in watershed and expand outside city limits.

Near-Lake Alternatives were further deconstructed into three categories: Constructed/CREP Wetlands, Sediment Forebays, and Detention Basins.

Constructed/CREP wetland alternatives include: control large drainage area, intercept overland runoff and tile drain outlets to lake, and dissolved nutrient uptake and trap sediment-attached nutrients.

Detention Basins alternatives include control large drainage area, intercept overland runoff dissolved, and trap sediment-attached nutrients.

Sediment Forebays include: control large drainage area, intercept overland runoff dissolved, and trap sediment-attached nutrients.

In-Lake alternatives were further divided into six sub-categories: Rough Fish management, Phosphorus Inactivation, Dredging, Large Wetland Area, Shallow Vegetation/Lake Level Management, and Wake Zone Management.

Rough Fish Management includes: fish removal (especially carp in Five Island Lake), reduce spawning habit, fish passage barrier, and public education.

Phosphorus inactivation includes: applying a chemical agent called aluminum sulfate to the lake surface- this binds with phosphorus in the water column and lakebed sediments.

Dredging involves removal of lakebed material. It helps to increase lake depth and volume, and reduce resuspension. This is not a very viable alternative due to cost as well as the fact that Five Island Lake has previously been dredged, so there will not be as much of an impact this time around.

Large wetland areas would help to dissolve the nutrient uptake and trap sediment-attached nutrients. A wetland area would reduce the resuspension of lakebed sediment as well as have benefits for aquatic habitats.

Shallow Vegetation/ Lake Level Management gives engineers the ability to manipulate the water level in the lake. It also enhances the ability to establish shallow aquatic vegetation.

Wake Zone Management includes controlling wakes in shallow areas and near shorelines, especially on the north side of the lake.

The current goal is to reduce the load of phosphorus in the lake. The current annual total is 12,586 pounds. The goal is to reduce this amount by 5,034- 8,810, which is roughly 40-70% of the current load.

The meeting proceeded to split into breakout sessions so those that attended could ask more specific questions on the proposed alternatives. The group came back together to discuss the most viable options for reducing the phosphorus load. The most popular alternatives were in-lake management such as decreasing the rough fish population.

The watershed study and public input is an on-going process and no decisions have been made at this time.