Proposed Designs

Design Factors

Yahara River Discharge Information 
USGS Measurement Station – Yahara River at State Highway 113, Madison, WI

Water Year

Suspended Sediment

Tons/day

Average Discharge

ft³/sec

Phosphorus Discharge

lbs/day

2003

2.96

45.3

30.14

2004

 

77.2

 

2005

 

60

 

2006

 

53.1

 

2007

 

82.8

 

2008

 

136.7

Table 1:  Average discharge per year of the Yahara River into Lake Mendota.  Values for suspended sediment and phosphorus are provided for the year 2003.

Peak Flow in Yahara
Since 2002, the largest recorded stream flow was 1,450 ft³/sec on June 9, 2008

Cross-sectional area of the Yahara River at the measuring station
68.4 feet long by 9.5 feet deep = 649.7 ft²

Lake Mendota Bathymetry
lake mendota

A better Lake Mendota bathymetry map can be found here at the Wisconsin DNR website.

Lake Mendota Limnological Information

Lake Mendota Maximum Historic Ice Thickness
30 inches
*Determined via limnology information above

Design Options

Two design options have been created for the Lake Mendota algae farm.  The main difference between the two designs is the location of the algae retaining walls and the inputs entering the system.  Design 1 has only the Yahara River entering the system and Design 2 has the Yahara River and Dorn Creek.  The location of the algae retaining wall also affects the total area that is able to be farmed and the number of homes and business that are affected.  Both designs utilize the Yahara River Estuary. 

Design #1 

Yahara River Estuary and Lake Mendota Design #1

design 1.1
design 1.2

Total Algae Farming Area = 27,646,597 ft²

Algae Farm Wall Length = 4283.68 ft 

Water Discharge
1) Yahara River

Houses and Businesses Directly Effected
6 Marina
40 Houses

Design #2

Yahara River Estuary and Lake Mendota Design #2

design 2.2
desing 2.2

Total Algae Farming Area = 44,954,793 ft²

Algae Farm Wall Length = 6117.3 ft 

Water Discharge
1) Yahara River
2) Dorn Creek
 
Houses and Businesses Directly Effected
6 Marinas
78 Houses
             

Potential Wall Design

*This wall design is not the final design and before any construction, structural engineers will be consulted in order to verify or modify the structural aspects of the wall. The intention of this design is to specify the flow parameters that will be created by this structure and utilized in the analysis of our model to determine in algae and phosphorus capture can occur in the system.  

In order to retain the algae in the farm and allow water to be discharged we have designed the following retaining structure.  The structure will consist of 20 foot segments that will be connected together to form a wall across the lake.  

Starting from the bottom, each segment has the following features:

1)      Each section will be anchored by a pile which will serve as the hinge for the rotating ice gate. 

2)      Each section will have a 2 foot wide concrete base that is to be buried below the lake bottom. 

3)      Above the concrete base is a concrete wall that begins at the bottom of the lake.  Six inches above the lake bottom there is a six inch gap (with rebar gating) to allow for water to be discharged without algae.  Above the gap is more concrete wall, either 1.5 feet for Design #1 or 2.5 feet for Design #2.  The discharge gate for either design is much larger than the river inputs into the system, thus water should able to leave the algae farm and prevent flooding.  Modeling will be done to help demonstrate this.

4)      Above the concrete wall is a 3.5 feet high removable wall piece that is centered on the piling post.  This removable piece will be removed during the winter to prevent ice damage to the wall.  It sits 2.5 feet below the water level and 1 foot above.  This piece is designed to rotate around the pile and can be open in times of flooding in order allow extra water to flow past the wall and prevent flooding in the area.

The specifications in the design of this wall are based on creating a design that can withstand the flow from the Yahara and Dorn Rivers while retaining algae and phosphorus within the algae farm.  The structural parameters of the wall needed to support wave energies and linear momentum forces will be analyzed in future analysis if such an algae farm is to be built in Lake Mendota.  The issue of structural parameters is touched on in the Future Analysis section.

Cross Sectional Flow Areas

Inputs
Yahara River = 650 ft²
Six Mile Creek = 216 ft²

Outputs
Design 1, 6” gap: 2,141.84 ft²
Design 2, 6” gap: 3,058.65 ft²
Design 1, ice gate open + 6” gap:12,851.04 ft²
Design 2, ice gate open + 6” gap:13,767.85 ft²

Wall Design Drawings

wall

wall 2