Hamlin Lake Preservation Society



Protecting Hamlin Lake for future generations
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Report on the Sluice Gates on the Hamlin Lake Dam

This is a report on a walk-around-the-dam, on the Big Sable River in the Ludington State Park, on Thursday, January 10, 2013.  As you can see by the pictures, there had not been much precipitation in the preceding weeks .

All six of the gates were open.  The four north spillways had their weirs all the way down and had 14 inches of water going over them.  The two south spillways had their sluice gates open, but there was no water flowing thru them as their lip was six inches above the water.

This diagram shows the conditions of the four north spillways at this time.  The water going over the lip of the dam was measured as 14 inches deep.  The Lake level gage indicated 5.3 feet.  By difference the lip of the dam would be at 4.1 feet on the Lake Level Gage.
The Francis Formula was used to calculate the flow of water over a weir.  The formula accounts for the resistance caused by the sides, and the increase in flow with depth.  The weir coefficient was selected from literature based on the shape of the dam.  In this case only four spillways operating.
Width of the weir, w 11.0 feet
Depth of water going over the weir, h 14.4 inches
  1.20 feet
Effective width of weir, w-0.2h 10.8 feet
Weir Coefficient, c 3.25 sqrt(ft) per second
Francis Formula            q = c*(w-0.2h)*h^1.5
Flow over one weir, q 46.0 cubic feet per second
Number of weirs 4 each
Flow over the Hamlin Dam 184 cubic feet per second
  82,500 gallons per minute
  119 million gallons per day
This picture shows one of the two south spillways with the fixed panel preventing water from flowing.  The affixed panel is 20 inches tall with 14 inches of water against it on the upstream side.  The sluice gate is above the fixed panel and one of the two rods that lift it are visible.  The space between the affixed panel and the sluice gate is open so you can see the trees beyond the dam.
This diagram shows the conditions of the two south spillways at this time.  Water is prevented from going over the lip of the dam by the fixed panel.  Water only overflows into these spillways when the lake level is above 5.8 feet.

the level in Hamlin Lake is higher in the Winter because of these two fixed panel.
In order to calculate what the level of Hamlin Lake would be with six identical spillways operating, we assumed that the amount of water going over the dam (119 MGD) would be the same with either 4 or 6 spillways operating.  With six identical spillways, with weirs, operating, the calculations show that only 11 inches of water would be going over the dam so Hamlin Lake would be 3 to 4 inches lower than at present.
Width of the weir, w 11.0 feet
Depth of water going over the weir, h 11.0 inches
  0.91 feet
Effective width of weir, w-0.2h 10.8 feet
Weir Coefficient, c 3.25 sqrt(ft) per second
Francis Formula            q = c*(w-0.2h)*h^1.5
Flow over one weir, q 30.7 cubic feet per second
Number of weirs 6 each
Flow over the Hamlin Dam 184 cubic feet per second
  82,600 gallons per minute
  119 million gallons per day

It appears that the existing sluice gates have two bad features:
1. They increase the lake level in the winter which results in the possibility of creating more shore damage.
2. They reduce the capacity of the dam to pass water during a high-water event.

Before we can draw any conclusions or make any recommendations, we need to know what reasons supported the installation of these sluice gates.

Lacking any compelling reason not to, the full capacity of the dam should be returned to its previous flow.

               Jim Clark
   
   
Hamlin Lake Preservation Society   PO Box 178, Ludington, MI 49431