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Observation of flow over the Dam, December 2009

By Jim Clark and Pete Compton

By observations of our shore at Partridge Pointe, we became curious as to whether the newly repaired dam allowed the lake water level to fall to as low a level as it had prior to the dam repair and if we were experiencing ice-damage as a result of it being higher than in the past.  On December 16, 2009, we made a trip to see for ourselves .  This was the same day that the lake froze over for the first time in the Fall of 2009.

Measuring Lake Level

Summary: The winter level after the repairs should be the same as before the repair.

First we measured down from the summer water mark to the ice and found it to be down 22 inches.  The ice may have pushed the tape up, but no more than an inch.

Height gage on dam

The gage on the dam shows a summer level of 7.5 feet and a
winter level 5.9 feet.  That calculates that the winter level is
down 19 inches from the summer level.  There may be a couple
of inches pushing up against this gage.

View of the front of the dam

The two gates at the south end are designed differently than the other four. This picture shows the mechanism is above and clear of the water, so they are not restricting the flow.

The screws are driven down to within four inches of the screw mechanism, so they can't go down much further.

This view is looking down at the crest of the dam. The adjustable weirs look to be below the concrete crest of the dam. We had no means for measuring the depth of water going over this crest. We could only estimate that the water was just over a foot deep in this picture. Adding the 22 inches down from summer levels, to 13 inches of flow over the crest, plus one inch of drop from the flow would give a nice round number of 36 inches.

The new gates do not appear to restricting the flow. Since the 'U' channels that used to hold the 'boards' in place are gone, one could assume that there is less restriction to water flow with the new dam than there was with the old system of raising the lake level.

In summary:
  1. The summer lake level is controlled by raising and lowering the wiers to maintain a lake level that is 36 inches above the crest of the dam.
  2. The winter level is determined by how much water is going over the crest of the dam.
  3. The very lowest the lake level can be is 36 inches below the summer level. That would occur when there is no water going over the dam.
  4. On December 16, 2009, the lake was 22 inches below the summer level.
  5. The lake level is what it is. As long as we are in this wet rain cycle, there is no likelihood that it will be dramatically lower than is was on December 16, 2009.
Water going over the spillway
  Hamlin Lake Preservation Society, PO Box 178, Ludington, MI 49431