Hopefully you will get lots of advice on how to do this. Following is my method that I have used several times including this past fall. There are lots of faster ways to do it, but I lower the level of my three acre pond about six feet in 3 weeks or so. If you need to do it faster you may want to try another method:
For years I have used a somewhat simpler method of syphoning. I have several lengths of 2 or perhaps 2 1/2 inch green plastic hose that I buy at farm supply stores. My pond is about three acres and when I draw it down in the fall I am in no particular hurry to drop the lake level.
It might take me three weeks or more to drop it four or five feet.
I attach a brick and a one gallon jug to the lake side end of the hose and, with one person standing on the dam, and another on an opposite bank or in a boat pull the hose out into deeper water. The reason for the person on the bank is to make sure the lakeside hose does not get pulled into the lake. If you don't have help you just stake one end to the bank so it isn't pulled into the water.
With the brick and jug, the hose is underwater but not on the bottom where it might pick up muck and stop the syphon. If you have someone on the bank they make sure the hose enters the water and fills rather than floats. If no one helps you all you need to do is make sure the hose goes underwater as soon as it is the water by forcing it under a heavy object. If you have a concrete block with holes in it and run the hose through it as it goes in the lake you won't have a floating problem.
When the hose is all the way in the lake and full of water, I put an adjustable plug we get where we get the hose and then pull the full hose over the dam until I am sure the dam side hose is lower than the lake side hose.
I then merely open the valve and let the water flow. I monitor the lake level each day and when I have removed as much water as I want I just pull the dam side hose up the back of the dam until the elevation breaks the syphon.
It may take a little longer than you have time for, but it often drops a couple of inches a day when the lake is full and then 5 or 6 inches when the level is down. The most I have dropped the water is about six feet in my pond which has 18 foot depth in spots.
At times I have started two of three shorter syphons and that really draws it down.
All together I have probably spent less than $150.00 for hose, clamps and plugs.
“Happiness is having a rare steak, a bottle of whisky, and a dog to eat the rare steak.”
– Johnny Carson