You already have a siphon system in place!

Do you want to have a siphon system to have the option of pulling down the lake level in the future?

If that is your desire, this is my suggestion:

Wait until the pond drains down to the level of the broken connection. Set some type of crude bench mark so you know the exact elevation of the top of the vertical pipe that sets the water level in your lake. Now determine exactly how you will repair the broken connection. Wrestle the pipe to the approximate location it will be after the repairs.

Cut off your vertical pipe at the height that you would like for your lowest lake elevation. Install a tee and a drain valve attached to the 90 degree portion of the tee. Re-install your vertical pipe. (You will have to cut down the top by the amount you added when the tee was installed plus/minus any changes due to the slightly moved location to repair the connection.)

Exactly match your old pipe top elevation. (Or you could change the height slightly if the families vote to slightly increase or decrease the normal pool level of the lake.)

Repair the broken connection. The length of the pipe below the broken connection does not matter (much). I assume there is some sort of splash pad below the vertical pipe opening to avoid erosion when your pipe is running water out of the top. Make sure you don't move the pipe off of your splash pad. (Or if you need to move it to repair the connection, it may be cheaper to expand the splash pad rather than make an excavation to install the pipe exactly as it was before.)

When you want the pond to siphon down, just open the valve at the tee. If you are there to observe, you can use that valve to partially pull down the lake to any level that your desire.

Good luck,
Rod