What is the condition of the valve and pipe and does it drain from the pond bottom ? How hard is it to open and shut the valve ? Here is a link to drawdowns. We use drawdowns for several reasons. Keep in mind that as the water goes down the rate of water level drop speeds up unless the pond is shaped like a cube. For example it may take 3 days for the level to drop 6 inches , but it may drop 18 inches in the next 3 days. You do not want to draw down the pond from the top 3 feet of water at this time of year (absent aeration) as that is where your O2 and plankton is. We do ours around Oct. 1st.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=7;t=000287;p=1#000000

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=17;t=000082;p=1#000001