I didn't find exactly what I was looking for above, but this website
Estimated Monthly Streamflow Entering Chesapeake Bay shows quite a bit of data.
The link above is for 2010 compared to long term averages, above normal, and below normal. You can use the right-left arrows to look back about 30 years at the graphs, and they stay pretty consistent.
I believe that the Chesapeake Bay Watershed very accurately represents the expected average water levels throughout Virginia.
As I mentioned above, the lowest periods are basically July through September -- and from personal experience, that is really from about the second week of July through the second or third week of September.
If I was going to build a new pond, that would be a good time to start moving dirt.
In the eight years we've owned this place, our pond/s have generally always been above full pool until early July, and are back at full pool by around mid October. Except for this year, they have always been below full pool from sometime in July to sometime in late September.
Ken
