Thanks guys, good advice. You've given me lots to think about...
I am pretty sure of the flow rate, the State Department of Water Rights rates it as a 1/2 cfs spring, and the have allocated downstream water rights based on that flow. That would be about 225 gpm. I can drain about 80% of the water from the pond, it only takes about 24 hr for the pond to refill. I figure that's about 200,000 gallons of water in 24 hours, or about 140 gpm. So I think the 100 something gpm range is about right. The dredging guy who looked at it estimated 100 to 200 gpm looking at the overflow. The spring is headwaters for a small creek, used for livestock watering and irrigation downstream.
No real way to sample the spring water directly, water flows in from most of the bottom, seeps really. I did not dig the pond, that was done over 50 years ago. What I think they did was find a sand lense and just dug it out.
I have had some estimates to clean the muck, $17k for hydraulic dredging, less for an excavator. However the guy who I spoke to about the excavator warned me that it was possible excavating could create a channel to drain the pond... The dredger was giving no guarantees, and $17k is a lot to spend for something that might work.
I have probed the bottom, where the pond is deepest, about 8 ft of water. Below that there is probably 4 or 5 feet of soft muck before hitting harder material. So maybe the original depth was ~12 ft.
I honestly would not mind the cattails, better than the algae. My fear is I might end up with both. Is there a water depth limit on cattails growing? These seem to grow slower than the cattails I have in wet areas just north of the pond, maybe the cold summer water?
I put the aerator in as a lower cost attempt at algae control. The water turbulence it creates does help maintain a smaller algae free area, and probably slows the algae's recovery, but it's no cure.
