Are there an legal issues diverting the stream water? Are there any issues with the effluent from the pond?
It's important you determine gpm in minimum and maximum flow depending on the season. If it was me I wouldn't gather as much factual data as possible before you start digging.
For me a rule of thumb for earthen ponds is 12 lbs. max of carrying capacity for trout per gpm of flow. That refers to the maximum pounds you think you will end up with vs. the lbs. you plant. However there are ways to increase carrying capacity without increasing flow as in the use of a a biofilter and clarifier if your water does not warm up too much. You can build them yourself and have them out of view for better aesthetics.
Smaller is better for keeping the water cool and and increased exchange rate. A liner could be the ticket as in preventing serious seepage problems and moving the suspended solids out faster. However they have a downside too. That is, there is less nitrification going on on the bottom with a liner vs. a natural bottom.
Is there anyway to contact the person that owns the trout pond in the video and get information from him or her? Usually if one is doing this for recreational purposes they are happy to share information. My guess is the pond is not only flow through but recirculating water through a biofilter and clarifier, but I could be wrong.
An economical book called Small Scale Aquaculture by Stephen Van Gorder is available that has a chapter on building a trout pond. In my honest opinion the low price of this book justifies just one chapter on trout ponds. It also covers the construction of bilofilters and clarifiers to save you lots of bucks. I recently built one myself.
http://www.altaqua.com/order.htm As far as 3 gpms supporting 300 trout that depends on the size of the trout. The weight of the trout is more important than the number and is closely tied into the amount of feed that will go into the water and subsequent waste products. Three things to consider in a trout pond:
1.) Water temperature (55 to 65 optimum)
2.) Oxygen levels (at least 5 ppm but higher more optimum)
3.) Ammonia, specifically unionzied that has to stay below a certain amount or your fish will have problems. You don't want your ammonia to go above .025 mg/l with trout. Higher temps and a higher PH will cause your unionized ammonia to spike higher.
Number's 2 and 3 are directly effected by the lbs. of fish and the amount they are fed.
Ammonia levels are lower in lower temps of water but oxygen is inversely proportional to water temperature. That is colder water holds more oxygen.
Here's a brookie out of my trout pond a few years ago a friend of my mother caught.
