Hi Dean. You are taking me back to my limnology methods class text book. For determining outflow of your pond you basically have to determine the cubic feet of water per second leaving the pond. 1 cu ft per sec is about 450 gallons per min. For a flow rate of less than 1 cuft/sec then gal per min is used. Obviously the volume of flow leaving your pond will vary widely depending on inflow, rainfall and watershed. IMO you should estimate the outflow several times during the year to get some sort of an average flow rate.
Simplest and easiest way to measure your pond's rate of outflow is to measure the time it takes for a float to pass over a selected section of outflowing water (channel). I suggest use 3, 5 or 10 ft of distance to time in seconds how long it takes for the float to traverse the distance. If the outflow channel water is deep enough,,, the best float to use is a fruit such as an orange that floats mainly under the surface or in the link below a capped bottle with weight such as gravel in it . Ideally you want the main part of the float to be under the surface because an item floating on top of the water will usually move differently than the deeper water. In your case you can use a surface float if the water is shallow. We want just a ball park estimate for you.
concrete overflow that has a constant flow of water going over it.
flow rate cuft/sec = ave width of channel ft X ave depth ft X 0.9 X float length tested as seconds for float to move through section
Example 2ft X 0.166ft X 0.9 X 2ft / 2sec = 0.59 cuft/sec - 450g/min X 0.59cfs = 265 gal per sec. (265X60sX60mX24hr) equals 22,296,000 gallons outflow per day
Pond volume 5 ac X ave depth ~4.5ft = 22.5ac ft. 22.5 X 325,850 gal/acft = 7,331,625 g. Retention time = 0.328 days or it is every 7.8 hrs
With this amount of retention time the pond will never develop a very big plankton bloom - too fast or too much flow through. Fish feeders would be required to grow a high quality fishery in this situation.
See the information in this link for several other ways to calculate flow in a small stream. Be creative. If the flow is not very large then try the stream blockage method and put a pipe through a dam that you build. Collect water going out the pipe in maybe a 55gallon barrel.
https://www.fao.org/fishery/docs/CDrom/FAO_Training/FAO_Training/General/x6705e/x6705e03.htmCommentary - Dean - you say "I have been working on developing this pond into a possible trophy bass pond with fish in the double digit range. The pond is 5 acres and has a constant flow. The pond is always full. Maximum depth is around 9' with the majority of the pond being 5' to 6' deep." And " The fishery guy that surveys my pond and supplies my fish recommended that I not lime the pond because of the amount of flow through that I have so I have not. I asked him recently about fertilization and he strongly discouraged that as well. I have owned the pond for almost 4 years and do not think that I have ever seen a plankton bloom. Is this common or am I just missing something? I have a water clarity of around 40" and the water usually has a brown tint to it most of the year."
First thing to do is use the above information to try figure out an actual flow rate and retention time for the pond.
Second if flow is high then IMO you should pattern your fishery similar to that of Richmond Mill. First thing probably to do is add a couple fish feeders at 1 per acre (5 feeders for 5 ac). This will boost overall pond productivity that would be equivalent to a plankton bloom.
Thirdly get some good ideas of how to manage the fishery for your goals. You may want to modify your fishery goals based on realistic features or characteristics of the pond. We here at the forum could help provide some options for an improved fishery in your type of pond. I have some information that I can provide of what it takes in time money and effort to grow trophy bass. I see that B.Lusk has a new podcast for growing trophy bass. See link. Maybe you want to adjust your fishery goals based on the characteristics of the pond?
