Ponds and Water Gardens - Drain Culvert Fish Grate?

Does anyone have a good design for a drain pipe/culvert fish grate? Something to go on the infeed end of a 12" diameter pipe to prevent my larger fish from escaping my pond? I want something that will resist clogging from branches and leaves but still prevent larger fish from fitting through.



Here is the long story:

Last week we had heavy rains which of course raised the level of my pond so that water was flowing quite strongly out the drain culvert. Saturday (two days after the heavy rains) I went down to my firing range on the back side of the dam and saw one of my koi in pool where my pond drains. After 3 hours hiking through the woods I located 5 of my fish. I got 4 back into the pond alive (one was a prized 16") but some animal had gotten to one. I lost a 32", 16 pound koi I have had for 7 years.

It is amazing that any survived since this is the only way out of the pond.
http://i228.photobucket.com/albums/ee177/pilotdane/misc/Sluce1.jpg

I found two koi in the pool right at the bottom of the sluce, one about 300 feet down the creek in a deep pool and the last one I found alive was a solid 1/4 mile downstream. Not an easy hike through raw forest carrying a 24x30" plastic tub with 5 gallons of sloshing water and a fish.

I had always assumed I lost some fish through the culvert and have often seen minnows in the creek. I assumed since the koi did not spend too much time at the surface that my loss was minimal, but now that I know I've lost at least 5 through the pipe in just one rain event I am concerned. I'm probably loosing 30-50 koi a year. Unacceptable.

Add a 90 degree ell to the end of the drain with the free end turned down into the water and covered with hardware cloth. My 2 cents. Good luck with your project.

I would take some rebar and build a cage then cover that with fencing. 3/8 or 1/2 inch rebar and maybe 2x4 inch fencing. Build the top angled at 45 degrees so the sticks and such will roll off when they dry out.
For a 12 inch pipe I would think 14 inch square in the part over the pipe. Then 14 inches out from there, making the top 20 inches if my math is correct. I would add center braces on all sides except the back where it goes over the pipe.
Cut the fencing out near the bottom of the back to go over the pipe, so there is more over the pipe top. Then depending on the depth of the pond how you would mount the cover. I was thinking about metal t-posts on the 4 corners driven into the pond bottom. But if the pond is over 6 feet deep there the 8 foot post might be too short.
You could adjust the size of the fencing to better match the fish size. The larger the holes the better for water flow and no plugging from debris. Hardware cloth will plug up very quickly. Even with the 2x4 fencing it may need to be cleaned off often.
Or you could leave the pipe open and build a fence around the pipe with say 4 feet clearance all around the pipe. But that would have to extend to the bottom of the pond and say at least 6 inches above flood stage to prevent any fish from getting near the pipe.
This must qualify for at least 5 cents worth!

Different issue that may offer a solution.

Beaver problem, culvert, plugged culvert, beaver (http://beaverculvert.com/)

Search on Beaver Control for Culverts or similar phrases.

Bud

Thank you everyone for the prompt replies. All good ideas.

I would be concerned that anything right at the pipe might cause too much suction and hold the fish there until the water stopped flowing. I don't know how long a fish can live stuck to the side of a pipe.

I have welded up a "grate" that protrudes about 18" from the culvert to increase the surface area and minimize the suction affect. I spaced 5/16 stainless steel rods about 2" apart vertically. So far (only a few days) I have not had any clogging problems. I only installed the fish grate on the lower half of the culvert. If we get a heavy rain and the water rises the upper half is totall open.

Sounds like a good plan. Has the pond ever gotten higher than 1/2 way up the pipe anyways? Seems like that may be enough but time will tell. You can always add on if needed.

When the water gets half way up the drain culvert it starts flowing over the spillway (which is very wide) so I have never seen the culvert get more than 2/3 under water. I suppose I should put some fencing up on the infeed of the spillway when we are expecting heavy rains. The koi love to go exploring when the water is up.

Since I've been talking about my koi here is a baby picture of the fish I added to the pond earlier today. I started the pond with about 100 koi and try to add 30 to 50 every two or three years.

http://i228.photobucket.com/albums/ee177/pilotdane/2009/Animals/ThisYearsFish.jpg