Marshall
Turtle Keeper + CPL(H)
I finished the flood barrier and re graded the reservoir spillway a few days ago and tested it yesterday and today (test takes 2 days) and it passed and worked much better than expected. In a flood situation like the one I experienced the only failure would be the spillway and whatever topped the dam so for the test I removed all the breaks from the spillway and opened the dam completely as this is 8 to 10 times more water than would occur in a real accident. For the first part of the test approx 12,000 gallons of water rushed the flood wall in less than 5 minutes creating a wave about 2.5' tall and the barrier stood strong and diverted all the water into the guide trench with not even a drop making it to the pond area. The second half of the test was to lower the dam to 1/3 its normal height in order to allow a large amount of water to flow through the spillway, barrier gradient and diversion trenches for a sustained amount of time (24h). The spillway did not erode even with most of the anchoring stones removed and there were no eddy formed around the barrier either. I am going to put the dam back together today and put the rocks back into the spillway so I can test the emergency water supply system which is simply a gravity fed 8" underground pipe that allows me to divert water from the reservoir into the pond(s) for emergency leaks and regular water changes. I will take some pictures after I get everything back together and the video of the first test is scheduled to upload from my server to YouTube later today so I will post that as well. I also took heed of the advice 
that was given to me from here to not go any deeper than 4 feet or so in the koi pond so I only used the original plan of 5 feet sloping to 8 feet in the turtle only pond because in order for them to survive winter you have to add about a foot of silt/mud in the bottom so after all is done the actual depth ends up being approx 4.5 to 5.5 feet deep from floor to water level.
PS: The amount of pressure that the flood wall withstood was in the neighborhood of 15,000 to 20,000 gallons over an hour or so until the reservoir had drained off enough that only the flood gates were releasing water when the water level got down to the same height as the dams foundation which is about 2 feet tall when the upper slabs are removed.
that was given to me from here to not go any deeper than 4 feet or so in the koi pond so I only used the original plan of 5 feet sloping to 8 feet in the turtle only pond because in order for them to survive winter you have to add about a foot of silt/mud in the bottom so after all is done the actual depth ends up being approx 4.5 to 5.5 feet deep from floor to water level. PS: The amount of pressure that the flood wall withstood was in the neighborhood of 15,000 to 20,000 gallons over an hour or so until the reservoir had drained off enough that only the flood gates were releasing water when the water level got down to the same height as the dams foundation which is about 2 feet tall when the upper slabs are removed.
[my main reason for refusing one in the UK ].....