Thanks for your input. The pics are actual photos that I took of my existing erosion problem. The drawings are two of several that I made using an old version of Shetchup,
primarily, to get NRCS's opinion of the possible solutions.
The pond is 19 years old , and overflow water always dispersed and spread out over a large brush and high grass area to a drainage ravine that runs to bottom of the property
and into a creek that borders the south boundary of the property.. The current problem showed up a year and half ago. The first pic shows the initial attempt to fix the problem.
Small rain events were never a problem , but 5" over soaked soil was too much.
The current 12" siphon pipe was set 20" too low when the dam was built, and if left on permanently would lower the pond to a level that would leave my floating dock setting in mud.
I try to open the pipe on large rain events , but sometimes it's a hit and miss situation. My current thinking is to install two 36" hdpe culvert pipes , requiring six 20 ft sections..
That would allow ~14 sq ft to void water flow. Incidently, the concrete structure in photo would allow 15 sq ft with a 5 ft spillway and 3' high walls. Regardless, permanent fixes
will probably have to wait for summer when the ground is bone dry.