From the last blog post we saw water flow over a dam, yep it still stands. When we got home from shopping that morning I went straight to the pond to see how full it had gotten. The video is at the end of the post.
Here’s the deal if the rain fall is 1″ inch the pond will receive a 2″ raise. This only happens when the grounds around the pond are already saturated with water. If the ground is dry the results are 1 for 1 and sometimes less, again depending on how dry the ground is.
This particular storm dumped 3-4″ of rain and the ground was saturated double that and that is what the pond received and had to get rid of in case another storm hit.
In the picture you’ll see the normal level of the pond. In the video you’ll see the pipe under water. There is a point at which the size of pipe will no longer be able to handle the influx of water disposal. If the rain continued the spillway would be the next place for the water to exit the pond in a safe manner.
Do you have to use an overflow pipe? Not all the time but the spillway will need to be large enough to handle the biggest rain storm you ever heard of. Remember the spillway should be wide and the fall, taper or slope away from the pond should be gradual so the water can flow out slowly. Water running too fast could start erosion. Spillway can be seeded with grass, anti erosion screen or stoned to keep erosion from happening.
The height from the overflow pipe to the spill way and from the spillway to the top of the dam is also very important.
I am happy to say that the emergency spillway has never had water flowing across it. And have never had water over the dam. Part of the four 4″ pipes was to have an additional exit and to have a waterfall at the end so when coming home you could see the water fall and a tell tale sign if it had rained hard that day.