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Joined: Jun 2010
Posts: 6
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OP
Joined: Jun 2010
Posts: 6 |
I have an 8 year old dam (3 acre pond). Dam is about 20 feet tall. Just had 6 inch rain in 3 days. Draining water fast as it could, emergency spillway never required. BUT I suspect water at least 18 inches higher than normal level. Right behind the down drain is suddenly a pocket of missing dam!! 3 feet by 4 feet and about 3 to 4 feet deep (to present level of the pond) at normal level. No obvious flow into the pocket but soil is fully saturated at least 2 feet below bottom of the pocket. No obvious leak on back side of dam but minor sink hole depression 10 feet below water level about 2x2 feet (I do not know if this is new but it is NOT wet). But no water seen on back side near this depression. What do I do? Venturi effect from drain and high water on the dam caused erosion where dam rip-rap was poor? Or is this how a dam failure starts?
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Joined: May 2014
Posts: 3,861 Likes: 298
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Joined: May 2014
Posts: 3,861 Likes: 298 |
Sounds like you need a dam pro to examine the situation, Chip. Especially if more rain is in the forecast!
7ac 2015 CNBG RES FHM 2016 TP FLMB 2017 NLMB GSH L 2018 TP & 70 HSB PK 2019 TP RBT 2020 TFS TP 25 HSB 250 F1,L,RBT -206 2021 TFS TP GSH L,-312 2022 GSH TP CR TFS RBT -234, 2023 BG TP TFS NLMB, -160
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Joined: Jun 2016
Posts: 2,344 Likes: 101
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Joined: Jun 2016
Posts: 2,344 Likes: 101 |
You'll, at least, get more opinions if you can supply some pictures. I am having a hard time imagining your situation with any confidence, but it seems like your drain pipe is washing out below the output and cutting back into the dam. I'm no expert and am having a hard time understanding what's washing out exactly.
Fish on!, Noel
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Joined: May 2011
Posts: 1,748 Likes: 33
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Joined: May 2011
Posts: 1,748 Likes: 33 |
You probably won't know until the water goes but it sounds like you have water that traveled next to the pipe and eventually washed out the dirt. This is just a guess.
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Joined: Jul 2008
Posts: 1,093 Likes: 1
Lunker
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Lunker
Joined: Jul 2008
Posts: 1,093 Likes: 1 |
I second what quarter acre says, a pic would be nice. sounds like you have a straight pipe thru the dam instead of a traditional L shaped stand pipe, right? when this event is over, i would recommend lowering the emergency spillway. I've always heard the e-spillway should be 1 foot higher than full pool and top of the dam should be 2ft higher than e spillway. 6 inches in 3 days isn't unheard of, it will happen again for sure.
Scott Hanners
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