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Mandelon
04-01-2005, 08:48 AM
A customer of mine has a flood control channel that runs through his back yard. He lives in Crest. After the big fires out there, the ground cover was gone and the rains brought down tons and tons of silt and sand down into the channel.
The big rains caused his house to flood, his back yard to become a swamp and his swimiming pool to float up out of the ground. You may have seen him in the SD Newspaper or on the news.
His insurance companies' are trying to deny him coverage as is the County who supposedly is supposed to maintain the channel. He even works for the County....
Anyway the insurance co adjuster says that even if the channel was empty it could not have handled the flow...... :confused: We want to determine what flow could have been carried in the channel.
It is a concrete lined Channel, with vertical sides that rise 7 courses of 8" block. It is 6' wide. He is trying to determine the gradient of the downhill slope now. There will be some loss due to friction from the cinder block. It is several hundred yards long.
Anyone have a clue on how to determine how much water can run down this?
Thanks.

Tom Brown
04-01-2005, 08:50 AM
Where's hoolign when you need him?

Captain Dan
04-01-2005, 09:19 AM
A customer of mine has a flood control channel that runs through his back yard. He lives in Crest. After the big fires out there, the ground cover was gone and the rains brought down tons and tons of silt and sand down into the channel.
The big rains caused his house to flood, his back yard to become a swamp and his swimiming pool to float up out of the ground. You may have seen him in the SD Newspaper or on the news.
His insurance companies' are trying to deny him coverage as is the County who supposedly is supposed to maintain the channel. He even works for the County....
Anyway the insurance co adjuster says that even if the channel was empty it could not have handled the flow...... :confused: We want to determine what flow could have been carried in the channel.
It is a concrete lined Channel, with vertical sides that rise 7 courses of 8" block. It is 6' wide. He is trying to determine the gradient of the downhill slope now. There will be some loss due to friction from the cinder block. It is several hundred yards long.
Anyone have a clue on how to determine how much water can run down this?
Thanks.
I'm a civil engineer - I can calc the flow for you, but I will need the slope on the channel. Also, what is the botton made of? Rough or smooth? Is it a free outlet, or something there that could back up the flow?
Even if you know how much the channel will take, what are you comparing it against? Has someone prepared a hydrology study to quantify what flow should be tributary to the channel? What I'm getting at here is that calculating what the channel can carry is only part of the story.

Mandelon
04-01-2005, 09:36 AM
I will forward your questions to Edgar, the fellow with the troubles. Thanks!!
The bottom was smooth.

Captain Dan
04-01-2005, 09:49 AM
Without the entire story, here are some ballpark numbers for you:
Assume:
rectangular channel, smooth concrete bottom 6' wide
sides are 7x8 = 56" = 4.7 feet high
assume flowing full, (to the 4.7 foot mark)
no obstructions downstream, (no backwater effect)
assume manning's n=0.017, conservative (in case anyone asks)
if channel is at 0.5% longitudinal slope, flow conveyed is 260.9
if at 1%, flow is 369.0 cfs
if at 1.5% flow is 451.9 cfs
if at 2%, flow is 521.8 cfs
cfs = cubic feet per second
a burned area bringing down silt will silt up the channel and impede on the channel's abililty to convey these flows

Mandelon
04-01-2005, 09:55 AM
Thanks Cap'n !

CornWater
04-01-2005, 10:08 AM
Without the entire story, here are some ballpark numbers for you:
Assume:
rectangular channel, smooth concrete bottom 6' wide
sides are 7x8 = 56" = 4.7 feet high
assume flowing full, (to the 4.7 foot mark)
no obstructions downstream, (no backwater effect)
assume manning's n=0.017, conservative (in case anyone asks)
if channel is at 0.5% longitudinal slope, flow conveyed is 260.9
if at 1%, flow is 369.0 cfs
if at 1.5% flow is 451.9 cfs
if at 2%, flow is 521.8 cfs
cfs = cubic feet per second
a burned area bringing down silt will silt up the channel and impede on the channel's abililty to convey these flows
Hmmm... another dirt nerd, now I don't feel so all alone.. :D

Captain Dan
04-01-2005, 11:00 AM
Hmmm... another dirt nerd, now I don't feel so all alone.. :D
You are not alone. We all need to make $$ somehow.......