Passing by Disney World on I-4, I noticed a new series of concrete dams placed along the wide Interstate ditches there. They are about 300 yards apart, but differ in that the "dams" are engineered with a 10" empty space in the middle—top to bottom.
The effect on floodwaters is to make a series of temporary
huge holding ponds, but allow floodwaters to pass through and gradually permit the holding ponds to drain out.
Around Lake Winnipesaukee's many hills, it seems that the same principle can be applied to the many culverts associated with hillside lots. That is, rather than place the usual single culvert, stack two or more smaller culverts to create the same temporary roadside holding ponds: Silt-laden floods would be delayed from rushing to the lake.
Quote:
Originally Posted by SIKSUKR
Why would crushed stone be considered impervious?It is used for exactly the opposite purpose in drainage situations.
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As
krm advised, the stones fill up with "fines".
The top photo is of a developer's deep ditch filled with "rip-rap". As can be seen, grass has started growing in from the right side. Since this 2007 photo, after only three years in existence, this ditch is now 60% full of sand!
The bottom photo shows (
I think) the futility of using rock to stop erosion on a collapsed lakeside shoreline.
Note the stumps to the right, and one eroded stump to the left. The loss of cover precipitated another mature tree's fall into the lake. Due to loss of tree cover (leaf "canopy") there are about a dozen collapsed shorelines within an afternoon's paddle from my place. Some are
many times higher and wider than this one.
