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| I think that natural river bed has a couple details important to it not filling. First there's smaller and smaller gravel on top down to a layer of sand that acts as the dirt retainer. Over time the gravel has been graded into several layers from the largest rocks on the bottom to the finest sand on the top. Then the top layer of sand has a layer of a clay virtually impervious to water that further caps the sand. And so the gravel is getting water from below, not from above.
It started out many millenia ago relatively uniform, but the fines in the gravel washed downstream.
Gerald J. | |
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Field drainage with gravel instead of tubes?
