[AT] OT Low water crossings

[Don Bowen]

My driveway crosses two little creeks.  They are usually dry except 
during storms when they can be as much as four feet deep.  After a storm 
it may take days for them to come down.  The first crossing is gravel 
and the previous owner had build a concrete and rock dam on the 
downstream side to control washouts.  The result kept the water over a 
foot deep for days after a small rain.  I cut a slot in the dam and now 
it drains down to about 6 inches in a day.

The second crossing is a concrete low water bridge with two culverts.  
usually within a few hours of a rain the water is under the concrete 
flowing though the culverts.  The problem here is that the culverts plug 
with gravel in heavy rains.  The reason is that who ever built the 
crossing has the outlet end of the culverts higher than the inlet by 
several inches.

I plan to take out the culverts and replace them with a single larger 
culvert properly installed.  What I need to know is how thick the 
concrete must be above a given size of pipe.  I am assuming that the 
larger the culvert diameter the thicker the slab over it must me.

As for the gravel crossing I want to build a concrete crossing.  I need 
to know what I need to do and references.  I have a good idea what is 
needed but I would like comments from those with experience.

You can see in this picture the right culvert is plugged.  The water at 
the inlet is almost at the top of the culvert.
http://www.braingarage.com/Dons/Travels/journal/May%2011/images/flowing.jpg

This is what it looks like after a heavy rain.
http://www.braingarage.com/Dons/Travels/journal/April%2011/images/flooded%20drive.jpg

And a heavier rain.
http://www.braingarage.com/Dons/Travels/journal/April%2011/images/flooded%20drive.jpg

The gravel crossing after a rain before I opened up the dam a 
little\http://www.braingarage.com/Dons/Travels/journal/January%2011/images/summer.jpg


-- 
Don Bowen           KI6DIU
http://www.braingarage.com/Dons/Travels/journal/Journal.html