It never amazes me to see people trying to drive through a foot-and-a-half or more of rushing water. It doesn't take much to move a car or knock someone off their feet. In San Diego, the local TV news used to show one low spot that flooded in a heavy rain in Fashion Valley by one of the malls. Now, whenever we have a heavy rain, the police put up barricades to prevent people from driving across it.
It's amazing, and it requires one does ones roadside math correctly as well.
I drove through four spots which was exactly as bad as the one in the TV clip. The one in the clip was the last one.
I wasn't born yesterday and fording streams is not a new thing for me. It's what Fords are made for, although Dodge pickups cross rivers and streams fairly well too.
At each of those spots where water was flowing over the bridges I would pull off and watch other cars and trucks first to assess when it was time for me to proceed. And by then I would have the route plotted in my head to get through it after having considered currents and depth. Watching other cars is how I knew where and how the currents were affecting the cars.
When I drove through those spots they were all exactly the same insofar as depth because I was in essence measuring the depth before I tackled it, waiting for the waters to recede to the point it was safe for my car. I measured the depth by watching other cars with the same sized tires as my car had, watching for how high the water was in comparison to the tire height. The maximum safe depth for my car in moderate current is 1 1/2 feet. I had to worry about that because my car would float.
Floating is bad. One never needs to worry about that with a Ford pickup when fording streams. They leaked so badly that if one drove into water deeper than the floor boards ones feet would be standing in water almost instantly, and because of that a Ford simply would not float. That means they were ideal for fording rivers and streams when I was growing up.
We had a Dodge because Henry was such an anti-Semite we wouldn't own one of the bastards pickups. It leaked pretty good too. One time I got in a bit too deep when fording the Dolores River just west of the town of Dolores. The way I figured that out was I had water up to my crotch, it was cold. That ford is now at the bottom of a lake, they built a dam down stream of that county road ford. So it's gone now.
My car's clearance, the height of the floor boards is about 7 inches. But as the car is lifted the tires descend on the springs about 6 more inches. If the floor boards get a foot under the water level the car would car have the buoyancy to completely float free of the bottom. The way I know that is I estimated full buoyancy, 6 x 10 x 64 x (X) = 3800 lbs the weight of my car. It turns out X = 1 foot which is 12 inches. That's a fun equation to solve in ones head along the roadside in the pouring rain.
So in order for the body of my car to be lifted all the way up enough for the tires to still touch the bottom and still have enough traction, the floor boards would have to be about 6 inches under the water level. So for the water to be of a depth where the tires still touch bottom with enough force, (half the weight of the car), to still have some traction to resist currents, 6+7+6 = 19 inches. I rounded that down to a foot and a half for added safety margin.
Knowing that one cubic foot of water weighs 64 lbs is something I use all the time. It is a very useful constant to be aware of and have memorized if one is a sailor or a one owns a water well. Water pressure at depth can also be calculated using it. Or the amount of pressure a pump will need to develop in order to be able to lift water from a well.
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