For the barge to float and neither rise nor fall, there must be equilibrium of forces.
For it to float, the resistance of the water must be greater than the force applied by the barge, hence it will settle in the water, until it reaches that point where the resistance is equal and opposite to the pressure over the surface area of the barge in contact with the water.
So, take a solid ball of metal, say cricket ball sized and it will sink like a stone. Take the same weight of metal, make it in the shape of a barge over a larger surface area and it will float.
The displaced water must go somewhere, as it does not compress. So, the volume outside the footprint of the barge will rise; the amount that this rises depends on whether or not the water is confined (think of getting in the bath, as opposed to getting in a swimming pool). As the water has risen beyond the barge, then at its base, the pressure will be slightly greater.
There will be less water under the barge, so the water pressure alone will be less at its base; however, there is the pressure of the barge at the top of this water, so this must also be added to the base pressure, for equilibrium to exist. But, as the variation in height of the water is equal to the displacement due to the weight of the barge, there will be no increase in pressure at the base of the water, relative to the base pressure beyond the barge, although the pressure as a whole on the viaduct will have increased proportionally to the mass of the barge divided by the area of the viaduct.
Theoretically.
In reality, as the water is not confined, the water will actually have a slight slope in the water level as it runs away from the barge - to remain dead level, all the connected water in the world would have to rise instantaneously by the requisite amount - so the pressure will be slightly greater beneath and within the immediate vicinity of the barge, tailing off with an increase in distance from the barge. Thus, there will be some slight variation in pressure as the barge moves along.
For it to float, the resistance of the water must be greater than the force applied by the barge, hence it will settle in the water, until it reaches that point where the resistance is equal and opposite to the pressure over the surface area of the barge in contact with the water.
So, take a solid ball of metal, say cricket ball sized and it will sink like a stone. Take the same weight of metal, make it in the shape of a barge over a larger surface area and it will float.
The displaced water must go somewhere, as it does not compress. So, the volume outside the footprint of the barge will rise; the amount that this rises depends on whether or not the water is confined (think of getting in the bath, as opposed to getting in a swimming pool). As the water has risen beyond the barge, then at its base, the pressure will be slightly greater.
There will be less water under the barge, so the water pressure alone will be less at its base; however, there is the pressure of the barge at the top of this water, so this must also be added to the base pressure, for equilibrium to exist. But, as the variation in height of the water is equal to the displacement due to the weight of the barge, there will be no increase in pressure at the base of the water, relative to the base pressure beyond the barge, although the pressure as a whole on the viaduct will have increased proportionally to the mass of the barge divided by the area of the viaduct.
Theoretically.
In reality, as the water is not confined, the water will actually have a slight slope in the water level as it runs away from the barge - to remain dead level, all the connected water in the world would have to rise instantaneously by the requisite amount - so the pressure will be slightly greater beneath and within the immediate vicinity of the barge, tailing off with an increase in distance from the barge. Thus, there will be some slight variation in pressure as the barge moves along.
