What is the theory behind flowlines and equipotential lines

What is the theory behind flowlines and equipotential lines meeting at 90 degrees? Can you explain why this happens?

Solution

The flow net in the seepage of water through a soil medium is a network of flow lines and equipotential lines. The flow net is used to determine the seepage flow, hydro-static pressure, seepage pressure and exit gradient. A flow line or stream line in a seepage through a soil medium is defined as the path of particles of water through a saturated soil mass. The equipotential line in a seepage through a soil mass is defined as the line connecting the points of equal head of water. The direction of seepage is always perpendicular to the euipotential lines. The flow lines and equipotential line are intersecting lines at 90 degree to each other. beacause the upstream and downstream surfaces of the permeable layers are equipotential lines.So, this is the first boundary condition. Now second onde are equipotential lines all the flow lines intersect them at right angles. It has to be right. So, that is the important criteria for flow lines and equipotential lines to be constructed.So, the boundary of the impervious layer is a flow line right. Because you are considering the flow line, the flow can occur along the line. So, is the surface of the impervious sheet pile. So, this line is also a flow line. So, flow can occur. Flow cannot occur across the sheet pile but it can occur along that line.So, it is one of the flow lines. Now the equipotential line intersects at right angles. So,equipotential line whatever equipotential line is cutting or intersecting the line as well as they will be making 90°. So, these are the things that must be satisfied.