Basic Criteria for Drawing Graphical Flow Nets

• Darcy’s Law is valid
• Hydraulic conductivity of the material is homogeneous
• Hydraulic conductivity of the material is isotropic
• The material is fully saturated
• Flow is steady
• The fluid has constant density
• The fluid has constant viscosity
• The vertical and horizontal axes are drawn to scale.

Steps for Drawing a Flow Net Using Pencil and Paper

1. Draw the outline of the flow system to scale and label the nature of each boundary
2. Draw equipotential lines along the boundaries where a single value of hydraulic head is specified along the boundary
3. Draw flow lines along no-flow boundaries
4. Within the flow domain, draw flow lines along paths where you envision groundwater flowing, ensuring they are perpendicular to equipotential lines on the boundaries
5. Draw equipotential lines within the flow domain, ensuring they:
   • are perpendicular to no-flow boundaries;
   • are perpendicular to flow lines; and,
   • together with flow lines, form shapes of constant aspect ratio, preferably “curvilinear squares.” A curvilinear square is a four-sided shape with curved edges and an aspect ratio close to one.
6. Calculate the contour interval and label the equipotential lines
7. Calculate flow through the net using the equation for total discharge through a flow net which is presented in Section 2.4 following the description of the procedure for drawing a flow net.