Darcy’s Law
- Darcy’s Law is the generalized relationship for water flow in porous medium. It shows the volumetric water flow is the function of the flow area, elevation, fluid pressure, flow length and proportionally constant.
- It may be stated in different forms depending on the flow condition. It was established in saturated flow condition; however, it may be adjusted to the unsaturated and multiphase flow.
- Darcy’s Law states that the rate of water flow (Q) is directly proportional to the cross-sectional area of flow and to the hydraulic head drop and inversely proportional to the length of soil column.
Darcy’s Law for Horizontal Saturated Flow
The saturated flow in horizontal column is illustrated in figure. When the soil is subjected to the hydraulic potential head difference (ΔH) as shown in figure , with head at both ends of soil column maintained at constant, the steady flow occurs from left to right, the hydraulic head gradient across soil matrix will be
Where, Hi is the hydraulic head at inflow and Ho is the hydraulic head at outflow of soil matrix;
L is the length of flow or soil matrix.
In horizontal flow, the gravitational head is constant everywhere in the soil system and the pressure head is the only driving force. In this case, total hydraulic head at inflow and outflow will be equal to pressure head (Hpi) at inflow and pressure head (Hpo) at outflow. Then, the hydraulic gradient will be