Fractured rock, water velocity

The Retention Factor. The water velocity v, [m/s] in fractured rock can be calculated from the basic flow equation... 

The velocity of contaminants may also be influenced by the diffusion of contaminants into dead space pores or fractures (where the ground water velocity is essentially negligible) or within grains. These processes may become significant in attenuating the movement of contaminants at sites where soil and rocks have been exposed to contamination for long periods. 

Matrix diffusion is another mechanism that causes mixing. The rock matrix is porous with a porosity Ep in granites of typically 0.1-0. 5 %. The water in the rock matrix is stagnant. Mixing between the flowing water in the fractures and the matrix water takes place by molecular diffusion. A water package in the fracture that equilibrates with the matrix water by molecular diffusion will be diluted. A contaminant pulse travelling in a fracture will be retarded in relation to the advective velocity of the water. 

Here, we assume a dipole fluid flow initialized by the infiltration of cold water in a hot rock and its extraction after the heating-up, see Fig. 4. A fracture with a stress dependent transmissivity is located in the front part of the domain. Due to the thermal contraction of the rock the transmissivity of the fracture increases. Fig. 5 shows the different velocity curves in the fracture and in the non-affected matrix. Fig. 6 shows the final temperature field in the deformed configuration. 

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