The scaling of hydraulic conductivity in rock fracture zones

Beyond the scale of a few meters, fracture traces as viewed on aerial photo graphs represent fracture zones. Thus for bulk fractured rock permeability, the hydraulic properties of fracture zones are important. Here, observatio ns on joint zones in sandstones from western Norway are used to build a qua ntitative model relating joint zone length and effective hydraulic conducti vity. Using simple rules for hydraulic conductors in series and parallel ap plied to joint zone geometry, the 'effective' hydraulic aperture (the apert ure of a single parallel-walled channel that conducts the same flow) is est imated for 72 joint zones of known length. A power law relation between tra ce length, l, and effective hydraulic aperture, b(e), with an effective exp onent of around 0.27 is found which may extend to kin scales. This exponent contrasts with values of 0.5 to 2.0 reported for veins.