hydrogeologic settings for fractured rocks. sheeting joints in granite yosemite,ca unloading...
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Hydrogeologic settings for fractured rocks
Sheeting joints in graniteYosemite,CA
Unloading fractures in graniteScottsdale, AZ
Fractured graniteFlorissant, CO
granite batholith, NE WI
Lineaments in granitic terrain(taken from plane)
granite, Albuquerque, NM
vertical foliation, eastern US
vertical foliation, Black Canyon of Gunnison
metavolcanics, central WI
Fractured crystalline rock, Alps
Precambrian quartzitecentral WI
Columnar jointed basaltsEastern, OR
Devil’s CausewayIreland
Volcanic mudflowClarno, OR
Dipping carbonates, Pyrennes
Fractured dolomite, Germany
Canyonlands, Utah
sandstone, SE WI
sandstone, Arches
sandstone, Kansas
clayey till, NW WI
Fractures Fractures — mechanical breaks in rock
• fracture is a term used for all types of generic discontinuities
Joints — dilating fractures; formed under tension Shearing fractures/faults — formed under
compression• surfaces move predominantly parallel to each other
Closing fractures/pressure solution surfaces
Fracture Network Geometry
Comparison of aquifer types Granular Fractured
Effective Mostly primary Mostly secondaryPorosity intergranular pores concentration of joints, fractures
bedding plane partings
Flow Slow, laminar Possibly fast & turbulent
Isotropy More isotropic Probably anisotropic
Homogeneity More homogeneous Highly heterogeneous
Flow Darcy's law Darcy's lawusually applies may not apply
Head Minimal variation Can be “flashy”
Water Chem Minimal variation More variation
Characteristics of Fractured Aquifers porosity is primarily secondary hydraulic conductivity distribution is very heterogeneous
• ranging over several orders of magnitude• may be bimodal• frequently anisotropic
flow paths rapid flow in fractures, slower paths in matrix blocks
flow rates may be rapid and difficult to predict recharge ranges from focused (point) to dispersed
(diffuse) storage is primarily from matrix blocks
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