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GW storage
exploring how aquifers store water
Question | Answer |
---|---|
what is compressibility? | material property relating the change in volume per unit volume to the applied pressure (or stress) As pressure increases, volume decreases proportionally |
what causes changes in the volume of the porous medium as a result of compression or expansion? | 1. water or air in voids 2. solid grains 3. aquifer matrix (solids-voids framework) |
what is effective stress? | forces across grain to grain contacts pore water pressure |
what is consolidation? | the collective reorientation of soil grains & reduction in pore volume |
what is specific storage (Ss)? | Volume of water released from storage per unit volume of porous medium per unit decline in hydraulic head Water is released by the: 1. Expansion of water (βw) 2. Consolidation of the matrix (α) higher for clays & lower for sands |
what is storativity (S)? | represents the volume of water released from storage per unit surface area per unit decline in head involves vertical thickness of an aquifer |
what is specific yield (Sy)? | water is released by fluid expansion and matrix compression (as in the saturated case), but the pores themselves also drain drainage in this case = specific yield Sy = n - Sr coarser material, more closely Sy approaches n |
what is Sr? | specific retention; ratio of the volume of water a soil retains after gravity drainage to the total volume of soil (Sr = Vr/VT) amount of H2O retained after drainage = fun of cap. forces |
what are the differences between confined vs unconfined storage? | S = Sy + b∙Ss (unconfined); subjected to specific yield S = b∙Ss (confined) |