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%3Cp%3E%3Cimg%20class%3D%22user-upload%22%20src%3D%0A%22http%3A%2F%2Fmedia.cheggcdn.com%2Fmedia%252F3a6%252F3a6c310a-80a5-416c-84fd-325409cd097e%252FphprDSx8j.png%22%0Aheight%3D%22592%22%20width%3D%22463%22%20%2F%3E%3C%2Fp%3E%0A%3Cp%3E%3Cbr%20%2F%3E%3C%2Fp%3E%0A%3Cp%3E(a)%20Determine%20the%20amount%20of%20water%20that%20flows%20through%20the%20system.%0A(cubic%20feet%2F%20seconds)%3C%2Fp%3E%0A%3Cp%3E%3Cbr%20%2F%3E%3C%2Fp%3E%0A%3Cp%3E(b)%20Calculate%20Total%20Head%2C%20Head%20Elevation%20and%20Pressure%20Head%20in%0Apoints%20C%2CD%2CE%2CF.%3C%2Fp%3E%0A%3Cp%3E%3Cbr%20%2F%3E%3C%2Fp%3E%0A%3Cp%3EPlease%20Explain%3C%2Fp%3E%0AExplanation / Answer
I have to disagree with the post by Joachin Murrieta.
While permeability does of course play a role, it is not the only thing controlling water flow through soil. Porosity is the second factor. They must be evaluated TOGETHER.
Permeability only describes the connectedness of the air pockets in soil. Porosity describes the size of those spaces (air pockets) in the soil and can also describe cracks in otherwise solid rocks. A material needs to be both porous (with gaps between sediment or cracks) and permeable (the gaps or cracks are connected) to allow the most water to flow through it.
Shale and slate are two examples of impermeable rocks. The way they form leaves next to no empty voids (no porosity) and they're obviously impermeable with no gaps to even be connected. However, if these rocks develop cracks, water can enter through those voids. You could then consider them porous, but in order for these cracks to allow water to pass through the substance they must ALSO be connected. The substance MUST have both porosity and permeability.
This is true for all substances, not just shales and slates. The pores don't have to be gaping holes, just enough space for water to move through. Without pores, water cannot flow. And if there are pores, but they're not connected (like in a cork, for example) water cannot flow. The two factors taken together determine how easily water can flow through a substance.
Don't compare apples and oranges. If you want to look at water flowing through a sandstone, compare two sandstones - one made up of very fine grains of sand and another made up of coarser grains of sand. Water will obviously flow more easily through the coarser sandstone because the increase in porosity (bigger grains leave bigger spaces between them) will contribute to an increase in permeability when all other factors are kept constant.
FROM WIKIPEDIA:
"The porosity of a rock, or sedimentary layer, is an important consideration when attempting to evaluate the potential volume of water or hydrocarbons it may contain." One factor only and that is permeability if you have permeability the amount of porosity has no bearing on anything even if that fact seems counterintuitive. A 7% porosity dolomite with Cladiocoropsis-caused permeability of 5 darcies will transmit a whole lot more fluid than a 20% porosity sandstone with 100 milidarcies permeability.
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