4.10 Problem Set

Hint for #4: Convert your water potential difference from head units (e.g. cm) to pressure units (e.g. Pascals [Pa] which is the same as kg m-1 s-2) for use in Poiseuille’s Law. To do that, first express the water potential difference in meters and use the fact that P = ρw g H where ρw is the density of water (1000 kg m-3) and g is acceleration due to gravity (9.81 m s-2).

  1. A saturated soil column contains two soil layers, each 10. cm thick, with sand having Ks = 10. cm h-1 underneath loam having Ks = 5.0 cm h-1, and 10. cm of water is kept ponded on the surface. The bottom of the soil column is open to the atmosphere and drains freely.
    1. Draw a sketch of this soil column.
    2. Create a table to determine the difference in hydraulic head across the column.
    3. Calculate the hydraulic resistance for each layer.
    4. Calculate the flux of water through the column using Darcy’s Law for layered soil.
    5. Calculate the pressure head at the sand-loam interface.


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