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Homework Help: Surface runoff

  1. Jun 30, 2017 #1
    1. The problem statement, all variables and given/known data
    In my book , i was told that when the drainage of surface is high then the surface runoff will be low . However , i dont think it's correct .

    2. Relevant equations

    3. The attempt at a solution
    Definiton : Runoff can be described as the part of the water cycle that flows over land as surface water instead of being absorbed into groundwater or evaporating.

    I think that when the surface drainage is high , more water will be drained from the particular surface to another . This results in more water absorbed , resulting in higher surface runoff , correct me if i am wrong .
  2. jcsd
  3. Jun 30, 2017 #2


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    You have not given much context here. Are you modelling rain water flow over soil?
    The exact wording is very important.

    If the drainage into a surface is high, then there will be less to run off that surface onto another.
  4. Jun 30, 2017 #3
    why ?
    here it is

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  5. Jun 30, 2017 #4


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    Assuming natural ground with no pumping systems then any water flowing into a particular region can only do one of four things - accumulate , evaporate , soak in or run off to somewhere else .
  6. Jun 30, 2017 #5


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    The term Drainage is being used in two different ways.
    "Surface drainage density" is a different concept to "surface drainage". They are in effect perpendicular.

    Well-drained or poorly-drained is being used to describe the ability of a surface to absorb water vertically into a porous surface.

    "Drainage density" is defined as the length of horizontal surface channel per unit area that carry runoff.

    A well-drained surface is porous. Because it absorbs water, there is less water available to runoff and so there are less surface channels needed, which implies a lower surface drainage density is needed.
    Last edited: Jun 30, 2017
  7. Jul 14, 2017 #6


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    Wikipedia defines "Drainage Density" as..
    "Well drained material (porus) has a lower run-off potential" .- eg the water soaks into the ground therefore fewer rivers and streams form so drainage density is low

    "Poorly-drained material (non-porus) has a higher run-off potential" .... the water runs off because it can't soak into the ground. Therefore more rivers and streams are formed so drainage density is high.
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