# Surface runoff

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1. Jun 30, 2017

### fonseh

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. Jun 30, 2017

### Baluncore

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.

3. Jun 30, 2017

### fonseh

why ?
here it is

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4. Jun 30, 2017

### Nidum

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 .

5. Jun 30, 2017

### Baluncore

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
6. Jul 14, 2017

### CWatters

+1

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.