Runoff from the Researcher Perspective (2-D Processes)

In InterWET, the runoff from the researcher perspective gives a two dimensional view or process level view of runoff using the SCS-CN Method.
 

1.Runoff Calculator.

Click the button below to load the Runoff Calculator.



The calculator can be resized for your screen.

Runoff is driven by precipitation. Whenever there is a precipitation event, there is a chance that runoff will occur. The two main things that control runoff is the land cover and the soil. Runoff and infiltration do a balancing act. If the water can get to the soil and the soil can adsorb the water, then there will not be runoff. But, if land cover does not let water get to the soil (like paved) or the soil is full of water, then there will be runoff.


2.Effects of Land Cover

Set the rainfall to 3.0 inches, Land Cover to Forest, Soil Infiltration Rate to High, and Soil Moisture to Dry.

Before you hit calculate, what do you expect?

Now hit the calculate button. Since this soil has a high infiltration rate, is dry, and has a forest land cover, all the rain is infiltrated.

Now use the same values and change the land cover until you get runoff. Be sure to hit calculate each time. Clear will reset all values.

Notice that land covers are arranged in order of increasing runoff amounts.

3.Effects of Soil

Try changing only the soil infiltration rate or only the soil moisture, but keeping the others at the 2. levels.

Noticed that not much runoff occurred unless at low infiltration, wet soil moisture or row crop or parking lot land use.

4.Effects of Precipitation

Set rainfall to 3.0 inches, Residential land cover, Low infiltration rate, Moist soil moisture and click calculate.

About half of the rain becomes runoff. Now vary the rainfall amount. Notice how the runoff becomes a higher percent of the rainfall when the rainfall values go up. For instance, at 10 inches of rainfall, over 75% will be become runoff.

Summary

Runoff goes up when:
1. Land Cover allows less infiltration,
2. Soil infiltration is lower,
3. Soil moisture is higher.

More Details?

Check out the on-line dissertation on InterWET for more information behind the theory and techniques used to make this calculator.


 
 

Back for Water Resources
Back for Perspectives
Home
Next for Water Resources
Next for Perspectives

 

Questions or Problems? Let me know at parson@andassoc.com.
Last revision 9/9/01.
Created by Shane Parson, Copyright 1999.