Infiltration
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Infiltration. Rainwater that soaks into the ground and may reach the groundwater table. Base flow:  Where Groundwater Meets Surface Water. Base flow is the portion of stream flow that comes from subsurface flow: water infiltrated but returned to the surface in a stream channel.

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Infiltration

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Infiltration

Infiltration

Rainwater that soaks into the ground and may reach the groundwater table.


Base flow where groundwater meets surface water

Base flow:  Where Groundwater Meets Surface Water

  • Base flow is the portion of stream flow that comes from subsurface flow: water infiltrated but returned to the surface in a stream channel.

  • Streams run even when it hasn’t rained.

  • Base flow is very important for fish, invertebrates, aquatic plants and other life during dry spells.


Field tests

Field Tests

  • Infiltration is measured in the field with bottomless rings. Mariotte Tubes allow for measurement of liquid flow during the infiltration test by providing a constant water level in the 24 inch Infiltration Rings

24 inch double ring infiltrometer with Mariotte Tubes http://www.hilbec.com/STORMWATER.htm


Double ring infiltrometer

Double-ring Infiltrometer

  • Two rings eliminates overestimating the hydraulic conductivity

  • Outer ring contributes to lateral flow , so

  • Inner ring is contributing mostly to downward flow.

  • Water from Mariotte bottles to rings via tap at base of bottles. Ring water height equals that of the base of the bubble tube.

  • When water moves into the soil, reducing the height of ring water to below that of the bubble tube, more water is fed into the ring.


Estimates 1 horton s equation

Estimates 1: Horton’s Equation

  • Horton: The infiltration capacity decreases exponentially with time and ultimately reaches a constant rate

  • Infiltration capacity

  • Where ft is the infiltration rate at time t;

  • f0 is the initial infiltration rate or maximum infiltration rate;

  • fc is the constant or equilibrium infiltration rate after the soil has been saturated or minimum infiltration rate; NOTE e is a number, ~ 2.718

  • k is the decay constant specific to the soil.

  • the f’s have units in/hr and k is a time constant hr -1


Infiltration

Horton’s Infiltration Model for soil capacity

Infiltration starts at a constant rate, f0, and is decreasing exponentially with time, t. After some time when the soil saturation level reaches a critical value, the rate of infiltration will level off to the rate fc.


Infiltration

In a few minutes we will do an example using Horton’s Equationusing an average rectangle estimate to the area under the curve.


Infiltration

Estimates 2: F index

Infiltration Volume = total rainfall volume – runoff volume as measured in the rain gages and at the outlet gage, respectively.

F assumes infiltration volume resulted from a constant infiltration rate. It assumes a high initial infiltration is balanced by a low later infiltration.


Infiltration

Example: GuessingF

We will find F in this problem by guessing a value for F , calculating the total runoff that would result, and comparing our answer to the known runoff.


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