Unit 11

Unsaturated subsurface flow

This unit discusses the basic principles of unsaturated subsurface flow as part of the lithospheric path of the water cycle.

Goals

The goals of this unit are to apply the known concepts of surface tension, capillarity, hydraulic conductivity, and pressure to the soil matrix, introduce Darcy’s Law and the general unsaturated flow equation, to describe and explain the behavior of saturated and unsaturated subsurface flow of water. A further goal is to explain how to make soil moisture and subsurface flow measurements.

After successful completion of this unit students will be able to

  1. Explain and determine surface tension, soil capillarity, soil hydraulic conductivity, and soil pressure
  2. Apply Darcy’s Law and explain the general unsaturated flow (equation)
Liquid water flow through soil pores and in water films coating soil particle surfaces. The water flow rate depends on soil water potential (Ψm) gradients due to differences in height, pressure, dissolved solutes and soil moisture. Diagram from: https://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_water-water_flow.html (retrieved 2018)

Students’ tasks

  1. Read Dingman’s Chapter 7.4 to 7.4.7(included)
  2. Take notes
  3. Fill out the questionnaire before Thursday 2359 Alaska time
  4. Download this excel spread sheet for unit 11 on your laptop.
  5. Solve the tasks assigned at your class level in this Unit 11 Applications sheet and submit your scanned results by Thursday 2359 Alaska time

Additional resources

This Soil Triangle and Tests handout  is a helpful resource for determining the soil type in theory and practice.

Just for fun

Goto https://websoilsurvey.nrcs.usda.gov/app/ and download the soil data survey of Alaska. Read the descriptions of typical soil profiles and identify information about hydrologically critical properties in such as porosity, hydraulic conductivity, depth to water table, presence of impermeable layers, etc. for
a. Southwest Alaska
b. Yukon Flats
c. North Slope
d. Anchorage area
e. Panhandle
What do you find about Alaska’s soil distribution?

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