Week 5: Water Retention and Movement in Soil and Solute Transport

Question 1

Volumetric water content

Answer 1

Volume of water in the sample over the volume of the wet material.

Question 2

Gravimetric water content

Answer 2

Mass of water over the mass of the substance.

Question 3

Porosity

Answer 3

Volume of pore space by total volume – is dimensionless.

Porosity = specific yield (Sy) + specific retention (Sr)

Question 4

Tension

Answer 4

The elastic-like force existing in the surface of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid. Minimises surface area.

Question 5

Available water

Answer 5

The water available for plants to use.
Given as a fraction between field capacity and the permanent wilting point.
As plants use this water the stress on the plant increases and growth diminishes.

Question 6

Field capacity

Answer 6

The moisture content of the soil after the excess water has drained, often taken 1-3 after drainage from saturation has occurred. Taken when the pressure head is -10kPa.

Question 7

Pousille’s Law

Answer 7

In the case of laminar flow, the volume flowrate is given by the pressure difference divided by the viscous resistance.

Question 8

Hydraulic conductivity

Answer 8

Describes the ease with which a fluid (usually water) can move through pore spaces or fractures. Given by permeability x fluidity.

Question 9

Water retention

Answer 9

An equation to describe the relationship between soil water pressure (ψ) and water content (θ).

Question 10

Solute transport

Answer 10

The movement of solutes through the catchment.

Question 11

Advection

Answer 11

A transport mechanism of water due to a fluids bulk motion. E.g. the transportation of pollutants or silt in a river by water flow downstream.

Question 12

Dispersion

Answer 12

Distribution of particles over a wide area.

Question 13

Retardation

Answer 13

The process of delaying or impeding.