Soil water and Groundwater I

Question 1

what is infiltration?

Answer 1

water that moves from above-ground to the subsurface

Question 2

what is a water table?

Answer 2

subsurface boundary below which the ground is completely saturated with water

Question 3

what is percolation?

Answer 3

water that moves vertically through the soil toward the water table -> movement after infiltration

Question 4

what is recharge?

Answer 4

water that is added to the water table

Question 5

what is groundwater flow?

Answer 5

water that is flowing below the water table

Question 6

what is capillary fringe?

Answer 6

saturated zone above the water table, in which groundwater seeps upward due to capillary forces

Question 7

where is the subsurface?

Answer 7

under the surface, above water table

Question 8

what happens to water after infiltration?

Answer 8

• storage in shallow soil layers (stored as soil moisture)
• redistribution (vertically through perculation - groundwater recharge OR laterally through unsaturated flow or groundwater flow)

Question 9

what are pedologic horizons?

Answer 9

distinct layers of soil profile. Differentiated by color, texture, organic matter, degree of deposition or removal of material by physical and chemical processes.

Question 10

what are hydrologic horizons? and name them

Answer 10

defined by soil moisture.
Root zone - Intermediate zone - capillary fringe - groundwater

Question 11

Why is soil referred to as porous?

Answer 11

Within soil there is an interconnected network of pores (voids) filled with fluids (liquid or gas)

Question 12

what is soil texture?

Answer 12

term used to describe grain size distribution by weight for particles of less than 2 mm

Question 13

what is the equation for total porosity?

Answer 13

n= V(voids)/ V(total)

Question 14

what is the void ratio equation?

Answer 14

e= V (voids)/ V (solids)

Question 15

what is the volumetric soil moisture content equation?

Answer 15

omega = V (water)/ V (total)

Question 16

what is the degree of saturation equation?

Answer 16

S= Vwater/ (Vwater+Vgas)

Question 17

What is the equation for gravimetric soil moisture?

Answer 17

G= (Mwet soil - Mdrysoil)/ Mdrysoil

Question 18

what is the name for an unsaturated zone in the soil profile?

Answer 18

vadose zone

Question 19

what is the name for the saturated zone in the soil profile?

Answer 19

phreatic zone

Question 20

what does the capillary fringe look like?

Answer 20

• just above water table
• belt of variable thickness

Question 21

what is capillary action?

Answer 21

process of a liquid moving in a narrow space without the assistance of gravity. made possible through the forces of cohesion and adhesion, occurs when the adhesion forces of water to a solid material > cohesive forces between liquid water molecules

Question 22

how does water storage change based on different soil moisture?

Answer 22

at saturation: excess water drains under the influence of gravity
-> field capacity
intermediate to wet conditions: water held in soil pores (capillary water)
-> permanent wilting point
dry conditions: only thin films of water hold onto soil grains (hydroscopic water)

Question 23

what is the field capacity of a soil?

Answer 23

tension below which water cannot be drained by gravity. for subsurface flow to occur, soil moisture has to exceed field capacity

Question 24

what is the permanent wilting point of a soil?

Answer 24

WPW is soil moisture content produced after gravitational drainage + plant evapotranspiration losses
–> tension below which plant root systems cannot extract water from the soil

Question 25

what is plant available water?

Answer 25

PAW is the difference between field capacity and permanent wilting point

Question 26

what is soil water pressure?

Answer 26

force per unit area applied by water in all directions, measured relative to atmospheric pressure * at water table, water pressure = atmospheric pressure

Question 27

what is soil water tension?

Answer 27

measure of how tightly water is held to soil particles - expressed as negative pressure - miminum pressure that must be exerted to extract water from soil

Question 28

what path does soil water pressure follow in the soil profile?

Answer 28

unsaturated soils: negative (tension/suction) at water table: 0 saturated soils: positive

Question 29

what instrument is used to measure soil water tension?

Answer 29

tensiometer: a tube partically filled with water and a low-permeability porous cup at bottom that allows pressure equilibration with the soil

Question 30

how does water move in the subsurface?

Answer 30

- from high pressure (water less tightly bound to soil grains) to low pressure - from low tension to high tension

Question 31

what is hydraulic conductivity?

Answer 31

K describes the ease with which water can move through pore spaces or fractures in the soil

Question 32

rate sand, gravel, silt, clay from highest to lowest K?

Answer 32

gravel > sand > silt > clay