Lecture Panel 10

Question 1

Infiltration

Answer 1

movement of water from the soil surface into the soil

-inputs from precipitation and snowmelt

Question 2

Redistribution

Answer 2

Movement of infiltrated water within the unsaturated zone

Question 3

Exfiltration

Answer 3

Evaporation of water vapour from the upper layers of the soil (output)

Question 4

Vegetative Uptake

Answer 4

Soil water is absorbed by plant roots and subsequently released during transpiration

Question 5

Interflow

Answer 5

Soil water is carried down slope within the unsaturated zone

Question 6

Percolation and groundwater recharge

Answer 6

Soil flows downward through porous soil into the saturated zone and creates ground water recharge

Question 7

Capillary rise

Answer 7

Movement of water upward from the saturated zone to the unsaturated zone due to surface tension

Question 8

Why is it important to understand infiltration and redistribution?

Answer 8

to determine the water budget

Question 9

What is Darcy’s Law

Answer 9

Tells you discharge (Q) from a tube of saturated soil 
Q=-KAdh/dl
A= area
K= hydraulic conductivity
dh= change in head
dl= change in length

Question 10

Specific discharge

Answer 10

q=Q/A=-Kdh/dl

can say this is apparent velocity (v=L/t) of saturated flow

Question 11

Anisotropic unsaturated flow

Answer 11

flow rate differs depending on direction, due to grain shape and orientation

Question 12

How are hydraulic conductivity and water content related?

Answer 12

directly proportional - but the rates differ by soil texture

Question 13

Darcy’s law for unsaturated flow

Answer 13

Pressure head and connectivity are functions of moisture:

q = -K*(1+dpsi/dz)

Question 14

Infiltration rate

Answer 14

rate water enters soil

Question 15

infiltration capacity

Answer 15

maximum rate at which water can enter soil

Question 16

Water input rate

Answer 16

precipitation rate

Question 17

Time to ponding

Answer 17

time at which input rate exceeds infiltration capacity

Question 18

5 moisture zones during infiltration

Answer 18

1. saturated zone
2. transition zone
3. transmission zone
4. wetting zone
5. wetting front

Question 19

saturation zone

Answer 19

during infiltration - near the surface, extending up to 1.5 cm down

Question 20

transition zone

Answer 20

during infiltration - about 5cm thick and located below the saturated zone. rapid decrease in water content

Question 21

transmission zone

Answer 21

during infiltration - water content varies slowly with depth and time

Question 22

wetting zone

Answer 22

during infiltration - where sharp decrease in water content is observed

Question 23

wetting front

Answer 23

during infiltration - region of very steep moisture gradient. this represents the limit of moisture penetration into the soil

Question 24

infiltration and runoff over time during storm

Answer 24

infiltration starts out very fast and efficient, then can’t hold anything more due to saturation of the top layers. runoff is reciprocal

Question 25

Factors controlling infiltration

Answer 25

• water input rate
• hydraulic conductivity of the surface
• -soil organic layers
• -frost
• -swelling or drying
• -rain compaction
• -in-washing of sediment
• -human modification
• initial water content
• -wetter soils have higher unsaturated hydraulic conductivity but will also fill up faster
• slopes
• soil chemistry
• water chemistry
• -K at 30C almost 2x at 0

Question 26

Rings for infiltration rate measurement

Answer 26

ring in soil, water in ring at constant head

• we keep water level constant, and since we are just barely avoiding runoff we know we are at max infiltration rate
• issues are ring deforms soil, not nature conditions
• can use two rings to stop lateral spread

Question 27

Rainfall simulator

Answer 27

device for measuring infiltration with attempted realism

Question 28

Hortons early infiltration insight

Answer 28

infiltration begins at some rate of, and exponentially decreases until it reaches some constant rate, fc