Stream Flow Generation

Question 1

What is stream flow generation

Answer 1

How rainfall moves quickly through a catchment to produce riverflow in a storm

Question 2

What is direct in channel precipitation

Answer 2

Rainfall directly into river. Discounted bc most area is covered by vegetation so less than 1%

Question 3

What is infiltration excess (Hortian) overland flow

Answer 3

Dominant mechanism as thought by engineers is water that hits the ground surface and runs over it quickly to stream. Hortian overland flow

Question 4

What did Horton find

Answer 4

Rainfall intensity is bigger than infiltration capacity.
Soil surface acts as a seperatint surface and bite in ground act as a flow between storms.
Small quantity of water enters soil and keeps rivers flowing between storms.

Question 5

Why is hortian overland flow not the dominant mechanism for routing rainfall to rivers

Answer 5

Rarely seen or even measured in significantly quantities . Less than 5% of river flow at Danum.
Soil infiltration capacity usually bigger than rainfall intensities so it all goes in ground
Conservative tracers very variable in rainfall but damped in rivers.

Question 6

What is infiltration capacity also known as

Answer 6

Surface, saturated hydraulic conductivity

Question 7

What is surface saturated hydraulic conductivity

Answer 7

Permeability or the surface specifically at the surface

Question 8

How do we measure conservative tracers in rainfall

Answer 8

Natural tracers in rainfall itself - water enters soil and mixes with subsurface water in storage.
If catchment was impermeable rainfall would hit the ground and run into river, same chemistry. If not water mixes with that In catchment and chemistry changes.

Question 9

Where is hortian overland flow often localised to

Answer 9

Tree stem bases
Compacted surface roads
Desert surfaces (hydrophobic)

Question 10

How does water in the soil get to rivers in storms

Answer 10

Subsurface pathways

Question 11

Evidence that water goes through soil in subsurface pathways

Answer 11

Water table during flood event comes to surface as it is fed by water further up the slope. May even rise to surface before it gets to channel so you get streams.

Question 12

What happens as you look down the catchment as you go through a storm or season

Answer 12

The channel system that is contributing water expands or contracts. Downslope flow is more lost into channel. Saturation to soil.

Question 13

What is a computer model based on VSA concept

Answer 13

TOPMODEL (developed at Lancaster) sits under met office and formulates weather

Question 14

What is VSA

Answer 14

Variable source area concept by Hewlett

Question 15

What happens when the water channel fills up underground

Answer 15

It connects with other channels and extends. Expansion of stream networks in ephermal and intermittent streams.

Question 16

What are the water paths in river side areas

Answer 16

Channel bed inflow
Direct precipitation on saturated areas
Return flow

Question 17

What is channel bed inflow

Answer 17

Wet bits near the river. First mechanism is the loss of water from soil through the bed. But if you pour enough water down the slope it can’t get out into river fast enough and backs up the hill slope all the way to the surface and it’ll start to come out of the ground (exfiltration) called return flow which runs over slope before returning to river

Question 18

What is direct precipitation on saturated areas

Answer 18

Could have permeable soul but water is coming out or surfer bc the pores are full of water. If all things are wet the rain falling into surface can’t go in and goes into catchment

Question 19

What is return flow

Answer 19

Saturation excess overland flow. Water emerges at valley bottom before going into stream. Backs up.

Question 20

What happens when water is less than saturated

Answer 20

It delivers water quite slowly so most of the catchment isn’t wet. Important bc these pathways take contaminants with them

Question 21

What are recharge pathways for saturated soil

Answer 21

Water coming into the ground at different points of the catchment

Question 22

What are rapid paths in unsaturated soil

Answer 22

Might have high permeability on surface but meet something less permeable down into the profile. Can’t get in any further so gets thrown down into river. Very shallow. Unconsolidated geologic material throws water laterally. Laterally.

Question 23

Example of shallow water paths

Answer 23

Impeding layers in podzolic soils
Head deposits from siltstones
Natural soil pipes
Wave propagation

Question 24

How are head deposits from granite made

Answer 24

In Uk had freeze thaw which froze souls and smashed it up. Souls slid down hill side and froze again, smashed again. In profile you get layers pointing down stream. Solidfluction process

Question 25

What is a natural soil pipe

Answer 25

Formed by seepage forces of the water. Few cm in diameter and it will go a few m up hill slope. Soil around is dry even though there’s a stream going through it

Question 26

What do roofs a soil pipes collapse

Answer 26

They are unstable and create channels that are 5-10cm in diameter

Question 27

Where do you get soil pipes

Answer 27

Peaty souls
Soil in deep peat are big at 1m
Through podzol close to surface
Acidic mountain soils
In deserts
Caves in limestone

Question 28

Examples of soil pipes

Answer 28

Desert in south east Spain
Israel - so big buildings fall through
Baru catchment in Borneo

Question 29

What is wave propogation

Answer 29

Environment with discrete cave passage, see the pulse of water going into cave system will be delayed. When we try to model this we think about darcys law but channel movement is manning equation. Weir responds instantly to input of rainfall, how we measure most things is wrong bc of this

Question 30

What is difficult about stream flow measuring

Answer 30

Deciding how much of each of the paths matter