Runoff generation II

Question 1

what is the development of perched shallow subsurface stormflow?

Answer 1

perched SSSF occurs when percolating water reaches a less permeable layer that will not accept the wetting front, so saturation develops -> that wetting front rises towards the soil surface -> water flows laterally through the soil matrix

Question 2

why does perched shallow subsurface stormflow occur?

Answer 2

layers of soil have different hydraulic conductivity

Question 3

what are the 6 types of subsurface flow?

Answer 3

• matrix flow
• perched matrix flow
• subsurface fill and spill mechanism
• macropore flow
• pipeflow
• groundwater flow

Question 4

what is the development of SSSF?

Answer 4

1. percolation
2. water reaches water table
3. water table rises toward soil surface
4. before water table reaches the surface, most soil pores are filled with water and hydraulic conditions change -> lateral hydraulic conductivity > vertical hydraulic conductivity

Question 5

what is the subsurface fill and spill mechanism?

Answer 5

when impermeable boundaries (unweathered bedrock) in the hillslope subsurface have bedrock hollows that must be filled to the top before continuous flow pathways for subsurface stormflow can develop

Question 6

what factors increase macropore presence?

Answer 6

• since most macropores are biopores, anything supporting biodiversity (more organic matter) will have more macropores (forest > agri)
• heavy machinery decreases macropores

Question 7

what negative effect does macropore flow have?

Answer 7

enhanced contaminant transport risk

Question 8

what direction does water flow in macropores?

Answer 8

vertical percolation occurs preferencially in these networks, but also horizontal -oriented macropores exist in the subsurface

Question 9

how does macropore flow change based on the rate of infiltration?

Answer 9

it goes from subsurface storage (pool at bottom) to fast subsurface flow (vertical) to overland flow and lateral infiltration (vertical and horizontal)

Question 10

how can we investigate macropore flow in real life?

Answer 10

dye staining experiments

Question 11

what are the three types of macropores in soils?

Answer 11

• fauna (1 to 50 mm at surface)
• flora (35% volume decrease with depth)
• chemical or physical alterations

Question 12

what does macropore flow depend on?

Answer 12

• pore size distribution
• interconnection between pores

Question 13

where does preferential flow occur?

Answer 13

• in distinctive structures in the soil where water flows under gravity (ex macropores)
• in areas with higher permeability than the surrounding soil matrix (ex. soil-bedrock interface)

Question 14

which of the 6 subsurface flows are preferential runoff pathways?

Answer 14

• perched shallow subsurface SOMETIMES
• fill and spill
• macropore
• pipeflow