The Catchment System

Question 1

What is another term for catchment?

Answer 1

Drainage basin

Question 2

What is a catchment?

Answer 2

• A fundamental unit of hydrology and geomorphology
• Collects water over a natural drainage area
• Limited by watershed

Question 3

What are the different hydrological stores and flows?

Answer 3

• Precipitation - P
• Evaporation - E
• Interception - I
• Run off - Q
• Soil moisture storage - SM(S)
• Ground water storage - GW

Question 4

When was the significance of the catchment recognised?

Answer 4

17th Century

Question 5

What is the source of river flow?

Answer 5

• Basin rainfall is sole source of river flow

- Annual river flow is less than total volume of precipitation summed across the basin area

Question 6

What is the water balance?

Answer 6

The water balance looks at the amount of inputs and outputs of a catchment area

Question 7

What is the water balance equation?

Answer 7

• P= Q +E + I + S
• S ≈ 0 so that,
• P = Q + E + I
• E + I = P – Q
• Q = P – (E + I)

Question 8

What does the water balance not tell us?

Answer 8

Does not tell us why something happens in a drainage basin – does not give us a process-based understanding

Question 9

What is a hyetography?

Answer 9

Shows the quantity of rainfall in a period

Question 10

What is a hydrograph?

Answer 10

• Shows amount of water in a river channel - discharge connected
• Storm hydrograph includes relating inputs and outputs

Question 11

What are the different sections of a storm hydrograph?

Answer 11

• Rising limb - when storm begins
• Peak
• Recession limb - drop in discharge

Question 12

How do storm hydrographs help to predict floods?

Answer 12

• Peak to peak distance and time allow us to measure wave speed (celerity)
• Decline in wave height due to friction between two waves - attenuation

Question 13

What are the 4 pathways by which rain reaches the stream to become runoff?

Answer 13

1) Direct precipitation into open water
2) Overland flow - water flows across the ground surface to river
3) Throughflow - flow through unsaturated soil and rock pores
4) Groundwater flow - flow through the pores of saturated soils and rocks

Question 14

Who is Robert Horton?

Answer 14

• Opened Horton hydrological lab
• Wanted to measure variable to understand the amount of runoff generated by rainfall
• Did this through measuring the rate at which the water enters the soil

Question 15

How did Horton measure amount of runoff by rainfall?

Answer 15

• Algebraic model

- Predict infiltration rates as a negative exponential function of time since rainfall began

Question 16

What is the algebraic model used by Horton?

Answer 16

• Ft + Fc + (Fo-Fc) exp -kt
• K = rate constant
• Fo = initial rate
• Fc = final rate
• T = time
• If rainfall rate > infiltration rate = overland flow

Question 17

What is Hewlett;s model of runoff?

Answer 17

Outlined that:

• Precipitation infiltrates into soil
• Surface flow leads to development of riparian saturated zone
• This contributed to storm run off to channel directly
• Saturated zone – zero storage – over land flow
• Contributes to channel by saturation excess overland flow

Question 18

What are the 2 important aspects of Hewlett’s model?

Answer 18

1) Saturated zone expands and contracts according to supply of drainage
2) Interflow from unsaturated soils continues supply of water to channel between rainfall

Question 19

What is the variable source area model/theory?

Answer 19

Variable Source Area Hydrology is the concept that the majority of runoff exiting a watershed is driven by a relatively small portion of the watershed