Lec 2: Basic Concepts

Question 1

How are boundaries defined?

Answer 1

Often arbitrarily.
Often hydrological divides & catchment boundaries.

Question 2

What are the elements of a system?

Answer 2

Boundaries
Fluxes (aka boundary conditions)
Storage

Question 3

What are fluxes? What units are used to measure them?

Answer 3

a volume that crosses a defined boundary per time
Expressed in volume per time (e.g. m3/s), sometimes measured in height per time then multiplied by area of flux to find volume/time

Question 4

How does storage change in a steady state system vs in a transient state system

Answer 4

steady state: no change in storage (I = Q, delta S/delta t = 0)
transient state: it changes (delta S/delta t does not = 0, therefore I does not = Q)

Question 5

What is the basic equation for change in storage?

Answer 5

Flux in - Flux out = change in storage
I - Q = delta S

Question 6

What is residence time and what is another term for it? What is the equation for residence time in a steady state system?

Answer 6

The time it takes to replace all the
water stored in a system.
aka turnover time
T = S/Q

Question 7

What are fluxes into and out of the system in hydrology?

Answer 7

into:
- rainfall
- melting of snow (depends on available energy)
- groundwater inflow (from groundwater into rivers or lakes)

out of:
* evapotranspiration (loss to the atmosphere; depends
on energy)
* runoff from catchment (leaves catchment as discharge or stream flow)
* groundwater outflow (leaves catchment as
groundwater)

Question 8

What are stores in hydrology? (5)

Answer 8

►Surface water
* lakes, reservoirs, wetlands (and short-term: rivers)

► Soil water
* Aerated zone, wetlands

► Groundwater
* Below groundwater table

► Glaciers (and seasonally: snow)

► Biomass

Question 9

What is a watershed?
What is a catchment?
What is a basin?

Answer 9

They are all basically the same, except that a basin is bigger. Catchments are nested within each other (sub-catchments within sub-catchments)

catchment = all the (land surface) area that drains to the same outlet point

Question 10

What is another name for catchment boundary?

Answer 10

Watershed divide

Question 11

Where is the ultimate outlet point?

Answer 11

at the coast

Question 12

How are catchment boundaries derived?

Answer 12

• using contours on a topographic map
• using a DEM in GIS

Question 13

What are the main drainage basins of Canada? (5)

Answer 13

Atlantic Ocean
Hudson Bay
Arctic Ocean
Pacific Ocean
Gulf of Mexico

Question 14

What happens to catchment size if groundwater is taken into account?

Answer 14

Catchments can be bigger

Question 15

What is the water balance equation?

Answer 15

P + G(in) - ET - Q - G(out) = change in store

Flux in
- P: precipitation
- G(in): groundwater inflow (from adjacent catchments)

Flux out
- ET: evapotranspiration
- Q: discharge (or runoff R)
- G(out): groundwater outflow

Question 16

Explain how the water balance equation can be simplified to ET = P - R

Answer 16

In a steady state, change in storage is 0.
G(in) is assumed to be 0 (which it usually is not).
G(out) is assumed to be 0 (which it usually is).

Question 17

What is the water energy balance equation?

Answer 17

Q* = Q(g) + Q(h) + Q(e) + Q(m)

Q* = net energy
Qg = soil heat flux
Qh = sensible heat flux
Qe = latent heat flux (ET)
Qm = Heat flux for snow melt

Question 18

How can you relate the water mass and energy balance equations?

Answer 18

P relates to Qm (heat flux for snow melt)
ET relates to Qe (latent heat flux)