Hydrology; catchment water balance

Question 1

how much land precipitation (rainfall over the land) is from water derived from the ocean in AUS?

Answer 1

~30%, the rest is inland cycling from ET which is 2/3 of AUS precipitation

Question 2

what determines the amount of rainfall:

Answer 2

1. location (distance from coast decrease in moisture inland)
2. seasonality (summer vs winter dominated)
3. randomness (local convection and feedback)
4. Sea surface temperatures(ENSO, IPO etc)

Question 3

How much of AUS rainfall variability is explained by ENSO

Answer 3

14%. however, AUS has 25% rainfall variability therefore ENSO is 14/25 variability which is a lot

Question 4

what is the rainfall average in AUS, why is this not a good measure ?

Answer 4

455mm/year however high variability eg 3m northern QLD and 1.2m sydney, a better measure is to look at anomalies from the average

Question 5

what is time of concentration and what is it a function of

Answer 5

estimated travel time to catchment, amount of discharge for a given amount of rainfall.
- a function of slope and distance velocity and resistance

Question 6

why doesnt peak runoff rate include infiltration and ET

Answer 6

minimal (hortonian)

Question 7

how is volume of river measured

Answer 7

by a proxy: height

Question 8

what is the velocity area method

Answer 8

to estimate flow rate divide the river into cross-sections and calculate average velocity for all sections (more friction with depth)

Question 9

what is a rating curve and what are its limitations

Answer 9

measure of flow and depth however limitations dangerous with high flows and small flows have high variability

Question 10

what is mannings equation?

Answer 10

estimate of the flow of channel velocity using hydraulic principles between slope and area and resistance
useful for dangerous or remote flows

Question 11

what is mannings n coefficient

Answer 11

friction coefficient (flow resistance) based on ground cover (0-1 the higher the more resistance)

Question 12

why does increasing model complexity not always result in better results

Answer 12

decreases performances too specific therefore less successful, for better performance increase observations on simple model

Question 13

what is a cascading bucket

Answer 13

storage flow of landscape as flow moves from one bucket to the next

Question 14

what is the mean annual runoff for AUS

Answer 14

42 mm

Question 15

what is the variation of streamflow

Answer 15

0.68 about double rest of world (more variation that rainfall)

Question 16

why is there more variation in streamflow compared to rest of world

Answer 16

because of catchment area and location, in AUS small catchments are along coast while big catchments are in the flat centre with high residence times (geology)

Question 17

what is the penman montieth equation

Answer 17

measure of ET based on solar raditation etc very complexand needs a lot of data therefore other approaches are used

Question 18

what is sensible vs latent heat

Answer 18

sensible is heat that heats objects (feel)

latent heat causes an object to change state (eg evaporation liquid to gas)

Question 19

what is preisly Taylor

Answer 19

good for large regional scales bad for detail
ET for well-watered crop
only need temp and radiation, ignores diffusion ie wind and vapour

Question 20

what are the different methods to measure ET (equations)

Answer 20

1. penman Montieth (complex)

rest are simplified versions ignore diffusion

2. Preisly Taylor (large scale, temp and radiation)
3. Mortons complementary relationship (humidity and availability)
4. Budyko theory (availability and radiation)

Question 21

what is Mortons complementary relationship

Answer 21

measure the relationship between actual ET (plants) and point potential ET (open bucket)
PPET decreases with rainfall due to humidity
APET increases with rainfall due to higher water availability
= equilibrium point APET actual point potential maximum (humidity suppresses et)

Question 22

what is budyko theory

Answer 22

actual ET is a function of water availability and radiation (one limits the other eg central aus high radiation low water)

Question 23

how much ET is from intercept, plants and soil

Answer 23

intercept ~30
soil ~5
plants ~65

Question 24

what happens to heavy isotopes of water

Answer 24

heavy isotopes ie ocean water rain earlier and evaporate last therefore stays in the ground

Question 25

why is delta S always 0

Answer 25

assume under annual scales, easier to measure other fluxes eg Q, ET

Question 26

why do we need dams and why are they managed

Answer 26

water storage needed due to high variability of rainfall, need to be managed as PPET highest with dry conditions

Question 27

what needs to be considered when building a dam

Answer 27

1. reliability (consistent water with no drought)
2. vulnerability (how often do you have a drought)
3. resilience (how long does it take to recover after a drought

Question 28

how do you measure the effect of a dam

Answer 28

similar small areas simultaneously measure effects however need 10+ years and difficult for large areas

Question 29

how have dams affected stream flow

Answer 29

flattening of flow peak due to irrigation demand

Question 30

2 ways human shave impacted the global water cycle in relation to runoff and stream flow

Answer 30

1. runoff increased due to land management

2. stream flow decrease due to irrigation withdrawal