Hydrology; catchment water balance Flashcards
how much land precipitation (rainfall over the land) is from water derived from the ocean in AUS?
~30%, the rest is inland cycling from ET which is 2/3 of AUS precipitation
what determines the amount of rainfall:
- location (distance from coast decrease in moisture inland)
- seasonality (summer vs winter dominated)
- randomness (local convection and feedback)
- Sea surface temperatures(ENSO, IPO etc)
How much of AUS rainfall variability is explained by ENSO
14%. however, AUS has 25% rainfall variability therefore ENSO is 14/25 variability which is a lot
what is the rainfall average in AUS, why is this not a good measure ?
455mm/year however high variability eg 3m northern QLD and 1.2m sydney, a better measure is to look at anomalies from the average
what is time of concentration and what is it a function of
estimated travel time to catchment, amount of discharge for a given amount of rainfall.
- a function of slope and distance velocity and resistance
why doesnt peak runoff rate include infiltration and ET
minimal (hortonian)
how is volume of river measured
by a proxy: height
what is the velocity area method
to estimate flow rate divide the river into cross-sections and calculate average velocity for all sections (more friction with depth)
what is a rating curve and what are its limitations
measure of flow and depth however limitations dangerous with high flows and small flows have high variability
what is mannings equation?
estimate of the flow of channel velocity using hydraulic principles between slope and area and resistance
useful for dangerous or remote flows
what is mannings n coefficient
friction coefficient (flow resistance) based on ground cover (0-1 the higher the more resistance)
why does increasing model complexity not always result in better results
decreases performances too specific therefore less successful, for better performance increase observations on simple model
what is a cascading bucket
storage flow of landscape as flow moves from one bucket to the next
what is the mean annual runoff for AUS
42 mm
what is the variation of streamflow
0.68 about double rest of world (more variation that rainfall)
why is there more variation in streamflow compared to rest of world
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)
what is the penman montieth equation
measure of ET based on solar raditation etc very complexand needs a lot of data therefore other approaches are used
what is sensible vs latent heat
sensible is heat that heats objects (feel)
latent heat causes an object to change state (eg evaporation liquid to gas)
what is preisly Taylor
good for large regional scales bad for detail
ET for well-watered crop
only need temp and radiation, ignores diffusion ie wind and vapour
what are the different methods to measure ET (equations)
- penman Montieth (complex)
rest are simplified versions ignore diffusion
- Preisly Taylor (large scale, temp and radiation)
- Mortons complementary relationship (humidity and availability)
- Budyko theory (availability and radiation)
what is Mortons complementary relationship
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)
what is budyko theory
actual ET is a function of water availability and radiation (one limits the other eg central aus high radiation low water)
how much ET is from intercept, plants and soil
intercept ~30
soil ~5
plants ~65
what happens to heavy isotopes of water
heavy isotopes ie ocean water rain earlier and evaporate last therefore stays in the ground
why is delta S always 0
assume under annual scales, easier to measure other fluxes eg Q, ET
why do we need dams and why are they managed
water storage needed due to high variability of rainfall, need to be managed as PPET highest with dry conditions
what needs to be considered when building a dam
- reliability (consistent water with no drought)
- vulnerability (how often do you have a drought)
- resilience (how long does it take to recover after a drought
how do you measure the effect of a dam
similar small areas simultaneously measure effects however need 10+ years and difficult for large areas
how have dams affected stream flow
flattening of flow peak due to irrigation demand
2 ways human shave impacted the global water cycle in relation to runoff and stream flow
- runoff increased due to land management
2. stream flow decrease due to irrigation withdrawal
