Week 1 Flashcards
Components of hydrological cycle
Rain/snow
Glaciers
Volcanos and juvenile H2O
Infiltration
Saturated zone
Groundwater flow
Water table
Runoff
Overland flow
Evapotranspiration
P > VP =
PPT
P < VP =
EVAP
VP at high altitude
Low T
Low VP
= PPT
VP at low altitude
Higher VP (column of air above) e.g. SL ~100kPa
Higher T
= EVAP
Direct rainfall measurement
NON RECORDING RAIN GAUGE
- manually records mm/day
TIPPING BUCKET RAIN GAUGE
- continuous time b/w 0.2mm of rainfall
TILTING SYPHON RAIN GAUGE
- continuous water level w/ float gauge
- once can full = trigger = empties
Radar measurement
Good for spatial coverage
Electromagnetic energy pulse reflected by pption particles
Echo intensity = raindrop size
e.g. 15 radars in UK
5 in Ireland
Surface dominated catchment
Discharge reacts quickly to rainfall events - surface flow
Summer = low flow
Groundwater dominated catchment
Discharge less responsive
Substantial summer flows
Most flow from groundwater = springs/upwelling in river channels
Catchment water balance eqn
Discharge = rainfall - evapotranspiration - /\storage
N.B. /\ storage changes due to permeability
Velocity meters
Series of discrete points
Measures flow velocity and depth of water
Ideally 60% depth
–> Q
Stage =
River level above defined datum
Stage gauging
Auto-measurement = efficient and continuous flow measurement
Uses weir
STAGE(y)-DISCHARGE(x) RELATIONSHIP REQUIRED
What does Manning’s equation do?
Relates water level and flow rate
Empirical equation
Evaporation =
Loss of water from open surface
Evapotranspiration =
Loss of water from open surface and also wet canopy evaporation and transpiration
Potential evaporation =
Amount of water that would evaporate and transpire given an unlimited water source
Actual evaporation =
Actual amount of water that evaporates and transpires
Forest rainfall partitioning equation
Rainfall = stem flow + through flow + interception loss
Pan =
Open water surface
Pan evaporation =
Direct water loss measurement from open water surface over time
Pan evaporation eqn
PE = kp x Epan
kp = lumped correction factor; accounts for differences between pan/crop e.g.
- radiation balance due to albedo
- energy balance (lots of energy in water)
Design (colour/shape/sunken into ground etc) affects performance!!!
Factors affecting evaporation (explained)
SUNLIGHT
- energy required for latent heat
TEMP
- high T = water evaporated more readily AND air can hold more water
HUMIDITY
- air = vapour saturated = evaporation not possible
WIND
- multi scale Eddy patterns
- rate of dry air replenishment
SOIL WATER
- = evapotranspiration
PLANT TYPE
- transpire different rates
- interception
Automatic weather station
Takes all factors affecting evaporation into account:
Solar panel
Relative humidity/T sensor with radiation shield
Wind direction/speed
Solar radiation panel
Power supply and data logger
