Hydrological Processes Flashcards
What are 3 measurements that can be made in the hydrological cycle?
Precipitation
Evaporation
River discharge (river gauging)
What does the lag time show on a hydrograph?
The time between rainfall and water entering the stream
What do individual storm hydrographs show?
How quickly rainwater moves from the hillslope to the stream channel
How do you find the rise time in a storm hydrograph?
Look at the difference between the peak storm flow and the first recorded rainfall
How do you find the lag time on a flood hydrograph?
The difference from the midpoint of the rainstorm and the peak storm flow
What is the time scale for studying and monitoring rivers?
Hours, days, months
What is the time scale for catchment dynamics?
Months, years, decades
What is the time scale for human impacts?
Years, decades, centuries, millennia
What is the time scale for natural variability?
Centuries onwards
What two things are monitored and studies related to rivers?
Environmental quality
Geomorphological processes
What are two key aspects of catchment dynamics?
Fluvial and biological responses
Catchment management
What are 5 human impacts?
Acidification Eutrophication Desertification Land-use River channel change
What are 3 examples of natural variability?
Climate change
Sea level change
Vegetation dynamics
What type of precipitation is easiest to measure?
Rain
Why is it difficult to measure snow?
Due to under catch
Is the weather radar integrated or instantaneous?
Integrated
What is the range of the weather radar?
Up to 200km
What is the weather radar range in the UK?
15 km
What is the weather radar range in Europe?
Over 100 km
What are 7 advantages of weather radars?
Area rainfall estimates over a wide area
Information in near-real time
Information for remote land areas and over adjacent seas
Location of frontal and convective (shower) precipitation
Monitoring movement and development of precipitation areas
Short-range forecasts made by extrapolation
Data can be assimilated into numerical weather prediction models
What are 3 disadvantages to weather radars?
Display does not show rainfall actually at the surface
Display also shows non-meteorological echoes
Estimates liable to error due to technical and meteorological causes
Explain stochastic variations in precipitation
Variability of rainfall in areas of low precipitation as longer records are needed
Timing and magnitude of storms is stochastic
Explain periodic variations of precipitation
Regular or cyclic variations
Daily or annual cycles such as convection
Land and sea breezes
Mediterranean winter rain
Explain secular variations of precipitation
Climate change
What 5 things does precipitation data show?
Mean aerial input of rainfall from a series of point measurements Storm patterns and movement Storm recurrence Probable maximum precipitation Mean rainfall
What is evaporation a major control on?
The Earth’s energy budget
How much energy is used to evaporate water as opposed to heat it?
6x more energy is required to evaporate water than to heat if from 0-100 C
Where is evaporation highest?
In areas with the highest rainfall
Why is evaporation difficult to measure?
There is a loss of water at the surface
What needs to be determined to measure evaporation?
The water vapour flux
What is used to measure evaporation? (3)
Evaporation pans
Water vapour (lysimeter)
Weighing block
What two things are used to determine discharge?
Channel cross-sectional area
Stream flow velocity
What is the discharge equation?
Width x Depth x velocity
What is width measured in?
m
What is depth measured in?
m
What is velocity measured in?
ms-1
What are the units for discharge?
m3s-1`
What do v-notch weirs allow?
Calculation of discharge using spillway equation
What do propellors and impellors measure?
Velocity
How often are velocity measurements made?
They are time averaged
What are two advantages of measuring velocity with propellors and impellors?
They are robust and easy to use
What are two disadvantages of measuring velocity with propellors and impellors?
They disrupt the flow they seek to measure and there are problems of near-bed measuring
What is shear stress?
The rate of change of vertical velocity
What is Faraday’s principle?
A conductor (water) moving through a magnetic field (produced by the sensor) generates a voltage
What is voltage measured by in an electromagnetic current meter?
A pair of electrodes
What are two advantages of electromagnetic current meters?
Possible to measure flow velocity in different dimensions
Good for use in streams with lots of vegetation and weeds
What are ADVs?
Acoustic-Doppler Velocimeters
Where can 3D turbulent velocities be found?
In rivers and flumes
Where is the transmission of acoustic pulses from in ADVs?
From a transmitter at the probe head
What transmission is sent from ADVs?
Acoustic pulses of 10MHz
What happens to the acoustic pulse from an ADV?
It is reflected by air bubbles and suspended sediment within the flow
How many receivers are in ADVs and what do they surround?
3 receivers surround a sampling volume of water
What is the doppler shift from the ADV generated by?
It is generated by velocity differences between probe and scattering objects
What is a disadvantage of ADVs?
Cannot measure close to river bed or water surface
What are the velocities of ADVs?
Less than 2.5ms-1
How does velocity vary?
Vary almost instantaneously and in several directions
What are 3 main drawbacks of measuring river discharge?
Cannot gauge rivers all of the time
Need to find a simpler way of obtaining river discharge data over longer periods of time
Manual or automatic measurement of river level is much easier
What relationship is needed?
A stage-discharge relationship
What is the stage-discharge relationship derived from?
Multiple river gauging’s
What conversion is required for stage-discharge relationship?
Conversion of river level (stage) to river discharge values
