W9 - Measurement and monitoring Flashcards
(42 cards)
Why monitor river systems?
Evaluate the impacts of policy
Develop knowledge and understanding (…process)
Testing models
Measure, anticipate, and prevent the deterioration of environmental integrity
What is a sample?
Just one measurement of an environmental variable at one point in time and one point in space
Difference between monitoring and a survey
Monitoring is taking measurements over time all at the same place
A survey refers to measurements spread over space taken at the same time
What is the larger group that a sample is collected from called?
Population
Which variables would you use areal measurements?
Vegetation
Land use
Stream network density
Gully erosion
Which variables would you use point measurements?
Discharge
Water quality
Biological factors
Water table measurements
Soil characteristics
Stream velocity
Acidity (pH)
Types of primary data collection (spatial sampling techniques)
Random
Systematic
Stratified
Non-random
What is random sampling + pros/cons?
Every part of the study area has an equal and independent chance of receiving a sampling point
Gives uneven areal coverage which is a disadvantage if spatial variations are of interest
What is systematic sampling + pros/cons?
Initial point located randomly; all others determined by a fixed interval
Gives even areal coverage
If there is a spatial pattern in the data, the regularly spaced sample points could correspond with some parts of the pattern, giving a biased impression
What is stratified sampling + pros/cons?
Area is divided into sub-areas within which sample points are chosen randomly.
If a regular grid is superimposed, points may be located randomly within each grid square to ensure good areal coverage while preserving the advantages of randomness.
Even coverage of different categories i.e. soil type
Can also tailor sampling points to capture variability
More points in area of higher variability
What is non-random sampling + pros/cons?
Aka purposive or subjective sampling
Sample subjectively chosen by the investigator
* i.e. convenient sampling locations
Likely to be unusual or biased
What is the best size and shape of sampling units?
Regular - grid-like quadrats
Irregular - catchment-shaped quadrats
Spatial sampling of river networks: systematic or Stratified
Systematic would give an even spread over the system
Stratified might be better when trying to capture variability that depends on a specific variable
How frequently should you take measurements
You need to match the frequency with the variability – pilot study?
Collect high frequency data and degrade > data handling issues
Why are there problems with how frequently you need to take measurements?
Many environmental phenomena display regular temporal variation (cycles)
Measurements at fixed time intervals may record the same part of whatever cycles are present, missing the data’s variation
How long should you sample for?
The length of the established cycle when it is possible
What does scale mean?
Cartographic map scale - ratio of map distance to ground distance
Geographic scale - the size or spacial extent of the study, e.g. the watershed vs plot scale
Operational scale - a.k.a. the process scale or characteristic scale. Scale at which a process operates in the environment. Associated with the processes spatial extent and temporal duration (lifetime and scale)
Measurement scale - The space/time between samples (resolution) and the integration of time of a sample
Smallest discernible spacial unit (e.g. pixel) and event.
Fine vs. coarse resolution (space) low vs high resolution (time).
Extensive vs intensive studies
Extensive = large area in little detail
Intensive = small area in a lot of detail
Physical river catchment variables
o Land use
o Topography
o Precipitation
o Water quantity
o Sediment concentration/flux
o Soil properties
o Fluvial geomorphology
Chemical river catchment variables
o pH
o conductivity
o DO
o BOD
o Nutrients
o Metals
o Pesticides
Biological river catchment variables
o Macrophytes
o Invertebrates
o Diatoms
Why should we measure precipitation?
o Need total daily or monthly measurements for water resources
o Need continuous monitoring to assess rainfall intensity for flood warning
How do we measure precipitation?
o Rain gauges and snow gauges
o Suffer from air turbulence, evaporation losses, and wetting losses.
o Point measurements that must be interpolated
o Radar can provide an aerial measure
How do we measure velocity?
Floats
Current Metering
o Need to work out where the average velocity of the stream is – 0.4 Depth (or 0.2 and 0.8)
o propeller or electromagnetic – don’t want these in the stream for long periods of time
