Stream analysis

• Stream analysis measures streams in terms of their size and shape, their flow velocities and discharge levels.
• This type of primary research provides ample opportunities for the gathering, processing, and analysis of data to illustrate relationships between variables.
• The Bradshaw model is a theoretical model that shows the expected changes in a stream as it flows downstream.
• Equipment needed for stream analysis:

  • Tape measure (long and waterproof) (can be used for cross-section)
  • Metre rule (ranging poles can also be used)
  • Flow meter (hydro-prop) or vane or floating object (e.g., wood or orange)
  • Stop-watch.
  • A heavy chain
• Methodology: Planning

  • choose a stream that is not too wide, too deep or shallow, too fast-flowing or tidal ensure that you can gain easy access to the stream (you may need to ask permission)
  • identify a section of a stream that allows for changes in the measured criteria (e.g., channel size, discharge) and includes features that could influence flow and discharge (e.g. tributaries, changes in slope or land use).
• Methodology: Sampling strategy

  • how much data needs to be gathered to test any hypothesis (e.g., the SRCC needs at least ten pairs of data)
  • that it may take at least one hour to gather the data at each sample point.
  • that working in groups allows more sample points/data to be collected.
  • the benefits of repeat visits/sampling to allow for comparison of the gathered data over time, or following an event on the stream, such as after heavy rainfall.
• Methodology: Channel width

  the distance from one bank to the other can be measured just above the water level.
• Methodology: Bankfull width

  taken at obvious breaks in the slope of both banks. By securing a horizontal line across the stream channel you can identify and measure the maximum volume of water that the channel can hold.
• Methodology: Bankfull depth

  the vertical distance between the water level and the line representing the bankfull width. This should not vary across the river.
• Methodology: Channel depth

  measure the depth of the stream by resting a metre stick on the bed of the stream, with the thin side facing upstream, at regular intervals.
• Methodology: Wetted perimeter

  This is the total distance for which the river water is in contact with the bed and banks at a given cross section. It represents the friction that slows down the river velocity, so the longer the wetted perimeter, the more friction between channel and water.

  Wetted perimeter can be measured using a heavy chain, rope, or measure tape, which should be stretched across the riverbed from one bank to the other. This can be hard to do, especially in larger channels or where the bed is very rough. It is often better calculated from, the graphed results of the profile.
• Methodology: Flow velocity

  ideally use a flow meter (i.e., a hydro-prop with the propeller facing upstream) at the same points as the depth survey. You could also use a float (e.g. an orange) and see how long it takes to go a set distance of 5-10 m.
• Methodology: River discharge

  the discharge of a river is the volume of water which flows through it in a given time. It is usually measured in cubic metres per second. The volume of the discharge will be determined by factors such as climate, vegetation, soil type, drainage basin relief and human activity.
• Considerations and limitations of stream analysis 1:

  • Inaccessible and overgrown sample sites
  • Rate of flow (flood conditions) can make sampling dangerous.
  • Differences in flow rates across a meander (deeper on outside of bend)
  • Low volumes of water can create difficulties in measuring velocity (need to repeat and average)
  • A soft riverbed can affect values. Ensure that the ruler just touches the bed.
• Considerations and limitations of stream analysis 2:

  • A strong current or bow wave created by the ruler can give inaccurate depth readings. Ensure narrow edge faces upstream to reduce resistance.
  • Large boulders or debris, take care to record any anomalies in depth caused by irregularities in the riverbed.
• Processing techniques of stream analysis:

  • River cross section shows relationship between depth and width.
  • Scatter graphs can be used to compare different points on a river e.g. relationship between distance from source and discharge. Further statistical analysis (correlations) using Spearman Rank or Pearson's Product tests.
  • Dispersion graphs for comparison.