FWC Creek Flow Measurement Techniques - What is right?

What we do in terms of our SSIFWC field data collection?  The overarching FWC data collection programme is oriented towards gathering water quantity related information (the what being - largely surface runoff and groundwater baseflow flow volume(s) variability, and groundwater chemistry).  For some watersheds area this FWC field data collection programme has been fine-tuned to investigate other aspects of the island's freshwater, eg the impact of watershed restoration work on water quantity (more continuous stream flow, changing groundwater contributions, etc) and water quality (more contiguous stream stretches, with robust(ish) aquatic ecosystem health, for longer..., less sediment/turbidity in creeks, lakes, etc).

Note - on the which why to go on measuring (or the right flow...), the [1] to [3] ranking below is in a preferred order of measurement techniques used to determine creek flow, [4] is a useful fall-back.  However, if you are unable to record a quantitative flow using one of the above (no field kit, no time, no training), please capture seasonally a creek's qualitative flow (surging, steady, slow, and also importantly no flow/water!).

Depending on field location, and season, the creek flow measurement techniques used in FWC field data acquisition will be one of:  

1. Bucket and Timer [*FWC cloud database jargon - "BandT"] - involving recording the time to fill a vessel,  the most accurate flow measurement method.

2a. Measured Creek Cross-Section (profile), wetted width and a Velocity Meter [*FWC cloud database jargon - "Flow Meter or Flotation Complex Profile"] - more accurate, using area and velocity to determine flow, however not practicable in many (most) natural island creek field locations.

2b. Measured Creek Cross-Section (profile), wetted width and a Floatation Device (float-and-flow, ducky) [*FWC cloud database jargon - "Flow Meter or Flotation Complex Profile"] - using area and velocity to determine flow, usable at most island sites, but the least accurate measurement technique!

3. Float through Culvert [*FWC cloud database jargon - "Through Culvert"] - occasionally island creek flow conditions and the location are suitable for measuring creek flow using a float through a culvert. This approach uses a modified version of  2b. above (and is perhaps a little more accurate).  At higher-flow conditions this technique may be the only safe option! In addition (at selected field sites only) we use

4. A Staff Gauge - at some FWC field sites we now have a staff gauge installed.  Strictly speaking the gauge does not give a direct flow measurement technique but a means to record (indirectly, from the marked ruler) flow...   The flow determination relies on determining a relationship between calculated water flow volume at a location (using one of the methods 1. - 4. above, or 5. below) and the level on a staff gauge - defining a “rating curve”.  With this rating curve in-place flow can a simple "read-out" from the gauge-level in the water.  If a staff gauge is available at the site visited, the water level “as-is” on the ruler is what should be captured/recorded.

5. 24/7 Data Loggers - data from field devices that continuously record (temperature, water level and/or conductivity) is downloaded on an ad-hoc basis by the project coordinator and/or by island FWC stewardship groups.

The actual choice of the field measurement techniques [1] to [4] above is dependant on the site which should: be approved for access, allow safe measurement conditions, and supports a technique that is suitable for the in-creek flow conditions encountered. Winter measurement techniques often depend upon [2] through [4] above.  The use of [1] above is dependant upon the availability of some kind of in-creek weir (eg a natural waterfall, a culvert drop, or...) to measure at.

Note - measurements, at the same site, should be repeatable under all conditions, so suitable site selection is key! For more on creek profile types (shapes) cf our V3 Creek Profiles field notes.  Our small island creeks are somewhat challenging from a creek flow measurement perspective.  The island field conditions and constraints on sampling mean, at best, we can achieve consistent and moderately accurate baseline datasets, for longer term comparisons pre/post "events" and after restoration work. 

If/when our island FWC data becomes available In the province Aquarius database (we are working on it) most of our FWC data will likely be graded as category “U’.  This is a result of yawning gap between what the province’s certified professionals would like, and what is practicable in small creek systems (and with community science).  The BC Province RISC Hydrometric Assessment report gives an idea of the challenges…

1. Measuring with a vessel (using a bucket and timer) 

See the Flow 1. Bucket & Timer measurements page for a how-to

For all other flow measurement techniques measure a creek cross-section (profile) area (using wetted width, widths and depths).  This information is needed for both velocity meter and float-flow methods:

2. Recording creek velocity with a velocity meter (or Stream Velocity Board) & a creek profile

See Flow 2. Velocity Meter (or Stream Veloicyt Board) & Cross-Section (profile) measurements page for a how-to.  Cf.  Our FWC - Field Notes manuals for further information on the Swoffer and Marsh McBirney "velocity meters" and other instruments.

3. Recording creek velocity with a float (using a suitable float device, cork, wood, duck) & a creek cross-section (profile)

See Flow 3. Float-Flow & Profile measurements page for a how-to.

4. Float through culvert (using a suitable float device, cork, wood, duck) & a creek cross-section (profile)

See Flow 4. Float through Culvert measurements page for a how-to.

Notes:
- please proceed with caution in any near or in-stream flow/chemistry measurement situation.  
The key consideration for any field measurements IS - is it safe to proceed(?), if it is not do not proceed, or STOP!

- FWC cloud database jargon is only relevant to folks doing cloud database uploads from individual spreadsheets/data set compilations.