Water flow (litres/second)
What is it? Water flow is driven by gravity, with water always wanting to get from a high place to a low place. Water flow is an indicator of the amount of surface water flowing measured at a particular point. Water flow rates are affected by stream width/depth, often influenced by man made structures (bridges, culverts, dams etc) or by natural features (vegetation, tree stumps, waterfalls etc).
Why Is it Important? Water flow gives us important information on the source of our freshwater, helping to answer questions around: Is the water flow directly from seasonal precipitation (rainfall, or snow), is the water flow lake fed, or is the water flow from underground (groundwater) springs? Or from all of these…?
Knowing where flowing water comes from is important in improving our understanding of an areas hydrological cycle (surface water and ground water movements), in our understanding of freshwater availability, and in understanding the associated freshwater riparian/aquatic habitats (and their sensitivity) to flow variability.
What does it mean?
- No water flow - this may mean that this location is likely entirely dependant upon seasonal rain, or that someone/something has dammed the water flow!
- Year round water flow - in drier locations (without summer rainfall), year round flow indicates either a underground (groundwater) flow contribution and/or a surface lake inflow. Usually a surface lake inflow is easy to determine if you can see where the water flow is coming from (from a map)
- Seasonal water flow - may indicate that flow at a location is likely entirely dependant upon seasonal rain, or that there are man made controls on water flow (e.g. dams or sluice gates). Man made restrictions to flow are usually in place to preserve precious freshwater resources and habitats.
Protocol
- For measuring the rate of flow (litres/second) you will need a suitable container e.g. a 12 litre (3.17 gallon) bucket or 5 gallon bucket(18.9 litres), or other can/vessel. To make the flow measurement you will need to know the volume of the vessel (“x” litres or “x” gallons) and have a stopwatch of some type with a second hand(wrist watch or smartphones are good) to record how long the container takes to fill.
- Measure water flow volume at a safe, repeatable, defined point (e.g. a gauge/wier, stream “nick point” (waterfall/other), or at another fixed point (e.g. at a culvert).
- Install your container under suitable (repeatable) point to catch all water running and at the same time start the stopwatch. It is useful if there are two volunteers to ensure these are done at the same time. Record the time until the bucket is full (or to a marked volume level) and record the volume and the time - repeat this procedure three times.
- Convert the volume and seconds recorded numbers to litres/second (l/sec) litres divided by seconds = litres/second.
- Average the three measurements (add the three measurements together and divide by three) to give a single “average l/sec value for the flow.
Please remember that photographs tell part of the story of a location/area. Please remember to include a scale (ruler, hat, foot etc). Ideally, for a location with flowing water, a photograph looking upstream and downstream of where you are standing (with a location and date) should be captured.
Pro-tip: Repeat measurements at a location really help establish if water flow is related to seasonal changes (man made or climatic) and are to be made at this location. It is important that any water flow measurement recording is made at a safe location, and consider if you want to use this same location again! Remember the water flowing may vary dramatically from summer to winter (seasonal changes), and at certain locations at any time in between (dam, sluice gate opening).