While generally self-cleaning, flumes do require periodic maintenance and those measuring surface waters or in earthen channel installations usually requiring more than those in treatment plant settings. There are, however, no moving parts to wear out or replace.
Inspecting and Maintaing the Site
Over time obstructions can for upstream or downstream of the flume in the form of vegetative growth, trash, or the accumulation of silt. These should be cleared when present.
If submergence is suspected, an inspection for obstructions immediately downstream of the flume should be performed.
The channel banks and the area immediately upstream / downstream of the flume should be inspected for signs of scour or bypass. Where scour is present, geotextiles and armoring of the channel may be necessary. All of the flow of the monitored channel should go through the flume – bypass must be remedied if present.
Inspecting and Maintaining the Flume
For a flume to operate correctly it must be centered in the flow stream and be level from front-to-back and from side-to-side. Remember that natural channels may vary in their course over time and it may be necessary to reset the flume in the center of the channel. Similarly, scour / frost heave / etc. can move a position out of level.
While corrections have been developed for non-level Parshall and Cutthroat flume installations, it is generally better to reset the flume that it is to apply these corrections.
Flume used to monitor treatment plant effluent can form algal growth on the floor and sidewalls, this should be scrubbed off with a mild detergent. Once the surface is clean, it can then be inspected for signs of corrosion, wear, or surface deposits.
If flow rates are low and particulate loads are high, sediment may form in the flume itself. This should be cleaned out as necessary.
In surface water (water rights / irrigation) – applications, galvanized steel flumes are common. Wear – either by the flow stream or by animals may, compromising the protective galvanization on the flume. If this is discovered, the area of corrosion should be cleaned and a cold galvanization applied. If the corrosion is severe enough, the flume should be replaced.
When cleaning the flume, make sure to check that the staff / head gauge is readable. If wear or UV exposure make it no longer readable, replace the gauge.
Image Credit: Watershed UGA, Vadnais Lake Area Water Management Organization