Water level (maximum) – inky tape method

Parameter to be measured:

Maximum water level

Method:

Sections of 30 m tape measure are smeared with a thin coat of washable ink on both sides, allowed to dry then stretched along the inside of a thin PVC tube (20 mm) and attached at each end with electricians tape. These tubes have a single small hole at the top of the tube to allow air circulation and are left open at the bottom to allow water to enter; they are placed inside the larger diameter (25 mm) PVC wells then capped with an old sample tube taped on but leaving a hole to allow air to circulate in the tubes.

As the water level rises in the tubes ink is washed off to leave clean tape up to the height of the maximum water table. To read the maximum water table height over a given period you simply read the depth to which the ink has been washed off. To reset you re-coat the washed section of tape with washable ink.

Equipment:

Equipment design for maximum rise crest stage tube (A) with photographs of an example installed at the field site (B) and of a tape with the ink washed off to the maximum water level (C).

• PVC tube 25 mm diameter
• PVC tube 20 mm diameter
• Old 30 m fibre glass tape measure
• Washable ink
• Cap – I used old lab sample tubes.

Advantages:

• Very cheap
• Robust

Disadvantages:

• Hot weather can cause condensation in the tube which can run down the tape washing off some of the ink. This uncertainty can be limited during data collection by reading both sides of the tape and comparing their maximum stage estimate.
• The tapes need to be kept dry so re-setting is difficult in the rain.

What to watch out for:

The longer you leave these unattended the more likely they will suffer data loss particularly in summer.

Links

Projects that used the above equipment:

Other related web sites: