Automated water sampling and flow measuring devices for runoff and subsurface drainage

ABSTRACT:

Inexpensive devices that characterize water flow rates as well as take samples either during runoff or subsurface drainage are needed especially for developing countries where the commercially available equipment may be cost prohibitive. Even in the developed countries, these devices could save considerable money especially if a large number of units are needed such as in replicated plot experiments. This paper describes the design, construction and testing of such devices for characterizing flow rates and also for collecting water samples from surface tile inlets (runoff) and subsurface tile drains. For runoff, the tipping bucket device (about 4 L (1.06 gallon) per tip) sits on top of a sample holder. Flow rates, ranging from 1 to 116 L min⁻¹ (0.26 to 30.68 gallon min⁻¹) are measured by recording the number of tips and time between two consecutive tips. The maximum error in flow measurement is 0.4%. Water samples are collected by catching about 20 mL (0.68 oz) of flow every other tip (an equivalent to about 0.25% of the total runoff) in a polyethylene bottle in the sample holder. The sample holder houses 20 bottles, 19 are for sample collection. After a specific number of pre-programmed tips, the bottle is advanced so that the next empty bottle is under the sampling port. The device can be programmed to catch volume distributed or time distributed samples. The subsurface drainage measuring and sampling device consists of a tipping bucket (410 ml (13.85 oz) per tip) and a tygon tube connected to the sampling port at the base of the tipping bucket. A small fraction (3 ml (0.1 oz)) of the water collects in the tygon tube every other tip. The tube is emptied each day and the sample represents the daily composite drainage. A CR-10 data logger provides the electronic controls for automating the system.