A registration unit for drain outflow, groundwater depth and precipitation

Abstract

A description is given of an operational field registration unit for open and submerged drain outflow, groundwater depth and rainfall. The drain outflow meter has a measuring range from 20 to 400 cm 3/s, with a mean error in recorded sediment free outflow of 15% at flow rates below 60 cm 3/s and 1.5% at higher flow rates. Its weight is 6–8 kg, depending on the drain outlet it is adapted to, has a length of 90 cm and a height of 50 cm. The groundwater level meter has a measuring range of 1.25 m, but it can be adapted to deeper levels. Its accuracy is 0.5 cm when a float of 4.5 cm in a 5 cm diameter piezometer tube is used. Larger floats give higher accuracies. The transmission mechanism is housed in a 15 × 15 × 22 cm case to be placed on top of the piezometer tube. The rain gauge is commercial pluviograph changed from mechanical to electrical registration. Rainfall is automatically syphoned off after every 10 mm of rainfall. The recorder is a commercial 6-point resistance recorder adapted to battery power (15 V from two wire-fence batteries). To save power, the electric registration paper transport system was replaced by a handwound 14-day clock. The channels normally are activated during 1 min each giving one sweep in 6 min, but an added scanning system gives a choice in recording intervals. Recorder, power supply and scanning system is built in a dust- and waterproof box. The maximum distance between meters and recorder is about 150 m. When larger distances are involved the unit (total weight 37 kg) must be moved.