Abstract
Auto-start graduated siphon tube has been developed that has helped solve the problem of priming and measurement of hydraulic head differential while irrigating the field. This siphon tube is very simple in construction and is primed only. once in the beginning of irrigation season of a crop. Development of the siphon tube has fa-cilitated the recording of head differential and the corresponding flow passing through it.
INTRODUCTION measurement of hydraulic head differential while irrigating the fields.
Measurement of the available water supply on the farm is important for obtain-ing increased water use efficiency. The de-vices presently available for use in the country for the purpose offer certain prob-lems during water measurement on account of flat gradient in the watercourse system. Thus there is a need to develop a device that can measure and divert water into the fields without being affected by the flat gradient. Siphon tubes which are used to remove water from a head ditch for distributing it over a field through furrows or borders are also used to measure the rate of flow into these distribution systems. The disadvantage is that these need to be primed individually before use. The priming is the principal labour requirement which makes the use of siphon cumbersome for the farmers (Ali, 1982). Measurement of hydraulic head dif-ferential is also another difficult task for them during measurement. They, thus, usu-ally seem reluctant to employ it for water di-version and measurement inspire of its ex-treme usefulness for the purpose. The de-velopment of an auto-start siphon tube was needed to solve the problem of priming and
MATERIALS AND METHODS
Design of an auto-start siphon: The auto-start siphon is equipped with a cup on each end that holds water over the ends of the siphon so that air cannot enter the tube when the water supply level recedes or leaves the watercourse (Fig. 1). The cups hold enough water to maintain the water level above the tube ends for 10 to 14 days (between intervals of irrigation). The bot-tom of the inlet and outlet cups must be at the same elevation or the water in the higher cup will be lowered excessively and the siphon would not remain primed for the maximum period. The tube end sections are each bent to 45 degree angle with the tube center section. The inlet leg then conforms to the side of watercourse which usually has a side slope of 1:1. However, the tube length must be long enough to extend well down into the ditch, over the bank, and well out-side the bank to achieve a maximum head difference between the water in the water-course and lip of the outlet cup. The flow rate under these conditions is similar to that of standard siphon tube.
