Soil-limiting flow from subsurface emitters. II: Effect on uniformity

Soil variability can affect the flow rate of water from subsurface trickle emitters. This is because of a buildup of pressure in the soil when water cannot be easily transmitted away from the emitter. In this paper, an analysis was developed showing the relationship between discharge versus the design discharge as a function of emitter characteristics and the soil hydraulic properties. When the design flow volume increases or the hydraulic conductivity of the soil decreases, the pressure head of the soil next to the emitter increases, which reduces the flow rate (other factors remaining equal). The subsequent effect on irrigation uniformity was examined using soil data from a field in the Arava Valley, Israel. The average of the calculated ratio of the actual discharge to the designed discharge was 0.905, 0.825, and 0.704 for designed discharges of 1, 2, and 4 L/h, respectively. Corresponding coefficients of variability were 0.072, 0.124, and 0.193, respectively; likewise Christiansen's uniformities were 0.95, 0.91, and 0.85.