Hydraulic Performance Evaluation of Low-Cost Gravity-Fed Drip Irrigation Systems Under Falling Head Conditions

Abstract

Gravity-fed drip irrigation systems offer a cost-effective alternative to conventional systems fitted with pumps, thus making the technology accessible to small-scale farmers. However, these systems rely solely on gravitational pressure, raising concerns about their ability to maintain uniform water distribution which is a key factor for efficient irrigation and crop yield consistency. With limited studies on the performance of gravity-fed drip kits available in the Philippines, this study evaluated the hydraulic performance of two locally available drip kits, Drip Kit A and Drip Kit B, under falling head conditions to simulate actual field scenarios where the water level in the tank decreases as the water drains during operation. A 3.5 m tank platform height was utilized for practicality, with water heads ranging from 4.3 m to 3.7 m in 0.2 m increments which were constrained by the collection cups' volume capacity. Results showed a decline in emitter discharge rates as the operating head fell, where Drip Kit A exhibited slightly higher discharge rates (0.53 to 0.57 L/h) compared to Drip Kit B (0.52 to 0.54 L/h). Both kits exhibited excellent water distribution uniformity, with coefficient of uniformity (CU), emission uniformity (EU), and coefficient of variation (CV) ranging from 91.89% to 96.02%, 84.13% to 92.19%, and 0.08 to 0.15, respectively. Statistical analysis revealed no significant effect (α=5%) of the varying operating heads on CU, EU, and CV, indicating that water distribution uniformity was unaffected by a 0.2 m falling head difference and a total head difference of 0.6 m across trials. It is recommended that the operation of the Drip Kit A and B on a leveled terrain shall focus on managing emitter discharge rates to achieve the appropriate irrigation application time depending on the crop planted.