Performance assessment of water delivery to a smallholder irrigation scheme in Zimbabwe: Nyanyadzi case study

Abstract

The potential benefits from smallholder irrigation schemes are rarely realised due to unsatisfactory performance of their water delivery systems. A study was conducted to quantify and evaluate water delivery performance indicators of adequacy (Ad), equity (Eq) and dependability (Dp) in three sub-blocks of Nyanyadzi smallholder irrigation scheme using water requirement analysis and a questionnaire survey. The water delivery performance evaluation was carried out between October 1996 and January 1997 for two maize crops under supplementary irrigation and for two consecutive irrigation cycles. Water supply adequacy (ratio of supply to demand) in the first cycle was good (Ad>1.21) and became marginally good (0.96 to 1.01) and poor (Ad<0.74) in the second cycle. Adequacy of water supply to the sub-blocks decreased with increase in water requirement (r=-0.87). Water distribution equity (a spatial indicator) was poor in both cycles and Eq values ranged from 0.33 to 1.14. The management capability to distribute water fairly decreased with increase in irrigation requirement (r=0.67). The dependability of water supply was poor (Dp>0.2) at 73 percent of the 42 locations studied in the canal network. Results of a questionnaire survey revealed that the performance of the water delivery system was consistently low. Poor adequacy, equity and reliability of water supply were perceived respectively by 57 percent, 53 percent and 77 percent of the 30 irrigators interviewed. It was concluded that management input should be intensified in head block A to ensure better water deliveries to the scheme.