Abstract. A study was undertaken to evaluate the performance of sand-traps at Wonji-Shoa
Sugar Estate, Ethiopia. Inflow and outflow samples from the sand-traps and deposited sediment
samples from the sand-traps, main canal, and reservoirs were taken. The samples were analyzed
for sediment concentration and particle size distribution. During the study period, the sand-traps
were performing satisfactorily in removing a good portion of suspended sediment (as high as
63% in case of sand-trap A and 54% in case of sand-trap B) in the week after flushing and they
were performing poor (as low as −40% in case of sand-trap A and 6% in case of sand-trap
B) when the sand-trap was running without flushing for about two months. Sediment particle
size analyses of the samples indicated that the sand-traps retained almost all the sand fractions
(90–95%) greater than 0.15 mm. Fifty to sixty percent of the sediment particles passing the
sand-traps into the main canal was smaller than 0.002 mm. Sieve analyses of the bed materials
taken from the sand-traps showed that particles up to medium gravel size (6.3–13.2 mm) were
entering the sand-traps and almost all were trapped. This result shows that performance of
the sand-traps under the existing sediment load of Awash River was found to be satisfactory.
However, it was observed that performance level of the sand-traps was very much dependent
on the flushing interval of deposited sediment.