Developing a De-silting plan for the Lubigi Drainage Channel.

Abstract

The Lubigi Drainage Channel is heavily silted with sediments which have choked the channel and reduced its discharge capacity resulting in frequent flooding of the surrounding areas during periods of heavy rains. The main objective of the study was to develop a desilting plan for the Lubigi Drainage Channel which when adopted will help to reduce on the challenges faced due to the inadequate and ineffective operation and maintenance practices being used. The methodology used involved adaptation of the Karim and Kennedy Formula to determine the sediment loading rate. Four samples for the compacted bedload and four samples for the bouncing bedload were obtained from the identified points along the channel for use in determining the different parameters of the formula which include bulk density, mean particle diameter and specific gravity obtained through laboratory tests on the sediment samples. The average sediment loading rates for the compacted bedload and bouncing bedload were 6076.18 m3/day and 1547.85 m3/day which gave desilting intervals of 13 days and 50 days respectively. Since desilting after 13 days is rather uneconomical, a desilting interval of 50 days was adopted in developing the proposed operation, maintenance and de-silting plan, implying that it is required to de-silt the channel section 7 times a year at a total cost of 245 million (UGX) annually. In conclusion, it was established that the channel experiences a very high sedimentation rate of about 27kg/s due to the fine soil particles (i.e. silty sands) which are easily eroded and deposited by storm runoff into the channel. In order to curb this problem, it is recommended that further studies be carried out to identify how this maintenance plan can be implemented and enforced on the channel. This should be done including the creation of an enforcement unit along the channel, giving of hefty fines and penalties, and sensitization of the community in order to reduce the disposal of domestic and sewage waste into the channel.