The overall objective of the assignment was the supervision of the construction works for the Mwomboshi Dam and appurtenant structures in accordance with the International Federation of Consulting Engineers (FIDIC) Conditions of Contract.
The Mwomboshi site developed on both banks of the Mwomboshi River, in Chisamba District in Central Province to the east of the Great North (T2) Road and covers a total area irrigation of around 5,170 ha gross, abstracting water from the reservoir of the dam. The Dam is a composite structure, with a central concrete spillway of 115m length and 26m height (from foundation), and 26m high rockfill embankments with clay core on either spillway side. It collects water from a 954 km2 catchment, extending up to Mukamwanji Hills at the north, Lileta at the west and Namingele Hill at the south.
A 115m long concrete frontal un-gated dam spillway was proposed within the present riverbed area. The spillway works were designed for a 2,500 yrs recurrence interval and their capacity was also checked against a 10,000 yrs flood event. The design flood is 1,300 m3/s and the check flood 1,600 m3/s. Moreover, floods corresponding to 10, 25 and 50 yrs return periods were calculated, to allow the design of the necessary diversion works and of the culverts along streams and creeks that are crossed by the conveyance network.
The reservoir full supply level (FSL) is +1,091.75 masl as determined by the free overflow spillway design and corresponds to a total reservoir volume of 63.6Mcm. The dam crest is at an elevation of +1096m with a width of 8.0 m. The lengths of the embankment sections are 633.50 m for the right embankment and 1062.00 m for the left embankment. Z&A was also responsible for the detail design of the Dam.