Education
Kiira extension had design flaw
Publish Date: Feb 28, 2005
Newvision Archive
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I am glad that the Ministry of Energy has at last come out on the Owen Falls Extension, although in quite an unprofessional way (The New Vision, Monday, January 17). I was able though to get some clues to their design criteria. The question is, was the extension a correct investment decision? There are ample data that clearly point to technical errors or omissions in the design of a spillway that become a penstock for Kiira hydropower extension.
The ministry admits that Acres Company used only data recordings after 1961, an average flow of 1090m3/sec for the design of Kiira dam. The normal practice is to use 95% probability flow, or 800 m3/sec at Jinja as was done for Bujagali. My concern is that, Nalubaale’s nine of the ten turbines could use about 917 m3/sec, leaving only 173m3/sec of the 1090 for an extension. Kiira extension design has a capacity to take about 900m3/sec to produce 200 mw of energy. The three already installed turbines at Kiira take 540 m3/sec and if combined with the Nalubaale’s 917m3/sec, total discharge becomes 1457m3/sec.
UEGCL is currently releasing above 1400m3/sec to generate 220 mw of energy. It is the above mismatch that I consider the gist of the design error and is fundamental. Thus they are releasing more water than is physically sustainable.
The ministry is openly lying to Ugandans in the press that water release at the Owen Falls for power generation is only 807m3/sec and went ahead with some fictitious deductions to prove that they are not responsible for the dropping lake levels.
Their understanding of hydro-power design process was lacking. They confined major roles to only hydrologists and electro-mechanical engineers, quote:
“…Electro-mechanical engineers determine the capacity to install in a power station, taking into account the features one wants to incorporate into the design…etc”. In reality it is not as simple as that.
Below are the technical design processes in defining hydropower:
Design discharge (Q cu.m/sec) at the dam site, normally 95% probability flow is determined as per hydrological historical flow data if available, documented by hydrologists and analysed by hydropower civil engineers for the purposes of determining sustainable power generating flow.
The design height of a dam (H meter) is determined following hydrological, geological, topographical, environmental, demographic and economic considerations among others, involving relevant professionals. Effective power generation operational heights, maximum and minimum levels are then determined. Both Q and H are used in determining the power capacity and choosing the type of turbine needed.

The capacities of power installations are automatically determined by the parameters flow rate and dam operational height. For Nalubaale for example, based on a height of 18.9m and a water speed of 917 cubic metres per second, the power production is 180MW.
Design conditions, determine the power generation capacity to install at hydropower stations, not the wish of electro-mechanical engineers as UEGCL stated. Electro-mechanical engineers only design/choose appropriate turbines and generators.
The above is followed by structural design of the dam, the powerhouse and accessories like spillway, penstock, etc., conforming to flow rate and dam operational height, by civil engineers
The press release from the Ministry states: “While field surveys and investigations were already done to construct a spillway, it was decided that the work be incorporated into the extension work” — Kiira power generation extension.
A spillway is a facility through which excessive unexpected inflow to a dam reservoir is evacuated to protect the dam structures from the resultant overflow, not for power generation. The last excessive inflow at Owen Falls Bridge occurred 43 years ago.
The power authority states in the press that “rainfall data analysis shows that while in the last 100 years the inflow into the lake was averaging 73 million cubic meters per day, the average for 2004 is now 23 million cubic meters per day”.
This is wrong data. Hydrologists’ average recorded inflow into Lake Victoria over the years is 133 cubic kilometers per annum which translates into 364 million cubic meters of water per day and not 23 million cubic metres as UEGCL stated. This data is available in their records.
Reports from the Meteorological Department during the last 41 years, show stable rainfall regime, with fluctuating periods of dry spells. The recent dry period, June-September 2004, was followed by heavy rain during October-December 2004. This was predicted and the Minister of Energy referred to it as a small El-Nino, expected to restore the lake water level. In fact, a senior Egyptian dam construction specialist Prof. Ahmed Khttab wondered why engineers should worry that the lake level would drop further (Sunday Vision, September 19, 2004, Pg.4). He said “…..Within three to four weeks the water level will rise back to normal ….” Indeed, the rains came, but the level never rose back. Instead the lake levels have continued to drop.
Evaporation and precipitation (rainfall) are mutual as most rain around the lake basin is convectional. As in the recent case, delayed rains are compensated by heavy rain that follows.
Management of any hydropower reservoir is a long-term program, with clear long-term (3 — 10 years) projections, based on the hydrological data available and forecast predictions. The Nile has been observed for more than 100 years and those data could guide management.
To politicise electricity issues will only sink Uganda economically and socially. I am ready to take any challenge, backed by credible technical facts and not fiction.

Eng. Hilary Onek, MP Lamwo County, Kitgum.

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