By Hilary Onek
I read in your paper of September 19, 2004 on page 4, a statement of an Egyptian dam construction specialist, Prof. Ahmed Khttab, quote, â€œI don not see why engineers should say the drop in the lake levels of Lake Victoria will even go further. It is just because of the delayed rains. Within three to four weeks, the water level will rise back to normal.â€ He further stated it is normal for water levels to reduce annually, especially where rainy seasons were not on time.
I would like to disagree with the professor, basing on data available, during 1899-2004 observations of Lake Victoria and the Nile and information on the design parameters used in the construction of the Jinja Nalubale Dam. The current drop of the lake level is unusual.
The Owen Falls hydro-electricity power (HEP) station formally opened on Thursday April 29, 1954 by Her Majesty Queen Elizabeth of England is one investment that laid the foundation for industrialisation in Uganda. At a cost of Â£7,418,971, it was the largest investment in the then protectorate.
According to H. P. Povey and C. R. Westlake statements in the Owen Falls Opening Journal (1954), the damâ€™s original design and construction (1948-54) height was increased by one metre to guarantee Egyptians a reliable flow of the Nile from Lake Victoria.
The Egyptians agreed to pay for the cost of raising the dam and gave compensation, presumably to the displaced people living around the lake. This was solely to guarantee reliable flow statistics, needed by Egyptians to plan for irrigation.
Nile flow during 1899-1960 fluctuated with the season and could not be relied on for agricultural planning. Their other worry was the massive water losses in Sudan marshes for which they plan to dredge a canal to speed water flow and reduce losses.
Egyptians have since maintained a permanent presence at the dam to ensure the minimum required amount of water flow from Jinja, originally agreed upon in 1954, of not less than 594 cu.m/sec (21,000 cu.ft/sec) is guaranteed. They promptly communicate the amount of water leaving Jinja to their country to enable their government plan in advance.
The White Nile that begins at Lake Victoria, provides about 20% of the water that goes to Egypt.
The rest is from the Blue Nile, originating from Ethiopia. With the dam regulating the flow at Jinja, even if Lake Victoria discharges the 1899-1961 average of 660 cu.m/sec into the Nile, Egyptâ€™s interest will always be covered.
The design of the dam at Jinja is such that fluctuations in Lake Victoria water levels, taking into account dry spells or delayed rains has been considered. But not to the presently reported drop levels of about two metres.
The damâ€™s water head (height) of 18.9 metres was designed to fall by 0.5 metres during the dry period and increase by 0.5 metres during the rainy season. So the operating height of the dam is between 18.4m (minimum) and 19.4m (maximum).
The difference of one meter between the lowest and highest levels, provides the operational lake reservoir. It cushions and ensures the desired flow for power production at Jinja and the flow downstream. Therefore, Lake Victoria levels dropping by two metres is a disaster to be addressed urgently.
Hydropower dams are designed and constructed for the following main reasons:
l To create a water head or height through which water would fall to drive turbines, that facilitates generation of electricity.
l To create a reservoir from which power station would draw water. The reservoir stores excess water inflow, increasing water levels from the minimum to the maximum designed level during wet season. It releases the excess water stored during the wet season for power production during the dry period. The hydraulic design ensures the reservoir level does not fall below the minimum designed level before the next wet season. Precautions are always taken to cater for prolonged dry spells like we had recently.
l The designs for hydropower dams are concerned with maintaining the hydraulic regimes for rivers such that the net downstream flows remain unchanged. That explains why in the case of the Jinja dam, having a very large reservoir, the 104 years statistical average can be considered. But for smaller reservoirs, 95% probability flow-level is considered in hydropower generation.
The concerns currently are on the rate at which Lake Victoria level is dropping, considering the amount of water being released for power production, that by far exceed the expected performance of River Nile hydrology at Jinja.
Factors that facilitate water outflows from the lake can be grouped into two:
(a) the natural climatic, and environmental causes.
(b) human management of the water.
In the water balance statements from the Directorate of Water Development, water outflows or losses arising from the natural factors have been relatively stable for a long time and accounts for about 76%, while outflows at Jinja through the Nile account for about 24%. This water balance ratio if interfered with, could affect the hydrology and environment. Since we have little influence over outflows arising from the natural factors, it is the human management of outflows at Jinja that concerns us. After the commissioning of Kiira Power Plant, an extension that draws water from the same point, upstream of the Nalubale Dam (former Owen Falls), there has been a reported high rate drop in lake levels. The average outflow rate for the period 1961-2004 is 1050 cu.m/sec, while the 1899-2004 averages about 800 cu.m/sec (the parameter used for Bujagali). The human management of the Nile at Jinja, within the above parameters when operating the power facilities, would maintain the lake natural regime and its level.
The original Nalubale dam when fully operational, at its normal water head of 18.9m, is capable of using 916.92 cu.m/sec, whereby each of the nine duty turbines taking 101.88 cu.m/sec leaving one turbine on standby. The capacity of Nalubale Dam, when nine turbines are operational, would be 165 megawatts. But if all 10 turbines operate, 1018.8 cu.m/sec release would be needed to produce 180 megawatts.
When William Kiryahika of UETCL, says the normal power generation at Jinja stands at 270 megawatts (The New Vision, September 1, 2004), my interpretation is that 105 megawatts would be generated from Kiira plant to add to the 165 megawatts produced at Nalubale dam. Kiira plant, having a water head of 23 metre, would need a flow rate of 480 cu.m/sec to produce the expected power.
Therefore, to produce 270 megawatts of electricity, the rate of flow required is 1,396 cu.m/sec (or 916 for Nalubale + 480 for Kiira). This is far above the average flow of 1050 cu.m/sec (1961-2004) and Bujagaliâ€™s considered 800 cu.m/sec (1899-2004 average). If the current practice continues for another five to six years, the lake level and the Nile flow at Jinja will be reduced to the pre-dam 1954-level, with serious environmental and climatic consequences. If both Nalubale and Kiira (when completed) are put to full operation, they would need over 1,800 cu.m/sec, an amount almost twice the capacity of the Nile at Jinja. This is a serious miscalculation to which attention was drawn in my earlier report.
Data available clearly indicates violation of the correct hydraulic parameters at the dam. The operators, ESCOM, true to business methods, are keen to produce more electricity and make money regardless of what happens to the lake. It may also be true that their contract technically contains the design errors reflected in the decision to expand the facility at Jinja the way it is.
Lake Victoria levels have been steadily dropping at an alarming rate, which worries many of us who appreciate the hydrology of the Nile and the lake. The natural factors as stated above, have been relatively constant. However, manâ€™s interference with the flow at Jinja, releasing more water than permissible, causing hydrological imbalance of the lake, caused the ongoing drop in levels. A quick calculation shows the balanced natural ratio of Victoria outflow at: 76% evaporation ; 24% discharge to Nile, has now become: 68% evaporation ; 32% to Nile through excessive release.
Irresponsible management of the lake could easily return it to the pre-dam hydrology as the trend shows. The submerged Ripon Falls at the source of the Nile may then resume its original role before the dam was constructed â€” naturally regulating the outflow from Lake Victoria â€” rendering the dam ineffective even for power production.
There is need for both the ministry of water and that of energy to coordinate and put in place practical measures that will check the deteriorating Lake Victoria water balance that may reverse the lake back to its original hydrology.
The dam at Jinja had created a new hydrological balance that enables the production of electricity, which became the backbone of our industrial development. The Government, through its relevant ministries, has to come to terms with the fact that over release of water for power production at Jinja has over-stretched hydrological capability of the lake.
The assessment I carried out, based on hydrological data available, is to give a technical explanation of what I believe has contributed to the currently dropping lake level. I made the explanations simple for a non-engineer to understand.
In 1996, when I learnt of the extension at Jinja, I used the same data to arrive at the same conclusion. I asked the Minister of Energy to arrange for a discussion with his technical team in September 2002, but to date, nothing took place.
The writter is an engineer and MP Lamwo, Kitgum