It is possible to increase by over thirty per cent the nile water availability

Posted on August 16, 2013 in Water Savings (Nile, Niger ...)

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F. Lemperière

January 2011

The population of the Nile catchment is presently 250 Million and will probably reach 400 Million in 2040. The catchment includes two parts of about same population but with a very different climate.

–       The upstream rainy part (most of this area is in Ethiopia, Uganda and South Sudan).

–       The downstream dry part i.e North Sudan and Egypt.

The available water from the Nile runoff is evaluated as average as 72 Billion m3 /year; it is quite totally coming from the upstream part and used in the downstream part.

For their development the upstream populations (including also part of Tanzania, Kenya, Congo, Rwanda and Burundi) are now requiring a significant share of the run off generated from local rains when Egypt and North Sudan claim historic rights on the Nile Waters.

The best way to avoid conflicts is to increase the water availability for keeping in Egypt and North Sudan at least the water volume presently used and to allow to upstream countries the water resources necessary for their development, possibly in the range of 100 m3 / year / capita in 2030 or 2040.

The average total runoff of the Nile is in fact close to 140 Billion m3 / year but over 40 Billion evaporate in the South Sudan Swamps and 15 Billion in the reservoirs of Aswan and Northern Sudan.

A solution for reducing by half these two main losses is presented below: it is based upon a concrete knowledge of the local very specific data and upon a successful experience of adapted technical solutions.

1) Nile Data

Quite the total runoff of 140 Billion m³/year reaches the Sudan and includes yearly on average:

– An eastern flow of 83 Billion m³ (essentially from Ethiopia) through Sobat (16 Billion m³), Blue Nile (55 Billion m³) and Atbara (12 Billion m³); virtually all flows between July and November. 4 Billion m³ are lost from the Sobat in the East Swamps of the Southern Sudan. Seasonal storage will be possible in future at Ethiopian hydropower dams and could reduce the need for storage in Aswan Lake and at Merowe.

– A southern flow of 42 Billion m³ throughout the year from the White Nile upstream of Sudan; Most is lost by evaporation in the Central Swamps (the Sudd).

– A flow of up to 15 Billion m³ between August and December from the South Sudan tributaries (mainly the Jur and Lol) is virtually lost in the Western Swamps.

Over 40 Billion m³/ year are thus lost by evaporation in the swamps of southern Sudan. Major evaporation losses also occur at Aswan Lake up to 15 Billion m³/ year; and some billion evaporate in Sudan at the reservoirs of Merowe, Roseires and Djebel Aulia.

The annual precipitation depth at Victoria Lake exceeds the evaporation level, but evaporation is higher than the rainfall level by more than 2 m at Aswan reservoir where ten per cent of the storage evaporates each year. The water storage at the 67 000 km² Lake Victoria may thus be more attractive than the Aswan storage, but is poorly used at present, because 80 per cent of the flows over 10 Billion m³/ year / reaching the Sudd are lost there by evaporation.

The main possibilities of increasing the Nile’s water availability are thus in southern Sudan and by the management of main reservoirs.

2) Saving water from the Sudd

Half of the water losses by evaporation in Southern Sudan are in the Sudd.

The Sudd, i.e the central Swamps of Southern Sudan, is an extremely flat and impervious area receiving flows from the Upstream White Nile; These flows are as average over 40 Billion m3 /year but may vary from 15 billion m3/ year (as happened some years between 1910 and 1960) to 65 Billion m3/ year as happened in 1917 and since 1960 with disastrous flooding impacts on local population and wild life. The over years swamps area varied between 1 000 km2 in very dry years to 15 000 km2 in very wet years; the seasonal swamps area varied between 10 000 and 15 000 km2 and their place varies much according to years.

Average yearly rains over Swamps are close to 10 Billion m3 / year (5 to 15).

The total average yearly water reaching the Swamps is thus about 50 billion; the downstream flow is in the range of 15 Billion m3/ year. It is possible to save huge water volumes.

2.1) Past Designs

Many studies have been carried since 1900 aimed at reducing the loss by one or several canals bypassing the Sudd with capacities between 20 and 80 Million m3/ day according to various designs. Excavation of a 350 kms canal (called Jongley Canal) was undertaken in 1978 and reached 260 kms before stoppage in 1983 by the Civil War.

The basic design foreseen in 1978 was a canal totally excavated under the ground level with a cross section of 250 m2 and allowing a flow of 20 Million m3 / day.

French Contractors used an innovative cost effective solution for the excavation; and in 1980 they proposed an alternative design avoiding downstream structures and increasing the canal capacity up to 25 or 30 Million m3/ day with a water level in the canal 1,5m over the natural ground level. This was used for the 260 km excavated length.

Completing the canal as designed in 1980 would be anyway expensive because a totally new excavation equipment will be necessary, as well as Offtake structures; and for any canal design, important works will be required by Southern Sudan for improving conditions of the local populations. The total investment, even for the present canal design, will be probably in the range of one Billion U.S. $ for a water saving of 6 Billion m3/ year as average. Completion time, including mobilization, would be about 5 years.

2.2) A new canal design

A new solution has been studied recently by Engineers who optimized in 1978 the canal excavation methods and proposed the alternative solution chosen in 1980. This new solution is adapted to much increased water needs along the Nile and takes in account the huge annual flows variations since one century; it has three targets:

– To save much more water

– To improve conditions of local populations

– To favour overall water storage in Nile reservoirs

It takes care of the important environmental problems.

The two key points of the New Design are

–   A Dam across the Nile at the upstream canal Offtake (close to the Bor City) including a low gated structure and a lock and dykes across the Nile and along the upstream banks. It will favour the Sudd management and avoid there extreme floodings.

–   A modified canal cross section with a 300m width, a maximum water level about 2,5m over the natural ground; this requires two side dykes (4 m high with 8/1 slopes). The total excavation per m is about 400 m2 in the new part and 250 m2 in the part already excavated 30 years ago where dykes already existing need repairs. The total excavation is thus 260 kms x 250 m2 + 90 km2 x 400 m2 # 100 Million m3 (60 Million m3 had been excavated between 1980 and 1983).

The wet section of the canal will be about 1 200 m2 with a water speed of 0, 90 m/s and the discharge may thus reach 1 100 m3/s in wet years (a capacity of 1000 m3/s had been already suggested in 1902); it may also in dry years be reduced to 100 m3/s, a lower part 40 m wide being then used for navigation.

The huge capacity of the proposed canal and the total Nile control by the Dam across the Nile near Bor have many advantages.

– The water saving is much increased and this extra saving is essentially during wet years. The saving will vary according to years and will be in average close to 15 Billion m3 / year.

– The flows to the swamps may be managed and optimized.

– The disastrous floodings of very wet years are avoided.

– The huge capacity of the canal favours more water storage in Victoria Lake than in Aswan Lake with relevant water saving in Aswan.

The direct extra cost of the solution as compared with the completion of the 1980 design will be about 500 Million  U.S $. But most or all of this extra cost will be balanced by power supply at no cost from extra water used in the existing hydropower plants of North Sudan and Egypt.

2.3) Impacts of the New Design on local population:

  • Local populations in the Swamps area or along the Canal will have significant direct benefits:

–       Floods mitigation.

–       Irrigation along the canal

–       Permanent road

–       Navigation along the canal

They will get also social facilities from the share of overall benefits devoted to South Sudan.

Two points will require great care

–       Canal crossings for people, road traffic, cattle and wild life.

–       Keeping seasonal swamps (toiches) presently used for traditional cattle grazing. They may be kept as they were during the first part of the 20th century, with anyway some 10 000 km2 in the Sudd, much more than needed. The possible seasonal management by the Nile Dam may optimize the utilization and quality of these seasonal swamps.

–       It is likely that such traditional utilization will be progressively replaced by modern irrigation.

3) Water saving in other swamps

About 4 Billion m³/year from the Sobat is lost in the Eastern Swamps. Most of this could be saved by a dam in Ethiopia and/or a canal in the swamps.

Up to 15 Billion m³/year are lost in the low Western Swamps from local tributaries (mainly Jur and Lol Rivers). A large amount could be saved by dams and/or canals similar to the Sudd canal design. Pumping could be used to obtain the necessary head in the canals.

All these schemes could save up to 10 Billion m³/year and be undertaken after the Sudd canal with the experience of its construction and operation. The cost per m3 of water saved could be higher than the cost for the Sudd canal, but remain very attractive.

4 ) Environnemental Impacts in the Sudd

Any canal bypassing the Sudd will probably raise many comments and criticism from Worldwide Ecologists about risks for Biodiversity. It is a serious problem which would be studied seriously. Three points should be analysed.

  • The true past and present  data
  • The future without canal
  • The future with a canal

– The Sudd was considered 100 years ago as a dangerous “World of Desolation” separating North and South Sudan. It may hardly even now be considered as a touristic area; people from industrialized countries should not like to share one week of the traditional life of local population moving in the seasonal swamps within 20 varieties of mosquitoes or staying six months in dry places without water resources.

But the Sudd is also viewed as one of the best world examples of swamps biodiversity including specific birds, fishes, crocodiles and vegetation. Many people abroad advocate keeping unmodified such natural marvel. This biodiversity is undoubtly very important but probably in fact not optimized because the present natural conditions vary at great extent according to years. The overyears swamps have reached sometimes over 10 000 km2 but may be reduced to 1000 or 2000 km2 along one or two years with corresponding disasters for many animals. And exceptional flooding along months of 20 000 km2 usually dry (as happened several years in a century) is probably not better for biodiversity than for the local population.

The management of the Victoria Lake according to rigid rules since 50 years has not improved the Sudd conditions as it did not reduced exceptional flooding and kept low flows during dry years.

– If the present conditions and Victoria Lake management are kept, the situation of the Sudd may be worst in the future for two reasons: the climatic change may increase the rains variations along years and thus the flood years and dry years. And a significant increase of water with drawal by Upstream Countries will increase the possibility of very dry years in the Sudd with huge detrimental impact on the area of permanent swamps and relevant biodiversity.

– The proposed new solution for the canal would divert as average 15 to 20 Billion m3/ year but 30 Billion in wettest years and 3 billion in very dry years. This could be associated with an improved management of the Victoria Lake.

The average flow to the Sudd would thus be usually 20 to 25 Billion m3 / year (as it was half years before 1960) and could be optimized along the year by the Nile Dam in Bor. It seems thus possible to guarantee about 5000 km2 of permanent Swamps and 10 000 km2 of seasonal Swamps. In very dry years it could be possible to draw some water from Victoria Lake storage for avoiding much reduction of these areas. In very wet years, the flow to the Sudd should be in the range of 30 Billion m3/ year instead of 60 avoiding disastrous flooding.

– Similar management would be adapted to the other Swamps which are mainly temporary.

5) Existing and possible storages

Water saving in the Aswan reservoir

– The Nile water storage will become even more important in the future with increased needs and possible impacts of Climatic Change. It is preferable in upstream countries where the rain depth on reservoirs about balances the loss per evaporation: it is more questionable in North Sudan and Egypt where the yearly evaporation is over 2 m and the rain depth 0,2 m.

The storage may be seasonal or over year. The needed seasonal storage is in the range of half the yearly utilization, i.e will be limited to about 50 Billion m3. The over years storage should be very high as far as the relevant evaporation losses are acceptable because there may be five or ten years of low rains and because there may be an excess of water of 200 Billion m3 in 3 years which should not be wasted as in the past.

The two main storage possibilities are the Victoria Lake and the Aswan Reservoir.

The past management of Lake Victoria, based on the rigid rules established 50 years ago, could be optimized and the capacity of a large Sudd canal would provide the opportunity of associating the management of Lake Victoria and the Aswan reservoir for overall optimization giving priority to the Lake Victoria storage.

The storage in the Aswan reservoir could reach 157 Billion m³. The necessary seasonal storage is 30 Billion m³ and will be probably reduced by the seasonal storage of future hydropower schemes in Ethiopia, Sudan or Uganda. The over-year storage of well over 100 Billion m³ is thus the key reason for the huge evaporation which has been
15 Billion m³/year over the last 10 years. Reducing by 50 Billion m³ as average the over-year storage would reduce the evaporation by 4 Billion m³/year and avoid huge losses of water by the Toshka spillway, as occurred recently. The overall saving will be 5 Billion m³/year. Extra storage in Lake Victoria may be used through the Sudd Canal and would balance the 50 Billion m³ reduction of over-year storage at Aswan.

The total over years storage of both reservoirs will be over 250 Billion m3.

– It is also technically possible to create a large reservoir in the 6000 km2 Lake Albert if raising by 20 m its level but this seems unnecessary and probably unacceptable locally. But it may be useful and locally favourable to have there a storage of few m operating within the extreme low and high levels reached in the past, i.e a storage of 3 to 5 m (20 to 30 Billion m3). It could be used for hydropower and give flexibility to the management of upstream Uganda hydroplants and to the seasonal management of South Sudan Swamps. It is however not urgent.

– The storage of future hydropower schemes in Ethiopia, Uganda and South Sudan may probably be essentially seasonal with a limited downstream impact, possibly favourable.

6) Schedule of Works

1st phasis:

  • The key part will be the Sudd Canal and the Nile dam in Bor to be studied and agreed within 3 or 4 next years. The works require about six years and could thus be completed in 2020.

A new management of Victoria and Aswan Lakes could be agreed upon and be initiated before 2015.

Various hydropower plants could be implemented in Ethiopia, Uganda and Sudan with a limited impact on water availability.

Water availability would reach 90 Billion m3/ year.

2nd phasis:

  • The key part would be the water saving in other parts of the South Sudan Swamps. The design could be optimized according to the experience of the first phases. Works could be completed in 2030.
  • A dam could be implemented on Lake Albert.
  • Some water losses should be avoided elsewhere for instance in Djebel Aulia reservoir where the annual evaporation equals the storage.

In 2030 the total water availability could reach 100 Billion m3.

7) Conclusion

A first phasis for improving Nile Waters availability is based on a very wide canal bypassing the Sudd associated with a Dam crossing the Nile at Bor. This favours an optimized management of Victoria and Aswan Lakes. Water saving will be 15 to 20 Billion m3 / year in 2020.

A second phasis may add 10 Billion m3 / year in 2030.

The solutions proposed above deserve evidently checking and precisions. It is however very likely that following conclusions will be confirmed:

–       The technical proposed solutions are realistic as well as water saving evaluations.

–       The benefits will be high for all Nile Countries.

–       The South Sudan should have a key part of decisions and a fair part of overall profits.

–       Sudd populations may and should get huge improvements.

–       The overall impacts on Biodiversity and the possible mitigation measures need careful and balanced studies: positive impacts may be as important as negative ones.

General Nile Catchement

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