By: Yosef Yacob, JD, LLM, PhD

Argwings Odera of the East African Standard in a December 12, 2003 article reported Egypt’s “strong reaction” to Kenya’s intended withdrawal from the Nile Basin Treaty, describing it as “an act of war”. [i] The Egyptian stance was triggered by Mr Raila Odinga a member of the Kenyan Parliament and a Senior Cabinet Member who reportedly advised the Kenyan parliament that “…the Nile Basin Treaty, which bars East African countries from exploiting the waters of Lake Victoria for economic gain, should be reviewed.[ii]

The article by Odera quoted Egypt’s Minister for Water Resources and Natural Resources, Mahmoud Abu-Zeid, as having “… accused Kenya of breaching international law by opting out of the treaty,” and … threatening that Kenya could “… not lay claim to sovereignty to protect itself from any action that Egypt may want to take’.”[iii] According to the newspaper account, the Egyptian Minister “…hinted at sanctions, saying Kenya would suffer if [Egypt] and the other nine decided to punish it for quitting the treaty.”[iv]

The Egyptian Minister then inquired “...how [would] Kenya benefit by withdrawing from the treaty” followed by the typical Egyptian retort that “…[Kenya’s] action [would] seriously hurt diplomatic co-operation.”[v]  According to the Egyptian Minister, if Kenya were to “…look at the laws and regulations, [Kenya’s] action is not right," and stressed “… this is a very serious action from one side” while underscoring “…our legal people will be studying Egypt’s response."[vi]

The comments by the Egyptian Minister of Water Resources are obviously calculated as implicit warnings to other Nile riparians, particularly Ethiopia. The Minister’s remarks therefore beg numerous and immediate questions. For instance, which Nile Basin riparian, other than Egypt and possibly Sudan would seek to sanction Kenya for exercising it sovereign right to meet the basic human needs of the Kenyan People?

Notwithstanding the Kenyan Cabinet Member’s insinuation of the existence of a Treaty “subject to review,” what is the legal status of the 1929 “treaty”, rules, and regulations on which the esteemed Egyptian Minister of Water Resources relies to accuse Kenya of breaching?

This article will begin by reviewing the position of the Egyptian legal scholars who continue to brown beat legitimate attempts to raise the issue of Equitable Use. The article will then review some of the applicable international law principles and conclude by highlight the expressed position of riparians who were and continue to be victims of past and present British and Western adventures in the Nile Basin.

Egypt’s Position

The Egyptian legal position was first articulated in 1959 and was explained as follows:

Natural and historical rights are nothing but vested rights resting upon a solid legal basis furnished by the principles of prior appropriation as acknowledged in international law and applied by the courts in international and quasi-international disputes. Thus Egypt's right to her present water requirements being fully protected by international law, whether or not they were provided for by the 1929 agreement, and even if that agreement did not exist. … It must be acknowledged that priority of appropriation gives superiority of rights.[vii]

Egypt maintains that the 1902 assurance made to Great Britain by Emperor Menelik is still binding on Ethiopia. In 1981, at a conference in Dakar, an Egyptian representative stated that:

All these treaties and agreements, … the Treaty of May 15, 1902, … the Agreement of the Agreement of 1929, … provide for the respect of the existing quota of the Nile water. They also ban the execution of any projects that may affect the volume of the Nile water or its quality before negotiating with the country at the Nile mouth.[viii]

Historically, Egypt argued that, by virtue of the principle of pacta sunt servanda,[ix] Nile riparians were legally obliged to observe certain limitations in the utilization of the waters of the Nile Basin.[x] Therefore, Ethiopia was to refrain from any works in the Blue Nile Sub-basin without prior Egyptian and Sudanese consent,[xi] and Article 4(11) the 1929 treaty between Egypt and Britain gave Egypt certain rights and guarantees. According to Egypt, the 1929 agreement with Britain has devolved to the former British colonies in East Africa, including Sudan,[xii] and is subject to the provisions of the Vienna Convention on the Law of Treaties,[xiii] which the International Court of Justice considers the Convention as codifying pre-existing customary international law.[xiv] Therefore, Egypt argues that, the Convention allows termination and suspension of the existing treaties only under the treaty provisions, by consent of the parties,[xv] or by a fundamental change of circumstances.[xvi] In addition to the treaty rights, Egypt asserts “established rights,” “historic rights,” “vested rights,” “priority of appropriations,” “superiority of rights,” and “natural rights,” which give Egypt precedence over other riparians in the utilization of the sub-basin waters.

In February 1997, Prof. Saleh El-Din Amer, Head of the Department of Public International Law of Cairo University in Egypt and advisor to the Government of Egypt, introduced an additional proposition to the position historically held by Egypt. After listing all of the colonial treaties, protocols concerning the Nile and the 1902 agreement between Ethiopia and Britain, he wrote:

All the above mentioned treaties and agreements are typical territorial treaties. Under the rules of general international law, the state parties and their successors are bound to accept the legal obligations of the treaties.[xvii]

Prof. Saleh El-Din is the first Egyptian scholar to characterize the Nile Basin agreements (including the two relevant to the Blue Nile Sub-basin) as territorial treaties and therefore binding. Egypt believes that an obligation is imposed because under general international law, “territorial treaties” are not affected by succession. While it has not been argued by Egypt, Ethiopia’s conduct since 1902 can also be construed as having acquiesced to the validity of the treaty or its maintenance in force or operation under Article 46 of the Convention.[xviii] This acquiescence is conveyed by Ethiopia’s compliance with the treaty provisions in seeking Egyptian and Sudanese consent during the Lake Tsana negotiations, and the non-utilization of the waters in contravention of article 3. The succession, validity and therefore applicability of the 1929 agreement and the 1902 agreement have and continue to dominate the heated dialogue involving the utilization of the Blue Nile Sub-basin.

Succession of Treaties

Traditionally, the method of dealing with treaties in relation to succession has been to classify them as “personal” or “real.”[xix] The postcolonial period completely challenged that position, resulting in the law being uncertain.[xx] State practice in the post-colonial period took several approaches: (1) “universal succession” - the full assumption of colonial treaties by newly independent states,[xxi] (2) “Nyrere Doctrine” - the acceptance of all obligations for a short period, to be followed by a declaration specifying those that were to be accepted,[xxii] and (3) “tabula rasa” or “clean slate” - adherence to rules of international law, but the rejection of adherence to any specific treaty.[xxiii]

Because of these extreme positions, the International law Commission completed the Vienna Convention on Succession of States in Respect to Treaties in 1978.[xxiv] The Convention is based on the principle on non- devolution of colonial obligations with the exception of treaties that delimit boundaries and obligations said to “run with the land and other territorial regimes.” While the Convention purports to codify customary international law, so far, only eight States, including Egypt and Ethiopia, have ratified the Convention and it appears unlikely that the Convention will enter into force.[xxv] 

Therefore, the question of succession of treaties is still governed by the rule of international law which, based on post-1945 state practice, emphasizes non-devolution of obligations, thus allowing new states, however they have emerged, to wipe the slate clean.[xxvi] However, the “clean slate” doctrine is subject to several exceptions.[xxvii] The successor state would still be bound by (a) the rules of international law, (b) dispositive or localized treaties (e.g. port rights, fishing rights, demilitarized zones, navigation rights etc.), and (c) boundary treaties.[xxviii]

Dispositive treaties create ‘real’ rights and obligations ‘resembling’ the conveyance of the English and American private law and the ‘acte transitif de propriété’ of some civil law countries.[xxix] As such, dispositive treaties are immune to the change of sovereignty and run with the land like the easements of English common law or the servitude of Roman law. In other words, they are not personal to the contracting parties and impress upon the territory a permanent status that remains unaffected by the change of territorial sovereignty. Personal treaties, on the other hand, concern political, administrative or economic relations; they are, therefore, fundamentally contractual in character in that they are personal to the parties and dependent on the continued existence of the parties.[xxx] 

Therefore, ‘if any of the parties to such a treaty disappears’ in relation to a part of its territory, ‘it ceases to be able to fulfill the obligations’[xxxi] undertaken as a sovereign power over that territory. Such treaties impose ‘obligations of repeated acts’ and, there­fore, ‘cannot remain in existence except through the continued existence of the contracting parties’.[xxxii] Even though writers such as Brownlie question the exception,[xxxiii] an overwhelming majority of writers accept the existence of such a special category of dispositive treaties devolving automatically on the successor states.[xxxiv]     

The conclusion to be drawn from the foregoing discussion is that there is a category of instruments, variously referred to as treaties creating ‘local rights and obligations’,[xxxv] ‘dispositive’ treaties,[xxxvi] agreements embodying ‘obligations and creating rights in rem’,[xxxvii] or treaties establishing ‘obligations attached to territory’,[xxxviii] and boundary treaties which devolve on the successor state. Egypt therefore argues that the 1902 treaty between Egypt and Ethiopia and the 1929 treaty between Egypt and Britain are treaties establishing obligations attached to territory, which have devolved automatically upon the succeeding states or, in Ethiopia’s case, government. However, it should be noted that ancillary provisions in a treaty, such as a provision on water use in a boundary treaty inserted in a treaty negotiated within the general context of frontier settlement, are in principle, severable from the latter.[xxxix]

Sudan’s Postion

Upon attaining independence, Sudan refused to be automatically bound by treaties of the former colonial administrators. The Sudan argued that, owing to fundamental change of circumstances, the 1929 Agreement and related instruments and measures no longer bound it. Therefore, in January 1956, the Government of Sudan formally announced that it did not consider itself bound by a treaty entered into on its behalf by the British colonial administration.[xl] Despite claims, which Egypt made to historic and natural rights and the binding nature of the 1929 Agreement on riparian and particularly the Sudan, Egypt was compelled to engage in negotiations with the Sudan in 1955, after the following Sudanese declaration:[xli]

It is important to remember that the Sudan was not a party to the Nile Waters agreement, which was concluded between the governments of Egypt and Great Britain. The present Sudan­ese government considers that it was an unjust agreement because it limited the development of irrigation in the Sudan, while leaving Egypt free to develop her irrigation as fast as she pleased. As a result, Egypt has increased her established rights in the waters of the Nile from 40 milliards in 1920 to 48 milliards at the present time. The Sudan does not dis­pute rights which have been established while her hands have been tied, but she claims that the time has now come to change the Nile Waters Agreement.[xlii]

Sudan’s position was consistent with African postcolonial regional attitudes affecting treaty relations. First, consultations were not held with the local people “whose hands were tied” when a treaty relating to or to be applied to the colonized territory was concluded by the colonial power nor was the consent of the colonized people sought.[xliii] Accordingly, many former African colonies rejected the validity of treaties concluded by former colonial administrations without the participation of the representatives of the native population.[xliv] The African states believed strongly that the colonial action completely erased and vitiated the element of consent rendering baseless any claim of succession of treaty obligations after their independence.[xlv]

Rebus Sic Stantibus

It was also argued, that the 1929 agreement was subject to the principle of conventio omnis intelligutur rebus sic stantibus,[xlvi] which would have the effect of vitiating the original treaty. Briefly, this doctrine of rebus sic stantibus asserts that if circumstances which constituted an essential basis of the consent of the parties to be bound by a treaty undergo such far-reaching changes as to transform radically the nature and scope of obligations still to be performed, the agreement may be terminated.[xlvii] A party may also invoke a fundamental change of circumstances as a ground for withdrawing from or suspending the operation of the treaty.[xlviii] Almost all of the contemporary jurists reluctantly admit the existence in international law of this principle[xlix] and the concept is also recognized in Article 62 of the Vienna Convention on the Law of Treaties.[l]

In the Fisheries Jurisdiction case (United Kingdom v. Iceland)[li] the International Court stated that Article 62 of the Vienna Convention “... may in many respects be considered as a codification of existing customary law on the sub­ject of the termination of a treaty relationship on account of change of circumstances.”[lii] Article 62, in part provides:

1. A fundamental change of circumstances which has occurred with regard to those existing at the time of the conclusion of a treaty, and which was not foreseen by the parties, may not be invoked as a ground for terminating or withdrawing from the treaty unless: (a) the existence of those circumstances constituted an essential basis of the consent of the parties to be bound by the treaty; and (b) the effect of the change is radically to transform the extent of obliga­tions still to be performed under the treaty. …

2. A fundamental change of circumstances may not be invoked as a ground for terminating or withdrawing from a treaty (a) if the treaty establishes a boundary.[liii]

Therefore, rebus sic stantibus is applicable only if 'the existence of a given factor or situation constituted an essential basis of the consent of the parties to the treaty' and if 'the effect of the change is to transform in an essential respect the character of obligations undertaken in the treaty.[liv] The question here is whether the changes introduced by the decolonization process and the emergence of independent states in areas, which were formerly territories under British administration, are of such fundamental importance as to permit the operation of the doctrine.

Following independence and in reference to the 1929 agreement, the former British colonies in East Africa, including Sudan, argued:

a treaty drawn up on the basis that 'His Majesty's Government in the United Kingdom regards the safeguarding of [Egyptian] interests as a funda­mental principle of British policy' loses its raison d'être when the position of a successor State is being considered and that the independence of the territories under British administration amounted to a vital change of circumstances with regard to the presumptions under which the 1929 Agreement was made in that the Sudan (and the East African States of Kenya, Tanzania and Uganda) can no longer be regarded as territories whose claim to development could be taken up only once the interests of Egypt, present and potential, have been assured.[lv]

Since independence, the position of the Sudan has greatly changed, both about its international status and to its economic and political development. Are these changes of such fundamental importance as to affect the validity of the 1929 Agreement? While, the argument that the agreement had become an inequitable burden on the Sudan[lvi] may not have been sufficient, a treaty drawn up on the basis that “[H]is Majesty's Government…regards the safeguarding of [Egyptian] rights as a fundamental principle of British policy” loses its reason for being when the position of a successor state is being considered. The 1929 agreement clearly resulted in a subordination of Sudanese sovereign interests to those of Egypt and Sudanese independence constituted a vital change of circumstances. An indepen­dent and sovereign Sudan could not be regarded or treated as a territory with a claim to development only after the interests of Egypt, present and potential, have been assured.[lvii]

Furthermore, the Sudan felt that “the 1929 settlement of the Nile waters was a political matter and that cannot be used as a precedent.”[lviii] Indeed, the fifth paragraph of the 1929 Agreement states that the agreement was to be of a temporary nature conditional on future political developments: [lix]

The present agreement can in no way be considered as affecting the control of the river which is reserved for free discussion between the two Governments in the negotiations on the question of the Sudan.

The Preamble of the 1959 Agreement also confirmed the temporary nature of the 1929 agreement:[lx]

Whereas the Nile Waters Agree­ment concluded in 1929 has only regulated a partial use of the na­tural river and did not cover the future conditions of the fully con­trolled river supply, the two riparians have agreed to the follow­ing ...”

The position of the Sudan Government challenging the 1929 colonial agreement expressed the shared attitudes of many former British colonies towards colonial treaties. These treaties were casually negotiated to promote British colonial interests without regard for the long-term interests of the colonized people. Particularly illustrative was Sudan’s ability to negotiate terms in the 1959 agreement, which was significantly more favorable than the agreement negotiated by Britain on Sudan’s behalf in 1929.

The Position(s) of Tanzania, Uganda and Kenya

On the eve of independence, the Prime Minister of Tanganyika, Mr. Julius Nyrere, made a policy statement on the subject of Tanganyika’s treaty obligations. Mr. Nyrere explained that he was making a somewhat lengthy statement because he thought it right that and the world in general should be aware, in advance of independence, of what the attitude of an independent Tanganyika would be to certain treaties by which the territory was then bound.[lxi] This policy of the Tanzanian Government was formally communicated to the Secretary General of the United Nations in the form of a Declaration to be circulated to all member nations. On July 2, 1962 the United Kingdom (the former colonial administrator) deposited with, and requested circulation by, the United Nations Secretariat a letter, which referred to the Tanganyika Declaration and disclaimed responsibility for the observance of existing treaties in relation to Tanganyika.[lxii]

This “Nyrere Doctrine on Succession of Treaties”, as it became known, was followed with more or less minor variations, by Uganda, Kenya, Malawi, Zambia, Botswana, Lesotho, and Swaziland. Indeed became described as regional international law on the succession of treaties in Eastern and Southern Africa. Some former colonies such as Nigeria exercised their right as sovereign states and repudiated some treaties conceived to be inconsistent with independence. Many of these former colonies felt that colonial treaties violate the rule of international law which prohibits colonialism in all its forms and manifestations and colonial treaties by their nature are therefore void or voidable.[lxiii]

Tanganyika was giving all treaties concluded by the United Kingdom and extended to its territory a two-year grace period during which time they could be renegotiated, and that all agreements not so renegotiated were to be considered terminated unless otherwise required by international law. The qualification 'unless international law requires otherwise' would tempt one to conclude that the 1929 Nile Waters Agreement, being a dispositive treaty devolved on Tanzania by operation of general inter­national law. However, following the declaration of the “Nyrere Doctrine”, Tanganyika, specifically announced that the 1929 Nile Waters Agreement no longer bound it.[lxiv]

The newly independent government took the view that an inherited agreement that purported to bind Tanganyika for all time to secure the prior consent of the Egyptian Government, before it undertook irrigation or power works or other similar measures on Lake Victoria or in its catchment area, appeared to be clearly incompatible with Tanganyika’s status as an independent sovereign state.[lxv] This announcement was conveyed through an official Note from the Government of Tanganyika[lxvi] dated July 4, 1962, addressed to the governments of Sudan, Egypt, and the United Kingdom.[lxvii] Copies of the same note were delivered to the governments of Kenya and Uganda, which were then under self-government status.[lxviii] Accordingly, the government of Tanganyika clarified its position on the matter in the following manner, without taking any further Diplomatic measures:[lxix]

“The Government of Tanganyika, conscious of the vital importance of Lake Victoria and its catchment area to the future needs and interests of the people of Tanganyika, has given the most serious consideration to the situation that arises from the emergence of Tanganyika as an independent sovereign state in relation to the provisions of the Nile Waters Agreement on the uses of the waters of the Nile entered into in 1929 by means of exchange of notes between the governments of Egypt and the United King­dom.

"As the result of such considerations, the Government of Tanganyika has come to the conclusion that the provisions of the 1929 agreement purporting to apply to the countries “under British administration”, are not binding on Tanganyika. At the same time, however, and recognizing the importance of the waters that have their source in Lake Victoria to the governments and peoples of all the Riparian states the Government of Tanganyika is willing to enter into discussions with other interested governments at appropriate times, with a view to formulating and agreeing on measures for the regulation and division of the waters in a man­ner that is just and equitable to all riparian states and of the greatest benefit to all their peoples.

"In the meantime, the Government of Tanganyika for its part attached considerable importance to the continuation of the present arrangements whereby technical experts from the United Arab Republic, the Sudan, and the three East African countries of Tanganyika, Kenya, and Uganda meet at intervals to discuss common technical problems connected with the uses of the waters of the Nile.”[lxx]

On November 21^st, 1963, Egypt, in a note replying to Tanganyika, simply submitted that “pending further agreement, the 1929 Nile Waters Agreement “… which has so far regulated the use of the Nile waters, remains valid and applicable.”[lxxi] The Note added that Egypt was in favor of continuing the unofficial talks between the technical experts from Egypt and the Sudan, on the one hand, and Tanganyika, Kenya and Uganda, on the other. Copies of the Note were sent to the Sudan and to the East African countries of Kenya and Uganda.[lxxii] On their accession to independence, the other upper-basin States, Kenya and Uganda adopted a position similar to that of Tanganyika. Like Tanganyika, they refused to conclude devolution agreements with Great Britain.

Upon its independence in 1962, Uganda too quickly adopted the position expressed in the Nyrere Doctrine.[lxxiii] In a letter addressed to the Secretary-General of the United Nations on 12 February 1963, its Prime Minister defined his country's position on the subject of treaties concluded by Britain and extended to the Protectorate of Uganda.[lxxiv] Part of this letter read as follows:

"(2) In respect of all treaties validly concluded by the United Kingdom on behalf of the Uganda Protectorate, or validly applied or extended by the former to the latter, before October 9, 1962 [the date of Uganda's indepen-dencea, the Government of Uganda will continue on a basis of reciprocity to apply the terms of such treaties from the time of its independence, that is to say, October 9, 1962, until December 31, 1963, unless such treaties are abrogated or modified by agreement with the high contracting parties before December 31, 1963. At the expiry of this period, or of any subsequent exten­sion of the period which may be notified in like manner, the Government of Uganda will regard such treaties, unless they must by the application of the rules of customary international law be regarded as otherwise surviving, as having terminated.

"(4) It is the earnest hope of the Government of Uganda that during the afore­mentioned period the normal process of diplomatic relations will enable it to reach satisfactory accord with the States concerned upon the possibility of the continuance or modification

of such treaties ...[lxxv]

A year later, in 1963, following its independence, Kenya also adopted a position similar to the Nyrere Doctrine, submitting however, that the Government of Kenya was willing to grant a two-year grace period in which the treaties would apply on the basis of reciprocity, or modified by mutual consent. Further, stating that those treaties which were not so modified or negotiated within the two years and “which cannot be regarded as surviving according to the rules of customary international law will be regarded as having terminated.”[lxxvi] Since Egypt did not reply, as far as the Kenyan Government is concerned the treaty ceased to have any effect with respect to Kenya as from December 12, 1965.[lxxvii]

 Therefore, like the Sudan, Tanzania, Uganda and Kenya – all formally repudiated the 1929 Agreement after they became independent, even though unlike the Sudan, they were only remotely referred to in the Agreement.[lxxviii] Save for the Owen Falls Agreement[lxxix] none of these countries appear to be under any obligation regarding the use of the waters flowing to the Lake Victoria and Nile Basins from their respective territories. There are no other agreements on the utilization of the waters of Lake Victoria directly involving all of the riparian states.[lxxx]

The Position(s) of Congo, Rwanda and Burundi

When the Congo, now Zaire, became inde­pendent in 1960, the question of the juridical status of treaties entered into by the departing colonial power and applied to the Congo was raised. Prime Minister Patrice Lumumba declared that all the agreements concluded by Belgium on behalf of his country would be taken over or renounced after thorough prior consideration.[lxxxi] But the treaty under consideration was neither expressly carried over nor expressly renounced. The Congolese Constitution of 1967 provided in its Article 6 that: "Treaties or international agreements concluded before 30 June I960 [the date of independence] will remain valid only to the extent that they have not been modified by national legislation'.[lxxxii] There is no evidence of any such modification of the Anglo-Belgian Agreement of May 9^th 1906. by national legislation. It could therefore be argued that the agreements continue to bind the Congo.

The Anglo-Belgian Agreement of November 22, 1934 concerned the water rights of Rwanda-Burundi and Tanganyika on the Kagera River system.[lxxxiii] Article I provided:

"Water diverted from a part of the watercourse situated wholly within either territory shall be returned without substantial reduction to its natural bed at some point before such watercourse flows into the other territory or at some point before such watercourse forms the common boundary."

The position of Tanzania on the question of colonial treaties has already been considered. When Rwanda became independent, the following general declaration was made:

"The Rwandese Republic undertakes to comply with the international treaties and agreement concluded by Belgium and applicable to Rwanda which the Rwandese Republic does not denounce or which have not given rise to any comments on its part. The Government of the Republic will decide which of these international treaties and agreements should in its opinion apply to independent Rwanda, and in so doing will base itself on international practice.[lxxxiv]

Burundi, in a Note of June 1964, made a much more elaborate declaration which was cast somewhat along the lines of that of Tanganyika.[lxxxv] This Declaration reads:

"... The Government of the Kingdom of Burundi is prepared to succeed to bilateral agreements subject to the following reservations: (1) the agreements in question must remain in force for a period of four years, from 1 July 1962, the date of independence of Burundi, that is to say until 1 July 1966; (2) the agreements in question must be applied on a basis of reciprocity; (3) the agreements in question must be renewable by agreement between the parties; (4) the agreements in question must have been effectively applied; (5) the agreements in question must be subject to the general conditions of the law of nations governing the modification and termination of international instruments; (6) the agreements in question must not be contrary to the letter or the spirit of the constitution ... of Burundi."[lxxxvi]

When the period thus specified had expired, any agreement which had not been renewed by the parties or had terminated under the rules of customary international law was regarded by the Government of Burundi as having lapsed.[lxxxvii] A Note of December 1966 had extended the period of grace specified in paragraph 1 of the Declaration by a further period of two years,[lxxxviii] which means that the 1934 Agreement lapsed in December 1968.

Arguably, Congo and Rwanda are therefore subject to the provisions of the 1906 and the 1934 agreements, respectively. The validity of the agreements do not appear to have been challenged nor renounced pursuant to the policies adopted following their independence.

The 1929 treaty is therefore defunct and has no legal significance in the Nile Basin. Therefore, rather than the polemics, wishful thinking, constant threats, and legal posturing which has thus far characterized the Egyptian attitude, the equitable utilization of the sub-basin’s waters is to be based upon a careful consideration of principles negotiated by the Nile Basin riparians.