Climate, Hydrology and Water Resources; Angolan Sector
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Climate, Hydrology and Water Resources; Angolan Sector Draft Translation Specialist Report prepared by Fiesa Namibia for : PERMANENT OKAVANGO RIVER BASIN COMMISSION Angola Botswana Namibia Ministério da Energia e Águas Ministry of Mineral Resources and Water Affairs Ministry of Agriculture, Water and Rural Development GABHIC Department of Water Affairs Department of Water Affairs Cx. P. 6695 Private Bag 0029 Private Bag 13193 LUANDA GABORONE WINDHOEK Tel: +244 2 393 681 Tel: +267 360 7100 Tel: +264 61 296 9111 Fax: +244 2 393 687 Fax: +267 303508 Fax: +264 61 232 861 Okavango River Basin Preparatory Assessment Study Specialist’s Report *** DRAFT TRANSLATION *** TABLE OF CONTENTS 1. Hydrology, Surface Hydraulics and Quality of water 1.1 Overall Description of the Basin 1.1.1 Geomorphology 1.1.2 Orography 1.1.3 Geological Features 1.2 Climate and Surface Water Resources 1.2 Climate 1.2.1 Overall Features of the Basin’s Climate 1.2.2 Rainfalls 1.2.3 Evaporation 1.2.4 Temperature 1.2.5 Humidity 1.2.6 Wind 1.3 Hydrological and Surface Hydraulics 1.3.1 General 1.3.2 Rainfalls 1.3.3 Flows and Drainage 1.3.4 Solid Flows 2 Current Utilization of Water Resources 2.1 General 2.2 Irrigation 2.3 Electricity 2.4 Water Supply 3. Future Utilization of Cubango Water Resources 3.1 General 3.2 Development Scheme 3.3 Sites Identified for Development 3.4 General Criteria for Study 3.4.1 Hydrological 3.4.2 Storage 3.4.3 Energy Climate, Hydrology and Water Resources; Angolan Sector Okavango River Basin Preparatory Assessment Study Specialist’s Report 3.4.4 Potency to be set 3.4.5 Irrigation 3.5 Proposed Scheme 3.5.1 Overall Considerations 3.6 Specific Description of Each Development 3.6.1 Development of Cavango (No. 1) 3.6.2 Development of Chazenga (No. 2) 3.6.3 Development of Mangonga (No. 3) 3.6.4 Development of Mumba (No. 4) 3.6.5 Development of Muculungungo (No. 5) 3.6.6 Development of Mbambi (No. 6) 3.6.7 Development of Calemba (No. 9) 3.6.8 Development of Cutato (No. 10) 3.6.9 Development of Malobas (No. 13) 3.6.10 Development of Cuangar (No. 18) 3.6.11 Development of Tondoro (No. 19) 3.6.12 Development of Sâmbio (No. 20) 3.6.13 Development of Mucusso (No. 21) 3.6.14 Development of Xamavera (No. 22) 3.7 Energy aspects of the Scheme 3.7.1 General 3.7.2 Energy production 3.7.3 Energy Production during Dry Season and Critical Season 3.7.4 Scales most Productive 3.8 Irrigation Aspects of the Scheme 3.8.1 Aspects of Flow Regulation 3.8.2 Meeting irrigation needs 3.9 Navigational ability 3.10 Cubango River and Water Supply to the Delta of Cuvelai River 4. Recommendations Climate, Hydrology and Water Resources; Angolan Sector Okavango River Basin Preparatory Assessment Study Specialist’s Report 1 Hydrology, Surface Hydraulics and Water Quality 1.1 Overall Description of the Basin 1.1.1 Geomorphology The Cubango River starts in the Bié plateau, Angola’s hydrographic centre, to the South of Vila Nova, at an altitude of 1800 m, and in its initial track, it runs North-South until Menongue, from where it heads Northwest-Southeast. Downstream Cuangar, its course evolves West-Eastwards and it continues to the Southern Angola/Namibian border until Mucusso, at a length of 975 Km, in the Angolan territory. In the territory of Namibia, the river is known as the Okavango river, its length does not exceed 55 Km. The river crosses the Caprivi strip in Caprivi Region as it enters the territory of Botswana, at a swampy area close to Ngami Lake, known as the Okavango Delta. Between its river and the Zambezi, there appears, still an unexplained mechanism, during flooding periods, the existance of a communication system through the Limyanti River, which, starts from Ngami Lake, and crosses the Botswana territory, towards the Zambezi. Its basin in the Angolan territory covers between parallels 12° 20' South and 18° South (Figure 1.1) and between the meridians 16° East and 21°30' East, covering parts of Cuando Cubango, Huambo, Bié, Moxico, Cunene and Huíla Provinces. To the East it meets the Cuando River, the Zambeze River basin to the Northeast, the Cuanza River basin to the North and the Cunene to the West, including the drainage area not clearly defined and known as the Cuvelai Delta River. In the Angolan territory the basin covers an area of 148 860 Sq. Km, of which 60 860 belongs to the basin of its main tributary, the Cuito River. The basin is elongated (Figure 1.2) and its axis is greater in the direction Northwest- Southeast, and it is extended to the North, evolving itself in its almost entirety, at the left margin of the river. The right side area of the basin to the North and South reaches up to 40 Km wide, but it is narrow at the central area, and at times it decreases into a small strip, which in many areas, it reaches below 10 Km wide. 1.1.2 Orography Orographically (Figure 1.3), it has to be considered at the Northwest side of the basin, North of the parallel that crosses the village of Chitembo, an uneven area with altitude higher than 1500 metres and increasing to the Northeast reaching heights of 1800metrs. From this area, which include the counter act of heights which preceed the western strip of the Angolan highlands, altitudes decrease towards the South as well as Eastwards, although in that direction, the decrease is slight and is not lower than 1400 m. From the 1400 m curve, altitudes decrease rapidly to the South as far as 1200 m and this marks the transition to the plain area that covers the meridional part of the basin with altitudes higher than 1000 m, although this decreases slightly to the South. This description shows that from the orographical point of view, the basin could be divided into four areas: Climate, Hydrology and Water Resources; Angolan Sector 3 Okavango River Basin Preparatory Assessment Study Specialist’s Report Figure 1.1 : Location of the Cubango River Basin Climate, Hydrology and Water Resources; Angolan Sector 4 Okavango River Basin Preparatory Assessment Study Specialist’s Report Figure 1.2 : Cubango River Basin Climate, Hydrology and Water Resources; Angolan Sector 5 Okavango River Basin Preparatory Assessment Study Specialist’s Report Figure 1.3 : Orography of the Cubango River Basin Climate, Hydrology and Water Resources; Angolan Sector 6 Okavango River Basin Preparatory Assessment Study Specialist’s Report Figure 1.4 : Geology of the Cubango River Basin Climate, Hydrology and Water Resources; Angolan Sector 7 Okavango River Basin Preparatory Assessment Study Specialist’s Report I An uneven area with altitudes between 1500 m and 1800 m, covering the whole of the Northwest of the basin ; II The Northwestern region’s relief is generally rippled, with altitudes higher than 1400 m, but not exceeding 1500 m of altitude, except on small and isolated nucleuses; III Transitional area, inclined Westwards with altitudes decreasing from 1400 m to 1200 m; IV The South of the basin is a plain area with a slightly uneven terrain and, although somehow steep Southwards, its altitudes are always higher than 1000 m. 1.1.3 Geological Features The geological design of Figure 1.4, the three largest rock groups can be observed at the basin. The eruptive and metamorphic rocks confined to the relief region especially at the Northwest side of the basin, and the sedimentary rocks at the plained areas of the Northeast and South which constitute the rest of the basin. Eruptive rocks cover part of that Northeastern region, and are represented by: Ante-permian formations, include generally, granites, porphyries and porphyritic and, to Northwest of Cavango (Artur Paiva), one of the small types of syenites; Undated ante-cambric formations, made up of granites, and granodiorites and quartzodiorites and, in Cubango region (Artur de Paiva), a small sport of dolerites. Metamorphic rocks form near the Northwest of the basin, where these are represented by formations of the Base Complex, made up of gneisses of different kinds, metamorphic schists, quartzites, quartzite schists and crystalline calcareous. On the metamorphic formations of the Upper Group of Oendolongo System scattered spots of eruptive rocks emerge, consisting of rocks of a weak metamorphism, namely ferruginous quartzites (of “banded-ironstone” type - itabiritos), quartzites and sandstones, which are crossed by felsites and porphyry dikes. Sedimentary formations, which cover most of the basin area, certainly constitute its most striking feature, resulting in inevitable consequences in the water course regime as well as in the economic potential. These are Upper Kalahari formations of Pleistocene, or even recent and essentially sandy, with some gravel levels and laterite deposits, resting on “polymorph sandstones”, quartzites, sandstones and millicified calcareous of the lower Kalahari. Still unknown are the mineral potential of the region. Rare occurrences are located at the older formations, but no signs of any Kalahari, or recent formations, which cover most of the Cubango basin, were identified. Climate, Hydrology and Water Resources; Angolan Sector 8 Okavango River Basin Preparatory Assessment Study Specialist’s Report Cupriferous impregnations of Menongue area can be identified which, under the current circumstances, neither correspond to a real economically exploring copper deposit, nor to the existence of manganese in Bela Vista region. This appears to be as a result of the laterite process, although there are no elements which allows us to ascertain its importance. It has also been observed throughout Southern Angola the existence of alluvial gold, most of which has already been explored, although not always under profitable technical and financial conditions.