|Nine Water Basins|
Wami/Ruvu and its associated Coast Rivers
The most noticeable plains are Lower Ruvu Plains and Mgeta plains in the Ruvu system and the Mkata-Wami, (400-800 m), lower Wami (200-400) and the Berega valley 800-1200 m.
1. Ukaguru Mountains to the north of the Wami (Altitude 400-1000 m).
2. Rubeho mountain, west of Kilosa (Altitude range 500-1000 m).
3. Nguru Mountains west of Kilosa (Altitude range 400-2000 m.
4. The Uluguru mountains south east of Morogoro (Altitude 400-2500 mamsl).
Wami/Ruvu basin consists of two main river systems, the Wami 40,000 km2 and the Ruvu 17,700 km2. Coastal rivers south of Dar es Salaam are part of this basin. The basin as a whole covers an area of 72.930 km2. This basin consists of wide plains and large mountain ranges. Four mountain blocks are distinguished and these are:
Internal Drainage Basin
Water Resources Management is undertaken by the Basin Water Office which is under the Basin Water Board. The Board is chosen by the minister responsible for Water according to Water utilization (control and Regulation) Act no. 42 of 1974 and its subsequent amendments No. 10 of 1981, No 17 of 1989, No 8 of 1997.
The basin is situated in the semi-arid region of Tanzania. The mean annual rainfall range from 500 mm/yr at Bahi to 900mm/yr in the highlands of Mbulu district. Rainfall varies greatly from year to year.
The Internal Drainage Basin is described by rivers/streams draining into a group of inland water bodies (lakes) that are located around the north-central part of the country. The system, mainly of troughs and faults runs southward from lake Natron at the border with Kenya to central Tanzania in the Bahi depression and varies in width from 30-90 km. Total basin area on the Tanzanian side is about 153,800 km2. The major drainage systems in this basin includes:- Lake Eyasi System, which drains areas in North Tabora Region and East Shinyanga by the Wembere and Manonga river systems, Lake Manyara System and Bubu complex where important features are the Bubu and Bubu swamps. Several other small independent lakes and swamps with no outlet existing in this basin include Lake Basuto and Lake Natron.
Internal drainage basins of Lake Eyasi, Manyara and Bubu Complex
Lake Victoria Basin
The eastern part of the basin especially in highlands of Tarime, the rainfall is distinctively bimodal. In the south portion in Mwanza Region, the pattern is unimodal with a wet and dry season. The western part receives rainfall almost throughout the year with minimum in July.There are considerable variations in the average yearly rainfall over the Lake surface and the surrounding land area. Over the extreme eastern area of the Lake, rainfall is between 500 and 750 mm per year. Westward from this area rainfall increase to an annual average of over 2,000mm in areas around Bukoba and the Ssese Islands south of the town. To the south of the lake, in Mwanza Region the yearly average rainfall is 750 to 1100 mm and in the eastern part in Mara Region rainfall is between 750-1000mm increasing to 1600 on the highland areas of Tarime.
The main rivers draining into the Lake include Kagera, Simiyu, Mbarageti, Grumet, Mara and Mori Rivers.
The Lake is shared between Uganda, Kenya and Tanzania.
The most important feature of this basin is the Lake Victoria which is the largest in Africa and source of the White Nile. Lake Victoria lies across the equator between latitudes 0 31N and 3 54S, longitudes 31 18E to 34 54E with an average depth of 80m.
Lake Tanganyika Basin
In addition to the Malagarasi, there are smaller basins draining into L. Tanganyika. To the north west of Kigoma, the Luiche is an important river. The lower part of the river forms the Luiche Delta which floods often during the rainy season.
Other major tributaries are the Ruchugi River which drains the hilly landscape north of Kasulu, running in a southerly direction through a low, partly swampy, undulating landscape, before it enters the Malagarasi River at Uvinza.
The Ugalla River drains an area of approximately 52.000km2. and before the confluence with the Malagarasi, it passes through large areas of swamps and marshlands, forming the seasonal Lakes of Sagara and Ugalla.
The basin is dominated by the Malagarasi river system which is 130,000 km2. The main river, the Malagarasi originates in the mountainous area close to the border with Burundi at an altitude of 1750 m.a.m.s.l. from where it runs northeasterly through hilly and mountainous landscape and then southward into the Malagarasi Swamps. Its major tributaries, the Myowosi and Igombe Rivers meet the Malagarasi in the seasonal Lake Nyamagoma. The Ugalla and Ruchugi Rivers join the main river downstream of Lake Nyamagoma. The river then runs west, through the Misito Escarpment where it forms the rapids and waterfalls before entering Lake Tanganyika.
Lake Tanganyika Basin is situated in the Western Part of the country. All the catchments that drain in Lake Tanganyika constitute the Lake Tanganyika basin. The total catchment of Lake Tanganyika basin as a whole is 239.000km2 and the area of the lake is 32,000 km2. The land surface of the basin on Tanzania side is 151,000km2 which contributes 60% of the total runoff to Lake Tanganyika.
Lake Rukwa Basin
Water in the basin is mainly for domestic water supply for major urban centres Mbeya and Sumbawanga, and other smaller towns like Vwawa, Chunya, Tunduma all in Mbeya Region, Mpanda in Rukwa Region and for rural areas. Water is also used for smallholder irrigation purposes and for the environment uses in the basin. Like most places water is a significant catalyst to livelihoods and development in the basin. The following chapters will describe other water uses.
The basin is moderately endowed with water for use by its inhabitants. The rivers with low to nil dry season flow and often spring – fed perennial steams dominate the surface water picture Lake Rukwa which is the largest surface water body is an inland drainage sink with no outlets. Old maps show the lake in two parts. The lake is quite shallow with mean depth of 4 m. It has a very high rate of evaporation of the order of 2,000 mm per annum and average annual rainfall of 900 mm. The lake has highly changing coastline and poor physical and chemical water quality but important source of water in the dry season for villages along the shoreline and animals both wild and livestock. The water in the basin is often affected by season water scarcity although of local nature and poor water quality.
The Rungwa River with a catchment of 20,000 km2, in Chunya district is the largest drainage area covering about 25% of the total basin area. Other river systems in the basin are the Songwe from the Poroto mountains, Momba and other small numerous rivers both in the east and west of the lake. Others are Luiche, Katuma and Katuma originating from the Ufipa plateau. Most rivers rise and fall with the rains in between the months of November and May.Groundwater is available in variable quantities and depths throughout the basin. Shallow groundwater can only be systematically exploited in the Rukwa valley but will occasionally be found in usable quantities in other areas. These other areas can provide groundwater from deep boreholes although yield predictions can be very difficult.
The Rufiji Basin Water Office (RBWO) was established after the inauguration of the first Basin Water Board (RBWB) on the 14/9/1993. It is one of the nine river basins declared in 1992 by Minister responsible for water affairs. The Office has been established in accordance to the Act No.11 of 2009. The Rufiji Basin Water Office has its Headquarters in Iringa Municipal Town. RBWO is under the Ministry of Water and Irrigation. All its workers are employed by this MoW
There are ten members of the RBWB. They are drawn from public institutions and the private sector (including representatives of NGO’s, Farmers and Livestock keepers, and women). The Minister of Water and Irrigation appoints the Chairman and the members of the Board.
The main objectives of the Office are in accordance to the National Water Law namely:
• To act as principal executors of the Water Resources Management Act No.11 of 2009.
• To carry out research pertaining to Water Resources Management in the
The Rufiji Basin covers an area of 183,791 square kilometers (about 20% of Tanzania). The river drains into the Indian Ocean. The Basin is situated between Longitudes 33o55’E and 39o25’E and between Latitudes 5o35,S and 10o45’S. The altitude of the basin rises from 0 at the Indian Ocean to above 2,960 meters above mean sea level (mamsl) in the highlands in Mbeya Region.
The land use in the Basin includes agriculture, mining, forestry, livestock keeping, fishing, wild life, navigation and human settlements.
The Rufiji Basin comprises of four major rivers namely:
• The Great Ruaha River - 85,554 km2
• The Kilombero River - 40,330 km2
• The Luwegu River - 25,288 km2
• The Rufiji (lower part of main river) - 32,619 km2
The climate in the basin differs from the coast to the highlands in the upper parts of the catchments. For instance, except for the lower parts of the basin, which experience two rainy seasons, the largest portion is characterized by unimodal rainfall. The Average rainfall varies from 400mm in the drier areas to 2000mm in wetter parts
The mean temperature in the coastal area is 260oC and that of the hinterland is 240oC. Annual and daily variations in temperature are small. Geomorphology: African, Post African and Congo/Coast land surfaces largely occupies the basin. Gondwana land surface occupy a small part near Songea. Coastal land surface covers Mtwara and Newala Districts. Post African land surface covers Nachingwea, Masasi and part of Tunduru Districts while the African land surface covers the rest of Tunduru, Songea and part of Mbinga Districts. Geology: Dominant rocks in the basin are Karoo and Usagaran crystalline limestone series of Masasi. The main catchments lie on an altitude between 305 – 710 m above mean sea level and drops almost gradually before entering the coastal plains. The Ruvuma River is shared by Tanzania and Mozambique and drains into Indian Ocean. It has the length of about 800 km of which about 650 km forms the border between Tanzania and Mozambique.
Lake Nyasa Basin
The Lake Nyasa is a shared lake between Tanzania, Malawi and Mozambique with a total drainage area of about 132,000km2. The lake has surface area of about 33,000km2. The basin area draining into the lake from the Tanzania side is about 37,000 km2. Major rivers are Songwe (shared with Malawi), Kiwira, Lufirio, Ruhuhu, and Rumakali.
The Ruvuma River Basin occupies an estimated catchments area of about 152,200 km2 out of which Tanzania occupies 52,200 km2 (34.3%), Mozambique occupies 99,530 km2 (65.39%) and Malawi occupies 470 km2 (0.31%) (SADC). Some large tributaries from Tanzania originate in Mbinga, Tunduru and Masasi districts. The mean annual runoff at the mouth is 15,000 Million Cubic meters. Ruvuma River and Southern Coast Basin has the area of about 104,270 km2 with the population of about 2,241,944 (2002).
Ruvuma River and Southern Coast Basin is comprised of five major independent river systems draining into Indian Ocean. The major river basin systems include:
i. River Matandu 18,565 km2;
ii. River Mavuji 5,600 km2;
iii. River Mbwemkuru 16,255 km2;
iv. River Lukuledi 12,950 km2; and
v. River Ruvuma tributaries 52,200 km2.
The Pangani Basin is located in the North Eastern Tanzania between latitude 3o03’S and 5o59’S and longitude 36o23’E and 39o13’E with an area of about 53,600 km2. Seventeen administrative districts of Arusha, Manyara, Kilimanjaro and Tanga Regions are within the Basin. The basin is composed of five sub-catchments, namely Pangani, Zigi, Umba, Mkulumuzi and Msangazi with main rivers draining to the Indian Ocean. Mount Kilimanjaro and Meru are the highest features in the basin. Pare and Usambara Mountains are other high features. The main rivers are Pangani, Umba, Msangazi, Zigi and Mkulumuzi. Lakes in the Basin are Chala, Jipe, Duluti, Manga and Karamba. Nyumba ya Mungu, Mabayani and Kalimawe Dams are man made reservoirs. Major uses water are domestic, irrigation, industries, hydropower, livestock, fisheries, recreation, transportation, etc.