UNITED REPUBLIC OF TANZANIA
MINISTRY OF WATER
INTERNAL DRAINAGE BASIN WATER BOARD
HYDROLOGICAL REPORT 2012/2013
Internal Drainage Basin Water Board
P.O Box 1673
Singida-Tanzania
Tel. /Fax: +255 (26) 2502418
E-Mail:
December, 2013
List of Tables ii
List of Figures iii
List of Appendices iii
EXECUTIVE SUMMARY iv
1.0 INTRODUCTION 1
1.1 Objectives of the Report 1
1.2 Location 1
1.3 CLIMATE 1
1.4 Physiography 1
1.4.1 Topography 1
1.4.2 Geomorphology 2
1.4.3 Drainage Pattern 2
1.4.4 Land Cover and Use 2
1.4.5 Soil 3
1.4.6 Main Features 3
1.4.7 Geology 3
2.0 MONITORING NETWORK 5
2.1 rainfall and other climatic stations 5
2.1.1 rainfall stations 5
2.1.2 weather stations 5
2.2 hydrometric stations 5
2.3 groundwater stations 5
2.4 water quality stations 5
2.5 spatial distribution of the stations 5
3.0 HYDRO-METEOROLOGICAL DATA 7
3.1 rainfall and other climatic data 7
3.2 discharge 7
3.3 water level 7
3.4 groundwater 7
3.3 water quality 7
4.0 HYDROLOGY OF THE BASIN 8
4.1 surface water 8
4.2 groundwater occurrence 9
4.3 Water Quality 10
5.0 GENERAL REMARKS AND WAY FORWARD 11
5.1 conclusion 11
5.2 challenges 11
5.3 way forward 11
6.0 APPENDICES 12
List of Tables
Table 2-1: Spatial distribution of the working monitoring stations 6
Table 4-1: Long-term average of rainfall in the Basin 8
Table 4-2: Maximum rainfall amounts 8
List of Figures
Figure 1-1: Location of Internal Drainage Basin 1
Figure 1-2: Map of IDB Showing Drainage Patterns 2
Figure 1-3: Land cover map of Internal Drainage Basin 2
Figure 1-4 Geological Map of IDB 4
Figure 4-1: Monthly rainfall in some stations 8
Figure 4-2: Water level recorded in Nhumbu River at Shinyanga Road Bridge 9
Figure 4-3: Water level recorded in Dudumera River at Kiru Six Road Bridge 9
Figure 4-4: Groundwater trend recorded at Singida Maji Yard 10
List of Appendices
Appendix 6.1: List and status of rainfall stations 12
Appendix 6-2: List and status of weather stations 14
Appendix 6-3 List and status of hydrometric stations 14
Appendix 6-4: List and status of groundwater monitoring stations 16
Appendix 6-5: List and status of water quality monitoring stations 16
Appendix 6-6: Rainfall data recorded at Shinyanga meteorological station 17
Appendix 6-7: Temperature data recorded at Shinyanga meteorological station 21
Appendix 6-8: Evaporation data recorded at Shinyanga meteorological station 21
Appendix 6-9 Flow data recorded in Lake Manyara Sub-basin – Spot measurements 22
Appendix 6-10: Water Levels in Dudumera and Nhumbu Rivers 23
Appendix 6-11: Water quality data 23
EXECUTIVE SUMMARY
Internal Drainage Basin (IDB) is located between latitudes 20 to 70 south of the Equator and longitudes 330 to 370 east of the Greenwich. It has a jurisdiction area of about 143,099 Km2. The climate of the Basin is characterized with temperature that range between 220C and 270C during day time and 150C and 200C. While average rainfall is between 600mm to 900mm, evaporation is as high as 2100mm annually.
This report provides an overview of the water status in the Basin for the 2012/2013 hydrologic year (November 2012 to October 2013). The report uses rainfalls, river flows, lake/reservoir/river levels and water quality data to analyse the situation.
The hydrology and meteorological monitoring network includes 100 rainfall stations in the Basin, but only 18 are working and among them only 6 are owned by the Basin. There are 11 weather stations, 8 of them are operating fully and 3 have only rain gauges. However, all (except Shinyanga) have no evaporations pans. Also there are 62 hydrometric stations. Among those 18 are working, 3 have no gauge readers, 6 require rehabilitation and the rest need full reconstruction. The groundwater network has 22 stations but only two are operating. In addition, the water quality monitoring network has 9 stations. The spatial distribution of the network is inadequate. In this hydrological year there were some improvements in rehabilitation of weather and hydrometric stations.
Data recording was conducted in all working stations. The data include rainfall, temperature, evaporation and water levels. However, their collection was not comprehensive as some data are still in the stations and some stations had no gauge readers. The normal discharge measurements were not conducted due to inadequate fund and effective planning and implementation. Furthermore, almost all dams are un-gauged. The analysis of the hydro-meteorological data showed that the water situation in this hydrological year was normal.
The report emphasizes on the need for establishments of a comprehensive and operational network for effective data recording, collection, processing, analysis and development of an updated database. Also, basic hydrological functions such as discharge measurements have to be conducted regularly.
The report is structured into six chapters where chapter one gives general information about the Basin and the objective of the report. While chapter two contains information on water resources monitoring network, chapter three presents the characteristics of hydrological data and chapter four describes the hydrology of the Basin for the reported period. In addition chapter five summarizes the challenges, conclusion and way forward. Chapter six contains the list of annexes.
ii
1.0 INTRODUCTION
1.1 Objectives of the Report
The main objective of this report is to give an overview of hydrological status for the November 2012 to October 2013 period. In specific the report aims to provide hydrological information of the Basin through rainfall, river flow, and water quality and lake/reservoir/water levels data.
1.2 Location
Internal Drainage Basin is located between latitudes 20 to 70 South of Equator and longitudes 330 to 370 East of Greenwich. It is located more or less in central part of Tanzania and it extends over 8 regions of Arusha, Dodoma, Kilimanjaro, Manyara, Shinyanga, Simiyu, Singida and Tabora, and 31 district councils at different proportions. The total area of the Basin is 143,099 Km2 which is about 16.4% of the country. The Basin is divided into 9 sub-basins/catchments. They are Lake Eyasi, Lake Manyara, Lake Natron, Bahi Depression, Namanga, Monduli I, Monduli II, Olduvai and Masai Steppe (Figure 1-1). The Basin is also transboundary (the Lake Natron sub basin is shared with the republic of Kenya).
Figure 1-1: Location of Internal Drainage Basin
1.3 CLIMATE
The climate of the Basin is essentially tropical savannah with day temperature that ranges between 250C and 270C while at night may go down to between 150C and 200C. The Basin has dry (June-October) and wet (November-May) seasons. The average annual rainfall in most parts of the Basin ranges from 600 to 900 mm/year, but in the north-eastern part near the border of Kenya the average rainfall may rise to above 1,000 mm/year. The Basin receives both unimodal and bimodal rainfall. While the unimodal rainfall ranges between 600mm-900mm in areas such as Dodoma, Shinyanga, Singida and Tabora, the bimodal is between 1000 mm and 1500mm in Kilimanjaro, Manyara and Arusha regions.
1.4 Physiography
1.4.1 Topography
The Basin is mainly a plateau with scattered hills and mountain ranges especially along the Eastern Rift Valley. The mountains include Meru and Hanang. Apart from the mountains, there is Ngorongoro Crater and Western Ridge of the Rift Valley located in the west of Babati town. These plateau areas do not have much possibility of orographic rainfalls. The altitude of the Basin ranges from an average of 1500 masl in Singida, Dodoma and Shinyanga areas to an average of 1900 masl in Mbulu highlands.
1.4.2 Geomorphology
Geomorphic and geological features of IDB are closely related to East African Rift Valley System (EARVS). The Eastern Rift of EARVS namely; “Gregory Rift” is running north - south and its tectonic movement caused the formation of lakes Natron, Eyasi and Manyara. Volcanic landforms such as Mount Kilimanjaro, Meru, Hanang and Ngorongoro Crater which are seen today are reported to have been formed during the EARS. The Rift Valley System caused many faults in the Basin which are worthy geological structures for groundwater exploration.
1.4.3 Drainage Pattern
Most of the rivers in the Basin are seasonal. However, there are perennial rivers and springs in the North Eastern part around lakes Natron and Manyara. They include Mto wa Mbu, Simba, Kirurumo, Ngarenanyuki, Endanahai, Err/Dudumera, Hainu, Nambis, Kowu and Magara. The rivers drain into the lakes (Figure 1-2). The Basin is internally drained. Most of the lakes are endorheic since they do not have outlets. The major lakes are Eyasi, Natron, Manyara, Singidani and Kindai which are saline and Basotu and Babati that have fresh water. Also the Basin has about 103 dams accumulated capacity of about 141,044,131m3.
Figure 1-2: Map of IDB Showing Drainage Patterns
1.4.4 Land Cover and Use
The Basin is covered by few forests, grasses, bare land both wet and dry (Figure 1-3). Other important land covers are national parks such as Lake Manyara and Tarangire, and Nogongoro Conservation Area Authority. These are protected areas. The major land uses in the Basin include settlement, livestock keeping, little forest and crop farming. They can further be categorized into four different uses; arable land suitable for farming, land suitable for grazing, forests and woodland and mining.
Figure 1-3: Land cover map of Internal Drainage Basin
(extracted from The Study on the Groundwater Resources Development and Management in the Internal Drainage Basin by JICA, 2008)
1.4.5 Soil
Soil types in the Basin range from pure sand soils to pure clay soils. In Dodoma and Singida regions the colours of soils include grey-yellow, reddish-brown and dark grey to black with variety of textures such as pure sand deposited by rivers, loam and clay soils. While the dark heavy clay cracks when drying the dark clay loam soils do not. Sandy soils are found mainly around flash riverbeds in the south of the Basin (Dodoma, Singida, Shinyanga and Tabora regions). The depths of sand, loam and clay soils in Shinyanga range from shallow, moderately deep to deep profiles. The parent materials of these soils include granite, gneiss, volcanic and alluvial.
1.4.6 Main Features
The main features in the Basin are plateaus such as Masai Steppe, hills and mountain ranges like Mount Meru, Mount Hanang and the Ngorongoro Crater. The mountainous areas are located in the northern parts of the Basin (in Kilimanjaro, Arusha and Manyara regions). The Rift valley and the National Parks are other important features in the Basin.
1.4.7 Geology
The geology of the Basin consists of three types of rocks; granitic, metamorphic of Precambrian and volcanic of tertiary to quaternary. Also sediments of Neogene to Holocene are distributed around Bahi and Wembere swamps. The Precambrian Basement Rocks include the Dodoman System (Archean: D) which is distributed around Dodoma while Nyanzian System (Archean: Z) are distributed in Shinyanga, Nzega, Igunga and Iramba districts. Gabbros outcrops cover the northern part of Singida region. Besides Kavirondian System (Archean: V) outcrops are confined near Nzega-Tabora. The Usagaran System (Archean: Xs, Xs-a and Xs-l) rocks crop out the large area of the eastern part of the Basin. Likewise, the Bukoban System (B) also known as Proterozoic consisting of sedimentary rocks (mudstone, shale and sandstone) exposures is found in the southern part of Bahi Swamp. From the central to the northwestern part of the Basin, there are volcanic features which are associated with rift valley faulting movements. The volcanic characteristics formed the present Mountains: Meru, Hanang and Kilimanjaro. These huge volcanic massifs consist of extensive alkaline lava and accumulations of pyroclastics. The volcanic activities in these mountainous areas are recognized to be dormant. In general, the alkaline volcanic rocks around these peaks have high volatile contents such as water (H2O), Carbon dioxide (CO2), and Fluoride (F) (Figure 1-4).
2.0 MONITORING NETWORK
2.1 rainfall and other climatic stations
2.1.1 rainfall stations
The Basin has about 100 rainfall stations which are owned by different organizations such district councils. The situation requires collaboration and data sharing between the owning organizations and the Basin. During this reporting year only 18 are functioning (Appendix 5-1). The Basin owns only 5 stations (Hainu, Puma, Singida Maji Yard, Bubu and Ning'wa dam). Most of the stations were established in early 1970s and stopped working in mid 1980s. Therefore, the available data has many missing years.
2.1.2 weather stations
Also the Basin has 11 weather stations. In the 2012/2013 hydrological year 8 were rehabilitated with automatic equipment and they are functioning fully. However, three (Gwandi, Sekenke and Bereko) have only rain gauges and they are functioning partially (Appendix 6-2). However, all except Shinyanga have no evaporation pans. The pans will be constructed in the year 2013/2014.
2.2 hydrometric stations
The Basin has 62 stations distributed in all sub-basins with different status (Appendix 6-3). During the 2012/2013 hydrological year only 18 were functioning fully, 3 are in order but there are no gauge readers and 6 require rehabilitation since they were demolished by flood. Hence there are 14 stations that are considered for rehabilitation to sum up 36 stations that were formerly planned for rehabilitation. The rehabilitation was carried out basing on the hydrological and socio-economic (water demand) importance of the river and station. The rest (26) were not in the rehabilitation plan and as such they are requiring a complete reconstruction.
2.3 groundwater stations
The Basin has 22 groundwater monitoring stations (Appendix 6-4) that were drilled since 2008. The plan is to have 30 stations. Among those only two (Singida Maji Yard and Sepuka) are functioning. Therefore, the only available groundwater trend is from these two sites. Three stations (Sepuka, Msingi and Hirbadaw) were installed with automatic data loggers but none is functioning due technical shortcomings.
2.4 water quality stations
The Basin has established a water quality monitoring network for both ground and surface water (Appendix 6-5). There are 9 stations. The monitoring is conducted in industries, mines, lakes, rivers and springs. Normally the routine is four times a year during wet and dry seasons.