SONGWECOM Hydrocensus
The Songwe River Basin (SRB) is a hydrologic catchment spreading across Tanzania and Malawi, occupying about 4,243 square kilometres (km2), of which about 55% is in Tanzania and 45% in Malawi. The basin’s topography is characteristic of a mountainous area occupying the southwest of Tanzania and the northeastern part of Malawi. The Songwe River originates in the upper catchment with contributions from major tributaries such as Mutumbisi, Kaseye, Kyungu and Makeye rivers, from where it meanders through the catchments to discharge into Lake Nyasa/Malawi. The topography of this catchment varies from >500 metres (m)+ in the alluvial plain to 2,300 m+ (Mt. Bogo) in the north, where the mountain ranges form the water divide with the Kiwira catchment and the Lake Rukwa basin in the north. The mean annual rainfall in the Songwe River basin is 1,482 millimetres (mm), which generates an average runoff of 457 mm per year (mm/year). The main drainage comes from Songwe, which forms the border between Tanzania and Malawi. This catchment contributes about 10% of the inflow into Lake Nyasa. Numerous thermal springs can be found adjacent to Songwe River, and they discharge hot water (50 – 80oC), which is rich in sodium bicarbonate (NaHCo3) (SMEC/LNBWB, 2015). The springs are often associated with CO2 gas vents (SMEC/LNBWB, 2015).
The basin serves a population of above 425,504 people, of which 80% are vulnerable communities. The population is exerting pressure on the basin land and water resource base, as evidenced by settlement and cultivation on marginal lands. A considerable part of the basin population lacks access to a safe water supply, estimated at 30% in the Lower Basin, 40% in the Middle Basin, and 50% in the Upper Basin.
The hydrocensus assessment, in particular, entailed documenting groundwater resources by locating existing boreholes and conducting site transect walks to identify potential groundwater pollution sources, collecting water samples from each borehole, and taking photographs of the area. Therefore, the main objective of a hydrocensus survey is to locate and gather information on boreholes, users, and sensitive ecological receptors within a defined development radius. The current exercise visited all the 2 administrative districts of the Malawi side, i.e., Karonga and Chitipa and the 5 districts in the Tanzania side, i.e., Kyela, Mbeya Rural, Ileje, Mbozi and Momba. The team visited 79 wells, of which 54 and 40 were sampled for in-situ measurements and further laboratory analysis. The exercise collected 365 more boreholes from existing institutions with different parameters (missing most), notably coordinates, depth, static water levels, drilling depth, and some water quality parameters, predominantly temperature, pH, turbidity, and electrical conductivity. The general status of boreholes from these data collection showed that:
- The average drilling depth is 56.55 m, with notable high temperatures beyond 80maround Kyela town.
- The static water level is 17.26 m.
- Average well yield is 5.20 m3/hr.
- Water quality parameters are within national standards for Malawi and Tanzaniaexcept for 16 well sites, as listed below.
- Saa tatu Feeling station: Iron (0.615mg/L).
- Njisi Mosque: EC (4,450μS/cm), TDS (2,670mg/L), Sulphate 366mg/L),
- Fluoride (1.37 mg/L), Calcium (369mg/L), Magnesium (210mg/L), Iron
- (2,113mg/L), Manganese (1,013mg/L), Total Hardness (1,790mg/L).
- KKKT Church Njisi: Iron (0.322mg/L)
- Kamu Lodge: Cadmium (0.008mg/L).
- Mapogoro village BH: Iron (0.28mg/L).
- Nyasa BH: Iron (0.605mg/L),
- Mapwa Pr School: Iron (1.451mg/L), Turbidity (36NTU).
- Ngisi Pri School: Iron (1.352mg/L), Turbidity (20.1NTU).
- Timothy Village BH: Iron (1.6mg/L), Manganese (0.71mg/L).
- Lumbasi: Fluoride (1.57mg/L), Iron (0.238mg/L)
- Bupighu Pri School: Fluoride (1.52mg/L).
- Zingalipiri: Iron (0.606mg/L)
- Kayanike Pri School: Iron (1.451mg/L),
- Maligumu: Fluoride (1.4mg/L).
- Mwachiyo: Fluoride (1.42mg/L) and Iron (0.238mg/L).
- Namayanga: Cadmium (0.041mg/L).
Based on the collected information, the basin has high-quality water and sufficient well yields for family consumption. However, further data collection and stronger enforcement of the law are recommended.
