The North-South Carrier (NSC) is a pipeline in Botswana that carries raw water south for a distance of to the capital city of Gaborone. Phase 1 was completed in 2000. Phase 2 of the NSC, under construction, will duplicate the pipeline to carry water from the Dikgatlhong Dam, which was completed in 2012. A proposed extension to deliver water from the Zambezi would add another to the total pipeline length. The NSC is the largest engineering project ever undertaken in Botswana.
Climate
Botswana has an arid climate, with little in the way of surface water supplies. Until recently, groundwater wells were used to meet about 80% of demand for water. Some of the groundwater accumulated long ago when the climate was wetter. "Groundwater mining" is not sustainable in areas where the water is not being renewed from the surface. The more populous eastern portion of Botswana lies in the Limpopo River basin, which is considered "closed". In the South African portion of the basin, water usage exceeds the potential water yield from the basin by 800,000,000 cubic metres (650,000 acre-feet) annually. Water has to be imported from the Vaal River to make up the shortfall.
Almost all rainfall occurs in the summer months of October through April, at a time when temperatures over cause high levels of evaporation. Rainfall is undependable. A drought period may last for several years. Precipitation is highest in the northeast, at about annually, and lowest in the southwest, at about annually. Annual average potential evaporation is about annually. Botswana has flat terrain that is mostly unsuitable for reservoirs.
Requirements
In 2008 Botswana had a population of 1,921,000. GDP per capita on a purchasing power parity (PPP) basis was $13,415. 83% of the people were literate. The percentage of people with access to safe drinking water rose from 77% to 96% between 1996 and 2006. The economy of Botswana is growing fast, as is the population, particularly in the Gaborone area. This is causing growth in per-capita demand for water, and rapid growth in total demand. The Gaborone region accounts for over 75% of water demand in eastern Botswana. The local Gaborone and Bokaa dams cannot meet the growing demand even with the help of reclamation from the Gaborone Water Treatment Works at Glen Valley.
Morupule Colliery uses three boreholes for water, but takes water from the NSC when needed through a pipeline from Palapye. Exploitation of coal deposits in Botswana related to the South African Waterberg coalfield will also contribute to demand for water. Water from the Dikgatlhong Dam, completed in 2012, will be used in part to supply the large coalfield and power station at Mmamabula via the NSC pipeline.
Plan
The Botswana National Water Master Plan (NWMP) identified promising sites for reservoirs in the northeast on the small, ephemeral Motloutse and Shashe tributaries of the Limpopo River. The North-South Carrier Water Project was launched to build a pipeline that would carry water from these sites to the area of highest demand around Gaborone in the southeast.
A 1994 review of environmental assessments conducted for the Norwegian Agency for Development Cooperation, which provided some of the funding for the project, concluded that the impact of the pipeline would be tolerable. The pipe would be buried. Native vegetation would soon regenerate along the route if the topsoil and subsoil were carefully removed and replaced without mixing. Plans for construction of the high rock-filled Letsibogo Dam on the Motloutse River also included careful environmental impact assessment studies. The impact of the Letsibogo reservoir on an ecology that has not been carefully studied would be greater. It would both destroy and create habitat. The review was cautious in its conclusions about the net impact. The review said "the socio-economic and archaeological issues seem to have been handled in a particularly outstanding way".
The plan was divided into two phases. The Letsibogo Dam would be built in Phase 1, with a pipeline about to carry the raw water south to a treatment plant and master balancing reservoir at Mmamashia, about northeast of Gaborone. An early version of the plan used the existing Bokaa Dam as the reservoir, but it was decided to instead build a covered reservoir closer to Gaborone to minimise loss of water through evaporation. A second dam, the Dikgatlhong Dam, would be built on the Sashe River in Phase 2. A second pipeline running parallel to the first would carry the water to the same treatment plant and reservoir near Gaborone.