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Zimbabwe’s border to the north with Zambia is the Zambezi river and to the south with South Africa is the Limpopo river, both of which flow into Mozambique. The country is divided into seven river catchments (EMA, 2014): Gwayi, Sanyati, Manyame, Mazowe (or Mazoe), Save (or Sabi), Runde and Mzingwane (Table 2). With the exception of the Save and Runde, which join at the border with Mozambique and then flow as one river to the Indian Ocean, all other main rivers drain into either the Zambezi or Limpopo. However, while the Gwayi river drains into the Zambezi river, the Nata (or Amanzamnyama) river, which is considered to be part of the Gwayi water catchment, drains into the Makgadikgadi Pans in Botswana, which in reality are not part of the Zambezi river basin, but of the South Interior basin. The Zambezi is particularly important to the country as it produces most of its electricity.
Zimbabwe has limited groundwater resources, mainly because the greater part of the country consists of ancient igneous rock formations where groundwater potential is low. Four aquifer systems are an exception with relatively high potential:
- The Lomagundi dolomite aquifer, lying northwest of Chinhoyi, about 120 km northwest of Harare;
- The forest sandstone formation in the Nyamandhlovu area, close to Bulawayo; the formation is part of the Karoo aquifers shared between Botswana, Namibia, South Africa, Zambia and Zimbabwe;
- The Kalahari sands which are widespread in the southwestern part of the country and where exploitable groundwater resources are related to the thickness of the sands;
- Alluvial deposits which mainly occur in the Save valley where they form a local aquifer, along the Zambezi, Manyame (Mushumbi pools area) and Musengezi rivers (Muzarabani areas).
As a result of these scarce groundwater resources, the country relies mainly on surface water resources. Internal renewable surface water resources are estimated at 11 260 million m³/year and renewable groundwater resources at around 6 000 million m³/year. About 5 000 million m³/year is considered to be overlap between surface water and groundwater, thus total internal renewable water resources (IRWR) are 12 260 million m³/year (Table 3). Total flow in border rivers amounts to 39 900 million m³/year, corresponding to both the Zambezi from Zambia and Limpopo from Botswana, but their accounted inflow is limited to 7 740 million m³/year. Total renewable water resources are thus 20 000 million m³/year, or 1 413 m³/year per capita in 2014. This per capita value is projected to fall under the absolute water scarcity threshold of 500 m³/year by 2030, due to population increase. Surface water leaving the country is estimated at 14 140 million m³/year, of which 14 100 million m³/year through the Mazowe river to Mozambique and 40 million m³/year through the Nata river to Botswana.
There are no natural lakes in Zimbabwe but numerous reservoirs thanks to the 2 200 dams, including 260 large ones (WB, 2014). Only 850 of them were constructed by the government, and their permits are owned by the Zimbabwe National Water Authority (ZINWA). The private dams are mostly small ones (AfDB, 2011). The total capacity of dams is estimated at 99 930 million m³, which includes half of the total reservoir capacity of 188 000 million m³ of the Kariba dam, shared with Zambia. The Kariba dam, completed in 1959 at the former Kariwa (Kariba) Gorge on the Zambezi river and owned by the Zambezi River Authority (ZRA), is the largest dam worldwide in terms of reservoir capacity. A rehabilitation project of the Kariba dam was approved in 2014. Other major dams in the country include Mutirikwi (or Kyle), Chivero, Manyame (or Darwendale/Robertson), Mazvikadei, Osborne and Manyuchi dams. Dams under construction such as the Tokwe-Mukosi (1 800 million m³) completed at 80 percent in 2015 and the Kondo dams (1 230 million m³) will improve water supplies in the Save-Limpopo region, where water for irrigation was previously imported from Lake Mutirikwi in the Central region (MENR, 2010). However, siltation considerably reduces the total dam capacity: by 2003, it was reduced by 29 million m³ and a large number of medium- and small-sized dams face operational difficulties because of sedimentation. Nonetheless, the ratio of water used compared to the water stored in dams is low (AfDB, 2011).
Some water transfers also take place and the Matabeleland Zambezi Water Project, also called the Bulawayo-Zambezi Water Supply Scheme, will bring water from the Zambezi river to Bulawayo. Its first phase is the Gwayi Shangani dam, commenced in 2004 but stopped in 2007 due to funding problems (SADC, 2012).
Surface water also takes the form of wetlands (IUCN, 1994):
- Floodplains: Mid-Zambezi Valley in Mana Pools area, and around the Save-Runde confluence
- Riverine wetlands: along the Save-Runde, Manyame, Gwayi-Shangani, Mazowe and Sanyati rivers
- Dambos or palustrine wetlands: covered 1.28 million ha in 1990s
- Pans: not widespread, in Hwange and Gonarezhou National Parks
- Swamps: limited to Tsamtsa, Kwaluzi and Binga swamps
Seven wetlands are Ramsar sites since 2013: Cleveland Dam, Chinhoyi Caves, Driefontein Grasslands, Lake Chivero and Manyame, Mana Pools, Monavale Wetland and Victoria Falls National Park, covering around 275 000 ha in total.