Rivers form the bulk of Zimbabwe's surface water resources and have a mean annual runoff . River flows are variable and characteristically seasonal , with the largest flows occurring down the rainy season (November to March).There are seven major river systems within Zimbabwe which carry about 65% of its run off, while the balance 35% originates from the country's northern (Zambia) and southern (South Africa) borders.Zimbabwe can be divided into six hydrolical zoneseach of which is well provided with gauging wires and flow measuring devices.In 1975 ther were about 866 gaugingweirs, the earliest of which dates back to 1907.
