The Fluvial ImaginationLandlocked and surrounded by South Africa on all sides, the mountain kingdom of Lesotho became the world's first "water exporting country" when it signed a 1986 treaty with its powerful neighbor. An elaborate network of dams and tunnels now carries water to Johannesburg, the subcontinent's water stressed economic epicenter. Hopes that receipts from water sales could improve Lesotho's fortunes, however, have clashed with fears that soil erosion from