<P> Since ~ 3000 yr BP (= years Before Present), human impact is seen in the delta . As a result of increasing land clearance (Bronze Age agriculture), in the upland areas (central Germany), the sediment load of the Rhine has strongly increased and delta growth has speeded up . This has caused increased flooding and sedimentation, ending peat formation in the delta . In the geologically recent past the main process distributing sediment across the delta has been the shifting of river channels to new locations on the floodplain (termed avulsion). Over the past 6000 years, approximately 80 avulsions have occurred . Direct human impact in the delta began with the mining of peat for salt and fuel from Roman times onward . This was followed by embankment of the major distributaries and damming of minor distributaries, which took place in the 11--13th century AD . Thereafter, canals were dug, bends were straightened and groynes were built to prevent the river's channels from migrating or silting up . </P> <P> At present, the branches Waal and Nederrijn - Lek discharge to the North Sea through the former Meuse estuary, near Rotterdam . The river IJssel branch flows to the north and enters the IJsselmeer (formerly the Zuider Zee), initially a brackish lagoon but a freshwater lake since 1932 . The discharge of the Rhine is divided into three branches: the Waal (6 / 9 of total discharge), the Nederrijn--Lek (2 / 9 of total discharge) and the IJssel (1 / 9 of total discharge). This discharge distribution has been maintained since 1709 by river engineering works including the digging of the Pannerdens canal and the installation, in the 20th century, of a series of weirs on the Nederrijn . </P> <Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2011) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2011) (Learn how and when to remove this template message) </Td> </Tr>

Why are most large cities located along rivers