Agriculture Reference
In-Depth Information
Inland valleys
Inland
valley
Terrace
Inland
valley
Alluvial fan
Terrace
Terrace
Coastal
Floodplain
Plain
Meander
Tidal
land
Sea
Marine sediments
Riverine sediments
Figure 1.4
Major wetland land forms (Moorman and van Breemen, 1978). Reproduced
by permission of IRRI
terracing has completely disturbed the original soil profile and also on valley
bottoms that have been perennially irrigated with muddy water.
Alluvial Fans
The soils again vary greatly with the age and origin of sediments, from young
Entisols to well-developed Alfisols and Ultisols. There are some common trends.
The deposits are often coarsest and youngest near the apex of a fan and they
become finer and older towards the more gently sloping base. There are corre-
sponding differences in hydrology with seepage of water from the better-drained
upper parts and accumulation in the lower resulting in marshland to develop
where fans meet adjacent floodplains. Entisols and Inceptisols are common in
the upper fans; Alfisols in the lower fans or Ultisols where the surrounding
uplands are highly weathered.
Active Floodplains
The main wetland areas are in the river basins. Levee deposits become increas-
ingly fine textured with distance downstream and distance away from the river.
The soils are mostly Entisols and Inceptisols, and, where levees grade into basins,
Alfisols or Ultisols. Soils in the basins are typically fine-textured and wet but
many types occur due to differences in parent materials, rates of deposition,
