Glossary - A - alluvium
| A | B | C | D | G | H | P | S | V | W |
A river is continually picking up and dropping solid particles of rock and sediment from its bed along its course. Where the river flow is fast, more particles are picked up than dropped (higher energy). Where the river flow is slow, more particles are dropped than picked up (low energy). Areas where more particles are deposited are called alluvial or flood plains, and the dropped particles are called alluvium.
Even small streams make alluvial deposits, but it is in the flood plains and deltas of large rivers that large, geologically-significant alluvial deposits are found.Alluvium is typically made up of a variety of materials. The finer material, or silt, consists of sand and mud. Larger particles, or gravel, are also typically present in a wide range of sizes.
Cross section of an alluvial valley - variation in material type shows the effect of aquifer thickness and hydrogeological boundaries on well yields.