Sand, silt, mud, silt - a brief history of sediments

Sedimentum is the Latin word for sediment. Sediments are small particles from the water that settle to the bottom of a body of water due to gravity. They consist of sand (2 - 0.063 mm), silt (0.063 - 0.002 mm), even smaller clay particles and plant remains, for example dead algae, which have decomposed over time. Sediments are therefore a natural component of bodies of water - they enter the river via side arms and the air, are deposited at the bottom, are stirred up again and transported further by the current. If they are in motion, the particles are called suspended solids; if they settle, we speak of sediments.

Sand is formed from weathered rock, usually quartz. It can also consist of limestone if it has been formed from mussel shells or coral. Sand is defined by its size: a grain of sand measures between 0.063 and 2 millimetres. If it is larger, we speak of gravel. Sand, which occurs in tidal waters, is rounded and further crushed by the constant movement of the water and friction with other grains.

Silt can be classified between sand and clay: Its grain size is 0.063 to 0.002 millimetres. It consists mainly of very fine weathered rock such as feldspar and quartz. Just like clay, it can bind water well due to its small size. Pure silt is rare in bodies of water - it is usually part of a mixture with sand and clay.
 

Clay particles are extremely fine and small, smaller than 0.002 millimetres. Clay consists mainly of minerals, i.e. non-organic components. When dry, it is very hard - then it shrinks and cracks. As soon as clay combines with water, it swells and has adhesive properties. It is an excellent moisture reservoir, but also binds other substances such as heavy metals or pesticides.

Silt is a natural component of the water and consists mainly of fine-grained sediments, i.e. clay and silt, as well as organic components such as algae, bacteria or plant remains. When this combination of suspended matter settles to the bottom of the water, silt is formed. Due to its high proportion of clay and its fine grain size, silt binds a lot of water - up to 50 percent. And this is precisely what gives it its characteristic "silty" consistency.</p

<p>By the way: several million tons of silt are dredged in the Port of Hamburg every year to ensure the necessary depth for shipping Here you can find out how we test the material and where it ends up afterwards.

Like silt, natural mud is a mixture of particles of different grain sizes and water. However, silt is not deposited in the tidal Elbe, but predominantly in lakes and inland rivers. This is why there is mud in the inland Elbe, but not in the tidal Elbe - where it is called silt.