Colmation
With clogging (also Kolmatation, Kolmatierung) is in Soil Science , hydrology and Hydrogeologie the process of reduction in permeability of the bottom scaffold called due to interactions between the bottom and the supernatant water column. As a rule, the exchange between surface waters and the groundwater is of interest, with the input of finer material, e.g. B. Suspended matter contributes to the colmation effect.
Importantly, in addition to the clogging caused by the water from the material displacements by erosion and by Suffosion .
Historical meaning
Originally, colmation, according to the origin of the Italian colmata (dt .: Auflandung, Aufspülung ), was primarily used to describe the elevation of low-lying land areas threatened by flooding by natural or artificial flooding with gravel , sand and mud. By supplying muddy water through artificial canals, attempts were made to raise swamp areas so that they were suitable for settlement.
Usage today
Colmation is used synonymously with the term self-sealing and today usually refers to all processes that lead to a temporary or permanent decrease in the permeability of the water bed via a reduction in the pore volume and a solidification of the sole material (filter layer) and thus the free exchange between groundwater and Obstruct flowing waters. In English this process is called clogging or soil clogging .
Processes
A distinction is made here between internal and external colmation. In the case of internal colmation, fine suspended matter particles (<0.002 mm) can penetrate deep into the river bed without, however, greatly reducing the permeability . Only larger particles (0.002 to 0.1 mm) succeed in doing this by accumulating in the pore space of the filter layer (under the outer, coarse cover layer). The outer colmation layer is created by the deposition of fine particles on the original river bed. To do this, the two prerequisites must be met that the internal colmation has already taken place and the flow velocities are so low that the deposited suspended matter cannot be transported further as debris. The second criterion is usually only met in the case of river impoundments.
The decisive boundary conditions that influence the formation of a colmation layer are summarized:
- Hydraulics of the river
- Geohydraulic conditions of the soil
- Material supply through the water
- Biology of the water
- Interference
Biocolmation
In addition to the mechanical processes listed, physico-chemical and biological processes can also play a role in colmation. The metabolic processes of bacteria are particularly important here, as they can transform dissolved organic material and remineralize nutrients.
The flocculation of iron or manganese compounds is called ochering and is often caused by oxygen enrichment in the groundwater. See also: Well regeneration .
Field problem
Colmation is, among other things, a problem for bio sewage treatment plants and infiltration systems . The soil pores can also clog (colmate) through root growth. In the case of artificial, standing surface water, the colmation causes a gradual migration of the tipping line into the groundwater upstream and thus a rise in the water level. Another form is the silting up of the soil by heavy or continuous rain, which is a problem in agriculture.
Web links
- Colmation processes using the example of the Freudenau 146 S storage space , PDF file
- Summary on bjoernsen.de (PDF file; 306 kB)
Individual evidence
- ↑ Meaning of the word in Italian
- ^ Lueger lexicon of all technology from 1904
- ↑ Diploma thesis (PDF file)
- ↑ Effects at Baggerseen (pdf) ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ Naßbaggerrung ( Memento of the original from December 24, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
