Muddy flood
Encyclopedia
A muddy flood is produced by an accumulation of runoff generated on cropland. Sediments are then detached by runoff and carried as suspended matter or bedload. Muddy runoff is more likely detected when it reaches inhabited areas.

Muddy floods are therefore a hillslope process, and confusion with mudflows produced by mass movements should be avoided.

Muddy floods mostly lead to damage to road infrastructure (leaving a mud blanket on it or clogging sewage network) and to private property.).

It has been referred to 'muddy floods' since 1980s. A similar designation appeared in French ('inondations boueuses') during the same period.

Muddy flood generation

Muddy runoff is generated on cropland when the soil surface is crusted and sparsely covered by vegetation. Large quantities of runoff (several hundreds or thousands of cubic meters) must be generated to trigger a muddy flood. This situation mostly occurs during heavy storms .

Muddy flood occurrence

Muddy floods are observed in the entire European loess belt. Most severely affected areas are the South Downs
South Downs
The South Downs is a range of chalk hills that extends for about across the south-eastern coastal counties of England from the Itchen Valley of Hampshire in the west to Beachy Head, near Eastbourne, East Sussex, in the east. It is bounded on its northern side by a steep escarpment, from whose...

 (southern England), Normandy
Normandy
Normandy is a geographical region corresponding to the former Duchy of Normandy. It is in France.The continental territory covers 30,627 km² and forms the preponderant part of Normandy and roughly 5% of the territory of France. It is divided for administrative purposes into two régions:...

 and Picardie
Picardie
Picardy is one of the 27 regions of France. It is located in the northern part of France.-History:The historical province of Picardy stretched from north of Noyon to Calais, via the whole of the Somme department and the north of the Aisne department...

 (France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

), central Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

 and southern Limburg
Limburg (Netherlands)
Limburg is the southernmost of the twelve provinces of the Netherlands. It is located in the southeastern part of the country and bordered by the province of Gelderland to the north, Germany to the east, Belgium to the south and part of the west, andthe Dutch province of North Brabant partly to...

, the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

.

Muddy floods have also been recently observed in Slovakia
Slovakia
The Slovak Republic is a landlocked state in Central Europe. It has a population of over five million and an area of about . Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south...

 and Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

.

Temporal evolution

An increase in muddy flood frequency has been observed during the last twenty years (e.g. in central Belgium,). This increase in their frequency can be due to the coincidence of the following factors:
  • shift to crops that are more sensitive to soil erosion;
  • land consolidation (enlargement of fields, removal of landscape buffer elements like hedges, road constructions in thalwegs, etc.);
  • construction of new houses, downstream of cropland;
  • increased frequency of heavy rainfall.

Control measures

Preventive or curative measures can be implemented to control muddy floods.

Preventive measures consist in limiting runoff generation and sediment production at the source. Farmers can for instance implement alternative farming practices (e.g. reduced tillage) to increase runoff infiltration and limit erosion in their fields.

Curative measures generally consist in installing retention ponds at the boundary between cropland and inhabited areas .

An alternative is to apply other measures than can be referred to as intermediate measures. Grass buffer strips along or within fields, a grassed waterway
Grassed waterway
A Grassed waterway consists in a to wide native grassland strip of green belt. It is generally installed in the thalweg, the deepest continuous line along a valley or watercourse, of a cultivated dry valley in order to control erosion. A study carried out on a grassed waterway during 8 years in...

(in the thalwegs of dry valleys) or earthen dams are good examples of this type of measures. They act as a buffer within landscape, retaining runoff temporarily and trapping sediments .

Implementation of these measures is best coordinated at the catchment scale.

External links

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