Among many other issues, the problems of killer flash floods, destruction of marine ecosystems such as fish kills, deteriorating marine life, low fish farming harvests, red tide, drought - scarcity of water supply, desertification among too many others are often caused by siltation - in many instances coupled with the unchecked deforestation of highlands from where surface runoff water come in large droves during heavy rain.
Sometimes, as in the case in the Mindoro and Ormoc tragedies in the past were countless people lost their lives, compounding the floods are log and debris stampede.
The stampede part is the most lethal particularly when it occurs at the time when people are asleep and have no defense nor countermeasure to rely upon as their physical safety all of a sudden totally goes south.
SiltationFrom Wikipedia, the free encyclopedia
Siltation is the pollution of water by fine particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments, and to the increased accumulation (temporary or permanent) of fine sediments on bottoms where they are undesirable. Siltation is most often caused by soil erosion or sediment spill.
Sometimes siltation is called sediment pollution, although that is an undesirable term since it is ambiguous, and can also be used to refer to a chemical contamination of sediments accumulated on the bottom, or pollutants bound to sediment particles. Siltation is the preferred term for being unambigiuous, even if not entirely stringent since it also includes other particle sizes than silt.
In recent time, while natural causes still figure as a factor in siltation, human-caused siltation-sedimentation has been observed to occur in alarming levels. More impending man-made catastrophes are expected in this sense, for which early solutions are required to at least lessen the future impact of societal and individual losses arising from simple siltation.
In Europe, marine ecosystems are taken seriously.
Tyne Rivers Trust - Proud Guardians of England's Rivers
Siltation and pressures on river habitats
The problem on global scale
The intensification of agricultural activities is a recognised contributory factor to the current rapid rate of soil erosion on a global scale. As well as being a valuable resource, topsoil also contains nutrients which can negatively alter the balance of freshwater ecosystems. Erosion by rivers is a natural process and the presence of sediment of all sizes is necessary to support healthy freshwater ecosystems. When fine sediment is over-supplied it can infill the spaces between river gravels and pebbles and lead to problems such as the loss in interspatial habitat, binding of polluting molecules and the de-oxygenation of the substrate. Siltation in rivers is intrinsically linked to the erosion of topsoil by wind and rain action but accelerated (we use the term ‘aggravated’) by land use and land management practices.
Read more about this article from here
Some Related Readings:
United Nations Sponsored Study on Dams, Siltation (download document in Word format here)
In relation to fish farming - or aquaculture the following site is recommended:
Wye and Usk Foundation
Siltation
A Wye tributary smothered by sedimentation
River restoration works helping to trap silt in the bank rather than it damaging gravelsSilt is a granular material derived from soil or rock of a grain size between sand and clay. It may occur as a soil or as suspended sediment in a surface "water body" (Water Framework Directive speak for river, stream, lake or groundwater source). It may also exist as soil deposited on a river or lake bed. Siltation is very bad news for our rivers and many of their inhabitants. With faster run-offs from forestry, increased grazing pressures and, typically, potato, strawberry or maize crops, fine sediment loads on some streams smother the bed and kill off invertebrates and fish eggs, resulting in reduced spawning success or abandonment by fish. The fine sediment loading of our rivers has trebled since 1980 and in the most severely affected streams egg survival has been reduced to 0%. Much of this damage is avoidable and our knowledge is increasing of the whereabouts of vulnerable sites and which land use practices put the rivers at the greatest risk.
Following on from more than a decade of leaflet drops and advisory booklets, the "Catchment Sensitive Farming Initiative" aims to mitigate damage in the most vulnerable catchments such as Lugg, Ithon and Garren but it too has the disadvantage of being only voluntary and has limited funding for remedial work. Cross compliance is built into the current grant scheme, whereby grants may be reduced or removed in the event of bad agricultural practices but it lacks the will for enforcement.
The Foundation continues to be alert to the damage caused by siltation and fencing out stock remains an absolute priority where it is a problem, as is preventing and repairing erosion. The subsequent restoration of natural widths (i.e. narrower) that result from fencing enable streams to resist more effectively the worst effects of siltation.
To summarise, silt affects aquatic life is in several ways:
· Spawning gravels become compacted· Invertebrate types and numbers are reduced· Acts as a vehicle for certain pesticides and phosphates· Read more from here
