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It is estimated that about 50% of improved agricultural land in Scotland has artificial drainage networks of surface ditches and/or sub-surface tile drains. Drainage of agricultural land modifies hydrological flow paths and flow rates. This may lead to accelerated runoff rates, and in turn may cause an increased risk of localized flooding. Conversely, a general lowering of the water-table can increase soil infiltration capacity which will tend to reduce the frequency of storm runoff. Changes in the hydrological flow paths have a secondary impact on water quality through changes in the transport of nutrients such as nitrogen and phosphorus. The presence of field drainage systems can increase the risk of contamination of ground and surface water with faecal pathogens after slurry or farm yard manure applications. In hill situations, particularly on blanket bog, some efforts are being made to block drains and restore the peatland hydrology (e.g. by SNH and RSPB).

There is very little information available on the extent or condition of agriculture-related artificial drainage systems in Scotland . Lack of grant support, high labour costs and low profitability may mean that many land managers are failing to maintain drainage systems. This could be having variable environmental effects and some monitoring should take place.

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