Code
F14
Sector
Forest
The complete description of the NWRM
Summary

Typically, overland flow areas are set asides used to minimize the negative impacts of forest management on water quality. They are most commonly associated with peatland forestry in Finland but could be applicable in other areas of Europe. Overland flow areas collect some of the excess sediment produced during ditch maintenance and other forest management operations such as road building or harvesting. Overland flow areas are created by building a semi-permeable dam in a forest ditch. Upstream of the dam, lateral ditches are constructed to transport water into the surrounding catchment. During periods of high flow, water will overflow the lateral ditches and travel across land to reach the receiving lake or stream. As the water travels across land, its velocity will be slowed and much of the sediment being carried will be deposited. At periods of low flows, the permeable dam will slow water flow and cause deposition of sediment. Existing wetlands may function as overland flow areas but the use of ecologically valuable and endangered mires should be avoided due to possible changes in vegetation composition. Overland flow areas can also be part of more complex system for water treatment from agricultural areas and landfills.

Illustration(s)

Ditch for overland flow (Slovakia)

Source: Michal Kravcík’s presentation, NWRM Workshop

 

Possible benefits with level
Benefits Level
BP1 - Store runoff
High
BP2 - Slow runoff
High
BP3 - Store river water
Low
BP4 - Slow river water
Medium
BP6 - Increase infiltration and/or groundwater recharge
Low
BP8 - Reduce pollutant sources
High
BP9 - Intercept pollution pathways
High
BP10 - Reduce erosion and/or sediment delivery
High
BP12 - Create aquatic habitat
Low
ES1 - Water storage
Medium
ES2 - Fish stocks and recruiting
Medium
ES4 - Biodiversity preservation
Medium
ES6 - Groundwater/aquifer recharge
Low
ES7 - Flood risk reduction
High
ES8 - Erosion/sediment control
High
ES9 - Filtration of pollutants
High
BP7 - Increase soil water retention
Medium
PO1 - Improving status of biology quality elements
Low
PO2 - Improving status of physico-chemical quality elements
Low
PO3 - Improving status of hydromorphology quality elements
Low
PO4 - Improving chemical status and priority substances
Low
PO5 - Improving quantitative status
Low
PO7 - Prevent surface water status deterioration
Medium
PO9 - Take adequate and co-ordinated measures to reduce flood risks
High
PO10 - Protection of important habitats
Medium
PO11 - Better protection for ecosystems and more use of Green Infrastructure
Medium
PO12 - More sustainable agriculture and forestry
Medium
PO13 - Better management of fish stocks
Medium
PO14 - Prevention of biodiversity loss
Medium

Case studies per NWRM