Forest

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.

A mulch is a layer of material applied to the surface of an area of soil. Its purpose is any or all of the following:

·       to conserve moisture

·       to improve the fertility and health of the soil

·       to reduce weed growth

·       to enhance the visual appeal of the area

Mulching as NWRM is using organic material (e.g. bark, wood chips, grape pulp, shell nuts, green waste, leftover crops, compost, manure, straw, dry grass, leaves etc.) to cover the surface of the soil. It may be applied to bare soil, or around existing plants. Mulches of manure or compost will be incorporated naturally into the soil by the activity of worms and other organisms. The process is used both in commercial crop production and in gardening, and when applied correctly can dramatically improve the capacity of soil to store water.

Land use conversion is a general term for large scale geographic change. Afforestation is one such land conversion in which trees are planted on previously non forested areas. Afforestation may occur deliberately or through the abandonment of marginal agricultural land. Depending on the tree species planted and the intensity of forest management, afforestation may have more or less environmental benefits. The NWRM related benefits include potentially enhanced evapotranspiration associated with growing forests and better water holding capacity associated with forest soils. The greatest environmental benefits are probably associated with planting of indigenous broadleaves and low intensity forestry. Plantation forestry with exotic species is likely to be less beneficial to the environment. It should be mentioned that afforestation in dry areas can cause or intensify water shortage. Even though afforestation may reduce available water supply at local scale, forest cover increases water supply regionally and globally, in particular through the intensification of the water cycle.

Continuous cover forestry is a broad range of forest management practices which may have some beneficial hydrological effects. The main idea behind continuous cover forestry is a reduction in the number or size of clear-cuts. Some definitions of continuous cover forestry state that no clear-cuts shall be larger than 0.25 ha. Continuous cover forestry ensures that there is an uninterrupted tree canopy and that the soil surface in never exposed. An uninterrupted tree canopy will have higher interception than a site with discontinuous tree cover. Ensuring that soils are never exposed will limit sediment production.

Off road driving has potentially severe negative consequences for water quality. Some of these damages can be minimized or mitigated if drivers of vehicles exercise a few simple precautions. Avoiding driving in wet areas whenever possible will limit soil compaction and rutting. Rutting can concentrate flow paths and lead to increased erosion. In colder regions of Europe, driving on frozen soils will also reduce the potential for compaction and damage. Driving parallel to contour lines of hill slopes will reduce the potential for rut formation and concentration of flow paths but may not always be feasible, especially in areas of high relief. Use of slash cover or specially designed logging mats in off road driving during forest logging operations may help to reduce soil compaction and rutting. Reduction of truck tire pressure on unpaved forest roads may also be considered as one aspect of this NWRM.

Forest access roads and other roads in rural areas often cross streams and other small watercourses. Design and material used in forest road building may have strong impact on erosion risk and water quality in streams. The bridges or culverts used to cross these watercourses must be designed appropriately if negative impacts on the aquatic environment are to be minimized. Poorly designed or poorly implemented stream crossings can have numerous negative effects on the aquatic environment including increased sediment mobilization and changes in flow patterns. For example, flooding upstream of the road crossing can occur when the bridge or culvert is unable to transport a sufficient volume of water.  Such floods can also wash out bridges or stream crossings, leading to increased costs for the road owner and downstream sediment pollution. Increased sediment mobilization results in loss of aquatic habitat and may extirpate threatened species including freshwater pearl mussel as well as destroying spawning habitat.

Sediment capture ponds are engineered ponds placed in networks of forest ditches to slow the velocity of water and cause the deposition of suspended materials. Sediment capture ponds are most useful for managing the effects of ditch construction and maintenance, road work and final feeling. While used primarily in forests, sediment capture ponds may be a useful temporary measure for preserving water quality in and around construction sites or mines.  They may also be useful for capturing sediment in agricultural runoff. Sediment capture ponds have a limited lifespan, depending on how much suspended material is in the inflowing water. However, ponds can be maintained by removal of accumulated sediment. As most water protection methods, sediment capture ponds function well during base and moderate flow events. Catchment area, hydraulic properties of ditches, discharge rate and soil characteristics are among factors influencing functioning of sedimentation capture ponds. Effective functioning largely depends also on expertise and skill of professionals designing and implementing this and also many other measures.

Coarse woody debris in stream channels has multiple ecological and hydrologic benefits. Coarse woody debris consists of large sections of deadfall: tree stems or stumps that either fall into or are deliberately placed in streams. Coarse woody debris can be deployed with varying degrees of naturalness. At one extreme, coarse woody debris can be used to form coffer or placer dams which effectively limit water flow. At the other extreme, natural deadfall coarse woody debris is found when riparian trees are allowed to fall naturally into streams. Coarse woody debris will generally slow water flow velocity and can reduce the peak of flood hydrographs. In addition to its role in slowing streamflow and facilitating sediment accumulation, coarse woody debris can improve aquatic biodiversity by retaining food and providing additional habitat, such as refuges and spawning sites.

Urban forest parks can deliver a broad range of hydrology-related and other ecosystem services. Forests in urban areas have great amenity value, can improve air quality, moderate local microclimates, improve urban biodiversity and contribute to climate change mitigation as well as having ancillary hydrological benefits. Forest soils often have greater infiltration capacity than other urban land cover and can be an important location for aquifer recharge.

Trees in urban areas can have multiple benefits related to aesthetics, microclimate regulation and urban hydrology. Trees in urban areas can also be important biodiversity refuges and can contribute to reducing particulate air pollution. Trees intercept precipitation, reducing the amount of rainfall which must be processed by sewers and other water transporting infrastructure. The area around urban trees may also have greater infiltration capacity than the impermeable surfaces often found in urban areas. Trees also transpire, which dries the soil and gives greater capacity for rainfall storage.