Changes

Highly permeable soils (i.e., hydrologic soil groups A and B) function as important groundwater recharge areas.  Compacting or paving over these areas will have significant hydrologic impacts. To the greatest extent possible, these areas should be preserved in an undisturbed condition or set aside for stormwater infiltration practices.  On sites with a variety of soil types, impervious land cover should be concentrated in areas with the least permeable soils and underlying geology.  Where avoiding development on permeable soils is not possible, stormwater management should focus on mitigation of reduced groundwater recharge through application of stormwater infiltration practices.

Highly permeable soils (i.e., hydrologic soil groups A and B) function as important groundwater recharge areas.  Compacting or paving over these areas will have significant hydrologic impacts. To the greatest extent possible, these areas should be preserved in an undisturbed condition or set aside for stormwater infiltration practices.  On sites with a variety of soil types, impervious land cover should be concentrated in areas with the least permeable soils and underlying geology.  Where avoiding development on permeable soils is not possible, stormwater management should focus on mitigation of reduced groundwater recharge through application of stormwater infiltration practices.

===Preserve existing trees=== Mature stands of deciduous trees will intercept 10 to 20% of annual precipitation falling on them, and a stand of evergreens will intercept 15 to 40% (Cappiella, 2005).  Depending on understory vegetation, soils and topography, tree clusters may only produce surface runoff for major flood event storms.  Preserving mature trees will provide immediate benefits in new developments, whereas newly planted trees will take 10 years or more to provide equivalent benefits.  Tree clusters can be incorporated into development in many ways, including parking lot interiors or perimeters, private lawns, common open space areas, road buffers, and median strips (Figure 3.2.1).  Any areas of reforestation or new urban tree plantings need an uncompacted soil volume that allows the root systems to get air and water.  An uncompacted soil volume of 15 to 28 cubic metres is recommended to achieve a healthy mature tree with a long lifespan (Casey Trees, 2008).

===Preserve existing trees===  

Mature stands of deciduous trees will intercept 10 to 20% of annual precipitation falling on them, and a stand of evergreens will intercept 15 to 40% (Cappiella, 2005).  Depending on understory vegetation, soils and topography, tree clusters may only produce surface runoff for major flood event storms.  Preserving mature trees will provide immediate benefits in new developments, whereas newly planted trees will take 10 years or more to provide equivalent benefits.  Tree clusters can be incorporated into development in many ways, including parking lot interiors or perimeters, private lawns, common open space areas, road buffers, and median strips (Figure 3.2.1).  Any areas of reforestation or new urban tree plantings need an uncompacted soil volume that allows the root systems to get air and water.  An uncompacted soil volume of 15 to 28 cubic metres is recommended to achieve a healthy mature tree with a long lifespan (Casey Trees, 2008).