Changes

Opportunities for directing impervious surface runoff to pervious areas are first considered during the site layout stage. Sheet flow should be encouraged from all impervious surfaces draining to pervious areas. In cases of concentrated flow, the flow can be broken up with level spreaders or flow dissipating riprap. Use the following guidance for the pervious runoff receiving areas:

Opportunities for directing impervious surface runoff to pervious areas are first considered during the site layout stage. Sheet flow should be encouraged from all impervious surfaces draining to pervious areas. In cases of concentrated flow, the flow can be broken up with level spreaders or flow dissipating riprap. Use the following guidance for the pervious runoff receiving areas:

*Undisturbed densely vegetated areas and buffers – A hydrologist and/or ecologist should be consulted before designing a site to drain to sensitive natural heritage features like pocket wetlands.

*Undisturbed densely vegetated areas and buffers – A hydrologist and/or ecologist should be consulted before designing a site to drain to sensitive natural heritage features like pocket wetlands.

*Landscaped and disturbed areas – With the proper treatment, the landscaped areas of the site can accept runoff from impervious areas. Deep tilling or soil aeration is recommended for topsoil that has been replaced or compacted by construction equipment. Former agricultural lands tend to develop a “hardpan” or compacted layer 0.5-1 meter below the soil surface from repeated plowings and farm equipment. Breaking up the hardpan may improve infiltration rates. [[Soil amendments]] can be applied to hydrologic soil group (HSG) C and D soils to encourage runoff absorption. See Figure 3.2.5 for guidance. Use deep rooting vegetation in landscaped areas when possible which will maintain and possibly improve the infiltration rates over time.

*Landscaped and disturbed areas – With the proper treatment, the landscaped areas of the site can accept runoff from impervious areas. Deep tilling or soil aeration is recommended for topsoil that has been replaced or compacted by construction equipment. Former agricultural lands tend to develop a “hardpan” or compacted layer 0.5 - 1 m below the soil surface from repeated plowings and farm equipment. Breaking up the hardpan may improve infiltration rates. [[Soil amendments]] can be applied to hydrologic soil group (HSG) C and D soils to encourage runoff absorption. Use deep rooting vegetation in landscaped areas when possible which will maintain and possibly improve the infiltration rates over time.

===Preserve or create micro-topography===

===Preserve or create micro-topography===

===Extend drainage flow paths===

===Extend drainage flow paths===

Slowing down flows and lengthening flow paths allow more opportunities for stormwater to be filtered and infiltrated. Extending the travel time can also delay and lower peak flows.  Where suitable, flows should be conveyed using vegetated open channels (see [[Enhanced grass swale]] and [[Bioswales]]).

Slowing down flows and lengthening flow paths allow more opportunities for stormwater to be filtered and infiltrated. Extending the travel time can also delay and lower peak flows.  Where suitable, flows should be conveyed using vegetated open channels (see [[Enhanced grass swale]] and [[Bioswales]]).