Difference between revisions of "Infiltration"

From LID SWM Planning and Design Guide
Jump to navigation Jump to search
Line 29: Line 29:
  
 
{{textbox|Where infiltration is impossible, LID design alternatives exist which can still capture and retain  stormwater:
 
{{textbox|Where infiltration is impossible, LID design alternatives exist which can still capture and retain  stormwater:
*[[Bioretention: Non-infiltrating | Stormwater planters]]
+
*[[Biofilters]]
 
*[[Rainwater harvesting]]
 
*[[Rainwater harvesting]]
 
*[[Green roofs]]
 
*[[Green roofs]]

Revision as of 13:03, 10 October 2017

Infiltration of stormwater into underlying soils is one the priority level 1. mechanisms to achieve MOECC Runoff Volume Control targets. In many areas of Ontario, where municipal supplies of potable water are drawn from aquifers, it's also an important mechanism for groundwater recharge.

Infiltration is promoted through a number of LID BMPs:

Constraints[edit]

Infiltration practices are not recommended:

  1. over swelling clays or unstable sub-soils,
  2. over contaminated soils or sites with high risk of contamination from onsite activities,
  3. in flood prone areas where the wastewater system is sensitive to groundwater conditions causing sewer backups, and where LID BMPs have been found to be ineffective,
  4. in areas where the ecology and natural hydrology are dependent upon surface water,
  5. in areas where increased infiltration will result in elevated groundwater levels, which can be demonstrated to damage critical utilities or private property, or
  6. where prohibitions and/or restrictions exist per approved Source Protection Plans (see MOECC guidance).


Infiltration facilities should be designed with drainage modifications where:

  1. the underlying bedrock is within 1 m below the bottom of the proposed BMP, or
  2. the seasonal high groundwater level comes within 1 m below the bottom of the proposed BMP.

Designing with constraints[edit]

Infiltration can still be optimized over 'tight' soils with infiltration rates ≤ 15 mm/hr:

See also Low permeability soils

Where infiltration is impossible, LID design alternatives exist which can still capture and retain stormwater:

Planning[edit]

Hydrogeology

The Conservation Authorities Geoscience Group has prepared a guidance document which attempts to standardize the hydrogeological study requirements for development applications made to Conservation Authorities. It is a helpful guide for all low impact development applications which include infiltration. It is provided with the caveat that not all sections or content are necessary or appropriate for every case. Pre-consultation with your Conservation Authority and municipality is strongly recommended in all cases.

Hydrogeological Assessment Submissions Conservation Authority Guidelines for Development Applications


NEW CONTENT HERE? Needs advice on setbacks adding.

Soil infiltration rate

Infiltration tests must be undertaken at the location, depth and with a head of water that replicates the proposed design.

Suggested safety factors to be applied to measured percolation rate when designing infiltration facilities
Catchment area Consequence of failure
No damage or inconvenience Minor damage or inconvenience to external structures (e.g. ponding in parking lot) Significant damage to buildings or infrastructure (e.g. flooding damage)
<100 m2 1.5 2 10
100 - 1000 m2 1.5 3 10