๐๐ง️ Approaches for LID Control Placement in Subcatchments
Implementing Low Impact Development (LID) controls within a subcatchment can be approached in two distinct ways, each catering to different urban planning and environmental objectives:
1. Mixed LID Placement in Existing Subcatchment ๐️๐ณ
- Method: Introduce one or more LID controls into an existing subcatchment. This displaces an equivalent non-LID area.
- Variety: Allows a mix of LIDs, each treating runoff from different non-LID areas of the subcatchment.
- Parallel Action: LID controls act in parallel, not in series. Meaning, outflow from one LID doesn't become inflow for another.
- Adjustments Needed: May require modifications to properties like Percent Impervious and Width to balance the area replaced by LIDs.
- Example: Transforming 75% of a 40% impervious area to permeable pavement changes the imperviousness to around 14.3%.
- Runoff Dynamics: LIDs like Green Roofs and Rooftop Disconnection treat only the precipitation directly falling on them, not capturing runoff from other areas.
2. Dedicated Single LID Practice in New Subcatchment ๐ฑ๐ง
- Approach: Create a new subcatchment entirely devoted to a single LID practice.
- Series Placement: Allows LID controls to be aligned in series and receive runoff from multiple upstream subcatchments.
- Subcatchment Adjustments: If carved out of existing subcatchments, modifications to Percent Impervious, Width, and Area properties might be necessary.
- Override Standard Properties: In a subcatchment fully occupied by an LID, standard surface properties are overridden by those specific to the LID.
- Routing Outflows: Surface and drain outflows from LIDs usually go to the same outlet as the parent subcatchment. Alternatives include routing all LID outflow back to the pervious area of the parent subcatchment or directing drain outflow to a separate outlet.
๐ง๐ง Implementation Considerations
- Spatial Planning: Deciding which approach to use depends on the spatial and environmental context of the subcatchment.
- Environmental Impact: Each method has different implications for water management, infiltration, and ecological impact.
- Urban Compatibility: Consideration of the urban landscape and existing infrastructure is crucial in selecting the appropriate method.
In conclusion, these two approaches offer flexible strategies for integrating LID controls into urban landscapes, each with its unique advantages and considerations. Proper planning and execution of these strategies can significantly enhance sustainable water management and ecological resilience in urban areas. ๐️๐ฑ๐ฐ
