Storage structures are considered as node volumes in MicroDrainage models, where as InfoDrainage allows a more complex approach in the shape of Stormwater Controls.

MDX - The structure is considered to be additional volume on the side of a Manhole in a given network. Often those manholes will be made into Junctions as they are simply a way to get a location to attach the structure to. As such we will import the structure as a stormwater control and replace that manhole to maintain the same connectivity.

SRCX - The structure is the centre point of the design with inflows and outlets connected which maps directly to a stormwater control with the inflows directly connected.

In both cases the storage structure is normally a single system, i.e. pond, bio-retention area, etc. However complex structures can be specified and will be imported as explained below.

Single Structures

MicroDrainage supports a range of storage structures that are typically designed in isolation. The list can be seen below with a brief explanation of how they will be imported into D2 as stormwater controls. Given the different approaches to these systems there are typically a few parameters that need to be mapped differently, or will be ignored, please see the notes given.

Tank/Pond

This is imported as a Pond stormwater control with all dimensions preserved.

Lined Soakaway

Currently there is no direct comparison within D2. As such this is imported as a Tank stormwater control with the Depth/Area table set to match the volume provided by the original structure.

Notes:

  • Area = Plan Area of Ring + Area of the surrounding square pit * porosity. This is then multiplied up by the number of structures.
  • Porosity will be set to 100% as the porosity is factored into the area calculation as above.
  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design.
  • Cap Infiltration cannot be imported so a warning is given.

House Soakaway

This is imported as a Soakaway stormwater control with appropriate dimensions.

Notes:

  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design.
  • Cap Volume and Infiltration values in MicroDrainage were measured from the bottom up, whereas D2 measures these from the top down, so they will be converted.

Infiltration Trench/Trench Soakaway

This is imported as an Infiltration Trench stormwater control with appropriate dimensions.

Notes:

  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design.
  • Cap Volume and Infiltration values cannot be imported so a warning is given.

Swale

This is imported as a Swale stormwater control with only the top swale section active. i.e. Trench turned off.

Notes:

  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design.
  • Cap Volume and Infiltration values cannot be imported so a warning is given.
  • 'Include Swale Volume' option is ignored in D2, a Swale's volume is always considered. As such a warning is given if the MicroDrainage file requests that the volume is ignored.
  • Swale porosity is imported and visible on the Advanced tab.

Infiltration Basin

This is imported as a Pond stormwater control with all dimensions preserved.

Notes:

  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design.

Infiltration Blanket

This is imported as a Soakaway structure with appropriate dimensions. i.e. Circular or rectangular based on the dimensions entered in MicroDrainage.

Notes:

  • Base Infiltration will be turned on if a positive rate is set in the MicroDrainage design.
  • Cap Volume value in MicroDrainage was measured from the bottom up, whereas D2 measures these from the top down, so it will be converted.

Porous Car Park

This is imported as a Porous Paving stormwater control with appropriate dimensions.

Notes:

  • Membrane Depth is imported as Paving Depth
  • Depression Storage is mapped to an equivalent Interception Volume based on the plan area of the structure. i.e. Length * Width * Depression storage depth.
  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design.
  • Cap Volume value cannot be imported so a warning is given.

Cellular Storage

This is imported as a Pond stormwater control utilising the specified Depth/Area table. We cannot directly map the MicroDrainage structure to the one in D2 due to the differences in their setup. i.e. Depth/Area table vs crates.

Notes:

  • Any Infiltration areas will be ignored as they are not supported - see the Shape option on the Advanced tab.
  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design.

Dry Swale

This is imported as a Swale stormwater control with both sections active. The swale section is imported as per the Swale section above, with the trench dimensions and under drain imported if present.

Notes:

  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design
  • Cap Volume and Infiltration values cannot be imported so a warning is given
  • 'Include Swale Volume' option is ignored in D2, a Swale's volume is always considered. As such a warning is given if the MicroDrainage file requests that the volume is ignored.
  • Swale porosity is imported and visible on the Advanced tab.

Filter Drain

This is imported as an Infiltration Trench stormwater control with appropriate dimensions.

Notes:

  • Under drain information will be imported, with the option turned on if a pipe diameter is found in the MicroDrainage design.
  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design.
  • Cap Volume and Infiltration values cannot be imported so a warning is given.

Bio-Retention Area/Sand Filter

This is imported as a Bioretention stormwater control for consistency.

Notes:

  • If a Depth/Area table has been used, not Flow Through Structure with Under drain, D2 will only extract the first two entries for the Top and Bottom areas.
  • Perimeters are not imported from the Depth/Area table, instead they will be set to a circular perimeters on the Advanced tab.
  • Infiltration options will be turned on if a positive rate is set in the MicroDrainage design
  • Filter layers will be imported if present, however the following rules apply:
    • If only one is specified this will become the soil layer
    • If there are two the first will be the storage and the second the Soil.
    • If there are more than two the first will still be the soil, but the others will be combined to form a single layer. A warning will be given where they are combined
    • Soil layers will be set to Sand.
    • Where a safety factor > 1 is specified the Percolation rate will equal the Filtration rate / safety factor. A warning will be given if one or more layers has a safety factor greater than 1.

Deep Bore Soakaway

These are not currently support in D2 and it is not possible to map them to an existing stormwater control due to their nature. As such a warning will be given to note that these have not been imported.

Pipe/Double Pipe/Box Culvert/Double Culvert

These are not supported as a stormwater control and will need to be respecified as a Connection within the design. This will give a much better representation of reality as flows will be calculated through the system as expected.

Complex Structures

MicroDrainage can only support one structure at a given location in a Pipe Network or a Source Control design. To combat this the concept of a complex structure was introduced to allow multiple to be considered at the same location.

D2 does not have this limitation and allows each structure to be modelled as intended in the correct location. As such we do not attempt to load a complex structure as a single stormwater control. Instead we will import the individual structures as their own stormwater control (as above) with the lowest inserted into the design. The remaining structures will then be placed around that stormwater control leaving the user to decide how to connect them into the rest of the system.