The following describes the available options under the main Onsite Detention and Retention tab:
Land Use %
The subarea breakup of the sub-catchment is described in the adjacent dialogs in terms of firstly the pervious area and in the second dialog the total impervious area.
The following roof, road and paved area percentages provide a description of the further breakup of the impervious surfaces within the sub-catchment:
Roof Area %
Road Area %
Paved Area %
The three component percentages should added up to 100%
The % capture values for each impervious component area is the % that enters the OSD/s.
Similarly the % of the pervious area component that enters the OSD/s is also required.
Average Allotment Density
The average allotment density in (number of lots per ha) is required mainly for the rainwater tank component of any OSD systems.
Dev Area Ratio
This ratio describes the area of controllable private land by OSD over the total sub-catchment area. For example if the total sub-catchment contains a large urban residential component that requires OSD control, however also contains say 20% of parkland and public road that is not controlled by OSD then the Dev Area/Total Area ratio would be 0.8