Modelling a Stormbloc^® Infiltration System Within The Micro Drainage Program Win Des - Source Control

This document outlines the method for sizing and checking the size of a Stormbloc^® Infiltration System using the Micro Drainage program Win Des . This example uses the Source Control Module but does not utilise the CASDeF feature of Win Des .

Design Criteria

For this Example we have used the following variables:

We have assumed that there is no outfall from the site and that all of the surface water run-off must soakaway.

1. Global Variables

   Model the units as cellular storage with no outflow control. An overflow can be selected if necessary, though for this example we will not be using one.

   

2. Rainfall and Network Details

   Enter the return period and other rainfall details as normal

   

3. Time/Area Diagram

   Enter the time area details as normal. In this instance the catchment area is relatively small with evenly shaped characteristics, we have therefore assumed that the time/area diagram is linear in form.

   

4. Cellular Storage Details

   Enter the dimensions of the Stormbloc^® Infiltration System here. For this instance the Stormbloc^® Infiltration System we are looking at is 16m (20 blocks) long, 6.4m (8 blocks) wide and 1.32 (2 blocks) deep. We therefore input the data as a surface area, in this case 16m x 6.4m gives a surface area of 102.4m². The pond/tank invert level should be input as the invert level of the bottom of the blocks. The cover level is the cover level above the infiltration system. For this example we have used relative levels of 8 for the invert level of the blocks and 10 for the cover level.

   The infiltration coefficient should be input for the base and/or sides. This coefficient can be calculated from test pit results using the calculator tool shown next to the input boxes on the left hand side of this window. A suitable factor of safety should also be used. The void ratio of the Stormbloc® modules is 96% and so a value of 0.96 should be used in the porosity box.

   

   The system can now be analysed by pressing the button.

5. Summary of Results

   The Stormbloc^® Infiltration System that we have modelled has dimensions of 16m x 6.4m x 1.32m deep. At a void ratio of 96% this will provide a storage capacity of 129.76m³.

   

   The summary below indicates a storage volume of 124.9m³ for the critical, winter storm of 360 minutes. The summary also indicates that the half-drain down time for this system will be 556 minutes, i.e. within the 24 hours required for soakaway designs.

   The proposed Stormbloc^® Infiltration System will therefore have sufficient capacity for this site.

   If the volume of the infiltration system is not sufficient, or the half drain down time is greater than 24 hours, then adjustments can be made to the size of the infiltration system by editing the cellular storage details.

   Micro Drainage and Win Des are registered trademarks of Micro Drainage Ltd. The software and screen displays are copyright Micro Drainage and all rights are reserved.