Appendix B - Sediment Basin Design and Operation - Draft document
APPENDIX B – DRAFT DOCUMENT REVISION DECEMBER 2016
This revision to Appendix B of IECA (2008) and sediment basin factsheet is provided here in DRAFT form for industry feedback and use. This draft is intended to allow industry to get familiar with and implement more modern, reliable and efficient methods to construct and operate sediment basins, then feed learnings, costings and performance data into the final version of this document. Although still in draft form and not mandated as the current standard, we encourage designers and contractors to familiarise themselves with the new approach so feedback on how the document can be improved can be provided.
IECA acknowledges the financial support provided by the Queensland Department of Environment and Heritage Protection (DEHP) to deliver the update of Appendix B of the 2008 Best Practice Erosion and Sediment control document and sediment basin factsheet.
What Are the Major Changes?
We have revised Appendix B to include the use of Type A and Type B basins for fine grained/dispersive soils where assisted settling of sediment occurs as runoff passes through the basin rather than the capture-treat-release approach adopted by Type D/F basins. The concept of continuous flow basins has been adapted from New Zealand where they have been utilised for over 20 years. The following provides a brief description of the basins:
Type A - similar to what we know as Auckland basins (TP-90 guidelines). Type A basins include an automated chemical dosing system and a decant structure at the outlet;
Type B – incorporate only an automated chemical dosing system and can be used for catchments with shorter disturbance timeframes.
The major changes to Appendix B & the Sediment Basin Fact Sheet include:
Step 1 – Table B1 revised to include an additional trigger for larger sites. Once the revised Appendix B is finalised, Table B1 will supersede Table 4.5.1 presented within Chapter 4 of IECA (2008);
Step 2 – Table B2 revised to include Type A and B basins;
Step 6 – inclusion of sizing procedure for Type A and B basins;
Steps 8 to 10 – Additional details provided on inlets, forebays, baffles and decant structures;
Step 17 – Details around operating, assessing performance and troubleshooting Type A and B basins;
Section B3 – Additional details on coagulants and flocculants, dosing systems and how to determine the optimum chemical for site soils.
We have also created a new fact sheet for coagulants and flocculants which provides details in addition to Appendix B and the Sediment Basin fact sheet revisions.
Why the Change?
Continuous flow sediment basins have been in use in New Zealand for over 20 years with great success. A major constraint on performance for Type D/F basins (capture-treat-release approach) is the basins overtopping during larger storm events and during consecutive rainfall events prior to treating and releasing. Type A and B basins will allow for treatment during both of these scenarios producing higher treatment efficiency and improved environmental outcomes.
Some other features of Type A and B basins include:
Automated dosing reduces labour requirements for water treatment;
Type B basins can be left full to provide water for site use. Although it is preferable to dewater all basins prior to a rainfall event, further details are provided in the revised Appendix B on the requirements and procedure for each basin allowing flexibility for basin management.
Where to from here?
The intention is to release the final version of this updated Appendix B in late 2017, although this timeframe is flexible and might be extended to allow for further industry analysis and comment. Industry comment on any part of this document is warmly encouraged at any time during the review period – send correspondence to AppendixB@austieca.com.au for the attention of the Appendix B Review Committee.
We encourage designers and contractors to implement some Type A and B basins in consultation with their regulatory authority to provide learnings and feedback to IECA Australasia and the Appendix B Review Committee. Although we believe there is sufficient information in the document to design, construct and manage a Type A or B basin, we are also working in the background to create standard drawings to aid basin construction. If you require additional information or assistance whilst designing, constructing or managing a Type A or B basin, please contact us at AppendixB@austieca.com.au.