OPW16/0021- Operational Works Application 2 of 4

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Two!tanks!are!proposed!in!the!hydraulic!design!by!FLOTH!(Appendix!1);!a!Rainwater!
Tank!and!a!Stormwater!Tank.!!The!size!and!outlet!pipework!have!been!specified!by!
FLOTH! and! are! included! in! the! model! as! shown! in! Table! 4! The! Stormwater! tank! is!
preceded!by!a!GPT!specified!by!FLOTH!as!a!ROCLA!Model!CDS!0506.!
Estimates! of! reuse! from! each! of! these! tanks! has! been! provided! by! FLOTH! and!
modelled!as!noted!Table!4.!
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Table!4:!MUSIC!Rainwater!Tank!Parameters!


                                                    Rainwater!      Stormwater!
                       Parameter!
                                                      Tank!            Tank!

                    Tank!Volume!(kL)!                   25!              60!
                    Surface!Area!(m2)!                 12.5!             30!
            Equivalent!Overflow!Pipe!(mm)!             212!              320!
            Constant!Daily!Outflow!to!Reuse!
                                                        1!               2.9!
                       (kL/d)!#!
#!ReZuse!estimates!provided!by!FLOTH!(8/12/15)!as!a!constant!daily!demand.!
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2.4.2 Bioretention!System!




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Bioretention! systems! use! ponding! above! a! treatment! surface! to! maximise! the!
volume! of! runoff! flowing! through! the! filtration! media.! They! typically! convey! flows!
above! the! design! event! through! overflow! pits.! ! The! treatment! system! operates! by!
firstly!filtering!surface!flows!through!surface!vegetation!and!then!percolating!runoff!
through! prescribed! filtration! media.! ! This! media! provides! treatment! through! fine!
filtration,!extended!detention!and!biological!uptake!of!nutrients.!!!
As! these! systems! take! approximately! 12Z24! h! to! drain,! the! maximum! depth! of!
ponding! allowed! to! occur! over! the! filter! area! has! been! limited! to! 300! mm.! ! The!
depth! of! the! filter! media! has! been! limited! to! 400! mm.! ! Table! 5! summarises! the!
proposed! design! parameters! for! the! bioretention! basin! for! this! development.!!
Indicative!bioretention!location!is!highlighted!in!Figure!5.!!
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