2014022_71_SeaviewTce_SWMP-revC_full · OPW16/0021

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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! 12T24! 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!locations!are!highlighted!in!Figure!5.!
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Table!5:!Bioretention!Basin!Design!Parameters!

                           Parameter!                    Bio1!         Bio2!
                Extended!Detention!Depth!(m)!            0.3!          0.3!
                                              2
                   Storage!Surface!Area!(m )!             5!            12!
                                          2
                     Filter!Media!Area!(m )!              5!            12!
              Unlined!Filter!Media!Perimeter!(m)!        0.01!         0.01!
               Saturated!Hydraulic!Conductivity!
                                                         200!          200!
                            (mm/hr)!
                       Filter!Depth!(m)!                 0.4!          0.4!
              TN!Content!of!Filter!Media!(mg/kg)!        800!          800!
               Orthophosphate!Content!of!Filter!
                                                          55!           55!
                         Media!(mg/kg)!
                   Exfiltration!Rate!(mm/hr)!            0.0!          0.0!
                   Overflow!Weir!Length!(m)!             5.0!          5.0!

2.4.3 Sediment!Forebays!
Due!to!the!size!(<2ha)!and!nature!of!the!development!it!is!sediment!forebays!are!not!
required.! Bioretention! areas! should! be! monitored! to! ensure! that! the! deposition! of!
coarse!sediment!on!the!filter!media!surface!does!not!affect!the!bioretention!system!
function.!!
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