Response to Information Request - Received on 19/04/2012 · OPW11/0335

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   EP-SMP-05: Maintaining the Swales or Catch Drains

   10. Corrective actions                                                                                                                       1) Restore breaches, gullying, or other structural damage to Swale
                                                                                                                                                (armouring the base of the Swale may be necessary);
                                                                                                                                                2) Restore vegetative cover in Swale;

                                                                                                                                                3) Remove build-up of silt, litter and detritus in Swale. Silt drapes on the
                                                                                                                                                Swale surface must be removed by a rake or spade, and revegetation might
                                                                                                                                                be necessary;
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                                                                                                                                                4)Site manager reinforcing the need to mow Swale at high blade setting
                                                                                                                                                and remove clippings.



                                                                                                                                                                                                                          :’-11
   EP-SMP-06: Maintaining the Bioretention Trenches

   1. ObjectivesfTargets                                                                                                               ,
                                                                                                                                                To remove nutrients and suspended sediments from stormwater to meet
                                                                                                                                                water quality objectives in the terminal wetland.

   2. Managemel1t Strategy                                                                                                                      1) Stormwater enters Bioretention Trench from Swale, or from Inlet
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                                                                                                                                                Pipework through Rock Filter to avoid erosion;
                                                                                                                                                2) Stormwater filters through permeable soil horizons of mulch/rock
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                                                                                                                                                (surface)and sand/planting soil (sub-surface);
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                                                                                                                                                3) Low flow exfiltrates through the gravel layer in the base of the
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                                                                                                                                                bioretention trench into the surrounding soil
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                                                                                                                                                4)Sedges/Reeds in the Bioretention Trenches assimilate nutrients from the
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                                                                                                                                                pore-water. The use of several littoral plant species that are tolerant of
                                                                                                            )it"                                inundation, and are adapted to varying stages of dryness and wetness, is
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                                     ’"          :                                                                                              recommended to ensure a maintenance free plant community; and
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                                                                                                                                                5)Overflow from the Bioretention Trench exits via a high flow outlet weir
                                                                                                                                                into the heath wetland.

   3. Tasks/Actions                                                                                                                             1) Inspect Bioretention Trench for accumulated debris and litter;

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                                                                                                             -=,-                               2) Inspect Bioretentio~ Trench for silt drapes;

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                                                                                                                                                3) Inspect Bioretention Trench for healthy growth of required plant species;
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                                                                                                                                                4)Inspect the high flow outlet weir grate for blockages or build-up of
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                                                                                                                                                detritus.
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                                     :>!i’~ ~-                                                              ,,~r y,~                   101      5) Inspect Bioretention trench for excessive water hold up or water-logging
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   4. Periormance                                                                                                                               1) Bioretention Trench and outlet weir grate are free of litter;
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                                                                                                                                                2) Bioretention Trench is free of silt drapes that block water infiltration into
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                                                                                                          ~                                     the trench substrate;
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                                                                                                                                  ’             3) Bioretention Trench has healthy growth of the required plant species, and
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                                                                                                                                       ~        is free of weeds,
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                                                                                                                                                4) Bioretention Trench drains freely to surrounding soil and is not clogged,
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                                                                                                                                                blocked or water logged

   3 Monitoring                                                                                                                                 1) Plastic litter;
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                                                                                                                                                2) Smothering of plants by sediment or coarse particulate matter;
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                                                                         I                                            i~’                       3) Silt drapes on trench floor; and
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                                 ’:                                                                                                             4)Vigorous vegetative cover, weeds.
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                                                                                       .;,              ."’l~                                   5) Excessive water ponding on surface, evidence of soaking or water-
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                                                                                                                                                logging of trench