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

EP-SMP-05: Maintaining the Swales or Catch Dl1lins                                                                                                                                                     ".




1. ObjectivesfTargets                                                                                            To channel the sheet-flow of stormwater into Bioretention Trenches.

2. Management Strategy                                                                                           1)Slow stormwater flow by rough (grass)surface, reducing the erosion
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                                                                                                                 2)Settle and trap coarse sediment and particulates flowing slowly over
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                                                                                                                 3) Slowly moving stormwater has time to infiltrate the permeable surface
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                                                                                                                 ,4)Assimilate nutrients from infiltrated water by grass. Periodic mowing
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                                                                                                                  increases grass production, and physically removes nutrients from the
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                                                                                                                  system in grass clippings; and
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                                                                                                  ’ij            5)Assimilate soil particles by grass growing over settled soil.
3. Tasks/Actions                                                                                                 1) Develop contour mound of permeable soil;
                                                                                                                 2)Vegetate Swale with appropriate grass or ephemeral wetland plants as
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                                                                                                                 appropriate;
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                                                                                                                 3) Inspect the integrity of the Swale (structure                -
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                                                                                                                 initial flows and vegetation cover);
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                                                                                                                 4) Inspect build-up of litter, detritus, and silt drapes as necessary; and
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                                               ,’:;1                                                             5) Periodically mow Swale at high blade setting, to maintain a rough
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                                                                                                                 surface. Remove grass clippings.

4. Performance                                                                                                   1) 1 00% v~getative cover along Swale; grass clipped at length to provide an
Indicators                                                                                                       effective rough surface;
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                                                               _:                                                2) No breaches or erosion of Swale;             ".I   ,-
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                                                                                                                 3) Swale free of litter and detritus; and
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                                                                                                                 4)Swale free of silt drapes that block infiltration of stormwater into the
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                                                                                                                 Swale.
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5,’ Monitorin~                                                                                                   1)Vegetative cover, structural integrity;                  ’l

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                                                                                                                 2) Litter/detritus/silt accumulation.
6. Frequency/Deadlines                                                                                           1)Vegetative cover, structural integrity: Monthly.
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                                                                                                                 2) Litter/detritus/silt accumulation: Weekly.
7. Responsibilities                                                                                              Site manager.

                                                                                                                 Landscape contractor.
8. Reporting and                                                                                                 Poor vegetative cover and lack of structural integrity to be reported to site
Review                                                                                                           manager and senior management.

9. Contingency                                                                                                   When loss of control of stormwater flow along the swale occurs:

                                                                                                                 1) I nform site manager, and request maintenance support;
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                                              rn                                                                 2) Redirect surface water flow to bypass damaged swale surface, and direct
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      .                                                                                                          flow onto stable ground surface;
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                                                                                                                 3) Bridge damaged swale surface (sandbag,erosion mat);
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                                                                                                                 4) Implement corrective actions.