MCU14-0039 Flood report and flood man Plan rev August 2015

Como Glasshouse P/L C/‐ Martoo Consulting P/L
Flood Impact Assessment – 305 Lake McDonald Drive Cooroy



         It is expected that flood impacts external to the site will be lower than those reported owing
          to the very conservative roughness condition of n=0.07 applied for the greenhouse. Flood
          impacts are expected to be significantly reduced in the event that an n=0.05 condition is used,
          which is more likely to be appropriate in this instance.

2.5               Conclusions and Recommendations
2.5.1             Summary of Findings
The following key findings are made: ‐
         Some minor flood impacts were found to occur in areas external to the site, with the largest
          increases estimated to occur in the 10% AEP design event. Impacts were found to be limited
          to a maximum of 50mm in the 1% AEP event. Flood impacts were found to not impact on any
          existing infrastructure, compromise any access provisions or result in a reduction in usable
          land. It is contended that these impacts are non‐worsening and will not result in any
          actionable nuisance;
         There were no fundamental changes in flood impacts at the site under the sensitivity case
          using a higher roughness of n=0.1 for the greenhouse. Flood impacts external to the site were
          therefore found to not be adversely affected by an increase in floodplain roughness; and
         It is expected that flood impacts external to the site will be lower than those reported owing
          to the very conservative roughness condition of n=0.07 applied for the greenhouse. Flood
          impacts are expected to be significantly reduced in the event that an n=0.05 condition is used,
          which is more likely to be appropriate in this instance.


2.5.2             Recommendations
Based on an assessment of existing and post‐developed conditions outlined in the sections above, and
with consideration of the resulting flood impacts at the site, the following recommendations are
made: ‐
      1. The greenhouse structure is to be fitted with lay‐down wall sheeting to the perimeter of the
         greenhouse. The lay‐down walls should be extended to a minimum height of 1.7m to facilitate
         flood waters flowing through the greenhouse during periods of severe flooding. The lay‐down
         wall sheeting should be configured to automatically drop down based on hydraulic head alone
         and in the absence of any mechanical or electrical systems which are prone to failure during
         flood events. It is considered that a simplistic and readily fail‐safe arrangement involving the
         lower wall sections being attached via Velcro strapping or similar to be appropriate in this
         instance.
      2. Bunds 1 and 2 currently constructed at the site should be removed to minimise flood impacts
         external from the site. The current Bund 3 can be retained given that the flood impacts from
         this bund were primarily limited to the site, with external impacts estimated to be minor and
         of little consequence.
      3. Following advice from Council, it is recommended that Bund 3 be moved to a location
         between 5 m and 10 m to the north of the vegetation lining the creek immediately south of
         the greenhouse to ensure the maintenance of a riparian buffer in this location.




3917‐01 / R01 v02 ‐ 31/08/2015                                                                         8