Vegetation (Floating River Vegetation) - Office of Public Works

gravel require loosening assess the abundance of floating river vegetation upstream and
downstream of the site. High levels of suspended solids due to gravel loosening at the time of
flowering will impact negatively on Ranunculus fluitans especially. Where there is an
abundance of floating river vegetation the plant species should be able to cope and adapt to
loosening of channel gravel. It may also be worth considering that the presence of Ranunculus
species growing in gravel on the channel bed may be indicative of a healthy gravel base with
plenty of aeration, nutrient cycling and loose gravel base, elements essential for plant growth.
•It is essential to note that floating river vegetation growth is seasonal. Local knowledge and
cross reference with Regional Fisheries Board requirements on channel clearing or river bed
aeration prior to the commencement of maintenance would be highly recommended.
5.3 Specific Office of Works mitigation measures and other Statutory Bodies
The following mitigation measures have been separated into those measures that can be
directly adopted by the Office of Public Works; and those that involve other Statutory Bodies.
Office of Public Works: At present the Office of Public Works have developed a ten step
Environmental Drainage Maintenance programme to provide appropriate habitats for fish. On a
long term basis a similar programme needs to be developed to identify floating river vegetation.
While this ecological assessment has made every effort to provide the reader with a detailed
overview of floating river diversity this needs to be developed further through training.
•On-site training and awareness of Office of Public Works staff members is essential for habitat
recognition and plant identification of floating river vegetation communities.
Office of Public Works: Arterial drainage work, undertaken in or adjacent to urban environments,
on watercourses supporting floating river vegetation should facilitate a rise in water levels during
winter months and the fall in water levels in summer. The cyclical change in level between flood
and low water levels is a necessary dynamic of floating river vegetation habitat. Fresh silt
deposition provides a renewed growing medium while the mechanical force of rising water
facilitates plant reproduction and distribution during rising water levels. A drop in water levels
during summer months favours the production of flowering structures (section 3.4).
•Variation in water levels through the year should be facilitated in the operation of existing
works and considered in the design of new works.
Office of Public Works: In horticulture ½ to ⅔ of the plant material may be removed (Spence, I.
2001) without adversely affecting the growth of plants. This rule of thumb for the removal or
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