Vegetation (Floating River Vegetation) - Office of Public Works

• Livestock should be restricted from entering watercourses except at fenced drinking slips.
This is a measure under REPS 3 and should be extended to other landholdings.
5.4 The impact of floating river vegetation on rising water levels and flow rate.
Identifying floating river vegetation, which may be impacting negatively upon water flow,
may not always be obvious. Since arterial drainage maintenance is typically on a four to six year
rotation (section 4.2), areas of floating river vegetation should be noted and recorded during
summer months and a similar assessment undertaken during the winter months (comparative digital
images would suffice) prior to the undertaking of arterial maintenance work. Such an undertaking
will assist in the selection of floating river vegetation impacting negatively on water flow during
winter months. It may be that non-floating river vegetation species may be impacting on water
dynamics, which in turn impacts negatively on floating river vegetation communities. The initial
impact may simply be a change in the pattern of floating river vegetation growth. Obstructions by
non-floating river vegetation is indicated in Fig. 9 by the rippling of the water flow and the
divergence of the floating river vegetation to either side of the restriction.
Restricted water flow
Oenanthe aquatica (Fine-leaved Water Dropwort)
NOT classified as floating river vegetation
Callitriche sp.
Water flow forcing
floating river
vegetation around
restricting growth
Fig. 9 Impact of Oenanthe aquatica on surrounding floating river vegetation and water flow.
A comparison between summer flow and winter flow suggests that the location of some
floating river vegetation may interfere or change flow capacity at higher water levels. Fig. 21 shows
photographs of the River Breagagh in Kilkenny during the summer with floating river vegetation
47
Ranunculus
sp.