Assess Your Waterways
A good time to assess your waterway is early winter through until late spring. Weed problems are more apparent at this time of year and the impacts of river flow can be clearly seen. Erosion, slumping banks and sediment deposition are more obvious when the river or creek is in full flow.
The creekline can be walked and graded following the Pen-Scott method of riparian assessment (Pen & Scott, 1995). Weeds and native vegetation are recorded and a weed control and revegetation plan can be developed accordingly.
When the native vegetation has been degraded through historic land uses such as grazing, a vegetated site close by can be used as a guide to choosing plants.
River foreshore condition assessment.
The Pen-Scott method of riparian assessment is used when grading our region’s waterways. This method provides a system which allows foreshores to be assessed and placed along a graded description. The scale runs from pristine (A grade) through to ditch (D grade).
A grade foreshore
The river embankments and/or channel are entirely vegetated with native species and there is no evidence of human presence or livestock damage. This category, if it exists at all, would be found only in the middle of large conservation reserves where the impact of human activities has been negligible.
A2: Near pristine
Native vegetation dominates but introduced weeds are occasionally present in the understory, though not to the extent that they displace native species. Otherwise there is no human impact. A river valley in this condition is about as good as can be found today.
A3: Slightly disturbed
Here there are areas of localised disturbance where the soil may be exposed and weed density is relatively heavy, such as along walking or vehicle tracks. Otherwise, native plants dominate and would quickly regenerate in disturbed areas should human activity decline.
B grade foreshore
B1: Degraded – weed infested
In this stage, weeds have become a significant component of the understory vegetation. Although native species remain dominant, a few have probably been replaced or are being replaced by weeds.
B2: Degraded – heavily weed infested
In the understory, weeds are about as abundant as native species. The regeneration of some tree and large shrub species may have declined.
B3: Degraded – weed dominated
Weeds dominate the understory, but many native species remain. Some tree and large shrub species may have declined or have disappeared.
C grade foreshore
C1: Erosion prone
While trees remain, possibly with some large shrubs or grass trees, the understory consists entirely of weeds, mainly annual grasses. Most of the trees will be of only a few resilient or long-lived species and their regeneration will be mostly negligible. In this state, where the soil is supported by short-lived weeds, a small increase in physical disturbance will expose the soil and render the river valley vulnerable to serious erosion.
C2: Soil exposed
Here, the annual grasses and weeds have been removed through heavy livestock damage and grazing, or as a result of recreational activities. Low level soil erosion has begun, by the action of either wind or water.
Soil is being washed away from beneath tree roots, trees are being undermined and unsupported embankments are subsiding into the river valley.
D grade foreshore
D1: Ditch – eroding
Fringing vegetation no longer acts to control erosion. Some trees and shrubs remain and act to retard erosion in certain spots, but all are doomed to be undermined eventually.
D2: Ditch – freely eroding
No significant fringing vegetation remains, and erosion is completely out of control. Undermined and subsided embankments are common, as are large sediment plumes along the river channel.
D3: Drain – weed dominated but stable
The highly eroded river valley has been fenced off enabling colonisation by perennial weeds. The river has become a simple drain, similar if not identical to the typical major urban drain.