Drainage feature protections

Drainage feature protection under the PNF Codes

The PNF Codes of Practice (PNF Codes) outline drainage feature protections. This is to mitigate soil erosion and water pollution by limiting forestry operations in riparian zones. The drainage feature protections in the PNF Codes (Section 8.4) details the riparian exclusion zones that apply for each Code. These riparian exclusion zones and drainage protections apply based on the type and hierarchy of the drainage feature.

How are drainage features defined under the PNF Codes?

A drainage feature is a drainage depression, drainage line, stream, river or watercourse.

Forests that are managed under the Northern, Southern and Cypress-Western Hardwood Codes are located within an erosional environment. In these areas, drainage lines are channels down which surface water naturally concentrates and flows. 

Forests that are managed under the River Red Gum Code are located within a depositional environment. In these areas, there is generally no active erosion, and drainage lines are channels which conduct rising floodwaters from major streams into the forest to spread out over the floodplains. Flooding in these streams and forests is rarely related to local rainfall but occurs due to distant heavy rainfall and/or snow melt or high regulated irrigation flows.  

Drainage lines exhibit one or more of the following features:

• evidence of active erosion or deposition (for example, gravel, pebble, rock, sand bed, scour hole or nick point)
• an incised channel more than 30 centimetres deep with clearly defined bed and banks
• a permanent flow.

These features distinguish them from drainage depressions.

Deposition means the laying down of solid material which has eroded and transported from a distant part of the land surface.

The definition of a stream, unmapped or mapped is an incised watercourse with:

1. a defined channel
2. bed and banks
3. minimum depth of 30 centimetres.

The Strahler System determines stream orders (see Figure 1).

A prescribed stream is a stream listed in the Major Rivers database.

About Strahler stream order

Catchments are comprised of a branching network of drainage features. Strahler stream order is a method to describe a stream’s hierarchy in a catchment based on the confluence (joining) of streams. Higher stream orders are typically larger streams and so have greater protection under the PNF Codes. 

Figure 1: Strahler stream order.

Identifying drainage features and stream order within your PNF Plan

When you get your approved PNF plan from Local Land Services, you will also get a map that includes mapped drainage features.

Not all drainage features appear on maps. You should be aware of unmapped drainage features in your PNF Plan area and apply the relevant riparian exclusion zones as per the PNF Code.

About Riparian Exclusion Zones

Riparian exclusion zones are areas next to drainage features where forestry operations are not permitted (see Figure 2). Riparian exclusion zones extend from the banks of the drainage feature out to the distance specified in the PNF Codes.

You cannot run forestry operations in riparian exclusion zones. Except where specifically permitted for drainage feature crossings and road construction or maintenance.

Harvesting machinery must not enter riparian exclusion zones, except at designated crossings or where otherwise allowed by the PNF Codes. For example, accidental felling.

How to apply riparian exclusion zones to your forest

Marking riparian exclusion zones

Riparian exclusion zones must be clearly marked on your Forest Management Plan Map. You must communicate this to all people involved in the forestry operation. You should clearly mark riparian exclusion zones in the forest ahead of forestry operations. The markings should remain visible throughout the operation.

Measuring riparian exclusion zones

Measure riparian exclusion zones from the top of the defined bank of the drainage line or stream or where there is no defined bank, from the edge of the channel of the drainage feature for the distance specified in the PNF Code.

Directional felling

You must not fell trees into a riparian exclusion zone, unless it is accidently felled. Where harvesting is occurring in or adjacent to riparian exclusions zones, all tree felling must employ directional felling to minimise disturbance to drainage features (see Figure 2).

Accidental felling

If a tree is accidentally felled into a riparian exclusion zone, the tree may only be removed if:

• you limit the disturbance to soil, groundcover and native vegetation to the minimum extent necessary
• limit harvesting machinery to the outer 5 metres of the riparian exclusion zone
• harvesting machinery that enters the riparian exclusion zone to retrieve the tree or part of the tree uses walkover techniques
• treat any soil disturbance or furrows following the tree’s removal, to prevent concentration of water flow or soil movement. This will help to restore the natural pattern of overland flow and protect soil from accelerated erosion  
• you must record any removal of an accidently felled tree in the Forest Management Plan within 10 days.

Roads and crossings

You may construct new roads and crossings and re-open old roads and crossings within riparian exclusion zones if:

• the road or crossing is identified in the Forest Management Plan;
• the road prism or crossing intersects with the riparian exclusion zone at right angles or as close to right angles as is practicable;
• you minimise the clearing and disturbance within the riparian exclusion zone
• you have obtained any other necessary permits.

The PNF Codes include prescriptions for:

• the construction and maintenance of roads
• road drainage
• roads crossing drainage features.

Figure 2: Riparian exclusion zones and directional felling (top) and drainage feature crossing (bottom) 

Additional resources