Landscapes and landforms

The soil around Wattamolla is very prone to erosion, with erosion on tracks and trails particularly bad. The main cause of erosion to tracks is rain run off. The faster the water travels the more erosion.

Erosion is exacerbated (made worse) because:

• Plants have been cleared to create tracks and trails. Where there are no plants, there are no plant roots to hold the soil in place. There is no vegetation to slow the flow of water.

• Walkers sometimes trample (walk over) plants at the edges of tracks or go walking off track, killing some plants. Therefore there are less plant roots to hold soil in place and less plants to slow rain runoff.

• Walking on and off tracks compacts the soil over time. This makes the soil similar to concrete. When it rains the water cannot seep into the soil. It runs even faster over the surface taking soil with it.

• Deer are an introduced, feral species in the Royal National Park. Their hard hooves compact the soil even more than people do. They create additional tracks in the bush by trampling vegetation. They kill some plants by rubbing their antlers on them. All of this leads to increased erosion.

Rock swale

Look at the rocks alongside the concrete road. This is a rock swale that has been built alongside the new concrete fire trail. A rock swale is a man-made shallow trench, or dry-creek bed, that captures rainwater runoff.

This rock swale collects rainwater that drains off the hard surface of the concrete fire trail. It slows down the flow of stormwater to minimise erosion.

Grooves

The grooves along the concrete fire trail collect and divert water off the fire trail. They direct stormwater into the rock swale. They also reduce the speed of water flow on the road, improving safety for vehicles.

Raised walkways

Over the past few years National Parks has built a huge amount of raised walkways along the coastline of the Royal National Park. As you can see in the photos, there were lots of erosion issues on the old walking track. The raised walkways help in the following ways:

• walkers are not compacting soil by walking on the ground

• plants are regrowing across the old track

• plants can grow right up to the edge of the walkway and even underneath it

• there is less trampling of plants by bushwalkers when they stay on the walkway.