Erosion

Sassafras has endured a fair amount of erosion and deposition during its' European history, which if you exclude the Cedar Getters of the 1880s only goes back about 108 years, though that only goes back to George and Henry Fords ownership. Before them was Thomas Skinner, back to 1889, I suspect he bought the lands that include Sassafras for timber. So perhaps we should say Europeans started having a big impact from about 1889 onwards, given that the Cedar Getters were only interested in the bigger and easiest Red Cedar to get at, while Red Cedar suffered greatly and they left might gouges in pulling them out roots and all they did not clear the land in a wholesale fashion.

Timber getting post 1889 still would not have been as catastrophic from an erosion point of view as clearing for agriculture and the dramatic increase in fires which only really started post 1903 when the Fords (followed by many others over the years) moved in to Mooral Creek.

The first time I wondered about ersion and silting of our internal creek was when I began to wonder why the 1:25000 topographic maps get the location and direction of the internal creek so totally wrong in many places. Some of this I put down to tree cover, with differential growth from differenct clearing regimes or soils, seeming to locate an unseen creek some where else. From an aerial photo you can only surmise the location of a creek when it is under heavey tree cover, if the creek is not under the lowest point in the trees then it is going to be recorded in the wrong location. That's how I believe at least one S bend is completely missed and how intersections of Category 1 streams with the Category 3 stream are usually wrong and how in general the location can only be described as fanciful, LIDAR based mapping will fix all of that, along with some bizarre contours that are way to shallow. I believe LIDAR will be used for the next generation of maps in New South Wales. However there are a couple of places where there are areas of creek flats where the direction may have actually changed.

Internal creek old location

The image to the left is actually from a 1929 road realignment survey and is similar in general details to the original Portion survey from 1889 that became the Portion plan, both put the creek as running in generally diagonally to the road as it crosses Mooral Creek. The creek is the black line beneath the words "Both gone".

Current creek location

At the right, marked in red, it now runs along Mooral Creek Road as much as 5 metres from the road reservation, in places somewhat closer and a very steep drop.

I find it a little hard to believe that Surveyors would have missed a creek running beside both the original and new (circa 1929) road reservations for 50 metres so I believe it really was where they had it marked.

All of the area where the creek deviates in is creek flat, the current creek banks are studded with logs and serpentine rocks and boulders of various sizes.

As a side note, all of the area I have shown here is blown up on the plan in great detail in an inset, as are all the congested areas of deviation though they do not show the internal creek in the relevent inset though they do show the shape of Mooral Creek at the bridge in some detail, along with a more accurate representation of property boundaries.

If it were not for a large chunk of rock that protrudes about 1.25 metres above the normal creek level and running about 2 metres along the bank, I believe our little creek would have punched straight through to Mooral Creek rather than turning right at 90 degrees, it really is that tight on the ground. The rock is gradually disintegrating, perhaps one day it will make it through.

soil erosion from land clearing

Now about some deposition, the log poking out of the creek bank is a sawn log. From the bridge, which is at the height of the creek flats, to the bottom edge of the log is one metre. It is about 15 metres across the creek flat here. That represents quite a lot of fill.

Interestingly, the soil below the log is littered with burnt pieces of timber.

This log only became visible a couple of years ago when a particularly long flood (a fresh) took place, an East Coast Low stayed put. Over a few days the creek dropped at least half a metre, more in places, down to a rocky bottom, that is clay studded with serpentine rocks, whereas before it was generally just a clay bottom. I believe in this area the creek is down to its' pre settlement level. In one spot there was a massive roll of small leaf privett bushes, perhaps 5 metres high, rolled up and scooped out of the creek. Imagine a wood shaving with a couple of spirals, then make it out of entire large small leaf privett bushes, roots and all rolled into a loop, spectacular.
On the upstream side of the bridge, just out of the photo, in a shallower soil stratum is a hollow core brick. This brick, and many others littering the surface of the creek flats further up stream will date from a dam wall collapse. Our internal creek is a category 3 stream, draining over 160 hectares.

Now it is not permitted to dam category 3 streams, many years ago when the dam on our neighbours place was built this was not the case, at least it was built with a pipe to maintain "environmental flow" though the water flowing in the creek below the dam is always more than what comes out of the pipe, seepage I guess. The first time the dam wall was built it was not consolidated enough. It collapsed during an an overtop event. The debris changed the nature of our creek again, in earlier years there were deep pools, deep enough on one bend for a swinging rope on one bend to jump into it. The rope was still here when we came and bought our place. That bend is quite shallow now, maybe 30cm deep.

Below the dam the creek flats are littered with all sorts of bits of bricks, rock, the odd small bit of concrete etc. Since we have been here the dam has overtoped twice but it has held, the massive size of the spillway is probably why it has survived, every flood makes it wider and deeper, now it is quite a substantial gouge through the rock on the hill side beside the dam.

Our little creek is a mighty roar in full flood. To give some insight, when it has not rained for a while you can throw a 10 litre bucket of water on the ground almost anywhere and it soaks in, it does not run away. Over the past year so there have been many months where, at least in the garden area, the water table has been within 50 millimetres of the surface, that is you see bandicoot scratching holes mostly full of water. Dig a hole to plant some thing and there is no need to water it it in, self watering holes. Combine that level of saturation with very intense rain events over the 4 to 500 acre watershed of our little creek and you get a lot of water trying to go somewhere.

A couple of weeks ago we had a good cloud burst, 32mm in around 12 to 15 minutes, it was another one of those days when it didn't seem to rain according to the BOM. The current rain event is slower, after 6 days of rain I have given up doing stuff outside for the moment, the 4 fledgling Swallows that left the nest on our front balcony on Sunday have never known what it is like to fly in clear air, without any of that wet stuff getting in the way. Light rain and heavy drizzle 20 to 24 hours a day, you don't have to wonder to hard why we used to have big trees and Standing Brush. Footer