Cooks river EarthCache

The history of the Cooks river

The Cooks River is a tidal river about 14 kilometer long, measured from Strathfield to the mouth in Botany Bay. The river is quiet shallow with a width of 5 meters at the beginning at Strathfield, but at the mouth it measures about 120 meters in width. It is fed by several small streams like the Cup and Saucer creek and Mackay Park Canal.

When first described in the reports of Captain Cook, it was assumed to be a fresh water source:

I found a very fine stream of fresh water on the north side in the first sandy cove within the island before which a ship might lay land-locked and wood for fuel may be got everywhere.

However, in 1788 the first settlers explored it more and found it to be less than useful: Instead of in place of Cook's 'fine meadow', Captain John Hunter and Lieutenant Bradley both mentioned the shallowness of the water and the large swamps. Despite this, the land around the river was settled and cultivated for farming food and animals.

(Waypoint DAM01) In 1840 a dam was build in the river in Tempe near the current Princes Highway crossing, to remove the influx of salty water and to create a fresh water supply for Sydney. However the Cook's River water above the dam remained brackish, and was not used as Sydney's water supply; the structure itself proved to be a disaster to the river's ecology, it prevented tidal flushing of deposited urban silt, and hastening ultimate logging and pollution.

(waypoint DAM02) In 1841 a second dam was build near Canturbury for the Sugarworks factory, to supply it with ample water for its operation.

Because the river flowed through flat land all the way from its source, the streams that fed it were not fast flowing enough to carry silt out to sea. The dam and weir not only prevented tidal flushing, but also actually made silt deposition happen. This became visible in May 1889 when after three days of rain more than 40 centimetres of rain had fallen in the Sydney area. The flat lands around the Cook's river were flooded, with more than 2 meters of water above Canterbury Road bridge and more than 3 meters of water over the Sugarworks dam. Bridges were damaged, people were evacuated, houses were flattened.

In 1896, engineer H B Henson wrote a paper to the engineering Association of NSW in June 1896 with several recommendations. Stage one was the removal of the two dams to prevent further silt build-up. Stage two was the construction of a canal and tunnel from Parramatta River to Cooks River. Water from fast flowing Sydney Harbour would thus clean up the river. Later in stage three the rivers would be joined from Homebush Bay via a canal through Strathfield to Chullora. The stage two canal would be large enough to allow barges from the Alexandria industrial area to the Sydney docks, reducing freight distances and costs. Nothing was, however, done apart from some desultory attempts at dredging.

It wasn't until 1928 during the depression that works performed during the "depression relief" were started on the dredging and concreting the riverbeds. In 1946 the policies of the Cooks River Improvement Act stated that the river and its feeding streams should changed from "undisciplined streams" towards a "river inside neat cement boundaries with no unruly reed beds to spoil the line". To accommodate the Mascot airport runways, the original river mouth was diverted to further west.

The Cooks River Project Report of 1976 made recommendations to bring back the nineteenth-century harmony. The Cooks River Valley Association has organised the work of cleaning up the river. This consists of tree planting, adding pollution traps in the streams feeding the river and in the river itself and creating saltmarshes for silt depositing and the bird rehabilitation.

Changes in the Cook's River

The following changes and their impact were made to the river:

• The construction of dams at Tempe and Canterbury: It prevented the tidal effect which caused more urban silt deposition into the river mudbanks. This caused reed beds to grow wider and this caused blockages for the traffic on the river.
• Ground clearing caused that storm water run-off happened faster, which meant that it caused more erosion which caused more surface dust into the river mudbanks and an increase in algae.
• Unfettered dumping of polluted water, this exterminated the water life, which broke down the food supply for the bird life.
• Concreting of the riverbed caused a faster flow of the water towards the bay, causing the salt marsh in the surrounding areas to dry out. The destruction of the salt marsh destroyed the habitats for birds. Also the pollution of the feeding rivers came into the Cook's River without any filtering.
• Diversion of the mouth of the Cook's River to make the area available for Sydney Airport. This moved the mouth about 1500 meters to the west and reducing the distance to Wolli Creek from 6.1 km to 3.2 km. See here for a map.

Online references:

• http://www2.canterbury.nsw.gov.au/cooknet/www/html/209-cooks-river-history.html
• https://strathfieldheritage.org/buildings/cooks-river-strathfield-timeline/
• https://en.wikipedia.org/wiki/Cooks_River

Questions

1. At waypoint MARSH03 the concreted riverbed is replaced with a rock rubble seawall with salt-tolerant plants behind it. This is enough to keep the salty water out. But how does the water from the river then get into the salt-marsh area?
2. At waypoint DRAIN05 the drain pipe is replaced by a rocky riverbed. What will the effect of this be?
3. If you look upstream at waypoint DAM02, you will see the rockwall on the left hand side and the concreted wall on the right hand side. On the left hand side you see the shrubs making it nearly all the way to the water, however on the right hand side they are far away. Why is this and why is it better?