Koolama Bay and Saint George Basin – Background Briefing

Koolama Bay

This is a u-shaped bay about 4km wide and 5km long facing NW (northwest) into the Timor Sea. It is surrounded by cliffs of Warton Sandstone that drop directly into the water on it SW (southwest) and NE (northeast) sides. The SE (southeast) of the bay has been built up from deposits from the King George River and its estuary. This is fronted with a sandy beach with about 1km deep mangrove covered wetlands to the SE, behind the beach. (See reference points 8 and 9 on adjacent map).

Tranquil Bay and Pangali Bay have been formed on the NW side of Koolama Bay where small run-off creeks have weathered and opened-up bays/inlets within cliff surrounds. Both bays have interesting natural and historic connections. (See reference points 5 and 6 on adjacent map).

A barrier beach and dune in Tranquil Bay encloses a tidal lagoon that connects the main Koolama Bay waters via a shallow channel that irregularly alternates between the north and south ends of the beach. On several locations along the back cliff wall of this bay, wet season waterfalls spill into the lagoon from the plateau above. There is plenty of fish life in the lagoon, conical shaped mud-creeper Whelks may be found from time to time on the edge of the lagoon and the tracks of a large Indo-Pacific crocodile (a ‘saltie’) are regularly seen on the southern lagoon shoreline.

Through the beach spinifex is on of the run-ff points and the cliffs behind the lagoon.
Vegetated sand dune and mangroves with the lagoon between the cliffs and the dune.

Washed up shells and coral pieces are common on the high water mark of the beach and the higher sections of the dune are stabilised with beach spinifex and goat’s foot convolvulus. A mixture of salt tolerant shrubs including two mangrove species and the beach tulip tree are found on the foreshore at either end of the lagoon.

Whelks ‘grazing’ on the organic debris accumulated in a shallow pool connected to the main lagoon.

An epic rescue of passengers and ship


The cargo and passenger ship Koolama, of the West Australian State Shipping Service sailing from Perth along the Kimberley coast had been purposefully beached at the south-eastern end of Koolama Bay after being bombed and disabled in February 1942. Volunteers who were repairing this bomb-damage holes in the hull were to complete their efforts after 10 days. The partly repaired but still greatly disabled, rudderless vessel was then skilfully backed off the beach at high tide and navigated via Joseph Bonaparte Gulf and Cambridge Gulf to the Wyndham dockside by Captain Jack Eggleston and his remaining crew.

Tenders had carried passengers and many of the crew, including Chief Officer Ken Renyolds, from the stranded vessel to a location in Pengali Bay, a small inlet off the NW side of the bay, for these people to camp at a safe distance from the ship.

In response to the initial distress radio signal from the ship and received at Drysdale Mission, 93 of those stranded at Pangali Bay were soon to be guided on a 150km arduous overland journey by seven Aboriginal men back to the Mission. The remaining passengers and crew were picked up by the mission’s lugger or flown out by a Qantas flying boat. There was no loss of life on the ship or the shore but unfortunately the unmanned pumps failed during an air raid when the Koolama was berthed at Wyndham. She started filling with water, broke her lines and sank.

Friends and family of those passengers and crew who were camped at Pangali Bay have since placed memorial plaques to commemorate the Koolama incident on the north-western cliff wall.

(A much fuller published account of this incident is given by Bill Loane, 2004, in his ‘Koolama Incident’ book)

Pangali Bay penetrates further inland than Tranquil Bay and the landward SW section has a thick stand of mangrove behind the beach and its very flat and shallow foreshore. Behind this 30m deep mangrove community is a triangular shaped grassy sandplain over 100m deep. The plain is surrounded by a gallery of mangroves with a small wet season creek draining from a ravine into the southwest corner of this mangrove.

A navigable channel at the SE end of the beach leads to a relatively active creek that often continues to run over the bare sandstone after the wet season. This creek originates from the escarpment above the cliffs and passes through a number of stepped rock pools and small falls in the Warton Sandstone before reaching the salt water. This creek provided fresh water for both the stranded passengers who camped on the grassy pain and for the volunteers who remained on the beached Koolama while she was being repaired.

Freshwater stream with waterfalls and pools spilling into Pangali Bay

Pangali is the traditional name for the inlet. Tranquil Bay probable takes its name from the enjoyable ambience of this little embayment and Koolama Bay became the official name after the incident. Prior to official naming it had been referred to a Calamity Bay and prior to this Rulhiere’s Bay.  

On the eastern side of the bay, Cape Rulhiere’s forms its most NE point, this rocky projection is joined to the mainland by a sandy tombolo fronted on the bay side by a 400m long sand beach. About 12km NW of the cape is the flat isolated Lesueur Island. It is recognised at night with its flashing navigation light (four flashes every 16 seconds). Unless the sea is quite calm and flat it is difficult during daylight hours to see the island with the naked eye from the bay. Both Lesueur Island and Cape Rulhieres were named by either Nicolas Baudin on Le Geographe or his junior companion Louis de Freycinet who mastered Le Casuarina in 1803.

River sediments have filled the land on the south-eastern side of the bay and a 2.8 km sand beach has formed. Most of this tidally flooded land behind the narrow beach is connected with the estuary or a channel off the bay at the south-easterly end of the beach and is populated by mangroves. A bombing incident had force beaching of MV Koolama. Captain Eggleston had beached the Koolama in the middle of this sand beach in 1942 to save his passengers and the sinking vessel. The vessel had been built with the capability of sitting on the sea floor as was necessary in Ports like Derby with its huge tidal ranges.

Both river mangrove and long style stilt mangrove are found just behind on the spit near the river/estuary mouth. The other side of the mouth is a cliff face with a sand beach running to the SW beneath the cliff. Sediments have also formed sand bars at various points within the bay some of which are exposed during low tides but others remain covered and may be a hazard for boats with a shallow draft.

Saint George Basin

The Saint George Basin is inland from Brunswick Bay with a narrow connecting tidal channel that becomes quite dangerous even for engine powered vessels with whirlpools and strong currents created during the tidal in- and out-flow. Phillip Parker King under sail in Mermaid experienced these waters when he first entered the basin in October 1820.

On entering Saint George Basin basin is the cliff lined mainland to the north and across the water in the same direction are some rounded hills and two flat-topped mountains. There are two relatively flat-topped islands in front of these features. Eastward across the 20km of water on a clear day, it is possible to see the foreshore margin of mangroves with a gap that marks the mouth of the Prince Regent River. Mangroves on either side of the river mouth form the largest population in the Kimberley, extending well over 100km2.

St Patrick Island (L) hiding Python Cliffs; Mt Trafalgar(391m) and Mt Waterloo(344m) in the background; rounded hill in front of mountains; and St Andrew Island (R)

The flat topped mountains are Mount Trafalgar and Mount Waterloo, and the sinuous cliffs on the western end of the basin are the Python Cliffs forming the edge of Marigui Promontory. Of the two flat topped Islands Saint Patrick is the smallest and St Andrew to its east is at least twice its size. Like the mountains, the islands have a flared apron below the cliffed margin of capping rock.

When the basin was formed it is likely that the original Prince Regent River flowed out to the sea across what has become the basin’s south -western margin. The river had cut down through its tough sandstone base of Warton Sandstone and exposed the edge of a large section of Carson Volcanic basalt rock. Comparatively the basalt weathers more rapidly than the sandstone resulting in the undermining and subsequent collapse of the sandstone above. The weathered sandstone fragments were eroded and carried out to sea, and so the wide water body forming the basin started to form. We can see where the sandstone remains as a resistant capping on the mountains, cliffs and islands and assume that over time this too will be undermined by the rapidly weathering basalt. There are a few rounded islands in front of Mt Trafalgar -these are basalt remnants of the original landscape minus a hard capping.

It is interesting to note the great difference between the rock formations in St George Basin and those for the Prince Regent River. For details see both ‘Background Briefing – overview of the Australian Kimberley’ and ‘Background Briefings – Rivers and the Well-Jointed Kimberley Landscape’