1. Regional Karst Hydrology & Subterranean Streams

The southern littoral of the Bibbullmun Sovereign Nation is defined by an intricate network of coastal river drainages, endorheic salt lake chains, and subterranean karst aquifers.^[1] Spanning the coast from Cape Naturaliste eastward past Albany to Esperance Bay, this expansive hydrological domain encompasses short, energetic coastal streams (Denmark River, Frankland River, Kalgan River, Pallinup River, Gairdner River) and perched coastal wetland basins.^[1][2]

Along the Tamala limestone ridges of the south-west and south coast, surface water rapidly infiltrates porous limestone, creating complex underground karst cave networks and subterranean rivers.^[2][3] In sites such as Jewel Cave, Lake Cave, and Yallingup Cave, ancient underground freshwater streams flow through calcified limestone caverns into coastal springs.^[3][4] Customary law reveres these subterranean waters as sacred spiritual conduits guarded by ancestral water spirits (Moorup), regulating cave entry under strict religious protocols.^[4][5]

2. Endorheic Salt Lake Chains & Boom-and-Bust Ecology

Inland from the coastal granite headlands lies a chain of ancient endorheic playa lake systems, including Lake Grace, Lake Dumbleyung, and the Esperance coastal lakes (Lake Gore, Pink Lake).^[6] These paleodrainage depressions have no marine outlets, acting as natural evaporation pans that fluctuate between hypersaline salt crusts in midsummer and vast brackish water bodies during wet winter cycles.^[6][7]

Bibbullmun custodians timed seasonal foraging assemblies to these hydrological boom-and-bust cycles.^[7][8] Following winter floodings, hundreds of thousands of migratory waterfowl—including black swans (Cygnus atratus, Maali), grey teal, and mountain ducks—nested around lake margins.^[8][9] Custodians harvested moulting birds, which were temporarily flightless, and gathered waterfowl eggs in controlled quotas, preserving abundant food reserves without destabilizing reproductive colonies.^[9][10]

3. Coastal Dunefield Aquifers: The Science of Kepa Freshwater Soaks

Along the expansive, wind-scoured quartz sand dunefields of the south coast, surface rivers are absent for tens of kilometres at a time.^[11] Survival across these arid coastal corridors relied upon profound indigenous knowledge of coastal sand dune micro-aquifers (Kepa).^[11][12]

Custodians excavated shallow freshwater wells in the sand swales immediately behind primary foredunes, tapping into lenses of low-density fresh rainwater that float buoyant atop denser seawater intruding from the ocean.^[12][13] These wells were shored with paperbark linings to prevent sand collapse and covered with flat stones to protect the potable water from blowing sand and animals.^[13][14] This micro-aquifer engineering enabled continuous seasonal travel and resource harvesting along hundreds of kilometres of remote southern beaches.^[14][15]

4. Estuarine Bar-Lagoon Management & Unceded Marine Title

Where southern coastal rivers meet the turbulent Southern Ocean, high-energy wave action creates permanent sandbars across river mouths, forming expansive coastal lagoons (Wilson Inlet, Beaufort Inlet, Gordon Inlet, Culham Inlet).^[16] During high-water winter cycles, custodians actively monitored water levels behind the sandbars.^[16][17]

When lagoons reached maximum capacity, custodians coordinated the controlled breaching of the sandbar, digging narrow pilot channels that allowed outgoing floodwaters to rush through, opening the estuary to the sea.^[17][18] This controlled breaching triggered massive inward migrations of ocean salmon, mullet, and bream, which were harvested in intertidal stone weirs constructed along lagoon mouths.^[18][19] Under modern international law and the principles established in Mabo [No 2], Bibbullmun sovereign authority over these coastal waterways, dune aquifers, and marine lagoons remains intact, unbroken, and unceded.^[19][20]