Lake Poorrarecup
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| Lake Poorrarecup | |
|---|---|
 Lake Poorrarecup December 2018 | |
  Lake Poorrarecup Location in Western Australia | |
| Location | Western Australia |
| Coordinates | 34°25′16″S 117°13′37″E / 34.42111°S 117.22694°E |
| Type | saline |
| Catchment area | 94 km2 (36 sq mi)[1][2] |
| Basin countries | Australia |
| Max. length | 1.85 km (1.15 mi)[3] |
| Max. width | 1.45 km (0.90 mi)[3] |
| Surface area | 1.99 km2 (0.77 sq mi)[1] |
| Average depth | 3 m (9.8 ft) maximum[1] |
| Shore length1 | 5.1 km (3.2 mi)[3] |
| Islands | none |
| Location | |
 | |
| 1 Shore length is not a well-defined measure. | |
Lake Poorrarecup, also known as Poorarecup Lagoon,[2] is an ephemeral salt lake located in the Great Southern region of Western Australia, approximately 34 km (21 mi) south west of Cranbrook and 65 km (40 mi) north west of Mount Barker. It is located in a watershed between the Kent River and Frankland River catchments and the Gordon River, a tributary of the Frankland.[4]
The lake was once freshwater but became saline by 1967[5] as a result of deforestation within the catchment area and lower rainfall.[1] It has a surface area of 1.99 km2 (0.77 sq mi), and holds 4.98 GL (176,000,000 cu ft) with a maximum depth of 3 m (9.8 ft) at full capacity. The catchment area occupies an area of approximately 94 km2 (36 sq mi) but only 59 km2 (23 sq mi) drains directly into the lake. The remainder drains into a number of smaller seasonal lakes and swamps further downstream with a total area of 3.8 km2 (1.5 sq mi).[1] The lake has a roughly circular shape and is on the remnants of a plateau[6] at an elevation of 225 m (738 ft).[1] The salinity of the water over the past couple of decades has been 10,500 mg/L.[5] The lake is sustained by rainfall and groundwater inflow.[4] It is part of an unfenced wetland vegetation buffer zone with a width of 38 to 350 m (125 to 1,148 ft) from the edge of the wetland.[2]
Catchment
The catchment area is flat or gently undulating, and few well-defined drainage courses are found. Surrounding catchments also have mature landforms but also have a degree of dissection with reasonably well defined drainage lines. Some of the surrounding lakes include Lake Matilda and Lake Balicup. The entire area is underlain by sediments of Tertiary or Quaternary age, which overlay Precambrian granites and migmatites. The low hills in the landscape are often capped with pisolitic laterite, but sandy lunettes, that were once ancient dunes, generally occur parallel to the lake margins.[4]
The area recorded an average annual inflow of 2.65 GL (94,000,000 cu ft) between 1973 and 2001, with approximately 78% of the water evaporating. The lake has neither dried up nor overflowed in the past two decades.[1]
Vegetation
Approximately 50% of the natural forests[2] have been cleared for agricultural development. The native vegetation within the catchment area is predominantly jarrah (Eucalyptus marginata) woodlands with mixed jarrah, wandoo (Eucalyptus wandoo, and swamp yate Eucalyptus occidentalis) forest in more elevated and sandy areas. In the wide drainage lines and swampy part woodlands of paperbark (species of Melaleuca including Melaleuca cuticularis), Banksia species with sedge swamps are found. Sandy flats support woodlands with a mix of jarrah, marri (Eucalyptus calophylla), wandoo and swamp yate.[1]
Ruppia megacarpa, a form a seagrass, is found on the floor of the lake and deposits of seagrass wrack are found on the shoreline.[2]
