The Shire of Boyup Brook lies within the upper reaches of the Blackwood and Collie River groundwater basins (as defined by the Department of Water). Limited investigations have been undertaken into the groundwater resources within the Shire.
The Wilga Basin is divided into two distinct basins. The Wilga West basin has been estimated to be in the order of 6km x 3km in area and the Wilga East basin 10km x 1-2km in area. Little is known of the water quality of this basin, although available data suggests a moderate source of fresh groundwater. The Wilga Basin is estimated to have in the order of a 4 x 10 m average annual recharge with a possible groundwater in-storage of 390 x 10 m. Further testing has been suggested to determine the extent of resources.
The Boyup Basin is again in two distinct basins. The East Boyup basin is approximately 9 km x 0.5 - 2 km wide. Little is known of the West Boyup basin, although it is suggested that it may cover an area of approximately 2km. Available data indicates, “that a reasonable volume of fresh to brackish groundwater may exist within the Boyup Basin”.
With further exploration, it is anticipated that the volumes, recharge and water quality of the Wilga and Boyup Basins could provide substantial alternative water sources for future growth (including industrial) within the Shire.
The major river system is the Blackwood River and its tributaries. Clearing of about 85% of the catchment of the Blackwood has resulted in a mean annual salinity level in the order of 1150 mg/litre total dissolved salt along its whole length. This is brackish water, which cannot be used for human consumption.
During winter many creeks are fresher than the Blackwood River. However by October, most creeks are far more saline than the Blackwood, with creeks that flow through summer having salinity readings between 2000 and 3780ms/ms. These creeks contribute to the rise and fall of the Blackwood River salinity levels. These salinity levels may continue to rise for many years as a result of past clearing.
The Collie River contributes to the catchment from the Northern area of the Shire and the Warren River contributes to the catchment of the South-eastern area of the Shire.
Boyup Brook Shire lies within the Darling Plateau System and consists of three main landform areas:
- The northern areas of the Shire occupy gently undulating dissected plateau surfaces with broad gravel crests and generally broad valleys.
- The Central areas have an undulating to moderately sloping plateau surface with some rock outcrops.
- The Southern portion of the Shire consists of undulating to hilly areas of the plateau surface.
Soils in the north of the Shire consist of crust and gravels on broad crests, gravely soils on slopes and grey sands, yellow sands and earths in wide valley floors.
North-west of Boyup Brook town site grey leached sands occur with some swampy areas and lakes. West of the town there are gravely soils on divides and yellow soils and red earths on valley slopes. Central areas, generally between the Blackwood and Tweed Rivers, have yellow gravely soils and ironstone gravels on gently undulating ridge crests. The southern portion of the Shire has yellow soils, gravel and leached sands in broad valleys.
Much of the Shire area is extensively cleared, with the main areas of remnant vegetation being contained in the large Department of Environment and Conservation (DEC) estate in the Wilga and Perup Reserves. This is predominantly mixed jarrah and marri forest, with important smaller stands of wandoo being found in upper stream valleys. Other significant varieties include banksia found throughout forested areas and wetlands in the west of the Shire.
The geology of the Shire is mainly comprised of Precambrian Rocks of the Darling Plateau that are approximately 2,500 years old. The Darling Plateau comprises mainly ancient granites and younger dolerite intrusions. Granite rocks include banded rocks of similar composition called gneisses and magnetite.
Over most of the plateau, basement rocks have been weathered to form a surface capping of laterite - some of which is suitable for use on gravel roads and some with enough potential free alumina to be classed as bauxite. There are potential coal bearing deposits to the north west of Boyup Brook town site. In the central western portion of the Shire there are metamorphic belts which are known to contain deposits of vandiferous, titaniferous, magnetite and nickel. There is potential for chromitite and platinum group elements. There are also glacial rock deposits occurring throughout the Shire.
There are two known coal deposits in the Boyup Brook Shire. Permian coal, similar to that in Collie, is known to exist in the Wilga Basin (8 km NE of Wilga) and the recently discovered Boyup Brook Basin (2km W of Boyup Brook). Similar to the formations at Collie, there are no surface exposures of coal or coal bearing strata. The exploration effort to date has been inhibited by access difficulties related to the state forest, and to a lesser extent, by failure to conclude compensation agreements with landowners.
It is estimated that coal bearing deposits at Wilga contain a measured resource of 30 million tonnes and an indicated resource of 53 million tonnes with further potential. A regional drilling program during 1983 discovered the Boyup Brook basin deposit that has coal resources in excess of 90 million tonnes. Most of this small basin occurs in quarantined state forest, hence exploration is progressing slowly and carefully. In 1990, application was made for a mining lease over the area of potentially economic coal development.
