The Loddon River Basin extends approximately 300km from the Great Dividing Range between Daylesford and Creswick, to Swan Hill on the Murray River. Varying in width from 15km at Swan Hill to 100km along the Divide, the Basin covers 1,531,998 hectares.
Land and stream network
Mount Alexander is the highest point within the Basin, peaking at 741m in the Great Dividing Range. The foothills of the range extend over much of the southern section of the Basin, where the hilly to undulating land is generally above 300m. The northern two-thirds of the Basin contain the flat alluvial plains of the Murray Valley with the rocky granite residuals of Mount Terrick, Pyramid Hill and Mount Hoper rising about 8 to 100m above the general level of the plains.
Eighty percent of the land has been cleared for agriculture while areas of forest remain between Daylesford and Castlemaine, Maryborough and Laanecoorie, and in the vicinity of Bendigo, Bridgewater and Wedderburn.
The 392km long Loddon River flows south to north draining the western sections of the Basin. Its principal tributaries are the Bet Bet and the Tullaroop Creeks in the south west. A series of creeks such as Gunbower, Reedy, Pyramid and Barr Creeks traverse the northern plains. Bullock Creek drains the north-central zone and Bendigo Creek carries run-off to Kow Swamp via the Piccaninny and Mount Hope Creeks in the east.
Rainfall and surface hydrology
Rainfall is generally low and variable in the Loddon River Basin and the physical characteristics of the area make it prone to flooding, particularly on the flat terrain of the northern plains. Average annual rainfall increases with elevation, being greater in the southern highlands. Kerang and Boort in the more arid regions of the north have average annual rainfalls approximately 55 per cent of that in the southern highlands. Run-off from rainfall within the Basin is relatively low and declines to negligible levels in the semi-arid north west. Most of the run-off comes from the southern highlands where rainfall is greater. However, Bendigo Creek also receives substantial run-off flowing to Kow Swamp via Piccaninny and Mt Hope Creeks.
Almost 60 per cent of average annual natural streamflow of the Loddon River at Laanecoorie occurs between July and September and less than 5 per cent occurs between January and March. Operation of the Cairn Curran, Tullaroop and Laanecoorie Reservoirs has enabled summer flows passing Laanecoorie to be maintained at higher levels for downstream diversions for irrigation and rural use with a corresponding reduction in spring flows.
The riverine plain in the north of the Basin is underlain by the shallow shoestring sand aquifers of the Shepparton Formation. These sands are surrounded by a matrix of clay and silt. The water table in the far north is very shallow and in places actually outcrops. Where the water table is shallow, the groundwater is highly saline, and there is significant land salinisation. The quality of groundwater in the Loddon River valley improves towards the south.
Within the highlands, the shallow aquifer system is represented by the Newer Volcanics and Quaternary alluvium associated with the present drainage system. Elsewhere the minor and heterogeneous fractured rock aquifers occur in the Palaeozoic basement of folded sediments, granite and metamorphic. Only 20 per cent of the divertible resource is considered fresh, the remainder being marginal to saline, and all of the minor resource is brackish.
Mixed grazing of sheep and cattle is common on the steep to undulating land in the south, with some crop production. Also important in the south are fruit, vegetable and forest industries. The main fruit-growing district is at Harcourt near Castlemaine.
Crops are a more important form of land use in the north of the Basin where wheat, barley, oats and hay are grown under irrigation. Pig and poultry farming are also significant throughout the Basin.
Loddon water storages
Cairn Curran Reservoir is located on the Loddon River, about 10 km west of Maldon.
Tullaroop Reservoir dams the Tullaroop Creek, a tributary of the Loddon River. The storage embankment is situated about 7 km south-east of Carisbrook.
Laanecoorie Reservoir is located on the Loddon River, 40 km south-west of Bendigo.