Aquaculture Groundwater Resource Atlas - Northampton area
Overview
The Northampton area refers to the area underlain by or adjacent to the Northampton Complex. The Northampton Complex is an area of basement consisting of granite, granulite (a granite-like rock formed by regional metamorphism) and migmatite. The basement is overlain, or abutted, by sedimentary rocks. The Silurian Tumblagooda Sandstone occurs on the western and eastern flanks. This is overlain in places by the Triassic Kockatea Shale, and by Jurassic sediments. The Jurassic sediments also directly overlie parts of the southern area of the Northampton Complex. In the south east, the basement is abutted by Permian and Jurassic sedimentary rocks of the Perth Basin. The western and coastal area is overlain by coastal dune systems.
Groundwater is generally available only in small supplies and is of variable salinity. In spite of this, however, groundwater is locally important for small scale horticulture and aquaculture, and is used for town water supply. Saline groundwater has also been used for aquaculture at Hutt Lagoon.
Geological map of the Northampton area
| Aquifers in the Northampton area | ||
|---|---|---|
| Formation | Hydrogeology | Groundwater salinity |
| Coastal dunes | Minor aquifer | Brackish to saline |
| Jurassic sediments | Minor aquifer | Fresh to brackish |
| Kockatea Shale | Aquiclude | Saline |
| Tumblagooda Sandstone | Minor to major aquifer | Fresh to brackish; hypersaline at Hutt Lagoon |
| Granite, granulite, migmatite, quartzite | Minor aquifer | Fresh to brackish |
Diagrammatic hydrogeological section of the Northampton area
Jurassic sediments
Jurassic sedimentary rocks directly overlie the crystalline rocks of the Northampton Complex, and also the Triassic Kockatea Shale. The sediments are mainly poorly sorted sandstones, with minor shale. The rocks are exposed as laterite capped mesas. The water table is generally deep, and only the basal part of the sequence is saturated. The aquifer is recharged by direct rainfall on the outcrop, and groundwater discharges through springs and soakages around the base of the mesas.
The Nabawa Sandplain, just east of Nabawa, is the largest area and only part to be systematically investigated (Hydrogeology Report 1995/38 by H. A. Koomberi). Groundwater salinity ranges from fresh to brackish. Springs have been developed for aquaculture on the margin of the sandplain.
References: GSWA Hydrogeology Report 1995/38 by H. A. Koomberi; WRC Hydrogeology Report HR 127 by N. Hundi (1999).
Tumblagooda Sandstone
The Tumblagooda Sandstone is a consolidated red sandstone of Silurian age, and ranges in thickness from 1000 to 2500 m. The formation abuts the Northampton Complex, commonly with a faulted contact, and is overlain by Triassic, Jurassic and Cretaceous sediments.
The sandstone appears to have both fracture and intergranular permeability. Bore yields presumably depend on intersection of either fractures or gravel layers within the formation. Bores drilled for Kalbarri town water supply obtain as much as 1000 kL/day.
Groundwater salinity is variable. East of the Northampton complex, the groundwater in the Tumblagooda Sandstone is generally brackish. Groundwater in the formation near Horrocks Beach is also brackish. At Kalbarri, the groundwater salinity is low, less than 0.5 ppt.
North of the Murchison River, the groundwater is brackish or saline. Groundwater adjacent to Hutt Lagoon is hypersaline.
Groundwater is used principally for town water supply at Kalbarri. Saline groundwater has also been used at Hutt Lagoon for the processing of algal material, and there is minor stock usage.
References: Berliat (1965, 1966); Whincup (1969); GSWA Hydrogeology Reports 1770, 1771, 1990/14, 1992/15.
Crystalline rocks of the Northampton Complex
The crystalline basement rocks of the Northampton Complex consist of granulite, granite and migmatite, with bands of quartzite. All these rocks are cut by dolerite dykes. The rocks are commonly weathered at the surface, but the weathered profile is thin, and air photos clearly show the strike of the underlying rocks.
Groundwater occurs in fractures in the crystalline bedrock. Bore yields vary, but rarely exceed 200 kL/day. A large amount of drilling has been carried out for the Northampton water supply, but with low success rates. Bore yields also decline markedly at the end of summer.
Groundwater is mainly fresh to brackish, reflecting the elevated topographical position of the bedrock, but saline groundwater may occur in low lying areas.
Groundwater is used for Northampton town water supply, for limited horticulture, and for stock watering.
References: Swarbrick (1963) GSWA Records 1963/30 and 1963/38; Boyd (1979); Ventriss and others (1982); GSWA Hydrogeology reports 1993/11, 1994/30
Coastal dunes
North of Geraldton, the coastal dunes contain small supplies of brackish to saline groundwater.
The superficial formations on the coastal plain south of Geraldton are described in the Perth Basin section.
Surficial sediments
The main area of surficial sediments is the alluvium in the Chapman River. These range up to 10 m thick and consist of sands, gravel and clay. Groundwater from the alluvium is used for Nabawa town water supply, with bore yields of around 100 kL/day. Groundwater salinity in the Chapman Valley alluvium is mainly brackish, reflecting the salinity of runoff in the river, and is fresh only along the margins.
| < Previous | Top |
