1.1.5.1 Surface water systems


Major surface water systems in the Gloucester subregion are rivers, with some limited surface water infrastructure such as farm dams and fish farm dams. The rivers in the northern part of the subregion flow into the Manning River and those in the southern part flow into the Karuah River. The Gloucester River, a tributary of the Manning River, is the major river flowing through the northern part of the subregion, while the Karuah River flows through the southern part of the subregion.

1.1.5.1.1 Surface drainage networks

The Gloucester subregion contains rivers flowing into two separate river basins, the Manning River Basin and the Karuah River Basin (Figure 26 and Figure 27). The northern part of the subregion contributes 2.2% (181 km2) of the catchment area of the Manning River Basin and the southern part contributes 11.4% (166 km2) of the catchment area of the Karuah River Basin.

The main river flowing through the northern part of the subregion is the Gloucester River. It originates below the Gloucester Tops, outside the Gloucester subregion, before flowing through the subregion and then further downstream to its junction with the Manning River. The total length of the Gloucester River is 102 km, with about 43 km of its middle and lower reaches falling within the Gloucester subregion. The total catchment area of the Gloucester River (above its junction with the Manning River) is 1650 km2, which represents 20% of the area of the Manning River Basin.

Figure 26

Figure 26 Location of the Gloucester subregion, towns, major watercourses, selected and neighbouring catchments

The main tributaries of the Gloucester River are the Avon, Barrington and Bowman rivers (Figure 27). The Avon River (catchment area 290 km2) flows into the Gloucester River within the subregion just north of the Gloucester township and about 1 km upstream of the junction with the Barrington River. About 54% (158 km2) of the catchment of the Avon River is located upstream of the subregion, both to the west and east of the subregion. About 46% (132 km2) of the Avon River’s catchment is located within the subregion, contributing 73% of the area of the northern part of the subregion (181 km2) (Table 6). The Avon River descends 412 m over its 42 km course.

Figure 27

Figure 27 Surface drainage network and gauges for selected catchments and subcatchments

The Barrington River (catchment area 715 km2) rises on the eastern slopes of the Mount Royal Range, within the Great Dividing Range, and flows generally east, before reaching its confluence with the Gloucester River near Gloucester. The Barrington River descends 1370 m over its 93 km course, and discharges approximately 435 GL per year at the Relf Rd streamflow gauge (208031) located about 1 km upstream from its confluence with the Gloucester River. The main tributaries of the Barrington River include the Kerripit, Cobark and Moppy rivers. Only about 0.59% (4 km2) of the Barrington River’s catchment is located within the subregion, contributing 2.0% of the area of the northern part of the subregion.

Table 6 Catchment area for the main rivers and their main tributaries flowing through the Gloucester subregion


Main rivers

Main tributaries

Catchment area (km2)

Above subregion

Within subregion

Below subregion

Total

Gloucester

1081

181

392

1650

Avon

158

132

0

290

Barrington

711

4

0

715

Bowman

0

0

231

231

Karuah

529

166

755

1450

Mammy Johnsons

208

111

0

319

Telegherry

74

0

0

74

Branch

0

0

215

215

The Bowman River joins the Gloucester River downstream of the Gloucester subregion and about 2 km downstream of the junction of the Gloucester and Barrington rivers. As such, all of its catchment area (231 km2) is below the subregion. The Bowman River descends around 635 m over its 54 km length.

The main river flowing through the southern part of the subregion is the Karuah River. It originates outside of the Gloucester subregion, before flowing through the subregion and then further downstream before discharging into Port Stephens near the township of Karuah. The total length of the Karuah River is 100 km, with about 40 km of its middle and lower reaches falling within the southern Gloucester subregion. The total catchment area of the Karuah River (above Port Stephens) is 1450 km2.

The main tributaries of the Karuah River are the Mammy Johnsons, Telegherry and Branch rivers (Figure 27). The Telegherry River joins the Karuah River upstream of the Gloucester subregion and its entire catchment area (74 km2) is outside the subregion. The Telegherry River descends around 771 m over its 28 km length.

The Mammy Johnsons River originates in the Myall River State Forest, outside the Gloucester subregion, before flowing into the subregion and joining the Karuah River, still within the subregion, near Stroud. The catchment area of the Mammy Johnsons River is 319 km2, about 67% (111 km2) of which is in the subregion (Table 6). The catchment of the Mammy Johnsons River thus contributes about two-thirds of the area of the southern part of the subregion. The main tributary of the Mammy Johnsons River is the Wards River, which occupies the northernmost part of the catchment of the Mammy Johnsons River. The Mammy Johnsons River descends 371 m over its 55 km course, and discharges approximately 59 GL per year at the Crossing streamflow gauge (gauge 209002), which is located just over half way along its length and is upstream of the junction with the Wards River.

The Branch River joins the Karuah River below the Gloucester subregion. All of its catchment area (215.3 km2) is below the subregion. The Branch River is 27 km long and has an elevation drop of 62 m.

1.1.5.1.2 Surface water infrastructure

There is some limited surface water infrastructure, such as farm dams and fish farm dams, within the Gloucester subregion. There is currently approximately combined storage capacity of 50 ML on the Tiedman property with 20 ML, 20ML, and 10 ML coming from the Tiedman North, South, and East dams respectively. These dams lie within the Avon River catchment, 10 km south of Gloucester and approximately 3 km north-east of Stratford (Figure 26). The two dams store water from new and existing CSG exploration wells, and supply water for agricultural irrigation. The two dams consist of a completely enclosed, above ground embankment, and are located on a ridgeline so can only be filled by reticulation. Therefore, they have very little impact on surface runoff water and total catchment flows (AGL Energy Limited, 2012).

There is a fish farm, the Pioneer Fish Farm, in the Gloucester subregion. It is 3 km to the south of Gloucester town. This fish farm consists of 20 ponds covering 5.8 ha plus three dedicated water storage reservoirs. The farm’s water supply is sourced from surface runoff, bore water and river water. The 28 ML headwater dam collects surface runoff. There are two settling ponds holding 21 ML and 48 ML respectively. The fish farm holds a licence that allows up to 390 ML of water per year to be pumped from the Gloucester River.

1.1.5.1.3 Flooding history

The largest reported flood for the Gloucester River occurred in 1929 (Gloucester Shire Council, 2004). The largest recorded flood for the Gloucester River occurred on 20 March 1978, with a maximum gauged level of 12.05 m and a maximum daily discharge of 227 GL at gauge 208003. The largest flood in the last 20 years occurred on 16 June 2011, with a maximum gauged level of 8.7 m and a maximum daily discharge of 92 GL at gauge 208003.

The largest recorded flood for the Karuah River occurred on 21 January 1971, with a maximum gauged level of 8.53 m and a maximum daily discharge of 144 GL at the gauge 209003. The largest flood in the last 20 years occurred on 8 May 2001, with a maximum gauged level of 7.32 m and a maximum daily discharge of 101 GL at the gauge 209003.

Last updated:
5 January 2018