PURPOSE

The Corangamite Catchment Management Authority has completed a detailed hydrological study of Anglesea River catchment to determine design flow estimates for the hydraulic floodplain modelling of the Anglesea Township. This study was required to update the flood information held by the CCMA received from the Flood Data Transfer Project completed for DSE in 2000. This work calibrates a detail RORB model with 2 small historic events to improve the reliability of the design flow estimates for modelling the Anglesea River floodplain. This work forms the basis of new flood overlays to be introduced into the Surf Coast Planning Scheme.

CCMA

General Description of Catchment

Anglesea River at the Great Ocean Road has a catchment area of 125 square kilometres. The headwaters of the river is located in the top of the Otway Rangers and approximately 90% of the catchment is forested within a state park with moderate stream gradients (Figure 1 and Figure 2).

Two main catchments, north branch (Anglesea River) and the South Branch (Salt Creek), run parallel west to east joining together at the Alcoa Power Station just north of Anglesea. The catchment of the northern branch is 65km2 with 91% forested and the southern branch is 51km2 with 95% forested. The average slope of the main tributaries is 0.7%. Figure 1 shows the catchment extent and land cover.

The description of the land system is taken from “A Study of the Land in the Catchments of the Otway Ranges and adjacent plains” by A.J.Pitt for the Soil Conservation Authority in 1981. [Ref 6] The Anglesea River catchment falls into the Anglesea land system (7.2) and is described by the following:

“Stretching inland from the coast between Bells Beach and Moggs Creek lies a dissected plain on Tertiary sediments. Long straight slopes emanate from spurs and ridges. The coastal margins are retreating and often abut the sea in steep cliffs or massive landslips and earthflows.

The parent material is very variable, ranging from lateralized sediments on the ridges to relatively unweathered alluvium in the drainage lines. Thus the soils are particularly variable.

In general, plant nutrient levels are low and surface horizons are weakly structured. Plant communities are mainly open forests less than 15m in height; the height decreases towards the coast under the influence of salt-bearing winds. The area is highly regarded for its diversity of flora. Some parts have been cleared for agriculture. The main hazards to land use are gully erosion and sheet erosion.”

In the component table for this land system 60% of the catchment is covered by Grey sand soil that is listed having a very high permeability with depths > 2m. The extent of this soil is shaded pink in Figure 3.