Yakamia – sister to a small creek

Yakamia Creek, Albany

Yakamia Creek is a waterway that traverses the southern town of Albany, Western Australia, from its steep upper catchment all the way to a point between Bayonet Head and Emu Point in the mighty Oyster Harbour.  It is also a major stormwater drain, collecting much of the rain falling on the inner suburbs of Albany and discharging it into the ocean. It is approximately 9 km in length, and drains a catchment area of ~21 km2 including urban, industrial, and rural land, as well as remnant native vegetation.

Yakamia is thought to mean ‘sister to a small creek’ in the local Aboriginal Noongar language.  If it is a sister, it definitely could be considered an attention-seeking one given that it has been a major source of flooding in Albany for a number of decades.

The natural hydrology of the Albany area is generally characterised by steep upper catchments, seasonally waterlogged soils, and incised watercourses with broad lower catchment floodplains. Much of the urbanised part of the Yakamia catchment is located in its steep upper catchment where there is not much space to detain stormwater, resulting in large and ‘flashy’ floods.  It doesn’t help that sedimentation has accumulated in the drain, associated with historic clearing for cattle grazing and land development, and a lack of drainage maintenance.  This has resulted in severe flooding in recent years putting local infrastructure and people’s homes at risk.

Some great work has been undertaken by the City of Albany in restoring degraded sections of Yakamia Creek by transforming them into a ‘living stream’. i.e. modifying a traditional straight drain into a natural, meandering channel with bank stabilised using native vegetation, in order to improve the ecological function of the waterway. Federal funding from the Regional Local Community Infrastructure Programme and corporate and community planting days allowed the earthworks and revegetation program to be successfully completed.

However, this project focussed on improving the ecological function of Yakamia Creek and did not address the larger scale flooding and drainage issues of the system.

To address these flooding issues the City of Albany engaged Essential Environmental to undertake detailed hydraulic modelling of Yakamia Creek and prepare both an Arterial Drainage Plan for Yakamia Creek and a Water Management Strategy for the Yakamia/Lange structure plan area.

The purpose of the Arterial Drainage Plan was to determine:

• the existing capacity and condition of the drainage system;
• how future development of Albany can be carried out to improve ecosystem management and nutrient reduction; and
• how to integrate drainage; and public open space (POS) infrastructure to provide protection from flooding and improve amenity/useability in POS in Albany.

Hydraulic modelling of the Yakamia catchment undertaken for the Arterial Drainage Plan was completed using a breakdown of sub-catchments for the 5 year and 100 year ARI rainfall events.  Flooding risk in pipe networks and overland flow paths were identified and prioritised.  Based on this information, infrastructure upgrades and design criteria were recommended to the City in order of priority, to assist them in allocating future budgets to drainage improvement.

The Yakamia/Lange structure plan Water Management Strategy was prepared to provide recommendations, criteria, strategies and actions to deliver better urban water management outcomes as part of future residential subdivision and development.  The Water Management Strategy particularly focussed on:

• protecting and restoring the water quality, hydrological and ecological function of Yakamia Creek and Oyster Harbour (recognised as a nationally important wetland);
• protecting and enhancing the rural and environmental character of Albany; and
• reduce water use overall and promoting ‘fit-for purpose’ use of all available water resources.

Oyster Harbour is recognised a nationally important wetland, and receives significant inputs of nutrients and other types of pollutants from Yakamia Creek and surrounding farmland and urban areas (Source: http://en.wikipedia.org/wiki/File:Green_Island_Oyster_Harbour_3.jpg)

The Water Management Strategy will provide guidance for future subdivision and development in the Yakamia/Lange structure plan area in Albany, defining the roles, responsibilities and timing of water planning requirements and associated actions to implement the recommended strategies.

Arterial Drainage Plans and Water Management Strategies, such as those prepared for Yakamia Creek, are critical for local government to understand the capacity of their systems, the risk of flooding to residents in their area, and how best to manage their waterways and catchments in order to protect people from flooding while maintaining and improving the ecological function of their wetlands and waterways.