Lower Serpentine drainage planning area
The
Lower Serpentine plan area is located on the Swan Coastal Plain and is bounded
by the Darling Scarp in the east, the Indian Ocean to the west, the Jandakot
Mound in the north and Dirk Brook in the south. The terrain is characterised by
gently undulating dunal systems near the coast, a number of wetland systems
that are associated with inter-dunal depressions, and an extensive open
drainage network. This network includes the Birrega, Oaklands, Peel and Punrak
Main Drains, associated branch drains, and the lower Serpentine River, which
eventually discharges to the Peel Harvey Estuary to the south of the plan area.
Parts of the plan area are prone to flooding and seasonal inundation from
groundwater.
Historically, development was not considered over much of the plan area, in favour of areas which were less constrained by groundwater. In order to meet the need for urban growth, development is now shifting to areas with significant water constraints. The Department of Water considers the Serpentine landscape will be able to support development with effective land and water planning, the application of water conservation strategies, and innovative solutions to water constraints.
State and local government and the development industry will need to be innovative to overcome water management challenges in this area. Water constraints that need to be adequately managed for urban development include flooding, inundation from groundwater, stormwater, water quality, availability and efficiency, and the interaction between groundwater and surface water.
Drainage and water management plans
The Department of Water prepares drainage and water management plans (DWMP). The DWMPs integrate total water cycle management and land use planning. The department is responsible for the production of DWMPs in areas where future development is identified. The Lower Serpentine area has been identified by the Western Australian Planning Commission and local governments for future urban growth. The department has initiated drainage planning in the area and will progressively produce drainage and water management plans and related technical studies for a number of catchments.
Birrega and Oaklands drainage and water
management plan 
A drainage and water management plan for Birrega and Oaklands is currently being prepared. The area is experiencing development pressure.Land in the Birrega and Oaklands plan area is predominantly zoned rural and rural residential, with large floodplains incised by deep and narrow rural drains, significant waterlogging in winter months, and flood-risks in some areas. The Department of Water has prepared technical studies to guide the development of the plan in this area.
North East Baldivis drainage and water management plan
A drainage and water management plan for North East Baldivis is currently being prepared. The drainage and water management plan area includes sections of the Peel, Serpentine and Birrega main drains, and a section of the Serpentine River. The Department of Water has prepared technical studies for the area to guide the development of the plan in this area.
Supporting technical studies
The Department of Water prepares technical studies that are used to prepare a DWMP and assist in making informed land use planning decisions. These studies provide the technical basis for the DWMP and will allow development to be undertaken in this highly challenging area.
Hydrological studies
The Lower Serpentine hydrological studies conceptualise and model regional-scale surface water and groundwater interaction in the Serpentine drainage planning area. These studies provide the technical information for the DWMPs in the area.
An integrated MikeSHE model is used to simulate climate, drainage and land use scenarios. The scenarios are simulated to determine the effects on the hydrological regime of the area for pre- and post-development conditions. The hydrological studies are presented in three separate reports:
- the conceptual model report which characterises the hydrology and hydrogeology of the Lower Serpentine area
- the model construction and calibration report which describes the construction of the MikeSHE numerical model based on the conceptual model and
- the Lower Serpentine hydrological studies: Land development, drainage and climate scenario report which analyses and discusses scenario results in the context of hydrological constraints.
All the reports have been finalised and are now available.
Floodplain studies
The floodplain studies are developed at a catchment scale. A hydrologic and hydraulic assessment is conducted for the designated catchment area. A hydraulic flood model using MikeFLOOD is generally used to simulate flood behaviour, map flood extent and determine water level and discharge at various locations. Most major rural drains in the Lower Serpentine area are managed by the Water Corporation. The Department of Water and the Water Corporation have dual responsibility for managing drainage and flooding in this area. The Department of Water’s drainage and water management plans will include management objectives for flooding that are suitable for the area.
Birrega and Oakland flood modelling and drainage study
The Birrega and oaklands flood modelling and drainage study has been finalised for the area and is now available. The area comprises a series of rural drains and farm drains that discharge to two main Water Corporation drains – Oaklands and Birrega Main Drains. These drains traverse the catchment and converge in the south-west of the catchment area. The area is located immediately north east of the North East Baldivis catchment area. The Birrega Main Drain enters the latter catchment and eventually discharges into the Serpentine River.
North East Baldivis flood modelling and drainage study
The North-east Baldivis flood modelling and drainage study has been finalised for the area and is now available. The area comprises a series of rural drains and farm drains that discharge to the Peel Main Drain – a Water Corporation managed main drain. The Peel Main Drain is divided by the Folly and Maramanup pools. The Serpentine River and the Birrega Main Drain transverse the catchment area discharging downstream, and outside of the catchment area, into the Peel Harvey Estuary.
