Gray,
the river @ Pelican Point, near the University of WA, Nedlands, would be the closest spot. Use whereis.com. Bus + reasonable walk should bring you there. Also, anywhere along the ocean coast. Just be aware that regulations exist at Pelican Point, Cottesloe and Leighton Beach. Refer to the WAKSA Perth Site Guides on the web.
Little wind on Monday though...
Have fun!