The hydraulic geometry and geomorphic sensitivity assessment of some rivers of Western Australia

The downstream hydraulic geometry and geomorphic sensitivity assessment of 47 sites in river channels of Western Australia were studied in order (1) to identify the characteristics of Western Australia rivers and to compare them to other Mediterranean type climate environments; (2) to analyze the sensitivity of the river channels in order to define stable or active morphological features. About half of the sites were in order one to three in drainage basins from less to a sq km to several tenths of sq km. The bankfull stage was determined in the field. The empirical relationship between the width, depth and velocity exponents- b>f> m in Mediterranean channels is valid for the studied area. The b exponent tends to be larger in areas with fragile banks and lack of vegetation.The width/depth values are generally high, with an average of 18.57 for all stations, due to the non cohesive material, mainly sand of the banks.These results are consistent to values found in environments with a silt and clay content of less than 10%. The sensitivity assessment has proved to be an important tool to monitor the effects of physical and Man-made changes in the relatively stable channel environment, but increased deforestation and probably climatic changes may increase the frequency of high floods and their morphological effects on river channels. The Western Australian rivers may represent a channel geometry adjusted to the Mediterranean environment hydrological regime, characterized by a long dry season, winter floods and probably recent human interference.