Lower Ord River Research Articles

Application of the functional habitat concept to the regulated Lower Ord River, Western Australia, Part I, macroinvertebrate assemblages

This paper tests the applicability of the Functional Habitat Concept (FHC) to a lowland tropical river in Australia. The underlying tenet of the FHC is that in-stream hydrological and physical processes form distinct habitats, and where these habitats support distinct macroinvertebrate assemblages they are considered ‘functional’ habitats. This concept has been employed in the northern hemisphere as a tool for river restoration and management, especially where habitats are easier to manage than species, but the FHC has yet to be tested in Australia. This study reports the application of the FHC to the regulated Lower Ord River (LOR) in the remote far north of Western Australia. Seven ‘potential’ in-stream habitat units were identified on the basis of their physical properties. Multivariate and species preference analysis of macroinvertebrate data indicated that these habitats supported six distinct macroinvertebrate assemblages, providing six ‘functional’ habitats (gravel runs and rock rapids, sand margins, mud/silt margins, flooded riparian vegetation, emergent vegetation, and submerged macrophyte beds). Macroinvertebrate preferences for particular habitats reflected the broad ecology and life-history characteristics of the species, which in turn reflected the physical attributes of the habitats. We argue that in a region where the fauna has been little studied, and for which there is little ecological information, the FHC is a valuable approach. For a river that is facing increased water abstraction, the FHC potentially aids in the preservation of macroinvertebrate diversity as it identifies critical functional habitats for managers to maintain.

Downstream morphological change in response to dam construction: a GIS based approach for the Lower Ord River, Western Australia

Flow regulation in the Lower Ord River began in 1963 with the completion of the Kununurra Diversion Dam, part of a large-scale irrigation scheme in the far north of Western Australia. What was previously an ephemeral river punctuated by large flood events now contains permanent, regulated flows all year round, and fundamental changes in the downstream channel morphology are now evident. Further changes to the regulated flow regime are planned as part of the eventual expansion of the irrigation area. It is necessary to understand and document the channel responses that have occurred in the Lower Ord so far as a result of flow regulation. This paper presents a GIS based investigation into morphological change in the Lower Ord River. Geomorphic surface data are largely generated from sequential aerial photographs, calibrated using field observations and historical records. Results illustrate the changes in the total area of each surface type, the direction of change in bar evolution and the significance of changes in channel width throughout the study reach.

Ecological perspectives on regulation and water allocation for the Ord River, Western Australia

AbstractWater management agencies throughout Australia are attempting to find a balance between the water requirements of ecological and socio‐economic environments as part of a holistic approach to managing flow‐dependent river ecosystems. Environmental water provisions are under consideration for the Ord River in far northern Western Australia. This river has been regulated for irrigation and there are plans for substantial expansion. Like other semi‐arid and tropical rivers, however, the hydrology of the Ord River is highly variable and unpredictable, and therefore, proportionate water release strategies for the environment that are based on average monthly flows are unsuitable. Regulation continues to produce pronounced ecological changes throughout the river system as the impacts of flow regime are negated. There is a dichotomy in optimal flow regimes for the contrasting management aspirations of ecological restoration based on low seasonal flows, and the dilution flows required for the drainage of agricultural effluent. Whilst current agricultural land and water management practices continue, the two cannot coincide, and consequently, a decision should be made regarding which environmental water allocation holds the primary value. Such a decision would guide the appropriate dry season flow regime on the lower Ord River. Copyright © 2002 John Wiley & Sons, Ltd.

Sedimentation in an Arid Macrotidal Alluvial River System: Ord River, Western Australia

In the Cambridge Gulf-Ord River region of Australia, an area that experiences a dry monsoonal climate and a high tidal range (5.9 m), a variety of tidal-plain and fluvial depositional environments were recognized. Near the coast, prograding shorelines are characterized by extensive mangrove successional sequences and scattered thin beach-ridge deposits. In the interfluve regions and farther inland along the coast, tidal-plain sedimentation has given rise to extensive flats that are bare of vegetation at approximately the high spring tide level. Evaporites, algal-layered silts and clays, and massive sandy deposits form the bulk of these tidal-flat sediments. Sinuous tidal channels, displaying low width/depth ratios and characterized by a progressive tide wave, are found throughout the coastal tidal-flat region. These channels migrate laterally, leaving preserved channel sand bodies isolated in tidal deposits. In the funnel-shaped channel of the Ord River, the major river in the region receiving freshwater runoff, the tide wave is symmetrical at the mouth but becomes deformed upstream owing to a high amplitude/depth ratio; thus the velocity of flood currents increasingly exceeds ebb velocities upstream and ebb flow increases in duration. In the upper portions of the tide-dominated river channel, the largest bedforms within the channel migrate upstream under the influence of dominant flood currents, choking the channel with sand deposits. Extensive channel migration and meandering are characteristic of this region of the channel. In addition, extensive overbank crevassing occurs, a process that forms the bulk of the fluvial deposition. In the lower Ord River, linear, elongate tidal ridges within and seaward of the channel form the major sand deposits of the delta. These environments and their distribution and geometrical relationships characterize arid, high-tidal-dominated river systems.

Heavy residues of soils from the lower Ord river valley, Western Australia

Abstract "The heavy detrital minerals in several types of alluvial soil and one soil derived from the disintegration of sandstones are described, and their value as indicators of the source material of the alluvium discussed."