Catchments In Queensland Research Articles

Water quality in sugar catchments of Queensland

Water quality condition and trend are important indicators of the impact of land use on the environment, as degraded water quality causes unwelcome changes to ecosystem composition and health. These concerns extend to the sea, where discharges of nutrients, sediments and toxicants above natural levels are unwelcome, particularly when they drain to the Great Barrier Reef World Heritage Area and other coastal waters of Queensland. Sugarcane is grown in 26 major river catchments in Queensland, most in environmentally sensitive areas. This puts pressure on the Queensland Sugar Industry to manage the land in ways that have minimum adverse off-site impacts. Sugar researchers including CRC Sugar have been associated with water quality studies in North Queensland. These include investigations and reviews to assess the role of groundwater as a pathway for nitrate loss from canelands in the Herbert Catchment, to find causes of oxygen depletion in water (including irrigation runoff) from Ingham to Mackay, to use residues of superseded pesticides as indicators of sediment loss to the sea, and to assemble information on water quality pressure and status in sugar catchments. Key findings, plus information on input pressures are described in this paper, and areas of concern and opportunities discussed.

Mapping and analysis of changes in the riparian landscape structure of the Lockyer Valley catchment, Queensland, Australia

A case study of the Lockyer Valley catchment in Queensland, Australia, was conducted to develop appropriate mapping and assessment techniques to quantify the nature and magnitude of riparian landscape structural changes within a catchment. The study employed digital image processing techniques to produce land cover maps from the 1973 and 1997 Landsat imagery. Fixed and variable width buffering of streams were implemented using a geographic information system (GIS) to estimate the riparian zone and to subsequently calculate the landscape patterns using the Patch Analyst (Grid) program (a FRAGSTATS interface). The nature of vegetation clearing was characterised based on land tenure, slope and stream order. Using the Pearson χ 2-test and Cramer’s V-statistic, the relationships between the vegetation clearing and land tenure were further assessed. The results show the significant decrease in woody vegetation areas mainly due to conversion to pasture. Riparian vegetation corridors have become more fragmented, isolated and of much smaller patches. Land tenure was found to be significantly associated with the vegetation clearing, although the strength of association was weak. The large proportion of deforested riparian zones within steep slopes or first-order streams raises serious questions about the catchment health and the longer term potential for land degradation by upland clearing. This study highlights the use of satellite imagery and GISs in mapping and analysis of landscape structural change, as well as the identification of key issues related to sensor spatial resolution, stream buffering widths, and the quantification of land transformation processes.

Estimating Peak Runoff for Risk-Based Assessment in Small Catchments

SummaryThe management and design of hydraulic infrastructure requires detailed analysis of the rainfall-runoff process, as well as the allocation of an acceptable level of risk. Risk-based assessment of the rainfall-runoff process requires methodologies that are both accurate and efficient. Although the Rational Method has been a popular analysis tool in risk based assessment, it has many short comings requiring significant subjective judgement by the engineer. Rainfallrunoff models have become increasingly popular in this regard, as they provide accurate tools to predict the deterministic processes taking place in the catchment. A methodology is presented in this paper for incorporating rainfall-runoff models in risk-based assessment that is both efficient in terms of computational effort and accurate. The method relies on the adoption of a storm pattern that embodies the characteristics contained within the statistically based rainfall data that is generally adopted in practice. The methodology has been tested on two hypothetical catchments and 47 small gauged catchments in Queensland. It is shown that using this methodology, statistically based peak runoff can be predicted at all locations in the catchment where suitable catchment subdivision had been undertaken.

Improving the management of dryland salinity in Australia through the national airborne geophysics project

A comprehensive evaluation of the application of airborne geophysics to the management of dryland salinity is currently underway in Australia. Known as the National Airborne Geophysics Project (NAGP), it is a joint initiative of the Commonwealth and State Governments designed to assess the value-added contribution that can be made by time domain EM, frequency domain EM, magnetics and radiometrics to those data (including topography, soils and satellite imagery) already in use for salinity management. The project will concentrate on five selected catchments in Queensland, New South Wales, Victoria and Western Australia.The focus of the project will be to define the geological characteristics, to measure three-dimensional variability in conductivity in the regolith system, and to determine the spatial variability in soil characteristics. The analysis will allow the derivation of products such as maps showing salinity hazard, water resource target, soils, regolith conductivity and thickness, and geological interpretation. These derived products will be integrated with other datasets to specifically assist with the development of land management plans at appropriate scales and to contribute to the understanding of hydrogeological processes. The project will also produce cost/benefit analyses and confidence level estimates associated with the use of airborne geophysical and other data (Woodgate et al., 1998).

Evaluating Partial Areas of Watershed Runoff

Variations in surface storage capacity over a watershed produce partial areas of saturation overland flow, which vary from storm to storm. A method is described by which the proportions of a watershed that contributes overland flow in different storms and at different times during the same storm can be determined by analysis of rainfall and runoff records. The method is demonstrated on two catchments in Queensland, Australia, with different hydrological characteristics. One watershed is 16.8 ha in area with only two to three events per year of overland flow (no baseflow) averaging 35 mm per annum runoff; the other is 7 km in area with substantial baseflow and an average of 920 mm per annum runoff. The calculated amounts and proportions of surface storage capacity are incorporated into water balance models of watershed runoff to show the accuracy of runoff estimation.

The estimated store of soluble salts in the Lake Eyre catchment in Queensland and their possible transport in streamflow to the lake

Analytical data from 145 samples of deeply weathered and unweathered rocks and 35 soil samples form the basis for a first approximation estimate of the store of soluble salts in the Lake Eyre catchment covering about 500 x 103 km2 in Queensland. A simple landscape model is defined to estimate the spatial distribution of the soluble chemical constituents of the various rocks and soils. The estimated quantities of soluble sodium and chloride in the catchment are 14x 109 and 25 x 109 tonnes respectively. Some weathered rocks also contain appreciable nitrate and ammonium ions. Available data indicate that bicarbonate, sodium and calcium are the dominant ions in stream flood flows, whereas halite and gypsum are the dominant salts in the lake. Precipitation or reconstitution of degraded clays in the suspended load may account for the absence of carbonates in the lake. It is concluded that the weathered and unweathered Cretaceous sedimentary rocks in the catchment contain large stores of soluble salts, and are the most likely sources of the bulk of the salts in the lake.