Tom Hatton

Water balance of a tropical woodland ecosystem, Northern Australia: A combination of micro-meteorological, soil physical and groundwater chemical approaches

A combination of micro-meteorological, soil physical and groundwater chemical methods enabled the water balance of a tropical eucalypt savanna ecosystem in Northern Australia to be estimated. Heat pulse and eddy correlation were used to determine overstory and total evapotranspiration, respectively. Measurements of soil water content, matric suction and water table variations were used to determine changes in soil moisture storage throughout the year. Groundwater dating with chlorofluorocarbons was used to estimate net groundwater recharge rates, and stream gauging was used to determine surface runoff. The wet season rainfall of 1585 mm is distributed as: evapotranspiration 810 mm, surface runoff (and shallow subsurface flow) into the river 410 mm, groundwater recharge 200 mm and increase in soil store 165 mm. Of the groundwater recharge, 160 mm enters the stream as baseflow in the wet season, 20 mm enters as baseflow in the dry season, and the balance (20 mm) is distributed to and used by minor vegetation types within the catchment or discharges to the sea. In the dry season, an evapotranspiration of 300 mm comprises 135 mm rainfall and 165 mm from the soil store. Because of the inherent errors of the different techniques, the water balance surplus (estimated at 20 mm) cannot be clearly distinguished from zero. It may also be as much as 140 mm. To our knowledge, this is the first time that such diverse methods have been combined to estimate all components of a catchments water balance.

Estimation of soil moisture and groundwater recharge using the TOPOG_IRM Model

A distributed parameter ecohydrological model (TOPOG_IRM) was applied to a 1.6 km2 pastoral catchment in southeast Australia for estimating soil moisture and groundwater recharge, for a period of 1992–1994. The main objective of TOPOG_IRM is to provide a realistic description of the key processes which control the soil moisture dynamics, evapotranspiration, and to investigate hydrological and ecological responses at a catchment scale. The model was not fitted but parameterised with field data and literature values. The soil moisture content at various depths was well simulated for six sites in the catchment representing different soil types and landscape positions. The spatial patterns of the soil moisture content appear to be controlled mainly by the soil types, and the results indicated that there is little lateral movement of water in the catchment. Average groundwater recharge was found to be 5% of the annual rainfall, and its spatial patterns were dominated by the soil types. The study has demonstrated potential application of TOPOG_IRM in simulating catchment scale responses under different land management options in the context of salinity control.

Estimating episodic recharge under different crop/pasture rotations in the Mallee region. Part 2. Recharge control by agronomic practices

Abstract Much environmental degradation, including salinity in the Mallee region of southeastern Australia, is associated with the loss of native vegetation and increased recharge. As a result, various agronomic practices have been proposed to reduce groundwater recharge. This study was conducted to evaluate the impact of these practices on recharge, in particular episodic recharge. A biophysically based model (WAVES) was used to estimate recharge rates under some typical crop and pasture rotations in the region using long-term meteorological data. Results show that: (1) recharge just below the root zone was episodic and that just 10% of annual recharge events contributed over 85% of long-term totals. Management options such as incorporating lucerne and deep-rooted non-fallow rotations can reduce both, mean annual recharge, and the number of episodic events, but not eliminate recharge completely; (2) winter fallows increased soil-water storage and some of the additional water was stored in the lower portion of the root zone or below it. This can increase the risk of recharge to groundwater system; (3) changes in land management may take a considerable period of time (>10 years) to have any noticeable impacts on recharge; and (4) recharge under lucerne was ≈30% of that under medic pasture.

Do faunal assemblages reflect the exchange intensity in groundwater zones

The exchange of water with groundwater is a key determinant of water quality and faunal assemblage. Water exchange not only occurs with running waters, but also through percolation, interception (soil, porous alluvium), and evaporation. The aim of this study was to identify how different types of exchange were related to the groundwater faunal assemblage of an alluvial aquifer. Hydrological exchange is largely governed by pore space and thus ultimately by geological formation. In the Marbling Brook catchment of Western Australia the different geological formations did not eventuate in hydrochemically distinct groundwater zones. The cluster analysis of faunal assemblages revealed five groups within the faunal samples which did not reflect spatial patterns such as geological, chemical or topographic features. Discriminant analysis showed that these five groups were best characterized by a range of abiotic features including dissolved oxygen, land-use, and temperature. These variables signal different types and intensities of exchange with the surface.

Predicting and controlling water logging and groundwater flow in sloping duplex soils in western Australia

Water logging and groundwater recharge were studied at a site in southwestern Australia characterised by sloping duplex soils in a Mediterranean environment. The specific objectives of the study were: (a) to determine the effectiveness of land management systems involving trees, shallow interceptor drains, and perennial pasture in reducing water logging and recharge risk; and (b) to predict water logging risk at the plot and catchment scale. We found that properties inherent in the site (soil hydraulics, topography, surface dams) had a larger control over seasonal water logging than differences in vegetation cover, with large variations in water logging and recharge over a relatively small area. Such variability would be difficult to capture in any detail using a process model of water logging. The tree/drain systems had local effects on water logging control, but this was mostly due to the direct effects of the trees, which provided localised discharge from deeper groundwater systems.

Estimating episodic recharge under different crop/pasture rotations in the Mallee region. Part 1. Experiments and model calibration

Abstract Changes in land use in the Mallee region of southeastern Australia have led to increased groundwater recharge and salinisation. This study was conducted to determine the impact of different agronomic practices on recharge control, in particular episodic recharge. During the period 1991–1995, two field experiments were carried out at Hillston (New South Wales) and Wallpeup (Victoria) where soil hydraulic properties, soil-moisture content, and leaf area index were measured. Various crop and pasture rotations were considered involving fallow, field pea (Piscum salivum L cv Dunndale), Indian mustard (Brassica juncca cv F2 cross), wheat (Triticum aestivum cv Janz Meering), oats (Avena sateva L. cv Coolabah), lucerne (Medicago sativa L. cv. Arora) and medic pastures (Medicago truncatula cv Parriagio, Sephi and Hykon). Data obtained from these experiments were used to calibrate and test a biophysically based model WAVES. With minimum calibration, the simulated soil-moisture content and leaf area index are in good agreement with field observations. The parameter values are within a physically reasonable range. The success of the model in simulating soil-moisture dynamics and plant growth was due to the accurate representation of the soil and canopy processes. WAVES combined with field measurements provides a powerful tool for estimating the impacts of land-management options on water balance.

Evaluation of the impacts of deep open drains on groundwater levels in the wheatbelt of Western Australia

Abstract. Over one million hectares of the wheatbelt of Western Australia (WA) are affected by secondary salinisation and this area is expected to increase to between 3 and 5 million hectares if current trends continue. Deep open drains, as an engineering solution to dryland salinity, have been promoted over the past few decades; however, the results of initial experiments were variable and no thorough analysis has been done. This research quantifies the effects of deep open drains on shallow and deep groundwater at farm and subcatchment level. Analysis of rainfall data showed that the only dry year (below average rainfall) after the construction of drainage in the Narembeen area of WA (in 1998 and 1999) was 2002. The dry year caused some decline in groundwater levels in the undrained areas but had no significant impact in the drained areas. The study found that the effect of drains on the groundwater levels was particularly significant if the initial water levels were well above the drain bed level, permeable materials were encountered, and drain depth was adequate (2.0–3.0 m). Visual observations and evidence derived from this study area suggested that if the drain depth cut through more permeable, macropore-dominated siliceous and ferruginous hardpans, which exist 1.5–3 m from the soil surface, its efficiency exceeded that predicted by simple drainage theory based on bulk soil texture. The effect of drains often extended to distances away (>200 m) from the drain. Immediately following construction, drains had a high discharge rate until a new hydrologic equilibrium was reached. After equilibrium, flow largely comprised regional groundwater discharge and was supplemented by quick responses driven by rainfall recharge. Comparison between the hydrology of the drained and undrained areas in the Wakeman subcatchment showed that, in the valley floors of the drained areas, the water levels fluctuated mainly between 1.5 and 2.5 m of the soil surface during most of the year. In the valley floors of the undrained areas, they fluctuated between 0 and 1 m of the soil surface. The impact of an extreme rainfall event (or unusual wet season) on drain performance was predicted to vary with distance from the drain. Within 100 m from the drain, water levels declined relatively quickly, whereas it took a year before the water levels at 200–300 m away from the drain responded. The main guidelines that can be recommended based on the results from this study are the drain depth and importance of ferricrete layer. In order to be effective, a drain should be more than 2 m deep and it should cut through the ferricrete layer that exists in many landscapes in the wheatbelt.

Measuring and monitoring the effects of agroforestry and drainage in the ‘Ucarro’ sub-catchment

A small sub-catchment in the western Australian wheatbelt was intensively monitored for approximately 5 years to investigate the effect of an established surface water management system, and associated tree belts, on the flow of water in the landscape. This change in approach to land management attempts to address the loss of farm productivity due to water logging and secondary salinity. The paper describes the geomorphological setting and the installation of various instrumentation used to monitor the flow of water at both field and catchment scale.

Framing an independent, integrated and evidence-based evaluation of the state of Australia's biophysical and human environments

A new approach was developed for Australias 2011 national State of the Environment (SoE) report to integrate the assessment of biophysical and human elements of the environment. A Common Assessment and Reporting Framework (CARF) guided design and implementation, responding to jurisdictional complexity, outstanding natural diversity and ecosystem values, high levels of cultural and heritage diversity, and a paucity of national-scale data. The CARF provided a transparent response to the need for an independent, robust and evidence-based national SoE report. We conclude that this framework will be effective for subsequent national SoE assessments and other integrated national-scale assessments in data-poor regions.

Comment on Wood et al. 2008, 'Impacts of fire on forest age and runoff in mountain ash forests'

Wood et al. (2008; FPB 35) concluded their measurements of evapotranspiration (ET) in Eucalyptus regnans F.Muell. forest at Wallaby Creek, Victoria showed that ET differs only slightly between regrowth and oldgrowth, contrary to the findings of previous research. We assert that the conclusions of Wood et al. are invalid and argue that Wood et al. substantially overestimated annual transpiration and rainfall. Monthly whole-forest ET measured by Wood et al. using eddy covariance in a 296-year-old stand sum to ~700 mm year–1; consistent with rainfall of 721 mm year–1 recorded nearby by the Bureau of Meteorology. However, the Wood et al. conclusions were based on 1077 mm annual transpiration at this site, which appears to be estimated from a few months of heat pulse velocity measurements. Transpiration alone cannot be 54% higher than whole-forest ET because the latter includes transpiration, rainfall interception and evaporation from the forest floor. We believe Wood et al. made errors in scaling heat pulse velocities to whole-stand annual transpiration. Their rainfall of 1175 mm year–1 averages 62% higher than at three Bureau of Meteorology and Melbourne Water sites nearby. The paper also contains inaccuracies in reporting of the literature and numerous other errors.