Melbourne School of Land and Environment Department of Forest and Ecosystem Science

Forests and Water
Research Group

Department of Forest and Ecosystem Science

The University of Melbourne

Connectivity of runoff and erosion following patchy forest fire

To better understand the potential impact of fires on water quality we need to think about ‘runoff connectivity’. That is, how well connected are the eroding areas to the streams.  The patchiness of prescribed fires makes them particularly interesting for studying runoff connectivity. There is often a range of fire severities and unburnt areas within a single burn. Each fire severity class is likely to erode at a different rate and the spatial arrangement of the fire severity patches is likely to affect the amount of runoff connectivity. Predicting the ‘runoff connectivity’ in areas burnt by patchy fires is the central theme of this research.  

A low intensity prescribed burn in north-eastern Victoria with a very patchy outcome

Hydrologic connectivity in forests

Native forests contain unique configurations of landscape elements (eg. roads, burnt areas, undisturbed areas, buffers).  Research to date has shown that these systems are unsuited to existing water quality modelling approaches that have largely been developed in an agricultural setting.  In Victorian forests the process of hydrologic and pollutant connectivity exerts a primary control on the water quality impacts of the key disturbances of fire, harvesting and roading.  Hydrologic connectivity describes the influence of the intrinsic organisation of heterogeneities on the global behaviour of the hydrologic system that contains those heterogeneities.  Connectivity can be usefully divided into structural connectivity, the description of continuum properties of state variables, and functional connectivity, describing the effect of heterogeneities on the rate of water transfer within such a system.  In this project we have developed analytically derived functional connectivity equations, called Stochastic Runoff Connectivity equations, that explicitly represent the effect of spatial variability of steady-state rainfall intensity and infiltration capacity on the infiltration-excess runoff delivery rate from an area.  These equations are currently being tested using 100 runoff collectors installed in a burnt forest in NE Victoria.

Post-fire salvage harvesting effects on erosion processes, streamflow and water quality: measurement and modelling

This project examines the effect of post-fire salvage harvesting of radiata pine on erosion processes, streamflow, and water quality in a small long-term research catchment. The steep burnt and logged catchment has experienced a dynamic erosion and water quality response compared to adjacent burnt eucalyptus forest catchments. Modelling using the Kineros2 runoff and erosion model will provide key process-based insights to explain the changes in streamflow, erosion and water quality observed in the harvested catchment compared to other catchments. It is hoped this research will help identify actions managers may take to mitigate potential water quality impacts from post-fire salvage harvesting activities.

Post fire hillslope processes generating extreme erosion events in SE Australia

The widespread wildfires in recent years indicate that dry Eucalypt forest environments in mountainous regions of Victoria are particularly sensitive to extreme erosion due to the efficient delivery of runoff and debris from steep and often severely burned hillslopes. These extreme erosion events are triggered by runoff and sediment entrainment processes on steep hillslopes, causing severe channel erosion and can have significant impacts on downstream water quality, aquatic habitats and infrastructure. This project is designed to parameterize and develop a hillslope erosion model that focuses on the processes and conditions that trigger post-fire debris flows and which take into account the temporal changes in the key properties of the system as it recovers from the wildfire disturbance.

Prescribed fire effects on water quality in south-east Australian native forests

Prescribed fire is an increasingly important tool used by forest managers to reduce understorey fuel loads and decrease the risk and intensity of wildfires. Given management control over prescribed burning, there is a need to assess the impact on stream water quality in native forest catchments treated with prescribed fires. This projects aims to quantify prescribed fire effects on hillslope erosion and catchment-scale water quality. Monitoring of hillslope erosion, as well as streamflow and water quality at the outlet of two catchments burnt by prescribed fires has been undertaken and will be used to assess the magnitude and duration of prescribed fire effects on these variables.

Wildfire and water quality in water supply catchments

The interaction of wildfire, subsequent rainfall events, landscape attributes (forest-soil types, stream networks), and erosion processes may result in a wide range of potential impacts on water quality in reservoirs. To examine this, a modelling approach which integrates these factors is required to enable the magnitude and associated risk of constituent loads entering reservoirs after wildfire to be assessed. This will form the focus of this project through the development of a model framework comprised of probabilistic (wildfires, rainfall events) and deterministic components (erosion processes).

Wildfire and water security project: modelling risks to water quality

Most of the water supplying Melbourne’s 3.7 million residents comes from forested catchments and undergoes minimal treatment prior to delivery. Risk analysis by Melbourne Water has identified wildfire as a major threat to the uninterrupted delivery of water. There is the potential that extensive and severe wildfire across the key water supply catchments could result in water supplies that are unfit for drinking.  Information on the probable magnitude and duration of potential contamination events is required to evaluate feasibility of remedial options and plan investment for treatment facilities.  This project aims to develop and parameterize probabilistic models of the occurrence frequency and magnitude of water quality impacts due to major wildfires in key water supply catchments.

Initiation thresholds, landscape controls, and sediment yields of post-fire runoff-generated debris flows

Recent evidence suggests that runoff generated debris flows are an important erosion process in Victorian catchments burned by wildfire. This PhD project involves surveys and hydrological experiments designed to quantify the sediment yield from post-fire debris flows and model the topographic controls and hydrological thresholds for debris flow initiation. The model will provide a tool for predicting the magnitude of debris flows after wildfire in these systems and the likelihood of occurrence under a given rainfall regime.

Wildfire and water security project: quantifying the risk of extreme post-fire erosion events

This project aims to assess the risk to water resources from wildfire and subsequent rainfall events that may erode and deliver large amounts of sediment, nutrients and other contaminants to reservoirs. This includes post-fire debris flows and large flood events which are of particular concern from a short-term water quality perspective, while also representing potentially important processes contributing to landscape change over longer timescales. This project seeks to develop a model that quantifies probabilities of wildfires and large rainfall events, the erosion process response to these events, and provides estimates of the magnitude of sediment, nutrient and other constituent loads entering water supply reservoirs.

Water use of mixed species eucalypt forests

Mixed species forests have received little attention in previous hydrological studies.  This project aims to quantify the catchment water balance by assessing within catchment variation in rainfall, evapotranspiration and soil water storage.  A number of gauged catchments are being monitored on the ground using sap flow sensors, automated throughfall gauges, portable evaporation dome and plot inventory data.  These will be combined with remote sensing techniques; cover photography and LIDAR to scale plot-based data to the entire catchment.  These monitoring efforts will form the basis of an ecohydrological model that combines hydrologic, physiological and structural attributes for predicting water yield.

Regionalising forest water use with forest growth models

This collaborative PhD project with the University of Tasmania is combining extensive growth plot data with LIDAR data to estimate temporal and spatial growth dynamics in Eucalyptus regnans forests in Victoria.  Forest growth models will be coupled with streamflow and rainfall data to infer the trend in forest water use.  The procedure involves a stochastic model to filter out the effect of natural variation in climate on streamflow to formulate a relationship between forest productivity and forest water use.

Predicting the effects of plantations on catchment water balances

There is a greater need to be able to estimate the effects of plantations on the hydrological balance of catchments. This project is developing and validating a process-based modelling approach using the 3PG+ forest growth model and CAT (Catchment Analysis Tool), resulting in a planning tool to predict the transpiration and hydrological impacts of existing or proposed plantations in relation to their location and management. 

Response of mixed species eucalypt forests to patchy burns: plant water use and hydraulic architecture

The sight of burnt trees bursting with new growth after fire is becoming a common sight in the Australian bushland, as fire becomes more frequent in our environment.  Suprisingly, we have a limited understanding on the water use dynamics of resprouting eucalypts (new growth via epicormic buds and/or lignotubers) during their recovery from fire and their likely influence on water cycling within the catchment.  This comparative study will asses the water use and hydraulic architecture or ‘plumbing’ of two common resprouting trees in one of southern Australia’s most fire prone forest types; the mixed species Eucalypt forest.

Modelling the long-term impacts of forest disturbance, wildfires and climate change on catchment streamflow

Forest management, fire and climate change can have profound and lasting effects on catchment water balances and water yields. Macaque, a process-based model, is being used in this project to examine the effects on catchment water balances and streamflow after the 2009 wildfires. Results are being used to guide catchment managers and to underpin the development of water and forest management strategies and policies.

Intra-annual hydrological responses to climate variation in native mixed-forest catchments.

Victoria has experienced a marked decline in rainfall over the past decade, but how has this affected streamflows? In particular, have the intra-annual flows vital to ecological and water resource management – seasonal, low and high end flows – altered? This PhD study aims to investigate how decreasing rainfall in native forest, medium rainfall catchments has impacted upon intra-annual flows, with an emphasis on whether soil moisture storages correlate with streamflow patterns.

Plantations and water resource management

Improved tools for assessing plantation impacts on water resources are required in Australia.  This Phd project is aimed at better understanding the effect of plantation species, growth dynamics and environmental factors on water use, and developing a robust model that will be readily used by water authorities and plantation managers for assessing hydrologic impacts at difference spatial and temporal scales.

Long term water use of mountain ash and the efficiency of heavily forested catchments

Analysis is being undertaken of long term paired catchment data from 1954 until 2007 to investigate the effects of forest management and catchment hydrology.  The main aim is to investigate the ‘catchment efficiency’ – the ratio of water entering to water leaving the catchment – across different forested catchments. The project will help examine what may be viewed as an “acceptable” catchment efficiency, and whether future generations will demand more runoff from these catchments than has historically been produced under either old growth or regrowth vegetation.

Post wildfire changes to plant morphology and physiology: implications for water yield in wet eucalypt forests

Large-scale disturbance, in particular fire, can have a profound influence in shaping vegetation composition and structure.  The effects of such disturbance on vegetation can have important implications for catchment water balance through changes in evapotranspiration.  To date research on post-fire water yield in Victoria has been largely confined to these Mountain Ash catchments.  This research aims to investigate the affects of bushfire on water yields in other vegetation communities, specifically, by examining the influence fire exerts on plant water relations in regenerating ecosystems.