Modelling the water balance and hydrologic dynamics of a farm dam

Author: Imogen Cescato

Cescato, Imogen, 2018 Modelling the water balance and hydrologic dynamics of a farm dam, Flinders University, College of Science and Engineering

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This study modelled the components of the water balance of a farm dam in Willunga, South Australia. It is hoped that a small intensive study on a single site would eliminate influences from confounding factors that are present in literature models of farm dam impacts. This is important as understanding the dynamics behind a single dam can be extrapolated into entire catchments, which can be utilised to understand how a network of farm dams influence the hydrologic dynamics of the larger catchment.

A main aim of this study was to identify and gain understanding of the processes that influence the water balance of a farm dam. The main drivers affecting the water balance of the dam identified in this study were rainfall, streamflow, evaporation, transpiration and infiltration. Other factors that were considered but not included in the water balance calculations were overland run-off and overflow from the dam.

Several limitations arose from the processes undertaken in this study. Another aim in this project was to successfully collate data from several sources or several estimation methods into a water balance equation. There were gaps in some essential data such as water levels which presented difficulties in achieving this. Data gaps were overcome by splitting results into periods where the most important data was available and estimating missing parameters; open water evaporation was estimated through atmospheric conditions where pan evaporation data was not available, and water uptake by trees around the dam was estimated through literature values.

Several recommendations for improvements on data collection and processing were made for future research, including the installation of streamflow gauges upstream and downstream of the dam, for quantifiable values on streamflow contributing to the dam, and any flow spilling over the dam in wet months. Developing and utilising a rainfall-run-off model for the sub catchment of the dam would facilitate determining the proportion of inflow coming from streamflow versus overland run-off. Having an evaporation pan properly placed and monitored all year round would provide more accurate estimates of evaporation from the surface of the dam. A more accurate estimate of water uptake from the trees surrounding the dam could be achieved through recording sap flow data. Properly testing the soil found at the bottom of the dam to determine a k-value would yield more precise estimates of infiltration from the dam. The addition of these processes would improve the overall reliability of the water balance.

It is hoped that a similar study to this could be extrapolated and provide the basis for a model of a larger catchment, which can more dependably deliver estimates of the impacts of farm dams, which in turn can advise decision making on farm dam and water resources management to ensure responsible and equitable allocation of resources to meet individual, industry wide, and environmental needs.

Keywords: Farm dam, water balance, environmental management

Subject: Environmental management thesis

Thesis type: Masters
Completed: 2018
School: College of Science and Engineering
Supervisor: Okke Batelaan