Modelling of complex daily environmental flow
Abstract
Water resource models across Victoria have typically been developed on a monthly time step and the majority of yield based water resource planning decisions can be made at this time step with minimal loss in accuracy. Environmental flow requirements developed on a daily basis are now being incorporated into water resource planning, without necessarily having a daily resource model available to assess their impact on consumptive users and downstream river flows. If only simple translucent flows (where a % of upstream flow is passed) or transparent minimum flows (where the lesser of a fixed minimum or natural flow is passed) are specified as the environmental flow requirement in a stream, then direct application of these daily flows on a monthly time step is generally appropriate. However, environmental flow requirements increasingly include river freshes or pulses of water of only a few days duration, which cannot easily be incorporated into a monthly water resource model. This paper discusses the approach used to convert daily environmental flow requirements to an equivalent monthly volume for scenario testing in monthly models, using the Thomson and Macalister River catchments in Victoria as an example application. This approach involves the derivation of natural daily flows at environmental flow sites, automated decision making for the
provision or otherwise of seasonal freshes of a given magnitude and a given annual frequency, independence between events, and the addition of rising and falling hydrograph limbs. The paper also considers some of the shortcomings of the approach, often constrained by data limitations, such as the difficulty in providing daily time step outputs to ecologists from monthly scenario modelling.
Authors
Brad Neal, Water Resources Engineer, SKM
Tony Sheedy, Water Resources Engineer, SKM
Bill Hansen, Project Officer, Department of Sustainability and Environment
Walter Godoy, Water Resources Engineer, Department of Sustainability and Environment