River Clyde Environmental Flow Assessment

Abstract

The River Clyde flows from the outlet of Lake Crescent in the Central Highlands, via the townships of Bothwell and Hamilton, to the Derwent River. The catchment has experienced extensive clearing, especially in its middle and lower sections, and is subject to varying intensity of landuse. Grazing production is supplemented by irrigation, frequently involving flood irrigation of pasture, and water management is seen as a critical aspect of agricultural production in a catchment which frequently experiences very dry summers. As a consequence, water management, particularly with regard to storage and releases from the Lake Sorell-Crescent system, has been in place since the mid-1800s and has been intensive for over 50 years. The magnitude and seasonal pattern of baseflows (flows between major flood events) in the Clyde are largely dictated by managed lake releases and downstream abstractions during the majority of the year. An environmental flow assessment was conducted for the River Clyde during the development of the River Clyde Water Management Plan (DPIWE 2004). This document summarises the work conducted and the main results. The study was conducted iteratively while both the River Clyde and the Lakes Sorell and Crescent WMPs were being developed, due to the need for integration of the environmental water requirement assessment for the river with that of the Lake Sorell and Clyde system, in its headwaters. The final result was therefore a trade-off between water management implications for the lake and river environments.