Hydrology of the Lower Daly River, Northern Territory

Abstract

This survey describes statistical behaviour of the freshwater discharge of the Daly River just upstream of the tidal limit, and inundation of the floodplains below the tidal limit. It is based on data collected across a set of recording stations operated by the Water Division of the Northern Territory Department of Transport and Works. This report is produced by the Mangroves and Tidal Rivers Program of the North Australia Research Unit. It is intended to assist the study of sedimentary, geomorphologic, and ecologic processes in the lower Daly channel and adjacent plains. Results are relevant to present and future land-use in the area.

Freshwater discharge of the Daly River, in common with other rivers of Northern Australia, is regulated by summer monsoonal rains of the “wet season”. In a normal wet season the rainfall is more or less uniformly distributed from December through March, but river discharge tends to increase as the wet advances. Flood peaks occur after heavy rainfalls. Heavy falls later in the wet season tend to generate larger discharges than do equivalent falls early in the season. The February/March discharge does not increase as a simple proportion of total rain, but increases roughly in proportion to total wet season raised to the third or fourth power. Variation of discharge from one wet season to another is much greater than variation of rainfall input.

Objectives of this report include description of the statistical behaviour of discharge throughout the wet season. Accordingly, records have been analysed to show differences between wet season months, as well as to give conventional statistics such as recurrence intervals and stage duration curves. Water surface profiles, relative to Australian Height Datum (AHD) also are established for selected flood stages. Rainfall-discharge relationships are modelled with a simple non-linear basin model, with the intention of extrapolating beyond the period of recorded data and to other ungauged catchments of interest as far as confidence limits allow. The study concludes with a brief review of the relationship between its results and the requirements of ecologic and resource management studies, and discusses further recordings which are desirable in future.

Primary data are not presented in this Bulletin, because of the space which would be needed. These data are principally a decade of daily records from 10 gauging stations and three rainfall stations, plus some chemical and other auxiliary data. All graphs, tables, and other results presented here are based on this primary data set. Show more