Recession of streamflow supplied from channel bed and bank storage

A streamflow recession formula for natural basins is derived by nonlinear hydrologie routing of inflow from channel bed and bank storage through a stream channel storage. The formula gives basin outflow as a two-parameter, inverse square function of time and is valid when the ratio of inflow to outflow is approximately constant. It provides a good fit to a master baseflow recession curve from each of 10 basins of differing areas in the greywacke geologic terrain of Canterbury, New Zealand. These basins have no significant lakes or springs and the formula applies to that section of a master recession curve between median flow and minimum recorded 7-day low flow, for the period January to March in a flow record. The master recession curve in an ungauged basin within the same terrain may be predicted if the volume of water to be discharged during this recession can be estimated. This volume is taken to be the product of total stream length, average cross-sectional area of channel bed and bank storage and storage porosity. It can be calculated if there is a reference basin available, similar in character to the ungauged basin, with a measured master recession curve. While further testing of the formula is needed, particularly in other geologic terrains, its application is relatively simple and it should be useful at basin scale for predicting master recession curves in basins where little is known about water storage behaviour.