Relating oxygen demand to flow: development of an in situ sediment oxygen demand measurement device.

This paper describes the continuation of an investigation into the effects of increased flow on the dissolved oxygen concentration in the River Maun, UK. A previous investigation indicated that an oxygen demand additional to that in the water phase is observed during and directly after intermittent discharges. Simplified modelling of the river indicated that the additional oxygen demand was possibly linked to the disturbance of sediment during such events. A device has been developed which can be used in situ to measure the effect of flow velocity (shear stress) on the additional demand. Preliminary tests have shown that the inferred demand is significant. It is proposed that the in situ device now be used to measure the oxygen demand of the bed material at a number of locations and flow speeds and that a relationship between the additional demand and velocity be established, with the aim of incorporating such a relationship into a simplified model.