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[1] This paper reports new experimental results on the mean velocity, excess fractional density, and turbulence structures of conservative and particulate density currents. Experiments were conducted in a laboratory flume consisting of a ramp followed by a horizontal bed. Instantaneous point velocity along the body of a continuous, developed underflow was measured using two 16 MHz Acoustic Doppler Velocity Probes (ADV). Mean velocity, turbulent kinetic energy (TKE) and Reynolds stress components have been derived from the instantaneous velocity data. The normalized mean velocity, Reynolds stress, and TKE profiles have been derived and plotted in different groups corresponding to saline and particulate gravity currents over sloping and horizontal beds. The Reynolds-averaged velocity shows excellent similarity collapse in these plots, while the Reynolds stress and the TKE profiles display good similarity in the wall-bounded shear flow region. Vertical profiles of the TKE display two peaks separated by a zone of low turbulence around the position of the maximum velocity. The ratio of the maximum to the layer-averaged TKE is found to be approximately 1.5. The TKE at the low turbulence zone between the peaks is approximately 50% of the depth-averaged value.Citation: Islam, M. A., and J. Imran (2010), Vertical structure of continuous release saline and turbidity currents, J. Geophys.

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[1] This paper describes the results of an experimental study involving density driven gravity underflow in a submarine sinuous channel. A single bend channel with sine generated planform was constructed inside a laboratory basin. Saline density flow was released at a constant rate at the upstream end of the channel which was submerged under fresh water. Instantaneous velocity data recorded within the body of the developed current were used to derive the vertical structures of the streamwise and cross-stream velocity. The vertical distributions of the streamwise and lateral velocity were found to vary modestly between cross sections and also within an individual cross section. The distance of the maximum velocity position from the bed was found to vary between 0.4 and 0.6 times the local current thickness. In the vicinity of the bend apex the curvature effect led to the development of two helical flow cells with one forming on top of the other. The sense of rotation of the bottom cell was similar to that observed in curved open channel flow, while the upper circulation cell had an opposite sense of rotation. Turbulent kinetic energy profiles were derived from the instantaneous velocity data. The observed turbulent kinetic energy profiles confirm some previous observations that the location of the maximum velocity in a density underflow also corresponds to significant reduction in turbulent kinetic energy.

Objective: This paper focuses on the use of ‘concurrent evaluation’ to evaluate a nationally scaled-up programme in Bangladesh that was implemented by BRAC (an international development organisation) using Shasthya Shebika (SS) – volunteer community health workers – to promote home fortification with micronutrient powders (MNP) for children under-five. Design: We developed a programme impact pathway to conceptualise the implementation and evaluation strategy and developed a strategic partnership among the key programme stakeholders for better use of evaluation evidence. We developed a multi-method concurrent evaluation strategy to provide insights into the BRAC programme and created provision for course correction to the implementation plan while it was in operation. Setting: One hundred sixty-four sub-districts and six urban slums in Bangladesh. Participants: Caregivers of children 6–59 months, SS and BRAC’s staff members. Results: The evaluation identified low awareness about home fortification among caregivers, inadequate supply and frequent MNP stockouts, and inadequate skills of BRAC’s SS to promote MNP at the community level as hindrances to the achievement of programme goals. The partners regularly discussed evaluation results during and after implementation activities to assess progress in programme coverage and any needs for modification. BRAC initiated a series of corrections to the original implementation plan to address these challenges, which improved the design of the MNP programme; this resulted in enhanced programme outcomes. Conclusions: Concurrent evaluation is an innovative approach to evaluate complex real-world programmes. Here it was utilised in implementing a large-scale nutrition programme to measure implementation process and effectiveness.