River scale model of an training dam using lightweight granulates
Vermeulen, B. ; Boersema, M.P. ; Hoitink, A.J.F. ; Sieben, J. ; Sloff, C.J. ; Wal, M.F. van der - \ 2014
Journal of Hydro-environment Research 8 (2014). - ISSN 1570-6443 - p. 88 - 94.
sediment transport - spur dikes - bed
Replacing existing river groynes with longitudinal training dams is considered as a promising flood mitigation measure in the main Dutch rivers, which can also serve to guarantee navigability during low flows and to create conditions favourable for ecological development. Whereas the bed response in the streamwise uniform part of a river trained by a longitudinal dam can be readily predicted, the bed response at the transition zones is unclear. In the present study, we investigate the local morphological effects resulting at the intake section of a longitudinal training dam, where the flow is distributed over the main channel and a side channel in between the dam and the river shore. A sediment recirculating model with a nearly undistorted geometry with respect to the prototype was setup. Lightweight polystyrene granulates were used as a surrogate for sediment, to properly scale the Shields parameter without compromising Froude scaling, and reach dynamical similarity. A laser scanner allowed collecting high-resolution bed elevation data. Results obtained under typical low flow and high flow conditions show a general deepening of the bed in the area adjacent to the training dam, in response to narrowing of the main channel. Scour at an upstream river groyne embedded in the model showed a scour hole which was deeper than realistic. Throughout the entire domain, bedforms developed featuring geometrical properties that reproduced the prototype conditions appropriately. Based on a comparison with characteristics from the River Waal, regarded as the prototype without a longitudinal dam, lightweight sediments were considered to be a proper choice for this study, in which bedload is the main sediment transport mode. The main conclusion regards the absence of significant morphodynamic developments at the intake section, both during the high flow experiment and during the low flow experiment, which can be attributed to the alignment of the dam with the local streamlines.
Using health promotion outcomes in formative evaluation studies to predict success factors in interventions: an application to an intervention for promoting physical activity in Dutch children (JUMP-in)
Jurg, M.E. ; Meij, J.S.B. de; Wal, M.F. van der; Koelen, M.A. - \ 2008
Health Promotion International 23 (2008)3. - ISSN 0957-4824 - p. 231 - 239.
elementary-school-children - obesity prevention - controlled-trial - public-health - risk-factors - model - challenges - education - literacy - program
JUMP-in is a systematically developed intervention aimed at promoting physical activity among primary school children. It is a joint project involving different authorities and entails six school-based programme components. Measuring effects of such an intervention is a complex challenge. A common problem is the lack of valid instruments to measure physical activity and its determinants. In addition, it usually takes years to find improvements in physical activity and related constructs like weight and fitness, or even in causal factors. For this reason different authors advocate for the establishment of `health promotion outcomes¿; (i) health literacy, (ii) social action and influence and (iii) healthy public policy and organizational practice. It is presumed that these health promotion outcomes lead to changes in determinants, behaviour and finally in health. Insight in these health promotion outcomes and information about input and through-put are important in discussing the impact and output. The formative evaluation study of the JUMP-in pilot shows the health promotion outcomes of the intervention. The health promotion outcomes `social action and influence¿ and `healthy public policy and organizational practices¿ were found to be positive. By measuring the presence of the conditions to achieve `health literacy¿, it became clear that more attention must be paid to implementation in the future. Based on the health promotion outcomes, we expect that JUMP-in will be an effective intervention in the future.