No abstract

No abstract

No abstract

No abstract

Abstract. An extensive field campaign, the Ems-Dollard Measurements (EDoM), was executed in the Ems Estuary, bordering the Netherlands and Germany, aimed at better understanding the mechanisms that drive the exchange of water and sediments between a relatively exposed outer estuary and a hyper-turbid tidal river. More specifically, the reasons for the large up-estuary sediment accumulation rates and the role of the tidal river on the turbidity in the outer estuary were insufficiently understood. The campaign was designed to unravel the hydrodynamic and sedimentary exchange mechanisms, comprising two hydrographic surveys during contrasting environmental conditions using eight concurrently operating ships and 10 moorings measuring for at least one spring–neap tidal cycle. All survey locations were equipped with sensors measuring flow velocity, salinity, and turbidity (and with stationary ship surveys taking water samples), while some of the survey ships also measured turbulence and sediment settling properties. These observations have provided important new insights into horizontal sediment fluxes and density-driven exchange flows, both laterally and longitudinally. An integral analysis of these observations suggests that large-scale residual transport is surprisingly similar during periods of high and low discharge, with higher river discharge resulting in both higher seaward-directed fluxes near the surface and landward-directed fluxes near the bed. Sediment exchange seems to be strongly influenced by a previously undocumented lateral circulation cell driving residual transport. Vertical density-driven flows in the outer estuary are influenced by variations in river discharge, with a near-bed landward flow being most pronounced in the days following a period with elevated river discharge. The study site is more turbid during winter conditions, when the estuarine turbidity maximum (ETM) is pushed seaward by river flow, resulting in a more pronounced impact of suspended sediments on hydrodynamics. All data collected during the EDoM campaign, but also standard monitoring data (waves, water levels, discharge, turbidity, and salinity) collected by Dutch and German authorities are made publicly available at 4TU Centre for Research Data (https://doi.org/10.4121/c.6056564.v3; van Maren et al., 2022).

No abstract

Abstract. An extensive field campaign (EDoM) was executed in the Ems estuary, bordering the Netherlands and Germany, aiming at better understanding the mechanisms driving exchange of water and sediments between a relatively exposed outer estuary and a hyperturbid tidal river. Particularly the reasons for the large up-estuary sediment accumulation rates and the role of the tidal river on the turbidity in the outer estuary were insufficiently understood. The campaign was designed to unravel the hydrodynamic and sedimentary exchange mechanisms, comprising two hydrographic surveys during contrasting environmental conditions using 8 concurrently operating ships and 10 moorings measuring for least one spring-neap tidal cycle. All survey locations were equipped with sensors measuring flow velocity, salinity, and turbidity (and with stationary ship surveys taking water samples), while some of the survey ships also measured turbulence and sediment settling properties. These observations have provided important new insights into horizontal transport fluxes and density-driven exchange flows, both laterally and longitudinally. An integral analysis of these observations suggest that large-scale residual transport is surprisingly similar during periods of high and low discharge, with higher river discharge resulting in both higher seaward-directed fluxes near the surface and landward-directed fluxes near the bed. Sediment exchange seems to be strongly influenced by a previously undocumented lateral circulation cell driving residual transport. Vertical density-driven flows in the outerestuary are influenced by variations in river discharge, with a near-bed landward flow being most pronounced in the days following a period with elevated river discharge. The study site is more turbid during winter conditions, when the Estuarine Turbidity Maximum is pushed seaward by river flow, resulting in more pronounced impact of suspended sediments on hydrodynamics. All data collected during the EDoM campaign, but also standard monitoring data (waves, water levels, discharge, turbidity and salinity) collected by Dutch and German authorities is made publicly available at 4TU Centre for Research Data (https://doi.org/10.4121/c.6056564.v3; van Maren et al., 2022).

<p>Nature-based solutions have become tremendously popular over the past few years. They are popular among large financing institutions such as the WorldBank and the Asian Development Bank up to very local governmental bodies that have heard of the many benefits these Nature-based solutions deliver. However, the supposed benefits of Nature-based solutions depend strongly on how, where and with what purpose these solutions are designed. The massive introduction of Nature-based solutions has led to many interesting and innovative projects that created multiple benefits. On the other hand, it has also led to projects in which the Nature-based component was not so clear, and the benefits were uncertain. This leads us to the question: are Nature-based solutions a way to solve all your challenges in the coastal zone and if they don’t, can we still call them a Nature-based solution? And, what do we actually mean with a Nature-based solution. We would like to tap on these questions with some examples of real projects and conceptual designs.</p><p>The projects and designs are all based in coastal areas where Nature-based solutions often take the form of wetlands or extended foreshores. These wetlands consist of mangrove systems in the tropics and salt-marsh systems in more temperate regions. The projects had different goals and different scales, they provided different benefits, but they all have in common that they were called a Nature-based solution. Depending on the goals and specific demands we encountered various interesting challenges. The final designs show that Nature-based solutions come in many sizes, shapes and forms. Sometimes they have the possibility to change livelihoods of people at a landscape scale and sometimes they only added a little green fringe.</p>