Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Blind estuaries during drought: The influences of a sandbar on mangrove trees

Small blind estuaries are a common phenomenon on the coast of Nicaragua, but unfortunately not much is known on their hydrological characteristics. A blind estuary can be identified by a sandbar that temporarily closes the estuary from sea. These blind estuaries often have very diverse flora and fauna on which they play an important ecological role. Mangrove forests growing in this ecosystem often play a central position, and are valued for a wide range of functions, productivities, uses and values. Unfortunately these forests are also under threat of destruction, which is often caused by human influences. In this research human impact, as well as the impact of drought caused by an El Niño event, have been included to understand the influence of a blind estuary on the well being of the mangrove forest. The study was performed in a blind estuary at the Pacific coast of Nicaragua; located near the village El Ostional. During a fieldwork period of approximately three months, the study area was observed and measurements on predominantly water levels and salinity were conducted. The resulting information was used (1) to classify the separate morphologic, biologic, and social structures in the area, (2) identify the interactions between mangrove well being and hydrological characteristics, and finally (3) do more in-depth analyses on the salt intrusion occurring in the area. The estuary contains two main landforms; the sandbar separating estuary and sea, and the back-barrier floodplain behind it. The sandbar is formed by wave action, and can be ruptured due to a highly seasonal river discharge. The floodplain inundates when accumulation of water behind the sandbar increases. A variety of common mangroves like the Red and White mangrove, and the Buttonwood tree, can be found in the floodplain. The floodplain next to this is home to the Tea mangrove, a very rare and low salt tolerance mangrove tree. Together these mangrove trees form an interior mangrove forest. The inhabitants of El Ostional mainly use the floodplain to shortcut their route to the shore. Their main interest in the estuary is for the fishes it provides. The inhabitants on occasions like to 'help' the sandbar to open, in order to have easy fishing possibilities. Inundation in the floodplain is revealed to be extremely beneficial for the mangrove population. The crab population in the floodplain turned out to play an important ecological role, where their burrows increase permeability. This enhances infiltration into the soil, which increases soil moisture and decreases soil salinity. The blind estuary is, although stressed by drought, able to maintain relatively low salinity levels. This is caused by a steady fresh groundwater inflow. An overall outflow of estuary water occurs through the sandbar, where head differences between sea tide and estuary water level are the main forces that induce a transmission through the sandbar. The resulting relatively fresh water in the estuary permits the growth of the Tea mangrove. A mainly pressure induced muted tide is revealed in the estuary. Together with the fresh water inflow and wind influence, a circulation is established that reveals a well-mixed salt intrusion, which is caused by over-wash events. Would the sandbar be ruptured manually during drought, then the result is an increase in salinity that would be devastating for the Tea mangrove, but supply the estuary and mangroves with more water and provide the connection between sea and estuary necessary for fish reproduction. Salt intrudes the floodplain during inundation, when sea water evaporates and salt is left behind, which accumulates in the soil. The more infrequent the inundation, the higher the salinity in the soil. This only occurs in the floodplain. Salt intrusion in the subsurface of the Ostional area is due to pressure differences between fresh water in the aquifer and sea tide. This induces a mixing zone of which the interface is still near the shore; most of the wells in Ostional maintain potable water salinities. In order to protect the mangrove forest, it is thus important to protect the complete ecosystem, in this case especially the crab population. It further is important to ensure the maintenance of a groundwater inflow, by protecting the upstream forests that enhance infiltration to the groundwater system. Whether the manual rupture of the sandbar during drought is considered problematic depends on the the value given to the Tea mangrove, the other mangrove population, or the nursery function the estuary provides. Further research and monitoring for the Ostional area is necessary to confirm the formulated hypotheses, and in order to keep track of salt intrusion in the estuary and subsurface.Water ResourcesWater ManagementCivil Engineering and Geoscience

On the generation of surfable ship waves, Part II: The application of stereo photo technique measuring water surface elevation and surface flow velocities

Wave pools are designed to mimic surfing conditions as they exist along coasts. The Liquid Time Wave Pool concept, invented by Greg Webber, suggests a new method for wave generation. Waves are generated by a hull which moves in a channel. These "ship waves" break on a slope creating surf. Key feature of the concept is to make ship waves surfable. To investigate the possibility of creating surfable ship waves an experiment is conducted. During this experiment hulls are towed through a channel and the generated waves are measured using a stereo photo technique. The objectives of this study are to: 1) Investigate the possibility of making ship waves surfable; 2) Investigate the capability of the stereo photo technique to measure water surface elevation and surface velocity over a specific area. Existing theory offers the possibility to estimate wave fields using Froude depth numbers and the blocking of the channel cross section by the hull. The Froude depth number represents the ratio of the ship speed and the shallow water celerity. When Froude depth numbers and blocking values are low, hull speeds are much smaller than the shallow water celerity. The regime is called sub-critical and a dominating secondary wave field is expected. When Froude depth numbers and blocking values are high, hull speeds are high and currents around the hull can become critical. The hull speed when return currents become critical is called the limit speed. Hull speeds exceeding the limit speed account for the trans-critical regime. The trans-critical regime holds a dominating primary wave system and a negligible secondary wave system. The angle of the generated wave determines the peel angle of the surfing wave. The peel angle is the angle enclosed by the wave crest and the path of the breakpoint. Peel angles mainly determine the surfer speed. To gain insight in wave angles and surface velocities of ship waves and to verify existing ship wave theory a physical experiment is conducted. In the experiment hulls with different blocking coefficients are towed through a channel at different speeds covering the sub-critical and trans-critical regime. The wave field generated by the hull is simultaneously photographed by two distinct calibrated cameras. These stereo photos taken by the cameras are input to the stereo photo algorithm. The output of the algorithm is the water surface elevation and the surface flow velocity of the wave field. It is found that the stereo photo technique offers a great possibility to derive water surface elevations and surface flow velocities. Water surface elevations are verified using parallel measurements by wave gauges. Accuracy of the technique highly depends on camera calibration which must be improved. Limiting factors for accuracy using the technique are the pixel resolution of the images, computational power and the density of the floats. Using the stereo photo technique theory is validated. It is found that the wave field in the trans-critical regime holds strong currents. These strong currents make the trans-critical regime not suitable for surfing. The sub-critical regime holds weak currents and wave angles suit the range of the required peel angles. The Liquid Time Wave Pool design should account for towing speeds and blocking coefficients leading to the sub-critical regime.Civil Engineering and Geoscience

4FFland

This paper presents a research which seeks ways to transform the Brettenzone, an existing recreational area in Amsterdam, into an energyscape: a landscape which produces renewable energy. Renewable energy production will increasingly start to compete with other forms of land use such as recreation, nature and agriculture. Its careful integration therefore becomes detrimental. This paper discusses renewable energy systems and what determines their sustainability. It offers a set of analysis methods which can be used when designing for renewable energy production. These methods include energy potential and system mapping. This paper also presents an analysis of Amsterdam’s energy system and it’s potentials for renewable energy production using the before mentioned methods. This analyses describes the design casus and seeks to identify possibilities for an intervention. It gives a set of possibilities producing renewable energy in the Brettenzone which include: recycling nutrients from industrial waste streams to agriculturally produce food and biogas, producing electrical power using PV cells, harvesting heat for the district network using solar collectors and aquifers, as well as harvesting cold for a future district network (Teleport) using deep water source cooling (Sloterplas), absorption cooling devices, the Binnen-IJ and aquifers. The most promising proposal, an agricultural enterprise producing food and biogas, is analysed further. Such an enterprise would produce food, feed and fuel whilst maintaining a theoretically closed cycle of fertilising nutrients. This paper present research into the requirements of such a food, feed, fuel and fertiliser farm entitled, the 4F farm. The paper presents the aspects which determine the sustainability of the 4F farm with an emphasis on the bioenergy aspect. It explores possible sources of plant biomass by comparing their biogas yield rates as well as their climatic requirements in comparison to the conditions in Amsterdam. A similar analysis is made for manure as a source of biomass. The biogas production process is also discussed as well as the required systems and equipment. From this paper it can be concluded that the described food and biogas farm should seek to optimize the yield of food, feed, fuel and fertilizer in that respective order of importance. Also it offers the required data and recommendations for designing the 4F farm. The paper notes however that the 4F’s energy yields per acre are not sufficient to fulfi ll the ambition of acting as an energyscape. For this goal to be reached the 4F farm should also integrate other energy harvesting techniques such as PV cells or solar collectors. The 4F farm can be suffi cient however to sustain a small autarkic neighbourhood.Architectural Engineering and TechnologyArchitecture and The Built Environmen

Physics of Blown Sand and Coastal Dunes

Hydraulic EngineeringCivil Engineering and Geoscience

Modelling aeolian sediment accumulations on a beach

This paper aims to conceptually simulate observed spatial and temporal variability in aeolian sediment transport rates, erosion and deposition on a beach. Traditional strategies of modeling aeolian sediment transport rates do not account for supply limitations that are common on natural beaches. A recently developed 1D linear advection model is used in which supply limitations are taken into account in a highly aggregated manner. It is shown that the model is able to simulate the appearance and disappearance of sediment accumulations. However, sediment accumulations alike observed in the field using ARGUS cameras behave on a different time and spatial scales.Hydraulic EngineeringCivil Engineering and Geoscience

Simulating spatiotemporal aeolian sediment supply at a mega nourishment

Mega nourishments are a novel approach to stimulating coastal safety and resilience. Mega nourishments are intended to spread along the coast on a decadal time scale by natural sediment transport processes with a minimum of intrusion into the natural coastal system. The supratidal morphodynamic behaviour of mega nourishments is not well understood due to complexities introduced by limitations in sediment availability to aeolian sediment transport. Consequently, the effectiveness of mega nourishments to stimulate coastal safety and to influence coastal landscape and habitat development remains unknown. In this paper we present a detailed 4-year hindcast of the morphological development of the Sand Motor mega nourishment in The Netherlands. We use the aeolian sediment transport and availability model AEOLIS that focuses specifically on the simulation of spatiotemporal variations in sediment availability. The model includes the recurrence relation between sediment availability and aeolian sediment transport through self-grading and beach armoring. We show that the model is able to reproduce multi-annual aeolian sediment transport rates in the Sand Motor domain in the four years after its construction. The RMSE is 3⋅104m3 (7% of the total sediment accumulation) and R2 is 0.93 when comparing timeseries of total sediment accumulation in the dunes, dune lake and lagoon. The combination of spatial and temporal variations in aeolian sediment availability, due to the combined influence of soil moisture, sediment sorting and beach armoring, is essential for an accurate estimate of the total sedimentation volume. The simulated feedback between aeolian sediment availability and transport is required for accurately describing compartmentalization of the beach and locating the aeolian sediment source areas in the Sand Motor domain.Accepted Author ManuscriptCoastal Engineerin

Field measurements on spatial variations in aeolian sediment availability at the Sand Motor mega nourishment

Spatial variations in aeolian sediment transport were measured at the Sand Motor mega nourishment in The Netherlands during a six week field campaign in the fall of 2014. A consistent significant increase in sediment transport in downwind direction (positive gradient) was measured over the intertidal beach area, indicating that the intertidal beach is a primary source of aeolian sediment, despite the high soil moisture contents. A small positive increase in transport in downwind direction was measured over the dry beach, indicating that local aeolian sediment supply was hampered. A consistent decrease in sediment transport in downwind direction (negative gradient) was measured at the transition between intertidal and dry beach, indicating local deposition of sediment. The negative gradients coincide with the berm edge and the onset of a shell pavement. Therefore deposition might be promoted by morphological feedback between a berm and the wind and the entrapment of sediment in the beach armor layer. The local sediment deposits cause the sediment supply to the dunes to be continued even during high water, resulting in a phased process. The influence of the beach armor layer reduces during storm events as the armor layer itself is being mobilized.Accepted Author ManuscriptCoastal Engineerin

A process-based model for aeolian sediment transport and spatiotemporal varying sediment availability

Aeolian sediment transport is influenced by a variety of bed surface properties, like moisture, shells, vegetation, and nonerodible elements. The bed surface properties influence aeolian sediment transport by changing the sediment transport capacity and/or the sediment availability. The effect of bed surface properties on the transport capacity and sediment availability is typically incorporated through the velocity threshold. This approach appears to be a critical limitation in existing aeolian sediment transport models for simulation of real-world cases with spatiotemporal variations in bed surface properties. This paper presents a new model approach for multifraction aeolian sediment transport in which sediment availability is simulated rather than parameterized through the velocity threshold. The model can cope with arbitrary spatiotemporal configurations of bed surface properties that either limit or enhance the sediment availability or sediment transport capacity. The performance of the model is illustrated using four prototype cases, the simulation of two wind tunnel experiments from literature and a sensitivity analysis of newly introduced parameters.Coastal Engineerin

Aeolian sediment supply at a mega nourishment

Mega nourishments are intended to enhance growth and resilience of coastal dunes on medium to long time scales by stimulation of natural sediment transport processes. The growth and resilience of coastal dunes largely depends on the presence of a continuous supply of aeolian sediment. A recent example of a mega nourishment is the 21 Mm3 mega nourishment known as the Sand Motor. The Sand Motor is intended to nourish the entire Holland coast over a period of two decades. Four years of bi-monthly topographic measurements of the Sand Motor domain provide an opportunity to analyze spatiotemporal variations in aeolian sediment supply using an aeolian sediment budget analysis. It appears that more than 58% of all aeolian sediment deposits originate from the low-lying beaches that are regularly reworked by waves. Aeolian sediment supply from higher beaches diminished after half a year after construction of the Sand Motor, likely due to the formation of deflation lag deposits that constitute a beach armor layer. The compartmentalization of the Sand Motor in armored and unarmored surfaces suggests that the construction height is an important design criterion that influences the lifetime and region of influence for any mega nourishment.Coastal Engineerin