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Nighttime cooling of an urban pond
One of the processes by which open water cools the air during hot summer days is by storing the heat and increasing its own temperature. This heat is then released at night. The aim of this paper is to analyze this cooling process by quantifying the magnitude of turbulent, latent and sensible, heat fluxes in comparison to radiative and ground fluxes. A detailed vertical temperature profile was measured in an urban pond (∼70 cm deep with surface area of 3,627 m2) in Delft (NL) using Distributed Temperature Sensing for a period of one month. The results show that, from the total of 2.7 MJm−2 of heat released by the pond on an average summer night, 43% of the thermal energy is emitted as longwave radiation, 39% as latent energy, and only 11% as sensible heat. An additional 0.10–0.32 MJm−2 is transferred into the bottom of the lake. Temperature distribution and cooling of the water profile is influenced by weather conditions during the preceding day. This paper provides an insight into a behavioral pattern of an urban pond at night. The results can shed some light into the potential of urban bodies to increase the air temperature of their surroundings at night.
Amplification and deformation of tidal wave in the Upper Scheldt Estuary
The records of HW and LW in the most upper part of the Scheldt Estuary since 1971 have been analysed together with the daily river discharge. The tidal range, the hydraulic head and the ratio between the rising tide period to falling tide period have been determined for investigating the tidal amplification, the water surface slope along the river and the tidal asymmetry. The purpose of the investigation is to find out if a regime shift to high turbidity and strong tidal amplification is developing in the system. The results of the analysis show that both the hydraulic head and the tidal amplification have increased over time. The tide in this part of the estuary is flood-dominant, but the flood-dominancy is decreasing in time. These developments of the tide can be plausibly explained by a decrease of the river width followed by gradual deepening in the river. The most upper part of the Scheldt Estuary still behaves normally as a not too muddy system. No decisive answer can be given whether or not a regime shift towards a high-turbid system with strong tidal amplification may develop. How the system will develop depends on the change in capacity of pumping mud towards the upper reaches of the estuary. The increasing tidal amplitude can enhance this capacity although the flood-dominance itself is decreasing. Further study is recommended to better specify the potential danger of a regime shift to high-turbid system.
Effects of wave orbital velocity parameterization on nearshore sediment transport and decadal morphodynamics
Nearshore morphological modelling is challenging due to complex feedback between hydrodynamics, sediment transport and morphology bridging scales from seconds to years. Such modelling is, however, needed to assess long-term effects of changing climates on coastal environments, for example. Due to computational efficiency, the sediment transport driven by currents and waves often requires a parameterization of wave orbital velocities. A frequently used parameterization of skewness-only was found to overfeed the coast unrealistically on a timescale of years-decades. To improve this, we implemented a recently developed parameterization accounting for skewness and asymmetry in a morphodynamic model (Delft3D). The objective was to compare the effects of parameterizations on long-term coastal morphodynamics. We performed simulations with default and calibrated sediment transport settings, for idealized coastlines, and compared the results with measured data from analogue natural systems. The skewness-asymmetry parameterization was found to predict overall stable coastlines within the measured envelope with wave-related calibration factors within a factor of 2. In contrast, the original parameterization required stronger calibration, which further affected the alongshore transport rates, and yet predicted erosion in deeper areas and unrealistic accretion near the shoreline. The skewness-asymmetry parameterization opens up the possibility of more realistic long-term morphological modelling of complex coastal systems.
Can the implementation of the Water-Energy-Food Nexus support economic growth in the Mediterranean region? : the current status and the way forward
Water resources is a crucial environmental good for the function of the human societies and the ecosystems. Moreover, water is an important input for the economy and an indispensable factor for economic growth. Especially in regions that are facing water scarcity, the adoption of water management policies and approaches fostering the sustainable use of resources while promoting economic growth becomes an emerging issue. The Mediterranean region is one of the most vulnerable regions regarding the availability of water resources due to climate change and human activities. The Water-Energy-Food (WEF) Nexus offers an integrated approach analyzing the synergies and trade-offs between the different sectors in order to maximize the efficiency of using the resources, whereas adapting optimum policies and institutional arrangements. The Mediterranean is a region where we observe a large spectrum of issues emanating from water pollution and natural resource degradation to water scarcity, large amounts of food loss and waste and increasing demand for energy and food. Agricultural practices, urban development, demand management for water, and protection of ecosystems, particularly aquatic ecosystems, are areas of particular intervention available to the decision-makers in enhancing availability of water for the various water using sectors. In this context, the current policy note paper aims to address a major issue: how can the implementation of the WEF Nexus support the economic growth in the Mediterranean? Based on the outcome of an experts and stakeholders regional workshop, this paper presents the current status, including the opportunities and the practices of applying the WEF Nexus in the Mediterranean and draws specific recommendations for the way forward. Regarding the later, the strengthening of WEF Nexus in the Mediterranean requires a set of interventions to strengthen the institutional capacities, to enhance the finance mechanisms, to support the intra-regional dialogue as well, to enhance data collection and management, as well as to implement economic instruments and integrated economic approaches to measure the impact of Nexus into economy and employment.
Parametric emulation and inference in computationally expensive integrated urban water quality simulators
Water quality environmental assessment often requires the joint simulation of several subsystems (e.g. wastewater treatment processes, urban drainage and receiving water bodies). The complexity of these integrated catchment models grows fast, leading to potentially over-parameterised and computationally expensive models. The receiving water body physical and biochemical parameters are often a dominant source of uncertainty when simulating dissolved oxygen depletion processes. Thus, the use of system observations to refine prior knowledge (from experts or literature) is usually required. Unfortunately, simulating realworld scale water quality processes results in a significant computational burden, for which the use of sampling intensive applications (e.g. parametric inference) is severely hampered. Data-driven emulation aims at creating an interpolation map between the parametric and output multidimensional spaces of a dynamic simulator, thus providing a fast approximation of the model response. In this study a large-scale integrated urban water quality model is used to simulate dissolved oxygen depletion processes in a sensitive river. A polynomial expansion emulator was proposed to approximate the link between four and eight river physical and biochemical river parameters and the dynamics of river flow and dissolved oxygen concentration during one year (at hourly frequency). The emulator scheme was used to perform a sensitivity analysis and a formal parametric inference using local system observations. The effect of different likelihood assumptions (e.g. heteroscedasticity, normality and autocorrelation) during the inference of dissolved oxygen processes is also discussed. This study shows how the use of datadriven emulators can facilitate the integration of formal uncertainty analysis schemes in the hydrological and water quality modelling community.
The influence of context on the use and added value of Planning Support Systems in workshops : an exploratory case study of climate adaptation planning in Guayaquil, Ecuador
Planning Support Systems (PSS) are a promising tool for involving stakeholders in urban adaptation workshops. Past research has focused on the use and added value of PSS. While earlier studies have widely acknowledged the importance of context in determining the effectiveness of PSS, there has so far been no dedicated study of the influence of context on the use and added value of these tools in real planning workshops. To address this gap, we made an in-depth exploratory case study of a PSS, called the Adaptation Support Tool (AST), used in an adaptation planning workshop in Guayaquil, Ecuador. The workshop used the AST to support collaborative spatial planning for urban water management, at the neighbourhood scale. Interviews, questionnaires, observations and document review were used to investigate the influence of three contextual factors on the use and added value of the AST. The studied contextual factors are: 1) the style of tool use, 2) the phase of planning, and 3) the local project setting. Our findings indicate that the style of tool use and the local project setting were the most important contextual factors in determining the use and added value of the AST during the workshop. Meanwhile, the phase of planning appears to be critical for achieving impacts at the project level. This exploratory case study is a modest first contribution to understanding the influence of context on the use and added value of PSS in practice. Nevertheless, the findings indicate that further exploration of this topic could offer important insights to PSS use in practice.
The rationality of groundwater governance in the Vietnamese Mekong Delta’s coastal zone
This article assesses the rationality of the governance of the Vietnamese coastal zone’s water system. We first specify five assessment criteria, which we apply to a case study. Based on document analysis, stakeholder surveys and in-depth interviews, we found an average score on the criterion that relevant water system knowledge must be available. The scores on the criteria that water usage is systematically monitored, that the legal framework is complied with, that long-term human and wider ecological interests are addressed, and that governance is decentralized appeared to be low. The article concludes with some recommendations to change the governance system.
Seafloor characterization using multibeam echosounder backscatter data : methodology and results in the North Sea
Seafloor characterization using multibeam echosounder (MBES) backscatter data is an active field of research. The observed backscatter curve (OBC) is used in an inversion algorithm with available physics-based models to determine the seafloor geoacoustic parameters. A complication is that the OBC cannot directly be coupled to the modeled backscatter curve (MBC) due to the correction of uncalibrated sonars. Grab samples at reference areas are usually required to estimate the angular calibration curve (ACC) prior to the inversion. We first attempt to estimate the MBES ACC without grab sampling by using the least squares cubic spline approximation method implemented in a dierential evolution optimization algorithm. The geoacoustic parameters are then inverted over the entire area using the OBCs corrected for the estimated ACC. The results indicate that a search for at least three geoacoustic parameters is required, which includes the sediment mean grain size, roughness parameter, and volume scattering parameter. The inverted mean grain sizes are in agreement with grab samples, indicating reliability and stability of the proposed method. Furthermore, the interaction between the geoacoustic parameters and Bayesian acoustic classes is investigated. It is observed that higher backscatter values, and thereby higher acoustic classes, should not only be attributed to (slightly) coarser sediment, especially in a homogeneous sedimentary environment such as the Brown Bank, North Sea. Higher acoustic classes should also be attributed to larger seafloor roughness and volume scattering parameters, which are not likely intrinsic to only sediment characteristics but also to other contributing factors.
3D numerical simulation of backward erosion piping tube experiments
Backward erosion piping (BEP) is an internal erosion mechanism, driven by the detachment of particles at the pipe tip and erosion of the particles along the pipe walls and bottom. This erosion mechanism was extensively studied in (Robbins et al., 2018), who describe horizontal tube experiments in which the head loss along the erosion pipe was measured during pipe formation. This study investigates the ability of numerical models to predict the head loss in the erosion pipe in a 3D situation by simulating the tube experiments using DgFlow (Van Esch et al., 2013), a finite element (FE) program in which the groundwater flow is coupled to the pipe flow using line elements, and using the 3D finite element program described in Robbins and Griffiths (2018), in which backward erosion is simulated by changing soil elements to pipe elements.
Analysis of pipe progression during backward erosion piping in the presence of a coarse sand barrier
The coarse sand barrier (CSB) is considered as a promising measure to prevent failure of embankments due to backward erosion piping. In this method, a trench consisting of coarse sand is placed below the blanket layer at the downstream side of the embankment, across the possible path of the pipe to prevent development of a pipe. A pipe can progress upstream until it encounters the CSB, which prevents further progression of the pipe unless a significantly higher head drop (compared to the case without CSB) is applied. This results in a much higher safety level for the levee. The increased strength is due to the barrier’s higher resistance against erosion, and the relatively high hydraulic conductivity contrast between the barrier and the background material leading to a reduction of the hydraulic load in the barrier. The feasibility of this method has been investigated in a three-phase experimental programme at Deltares consisting of small-, medium- and large-scale experiments, confirming this method as a highly effective piping inhibiting measure. This contribution presents the results of one phase of this research, the medium-scale experiments, during which several laboratory experiments were conducted. In this paper, the piping process and observations on the pipe progression in presence of a CSB are presented and analyzed to get a better insight in the principle of pipe progression with respect to different barrier materials.