3115 resultaten

  • The importance of snow sublimation on a Himalayan glacier

    Auteurs: Stigter, E.E.; Litt, M.; Steiner, J.F.; Bonekamp, P.N.J.; Shea, J.M.; Bierkens, M.F.P.; Immerzeel, W.W. (2018)
    Gepubliceerd in: Frontiers in earth science (2018), pagina 1-16

    Snow sublimation is a loss of water from the snowpack to the atmosphere. So far, snow sublimation has remained unquantified in the Himalaya, prohibiting a full understanding of the water balance and glacier mass balance. Hence, we measured surface latent heat fluxes with an eddy covariance system on Yala Glacier (5,350m a.s.l) in the Nepalese Himalaya to quantify the role snow sublimation plays in the water and glacier mass budget. Observations reveal that cumulative sublimation is 32mm for a 32-day period from October to November 2016, which is high compared to observations in other regions in the world. Multiple turbulent flux parameterizations were subsequently tested against this observed sublimation. The bulk-aerodynamic method offered the best performance, and we subsequently used this method to estimate cumulative sublimation and evaporation at the location of the eddy covariance system for the 2016–2017 winter season, which is 125 and 9mm respectively. This is equivalent to 21% of the annual snowfall. In addition, the spatial variation of total daily sublimation over Yala Glacier was simulated with the bulk-aerodynamic method for a humid and non-humid day. Required spatial fields of meteorological variables were obtained from high-resolution WRF simulations of the region in combination with field observations. The cumulative daily sublimation at the location of the eddy covariance system equals the simulated sublimation averaged over the entire glacier. Therefore, this location appears to be representative for Yala Glacier sublimation. The spatial distribution of sublimation is primarily controlled by wind speed. Close to the ridge of Yala Glacier cumulative daily sublimation is a factor 1.7 higher than at the location of the eddy covariance system, whereas it is a factor 0.8 lower at the snout of the glacier. This illustrates that the fraction of snowfall returned to the atmosphere may be much higher than 21% at wind-exposed locations. This is a considerable loss of water and illustrates the importance and need to account for sublimation in future hydrological and mass balance studies in the Himalaya.

  • Model uncertainty analysis for WAQUA in the context of the WTI project : literature study and plan of approach

    Auteurs: Stuparu, D.; Tijssen, A. (2013)

    In the context of the Wettelijk Toets Instrumentarium 2017 (WTI) project, the subproject Hydrodynamic modelling aims to identify and quantify the model uncertainty of WAQUA regarding the calculated water levels for the primary water systems in the Netherlands. The present study reports the work done for the first phase of the subproject and aims to give an overview of the currently available information regarding the model uncertainty for WAQUA and its propagation on the calculated water levels. A second objective is to propose an appropriate procedure for uncertainty quantification in the second phase. The research consists of two steps: first, the results of an extensive literature review are described. The review concludes that little information is present regarding the possible sources of model uncertainties and the magnitude of their contribution to the uncertainty of the water levels. Secondly, an expert meeting was organized with both developers and users of the model to arrive to a consensus regarding the identification and quantification of the main sources of model uncertainty. The outcome of the discussion revealed that the sources of uncertainty cannot be regarded independently during the uncertainty analysis, due to the implicit correlation introduced by the calibration process. Also, the most important source of uncertainty is the use of WAQUA outside the calibration and validation data range. By combining the results of the literature study with the results of the expert meeting, the present study makes a recommendation for a pragmatic quantification of the model uncertainty. An expert judgement based approach is proposed, based on a sensitivity analysis of the model with respect to the choices made in the calibration process. In this case, the calibration choices refer to the selection of parameters that are used to calibrate the model. Different sets of parameters may be used for calibration, resulting in equally good model performances with respect to both calibration and validation data. However, when extrapolating to extreme conditions, the behaviour of the model may be different. The sensitivity analysis will assess these possible differences and will stand as a basis for subsequent expert judgement. The approach will allow for a crude quantification, but will provide an estimation of the model uncertainty as a whole.

  • Morphodynamic impacts of large-scale engineering projects in the Yangtze River delta

    Auteurs: Luan, H.L.; Ding, P.X.; Wang, Z.B.; Yang, S.L.; Lu, J.Y. (2018)
    Gepubliceerd in: Coastal engineering : an international journal for coastal, harbour and offshore engineers, volume 141 (2018), pagina 1-11

    Morphodynamics of world's river deltas are increasingly affected by human activities, which are of great ecological, economic and social implications. However, impacts of human interventions in deltaic regions are insufficiently understood, especially superimposed upon diminishing sediment supplies. This study uses the heavily interfered Yangtze River delta as an example to address this issue. The morphodynamic impacts of the Deepwater Navigation Channel Project (DNCP) during 1997–2013 are investigated through process-based modeling approach (Delft3D) and bathymetric data analysis. The DNCP was implemented in the mouth bar area of the Yangtze River delta including the twin dikes and 19 groynes with the total length of 132.0 km. Hydrodynamic simulations indicate that the training walls resulted in weaker tidal flow and longer slack period at the East Hengsha Shoal (EHS) and stronger tidal flow at the subaqueous delta. Thus, the EHS is characterized as a sediment-starved status after the completion of the training walls. Subsequently, morphological modeling shows enhanced accretion at the EHS and enhanced erosion at the subaqueous delta when the training walls are taken into account. Numerical experiments further demonstrate that the above changes are mainly attributed to the seaward half of the northern training walls constructed in 2002–2005. This is probably the reason for the observed accretion peak of the EHS in 2002–2007 and the gradual increase in the erosion rate of the subaqueous delta after 2002. The schematized paths of sediment transport after the DNCP indicate that sediment eroded from the subaqueous delta serves as an important source for accretion of the mouth bar area. It is suggested that siltation promoting projects within the mouth bar area increased shallow shoal accretion and aggravated erosion at the subaqueous delta. With the overall erosion of the Yangtze River delta due to river sediment reduction, large-scale estuarine engineering projects substantially increase the complicacy of its morphodynamic pattern, which merits close attention for sustainable delta management.

  • Handleiding Steentoets 2010 : Excel-programma voor het toetsen en ontwerpen van steenzettingen

    Auteur: Klein Breteler, M.A. (2013)

    In het kader van de toetsing van de waterkeringen zoals voorgeschreven in de Waterwet dienen ook steenzettingen elke zes jaar getoetst te worden. Om de toetsing te vereenvoudigen is door Rijkswaterstaat in 2006 het initiatief genomen om een computerprogramma te laten ontwikkelen dat al het rekenwerk en de beoordelingen uitvoert. Er is gekozen voor een programma op basis van Microsoft Excel, omdat dit bij alle diensten van Rijkswaterstaat en de waterschappen gemakkelijk geïnstalleerd kan worden zonder tussenkomst van de ICT-afdeling. Bovendien geeft het de mogelijkheid om gemakkelijk aanvullende berekeningen aan de spreadsheet toe te voegen. In het rekenmodel STEENTOETS2010 zijn de nieuwste inzichten uit deze onderzoeksprojecten verwerkt voorzover ze niet in strijd zijn met het VTV2006. Dit programma is goedgekeurd door ENW en RWS en mag toegepast worden bij het toetsen van steenzettingen in de derde toetsronde. In het onderhavige rapport is uitgelegd hoe dit programma gebruikt kan worden. Opgemerkt moet worden dat dit slechts een hulpmiddel is bij het toetsen en ontwerpen van steenzettingen. De gebruiker blijft uiteindelijk altijd verantwoordelijk voor het resultaat.

  • A study on the siltation of the Bangkok bar channel : report on dredging

    Originally published in 1964

  • Tidal flat-wetland systems as flood defenses : understanding biogeomorphic controls

    Auteurs: Reed, D.W.; Wesenbeeck, B.K. van; Herman, P.M.J.; Meselhe, E. (2018)
    Gepubliceerd in: Estuarine, coastal and shelf science (2018), pagina 1-51

    Coastal managers worldwide increasingly recognize the importance of conservation and restoration of natural coastal ecosystems. This ensures coastal resilience and provision of essential ecosystem services, such as wave attenuation reducing coastal flooding and erosion. In the continuum from unvegetated tidal flats to salt marshes and mangroves, fundamental physical controls as well as biotic interactions, and feedbacks among them, determine morphology and vegetation distribution. Although these processes are well described in established literature, this information is rarely applied to understanding the role of these ecosystems as coastal defense. The focus is often on specific elements of the complex system, such as vegetation structure and cover, rather than on their complex natural dynamics. This review examines whether and how the dynamic nature of tidal flat - wetlands systems contributes to, or detracts from, their role in coastal defense. It discusses how the characteristics of the system adjust to external forcing and how these adjustments affect ecosystem services. It also considers how human interventions can take advantage of natural processes to enhance or accelerate achievement of natural coastal defense.

  • Developing a framework to quantify potential Sea level rise-driven environmental losses : a case study in Semarang coastal area, Indonesia

    Auteurs: Mehvar, S.; Filatova, T.; Syukri, I.; Dastgheib, A.; Ranasinghe, R. (2018)
    Gepubliceerd in: Environmental science and policy, volume 89 (2018), pagina 216-230

    Climate change triggers major alterations to coastal zones worldwide. Quantification of these adverse impacts to coastal ecosystems is often done on a coarse scale of global regions. Consistent local scale estimates of physical impacts on ecosystems and monetary assessment of associated losses are scarce, especially in developing countries. With aim of facilitating such assessment, which is increasingly required, here we propose a coherent three-step framework and subsequently apply it to quantify potential sea level rise-driven alterations in the monetary value of ecosystem services in the coastal area of Semarang in Indonesia. Within this framework, we (1) quantify the present value of coastal ecosystem services by using economic valuation techniques; (2) identify the potential impacts of relative sea level rise (RSLR)-induced inundation on ecosystem services (for the year 2100 inundation scenarios); and (3) monetize these impacts by developing a novel scenario-based approach. The results show that full inundation (scenario A with 4m RSLR) poses a median loss of 90% (US$ 2.8 – 3.5) and 25% (US$ 90 – 113) to the present art and fishery values per hectare, while amenity service is expected to lose up to 50% (US$ 3700 – 5400) of its present value. Additionally, recreation value of the coastal ecosystems in three selected sites (Marina and Maron beaches, and Plumbon estuary) will decrease by 70% (US$ 15,460 – 19,820) per hectare. However, in scenario B (RSLR of 1.1 m) with a 50% inundated area, these losses are estimated approximately 40% less than for scenario A. It is expected that researchers and policy makers may apply this approach in their areas of interest to gain a better understanding of the likely costs of sea level rise-driven environmental damages along coasts, ultimately contributing to the sustainable management of coastal environment in Indonesia and possibly in other developing countries.

  • Ex-ante-evaluatie van de mestmarkt en milieukwaliteit : evaluatie van de Meststoffenwet 2016

    Auteurs: Schoumans, O.F.; Blokland, P.W.; Cleij, P.; Groenendijk, P.; Koeijer, T.J. de; Luesink, H.H.; Renaud, L.V.; Roovaart, J. van den (2016)

  • Effecten van het mestbeleid op landbouw en milieu : beantwoording van de ex-postvragen in het kader van de evaluatie van de Meststoffenwet

    Auteurs: Velthof, G.L.; Koeijer, J.J.; Timmerman, M.; Hooijboer, A.; Rozemeijer, J.; Bruggen, C. van; Groenendijk, P. (2017)

  • European flat oysters on offshore wind farms, additional locations : opportunities for the development of European flat oyster (Ostrea edulis) populations on planned wind farms and additional locations in the Dutch section of the North Sea

    Auteurs: Kamermans, P.; Duren, L.A. van; Kleissen, F. (2018)

    To determine the relative suitability for development of self-sustaining European flat oyster (Ostrea edulis) beds, potential areas for offshore wind farms in the Dutch Exclusive Economic Zone (EEZ) were analysed. The studied locations are the new wind farm zones “Hollandse Kust (noordwest, west and zuidwest)”, “IJmuiden Ver” and the remaining lot of the North of the Frysian Islands Wind Farm Zone, but also 13 additional potential locations on the EEZ (i.e. CP4-CP6 and CP9-17) and, in addition, the nature area location Borkum Reef Ground (Borkumse Stenen). Biotic and abiotic factors of importance for flat oyster survival, growth, reproduction and recruitment, were compared for the 8 wind farm locations of Smaal et al. (2017) and the 18 new locations. For the locations on the Dutch EEZ the following habitat factors are important for flat oyster beds: shear stress, suspended sediment, larval retention, temperature, sediment composition and food availability. Presence in historic distribution area was used as a verification. Average shear stress, suspended sediment and temperature are within the range considered suitable for the development of an oyster bed at all locations. Thus, these factors do not discriminate between locations. Maximum shear stress is too high at one location and the sediment is too silty at 7 locations. However, habitat restoration efforts may make the environment more suitable, e.g. by placing shell material or 3D structures which elevate the oysters from the bottom. Based on the analysis described in this report we recommend to select the following locations that are suitable for flat oyster restoration. 1. Best: Borssele Wind Farm Zone, Buitengaats (part of the Gemini wind park) and CP9 (within historic distribution and high larval retention) ; 2. Very good: Hollandse Kust (zuidwest) Wind Farm Zone (high larval retention) ; 3. Good: Offshore Windpark Egmond aan Zee, Prinses Amalia Windpark, Windpark Eneco Luchterduinen, Hollandse Kust (zuid) Wind Farm Zone, Hollandse Kust (noord) Wind Farm Zone (medium larval retention) ; 4. Suitable: the remaining lot of the North of the Frysian Islands Wind Farm Zone, Zee-energie (part of the Gemini wind park), Borkum Reef Ground (Borkumse Stenen) (within historic distribution, medium or high larval retention, but locally too high maximum shear stress or too silty) ; 5. Suitable with introduction of substrate: CP5, CP6 (medium or high larval retention, but too silty without introduction of substrate).

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