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Viby, Denmark

Refsgaard J.C.,Geological Survey of Denmark | Christensen S.,University of Aarhus | Sonnenborg T.O.,Geological Survey of Denmark | Seifert D.,ALECTIA | And 2 more authors.
Advances in Water Resources | Year: 2012

The geologically related uncertainty in groundwater modeling originates from two main sources: geological structures and hydraulic parameter values within these structures. Within a geological structural element the parameter values will always exhibit local scale heterogeneity, which can be accounted for, but is often neglected, in assessments of prediction uncertainties. Strategies for assessing prediction uncertainty due to geologically related uncertainty may be divided into three main categories, accounting for uncertainty due to: (a) the geological structure; (b) effective model parameters; and (c) model parameters including local scale heterogeneity. The most common methodologies for uncertainty assessments within each of these categories, such as multiple modeling, Monte Carlo analysis, regression analysis and moment equation approach, are briefly described with emphasis on their key characteristics. Based on reviews of previous studies, assessments are made on the relative importance of the three uncertainty categories for different types of model predictions. Furthermore, the strengths, limitations and interactions of these methodologies are discussed and conclusions are made with respect to identifying key subjects for which further research is needed. When all sources of uncertainty are analyzed by exploring model parameter and local scale heterogeneity uncertainty for several plausible geological model structures the joint uncertainties can be assessed by use of model averaging techniques, such as Bayesian Model Averaging (BMA). General challenge in model averaging with respect to choosing mutually exclusive and collectively exhaustive choice models, as well as to assign weights when models are used beyond their calibration base, are discussed. © 2011 Elsevier Ltd.

Fryd O.,Copenhagen University | Backhaus A.,Copenhagen University | Birch H.,Technical University of Denmark | Fratini C.,Technical University of Denmark | And 7 more authors.
WSUD 2012 - 7th International Conference on Water Sensitive Urban Design: Building the Water Sensitive Community, Final Program and Abstract Book | Year: 2012

WSUD is emerging in Denmark. An integrated multidisciplinary case study has investigated the options for WSUD retrofitting in a 15 km2 combined sewer catchment area in Copenhagen, Denmark, with the aim of reducing combined sewer overflows. The study was developed in collaboration with the City of Copenhagen and its water utility board, and involved researchers representing hydrogeology, sewer hydraulics, environmental chemistry, economics, engineering, urban planning and landscape architecture. The resulting multi-level catchment strategy, with a target of disconnecting 60% of the impervious area, suggests the implementation of four substrategies. First, disconnection is focused within sites that are relatively easy to disconnect, due to water quality, soil conditions, and the provision of open space. Secondly, up to 30% of the annual stormwater run-off is infiltrated in areas with relatively deep groundwater levels. Third, neighbourhoods located near low-lying wetland areas are disconnected and the sloping terrain is utilised for the conveyance of stormwater runoff. Fourth, the promotion of coherent urban green infrastructures is linked with WSUD transformations, urban greening and urban climate-proofing. In combination, these make the goal of 60% disconnection achievable. The study has generated four scientific papers so far, as well as concrete outputs which are partially adopted and currently under full-scale testing by the City of Copenhagen.

Hviid C.A.,ALECTIA | Hviid C.A.,Technical University of Denmark | Svendsen S.,Technical University of Denmark
Energy and Buildings | Year: 2011

A core element in sustainable ventilation systems is the heat recovery system. Conventional heat recovery systems have a high pressure drop that acts as blockage to naturally driven airflow. The heat recovery system we propose here consists of two separated air-to-liquid heat exchangers interconnected by a liquid loop powered by a pump ideal as a component in a heat recovery system for passive ventilation systems. This paper describes the analytical framework and the experimental development of one exchanger in the liquid-loop. The exchanger was constructed from the 8 mm plastic tubing that is commonly used in water-based floor-heating systems. The pressure loss and temperature exchange efficiency was measured. For a design airflow rate of 560 L/s, the pressure loss was 0.37 Pa and the efficiency was 75.6%. The experimental results agree well with the literature or numerical fluid calculations. Within the analytical framework, the total heat recovery of two liquid-coupled exchangers was calculated to be in the range 64.5-75.4%, depending on the parasitic heat loss in the experimental setup. The total pressure drop of the heat recovery system is 0.74 Pa. Moreover, preliminary improvement calculations promise a future total efficiency of 80% with a pressure drop of 1.2 Pa. © 2010 Elsevier B.V. All rights reserved.

Qin H.,Peking University | Cao G.,Peking University | Kristensen M.,ALECTIA | Refsgaard J.C.,Geological Survey of Denmark | And 6 more authors.
Hydrology and Earth System Sciences | Year: 2013

Groundwater overdraft has caused fast water level decline in the North China Plain (NCP) since the 1980s. Although many hydrological models have been developed for the NCP in the past few decades, most of them deal only with the groundwater component or only at local scales. In the present study, a coupled surface water-groundwater model using the MIKE SHE code has been developed for the entire alluvial plain of the NCP. All the major processes in the land phase of the hydrological cycle are considered in the integrated modeling approach. The most important parameters of the model are first identified by a sensitivity analysis process and then calibrated for the period 2000-2005. The calibrated model is validated for the period 2006-2008 against daily observations of groundwater heads. The simulation results compare well with the observations where acceptable values of root mean square error (RMSE) (most values lie below 4 m) and correlation coefficient (R) (0.36-0.97) are obtained. The simulated evapotranspiration (ET) is then compared with the remote sensing (RS)-based ET data to further validate the model simulation. The comparison result with a R2 value of 0.93 between the monthly averaged values of simulated actual evapotranspiration (AET) and RS AET for the entire NCP shows a good performance of the model. The water balance results indicate that more than 70% of water leaving the flow system is attributed to the ET component, of which about 0.25% is taken from the saturated zone (SZ); about 29% comes from pumping, including irrigation pumping and non-irrigation pumping (net pumping). Sustainable water management analysis of the NCP is conducted using the simulation results obtained from the integrated model. An effective approach to improve water use efficiency in the NCP is by reducing the actual ET, e.g. by introducing water-saving technologies and changes in cropping. © 2013 Author(s).

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