A. van Mazijk

Bio: A. van Mazijk is an academic researcher from Delft University of Technology. The author has contributed to research in topics: Skewness & Groyne. The author has an hindex of 5, co-authored 6 publications receiving 301 citations. Previous affiliations of A. van Mazijk include Karlsruhe Institute of Technology.

Exchange Processes between a River and Its Groyne Fields: Model Experiments

Abstract: The exchange of dissolved matter between a groyne field and a main stream influences the transport and distribution of a pollutant cloud in a river. In forecasting models, groyne fields are represented as dead zones with effective properties like exchange coefficients and exchanging volume. Despite its relevance for such practical applications, little research has been done on the exchange process between a groyne field and the main stream itself. Therefore, this study is aimed at examining this exchange process and validating the dead-zone prediction model, which treats the exchange process as a first order system. A schematized physical model of a river with groynes was built in a laboratory flume. The exchange process was visualized quantitatively with dye in adjacent groyne fields. In order to couple the exchange process to the velocity field, particle tracking velocimetry measurements were performed. Two different types of exchange were observed. First, exchange takes place via the mixing layer that is formed at the river-groyne-field interface. The large eddies formed in the mixing layer are the major cause of this exchange. Second, under certain conditions, even larger eddies are shed from the upstream groyne tip. Distortions in the flow field caused by such intermittent structures cause a much larger exchange than that by the mixing layer alone. The occurrence of large shed eddies depends on the presence of a sufficiently large, stationary, secondary gyre located at the upstream corner of the groyne field. The overall exchange of matter could be characterized as a first-order process, in accordance with the dead-zone-theory. The corresponding exchange coefficients agreed reasonably well with the results of earlier experiments and the effective coefficients as found in experiments in real river flows.

First evaluation of new design concepts for self-cleaning distribution networks

Abstract: Ten years of joint research on the nature and causes of discoloured water has resulted in guidelines for the implementation of self-cleaning distribution networks. These were first introduced in the Netherlands in 1999. The self-cleaning concept has been monitored right from its beginnings. Based on this evaluation, significant observations were found on the contribution of changes in flow velocity to the self-cleaning characteristics of pipes. These observations will be further investigated and will form the basis for the concept of dynamic sediment transportation modelling.

Computer aided evaluation of planning scenarios to assess the impact of land-use changes on water balance

Abstract: The impact of land use scenarios on water availability is part of the analysis and evaluation of water resources planning options for a river basin. An increasing demand for proper planning and development strategies indicates the need for robust methodologies to analyse the relation between spatial planning and water resources availability. Such a need can be met, for instance, by means of a simple water balance, which relies on a grid description of the river basin. The distributed character of the basin water balance modelling allows to evaluate the influence of land use changes on runoff availability at any point in the river network, this being limited only by the size of the grid mesh. A pilot study in this direction has been undertaken, aiming at establishing a modular framework, which allows developing a computer aided estimation of impacts of land use changes on total runoff. An application to an actual case area has highlighted major advantages and some limitations of using such an approach in the early phase of planning. An example of such planning illustrates the impact of reforestation on run off and consequently on the expansion of a wastewater treatment plant.

Quantification of effects of climate variations and human activities on runoff by a monthly water balance model: A case study of the Chaobai River basin in northern China

Abstract: The Chaobai River basin in northern China consists of two major tributaries, the Chao River and Bai River. Monthly observations of precipitation, streamfiow, and panevaporation data are available for 35 years (1961-1966 and 1973-2001). Using the annual time series of the observed streamfiow, one break point at 1979 is detected and is adopted to divide the data set into two study periods, the "before" and "after" periods marking the onset of significant anthropogenic alteration of the flow (reservoirs and silt retention dams, five times increase in population) and significant changes in land use (conversion to terraced fields versus sloping fields). The distributed time-variant gain model (DTVGM) was used to evaluate the water resources of the area. Furthermore, the Bayesian method used by Engeland et al. (2005) was used in this paper to evaluate two uncertainty sources (i.e., the model parameter and model structure) and for assessing the DTVGM's performance over the Chaobai River basin. Comparing the annual precipitation means over 13 years (1961-1966 and 1973-1979), the means of the second period (1980-2001) decreased by 5.4% and 4.9% in the Chao River and Bai River basins, respectively. However, the related annual runoff decreased by 40.3% and 52.8%, respectively, a much greater decline than exhibited by precipitation. Through the monthly model simulation and the fixing-changing method, it is determined that decreases in runoff between the two periods can be attributed to 35% (31%) from climate variations and 68% (70%) from human activities in the Chao River (Bai River). Thus, human impact exerts a dominant influence upon runoff decline in the Chaobai River basin compared to climate. This study enhances our understanding of the relative roles of climate variations and human activities on runoff. © 2009 by the American Geophysical Union.

Quantitative analysis of lake area variations and the influence factors from 1971 to 2004 in the Nam Co basin of the Tibetan Plateau

Abstract: By using remote sensing and GIS technologies, spatial analysis and statistic analysis, we calculated the water area and volume variations of the Nam Co Lake from 1971–2004, and discussed their influence factors from the viewpoints of climatic change and water balance Data source in this study includes bathymetric data of the lake, aerial surveyed topographic maps of 1970, remote sensing images of 1991 and 2004 in the lake catchment, meteorological data from 17 stations within 1971–2004 in the adjacent area of the lake catchment The results showed that the lake area expanded from 1920 km2 to 2015 km2 during 1971 to 2004 with the mean annual increasing rate (MAIR) of 281 km2 a−1, and the lake volume augmented from 78323×108 m3 to 86377×108 m3 with the MAIR of 237×108 m3 Moreover, the MAIR of the lake area and volume are both higher during 1992 to 2004 (401 km2 a−1 and 361×108 m3 a−1) than those during 1971 to 1991 (206 km2 a−1 and 160×108 m3 a−1) Analyses of meteorological data indicated that the continue rising of air temperature conduced more glacier melting water This part of water supply, together with the increasing precipitation and the descending evaporation, contributed to the enlargement of Nam Co Lake The roughly water balance analyses of lake water volume implied that, in two study periods (1971–1991 and 1992–2004), the precipitation supplies (direct precipitations on the lake area and stream flow derived from precipitations) accounted for 63% and 6192% of the whole supplies, while the glacier melting water supplies occupied only 855% and 1148%, respectively This showed that precipitations were main water supplies of the Nam Co Lake However, for the reason of lake water increasing, the increased amount from precipitations accounted for 4667% of total increased water supplies, while the increased amount from glacier melting water reached 5286% of total increased water supplies The ratio of lake evaporation and lake volume augment showed that 9571% of total increased water supplies contributed to the augment of lake volume Therefore, the increased glacier melting water accounted for about 506% of augment of the lake volume, which suggested that the increased glacier melting water was the main reason for the quickly enlargement of the Nam Co lake under the continuous temperature rising

Model and laboratory study of dispersion in flows with submerged vegetation

Abstract: [1] Vegetation is ubiquitous in rivers, estuaries, and wetlands, strongly influencing water conveyance and mass transport. The plant canopy affects mean and turbulent flow structure, and thus both advection and dispersion. Accurate prediction for the transport of nutrients, microbes, dissolved oxygen and other scalars depends on our ability to quantify the impact of vegetation. In this paper, we focus on longitudinal dispersion, which traditionally has been modeled in vegetated channels by drawing analogy to rough boundary layers. This approach is inappropriate in many cases, as the vegetation provides a significant dead zone, which may trap scalars and augment dispersion. The dead zone process is not captured in the rough boundary model. This paper describes a new model for longitudinal dispersion in channels with submerged vegetation, and it validates the model with experimental observations.

On the optimal design of water distribution networks: a practical MINLP approach

Abstract: We propose a practical solution method for real-world instances of a water-network optimization problem with fixed topology using a nonconvex continuous NLP (NonLinear Programming) relaxation and a MINLP (Mixed Integer NonLinear Programming) search. Our approach employs a relatively simple and accurate model that pays some attention to the requirements of the solvers that we employ. Our view is that in doing so, with the goal of calculating only good feasible solutions, complicated algorithmics can be confined to the MINLP solver. We report successful computational experience using available open-source MINLP software on problems from the literature and on difficult real-world instances. An important contribution of this paper is that the solutions obtained, besides being low cost, are immediately usable in practice because they are characterized by an allocation of diameters to pipes that leads to a correct hydraulic operation of the network. This is not the case for most of the other methods presented in the literature.

Effects of Groyne Layout on the Flow in Groyne Fields: Laboratory Experiments

Abstract: This research is aimed at finding efficient alternative designs, in the physical, economical, and ecological sense, for the standard groynes as they are found in the large rivers of Europe In order to test the effects of various groyne shapes on the flow in a groyne field, experiments were performed in a physical model of a schematized river reach, geometrically scaled 1:40 Four different types of schematized groynes were tested, all arranged in an array of five identical groyne fields, ie, standard reference groynes, groynes with a head having a gentle slope and extending into the main channel, permeable groynes consisting of pile rows, and hybrid groynes consisting of a lowered impermeable groyne with a pile row on top Flow velocities were measured using particle tracking velocimetry The design of the experiment was such that the cross-sectional area blocked by the groyne was the same in all cases Depending on the groyne head shape and the extent of submergence variations in the intensity of vortex shedding and recirculation in the groyne field were observed The experimental data are used to understand the physical processes like vortex formation and detachment near the groyne head It is demonstrated that the turbulence properties near and downstream of the groyne can be manipulated by changing the permeability and slope of the groyne head It is also observed that for submerged conditions the flow becomes complex and locally dominated by three-dimensional effects, which will make it difficult to predict by applying depth average numerical models or by three-dimensional models with a coarse resolution in the vertical direction