Interaction of river hydraulics and vegetation dynamics

The universities of Ghent and Antwerp are investigating the impact of the vegetation on hydraulic characteristics of the river Aa (Antwerp, Belgium) and the Bierbza river (Poland). In these areas the interaction between groundwater, surface water and vegetation will be studied.In a first phase of this multidisciplinary study, the influence of the vegetation on the flow resistance in the stretch is examinated. Introducing the effective roughness of the bottom and the banks of the river into hydraulic computations is not that easy, but important. Different expressions for the roughness coefficient are available, each with their own restrictions. Certainly when plants occur in the channel and reduce the flow area, determination of the roughness coefficient is difficult. Simultaneousley, flood forecasting and other impacts of changing water levels and flows, ask for an accurate hydraulic model. Modelling summer situations with winter data and vice versa imply problems.The roughness coefficient of the river, as used in the Manning formula, is influenced by the vegetation. Further more, the Manning coefficient is also linked to the water velocity and the discharge. The kind of correlation is determined by the vegetation type.Field measurements are carried out to collect data on discharge and stage and on the amount and variation of aquatic weed growth. Velocity measurements in multiple cross sections are performed with both, a hydrometric propeller and an electromagnetic device. Further more, leakage or seepage from the groundwater influences the water balance and has to be included. Several measurement campaigns on both rivers allow to determine the variation of the friction factor (Manning n) as a function of time, vegetation and distance and the important hydraulic parameters, and all the information can be related to each other.Following a seasonal cycle, flow resistance increases with plant growth in spring, reaches a maximum in early summer and then decreases slowly to the minimum in winter. Knowledge of the variation of the biomass as a function of time should lead to appropriate use of roughness coefficients in modelling surface flow in rivers

Flood routing in the river Aa using ’Femme’

The software ’Femme’, (a flexible environment for mathematically modelling the environment) is developed by the Netherlands Institute of Ecology (NIOO)(Soetaert et al., 2004) and is used for the modelling of ecological processes. Femme’s code is open source and works on a modular base. The implementation of a one dimensional hydrodynamic model into ’Femme’ to study the interaction between ecological processes and surface water flow as a driving force and the validation using field measurements is subject of this research. For example, the presence of macrophytes has an influence on the discharge by way of the entire roughness of the river, expressed by the Manning coefficient.River hydraulics is characterised by changing discharges and water levels due to rain fall, so studies have to take into account the non-permanent character of the flow. In a first phase, the river characteristics and the simplified Saint-Venant equations have been built into the model. The simplification to the parabolic and the kinematic equations allow a faster and easier solution. The parabolic model is known as the convection-diffusion equation and describes the translation, deformation and attenuation of a wave in open channels and is valid for stretches with mild slopes. The kinematic model doesn’t take into account the flattening of the wave and can only be applied in short stretches.Calculation results are presented by the variation of the discharge as a function of distance. Also the influence of the roughness coefficient is shown.The integrated study of ecological processes and surface water flow is situated in a multidisciplinary research were attention is paid to the interaction of groundwater, surface water and the ecological system in order to describe the transport of matter through river basins (Buis et al.,2005). An important study area is the river Aa near Poederlee (Belgium, Flanders, province of Antwerp), were discharge, grondwater and biomass measurements are carried out on a regular base, to perform studies in the field and to collect calibration data for the integrated hydraulics and ecology model

Nail surface topography and onychochronobiology.

Peer reviewe

Quantification of the groundwater-surface water interaction by analysing temperature gradients in the streambed of the Aa river, Belgium

The aim of this research is to gain better insight in the diverse physical and biological processes in margins, inundation areas and the hyporheic zone of water courses on a local scale. Data and results presented are from a multidisciplinary study on exchange processes in river ecosystems in which biologists, hydrologists, ecologists and engineers cooperate.Groundwater and eco-biochemical models are integrated in order to determine the exchange of water, dissolved compounds and particulate matter. Several of these processes occur simultaneously and result in feedback to other processes; hence most of the investigations aim to determine net rates of exchange. GIS is used for data management, while FEMME (Soetaert et al., 2002) serves as a platform for the integration of the different models such as MODFLOW, DAFLOW, Delft3D, and WetSpa.An innovative but cost-effective method for field investigation is the measurement of streambed temperatures profiles, which lead to a delineation and quantification of the groundwater discharge on a local scale. For the Aa River site in Belgium, a typical low land river system, combinations of longitudinal and cross-sectional measurements of temperature profiles have been conducted. Along a 1400 m long section, 5 vertical measurements of up to 80-100 cm deep into the river bottom have been performed bi-monthly between August 2004 and February 2007 at 14 measurement points and 5 cross-sections. With this information we assessed the vertical component of the groundwater flux and the spatial and temporal variability of the groundwater-surface water exchange.A streambed temperature survey does not lead directly to an estimation of the groundwater flux. Additional information, especially thermodynamic parameters of the soilwater matrix are necessary.The groundwater fluxes were calculated as point values at the measurement locations on basis of an analytical solution presented by Arriaga et al. (2006), and which is solved with the help of Microsoft Excel Solver and MATLAB. The fundamental heat flow equation was also introduced in a diagenetic model, setup in FEMME and used to compare with the Arriaga et al. (2006) solution. Interpolation of the point estimates results in net groundwater fluxes on the scale of the surveyed area. These results show discharge as well as recharge dependent on the location along the section and the season. The upper reach shows in general higher discharge rates and no change in direction of the groundwater flow, whereas the lower reach is characterized by lower flow rates and a change of direction of flow

Regional integration of long-term national dense GNSS network solutions

The EUREF Permanent Network Densification is a collaborative effort of 26 European GNSS analysis centers providing series of daily or weekly station position estimates of dense national and regional GNSS networks, in order to combine them into one homogenized set of station positions and velocities. During the combination, the station meta-data, including station names, DOMES numbers, and position offset definitions were carefully homogenized, position outliers were efficiently eliminated, and the results were cross-checked for any remaining inconsistencies. The results cover the period from March 1999 to January 2017 (GPS week 1000-1933) and include 31 networks with positions and velocities for 3192 stations, well covering Europe. The positions and velocities are expressed in ITRF2014 and ETRF2014 reference frames based on the Minimum Constraint approach using a selected set of ITRF2014 reference stations. The position alignment with the ITRF2014 is at the level of 1.5, 1.2, and 3.2 mm RMS for the East, North, Up components, respectively, while the velocity RMS values are 0.17, 0.14, and 0.38 mm/year for the East, North, and Up components, respectively. The high quality of the combined solution is also reflected by the 1.1, 1.1, and 3.5 mm weighted RMS values for the East, North, and Up components, respectively

Regional integration of long-term national dense GNSS network solutions

The EUREF Permanent Network Densification is a collaborative effort of 26 European GNSS analysis centers providing series of daily or weekly station position estimates of dense national and regional GNSS networks, in order to combine them into one homogenized set of station positions and velocities. During the combination, the station meta-data, including station names, DOMES numbers, and position offset definitions were carefully homogenized, position outliers were efficiently eliminated, and the results were cross-checked for any remaining inconsistencies. The results cover the period from March 1999 to January 2017 (GPS week 1000-1933) and include 31 networks with positions and velocities for 3192 stations, well covering Europe. The positions and velocities are expressed in ITRF2014 and ETRF2014 reference frames based on the Minimum Constraint approach using a selected set of ITRF2014 reference stations. The position alignment with the ITRF2014 is at the level of 1.5, 1.2, and 3.2\ua0mm RMS for the East, North, Up components, respectively, while the velocity RMS values are 0.17, 0.14, and 0.38\ua0mm/year for the East, North, and Up components, respectively. The high quality of the combined solution is also reflected by the 1.1, 1.1, and 3.5\ua0mm weighted RMS values for the East, North, and Up components, respectively