Jean Berlamont

The characterisation of cohesive sediment properties

Abstract This paper describes apparatus, techniques and methods used by participants in MAST G6M project 4 (Cohesive Sediments) for determining cohesive sediment properties. This comparison of methods aims to stimulate a more general discussion on standardisation of techniques which will lead to characterisation of muds in terms of physical parameters. Such characterisation would allow inter-comparison of muds from different sources. Methods are given for sediment properties of grain size distribution, settling velocity and rheological parameters and for water-bed exchange properties of permeability, effective stress and critical shear stress for erosion and deposition. Accuracy and repeatability are discussed. A typical range of values is indicated for each of these parameters.

The effect of rainwater storage tanks on design storms

Abstract The effect of source control measures on the design of combined sewer systems can in most cases only be correctly assessed using the intrinsic temporal rainfall variability, because long antecedent periods can have an important influence. A conceptual model was built to assess the effect of rainwater tanks on the rainfall runoff using long term historical rainfall series. The outflow of the rainwater tank model is converted to equivalent rainfall series. Based on intensity/duration/frequency-relationships (IDF-relationships) for this equivalent flattened rainfall, modified design storms are developed.

Modelling of dissolved oxygen and biochemical oxygen demand in river water using a detailed and a simplified model

Abstract Different model types are available to model catchment surface water quantity and quality. They vary from detailed physically‐based models to simplified conceptual and empirical models. The most appropriate model type for a certain application depends on the project objectives and the data availability. The detailed models are very useful for short‐term simulations of representative events. For long‐term statistical information and as a management tool they cannot be used. For that purpose more simplified (conceptual or meta) models have to be used. In this study, dissolved oxygen (DO) and biochemical oxygen demand (BOD) dynamics are modelled in a river in Flanders. BOD sources from agricultural leaching and domestic point sources are considered. Based on this input, concentrations of DO and BOD in the river water are modelled in Mike11 (river modelling software from DHI Water & Environment). Advection and dispersion were taken into consideration, together with the most important biological and chemical processes. Model calibration was done on the basis of available measured water quality data. A more simplified model was calibrated to this detailed model, with the objective to yield more easily long‐term simulation results which can be used in a statistical analysis. Two aspects of adequacy of model results are highlighted, namely accuracy and model speed. The conceptual simplified model is 1800 times faster than the Mike11 model. Moreover, the two models have almost the same accuracy. The construction of the simplified model is, however, only possible using simulations with the detailed model. The detailed and the simplified model have to be used in a complementary way.

Modelling and forecasting of hydrological variables using artificial neural networks: the Kafue River sub-basin

Abstract A simple reservoir routing scheme is applied to the available hydrometeorlogical data from the Kafue River sub-drainage basin in Zambia to derive flow contributions from the ungauged parts of the basin. The derived flow series and the time series of historic flow measured at the Kafue Hook Bridge (KHB) are separately modelled using artificial neural networks (ANNs). For each of these two flow series, relevant input variables are determined with the help of input—output intercorrelations, where inputs are given to a host of three-layer feedforward back-propagation (FF-BP) ANNs to predict the current, derived flow or KHB flow. A couple of ANN models selected on the basis of defined criteria are then used to forecast the flows at m time steps ahead. To evaluate the forecasting performance of the best ANN models, comparison with best autoregressive moving average models with exogenous inputs, ARMAX, is made. In both cases the ANNs give more robust forecasts over long terms than the ARMAX models, thereby making ANNs a viable alternative in flow forecasting.

Rainfall input requirements for hydrological calculations

Rainfall is the most important input for many hydrological and hydraulic design calculations. Ideally, long historical rainfall series should be used and a statistical analysis should be performed on the hydraulic results afterwards. In combination with the detailed models that are commonly used nowadays, this leads to huge calculation times. This research was set up in order to verify which kind of simplifications can be made with respect to the rainfall input. One must find an optimum between accuracy of the modelling results and calculation effort. This optimum can be different for different applications. The different types of rainfall simplifications which are considered here are composite design storms, short selected rainfall series and modified single storm events. In many cases the optimum is more likely a simplified model in combination with continuous long term simulations. Well-calibrated (physically based) simplified models can reach almost the same accuracy as the corresponding detailed models within a fraction of the calculation time. Furthermore, these simplified models are very useful in order to select or compose the proper rainfall input for detailed modelling.

Coastal Evolution of the Upper Adriatic Sea due to Sea Level Rise and Natural and Anthropic Land Subsidence

The Upper Adriatic basin has experienced in recent times continuous changes due to the precarious setting of the coastal environment and the low ground elevation above m.s.l. of many coastal areas. Major events which may influence the future stability of the beach profile include the natural and anthropic land subsidence, the sea level rise caused by the climate global change, storm surge and wave set-up, and the reduced littoral sediment transport. In the CENAS project all these events are addressed and simulated with the aid of ad hoc numerical models, and the modeling results are used to predict the Upper Adriatic Sea coastal morphodynamics in the next century. The models are integrated and implemented into a GIS together with a large database of all the essential information and records needed for the analysis. These data concern geometry, geology, hydraulics and meteorology of the basin, and the related input parameters. The area investigated by the project is 350 km long and comprises three local sites south of the Po river delta (Ravenna, Cesenatico and Rimini) where a detailed coastal study has been performed. The results indicate that a general regression of the beach is to be expected in the next decades, mainly in the area south of the Po river delta, due to mean sea level rise and land subsidence, and that a large portion of the present coastal lowland is potentially flooded in 2100 during severe meteo-marine events. The basin as well as the local risk maps of inundation have been built using the GIS and some indication is given as to the locations where major coastal defence actions are to be undertaken in the years to come.

Flood Regulation by means of Model Predictive Control

In this chapter flooding regulation of the river Demer is discussed. The Demer is a river located in Belgium. In the past the river was the victim of several serious flooding events. Therefore, the local water administration provided the river with flood reservoirs and hydraulical structures in order to be able to better manage the water flows in the Demer basin. Though this measures have significantly reduced the floods in the basin, the recent floods in 1998 and 2002 showed that this was not enough. In order to improve this situation a pilot project is started with as main goal to regulate the Demer with a model predictive controller. In this chapter the results of this project are discussed. First a simplified model of the Demer basin is derived based on the reservoir model. The model is calibrated and validated using historical data obtained from the local water administration. On the one hand the resulting model is accurate enough to capture the most important dynamics of the river; on the other hand the model is fast enough to be used in a real-time setting. Afterwards, the focus will be shifted to the model predictive controller. The use of the model predictive controller will be justified by comparing it to other control strategies used in practice for flood regulation. Then, the more technical details of the model predictive controller will be discussed in more detail. Finally the chapter will be concluded by historical simulations in which the model predictive controller is compared with the current control strategy used by the local water administration.

A hindered settling model for the prediction of settling and consolidation of cohesive sediment

The prediction of the settling and consolidation behavior of mixtures of cohesive and non-cohesive sediment is possible using a numerical model that solves the solids mass balance for each fraction. Consistency with the hindered settling theory as well as classical soil mechanics is preserved. Semi-empirical relationships for settling rate and effective stress as a function of density are required as constitutive equations. A simple procedure, using settling column experiment data, for calibration is proposed. The possibility of distinguishing different kinds of particles allows prediction of layered deposits.

Storm Wave Simulation in the Adriatic Sea

When strong winds are blowing over a long fetch, high waves with a lot of energy are generated. In the Adriatic Sea, the Scirocco storms are marked by a steady south-easterly wind, which lasts for a few days. In the northern part of the sea, this results in powerful swell waves. They are very important for morphological effects during such a storm. The WAM wave model is used to hindcast the wave field during one of the historical Scirocco storms in the Adriatic Sea. At the local sites of Ravenna, Rimini and Cesenatico, the wave characteristics are determined. These are used for the morphological study during the storm. At several points in the Northern Adriatic Sea, the wave field is computed in order to estimate the wave set-up, which is needed to estimate the extreme high water elevation. The Scirocco storm is chosen from a set of selected historical storms. Using its pattern, the 1, 10 and 100 year storms are estimated. Each of these storms is simulated for the bathymetry at present and in the year 2050 and 2100. The bathymetry changes due to subsidence and sea level rise. The extreme water level at the local site of Ravenna is used to determine the return period of the storm.

In Sewer Sediment and Pollutant Transport Models

Several commercial software providers offer in addition to their hydrodynamic urban drainage modeling software a tool for water quality modeling. Yet these quality modeling tools are not common practice in urban drainage design. Prior to start using these quality modules it is of paramount importance to have an insight into these models in order to know what these models (can) do (and cannot do) and how they could be applied. The paper shows the results of a thorough analysis of the quality components of two widely spread hydrodynamic models, namely Mouse (DHI Software, Denmark) and HydroWorks / InfoWorks CS (Wallingford Software, United Kingdom). The focus will be on how both models deal in a different way with the same problem, namely in sewer transport of sediments. The analysis reveals that the adequacy of the quality modules is not as high as compared with the hydraulic model. Care should be taken when using these models. Especially in the case of insufficient field data, the generated results must be analyzed with care and attention. A case study illustrates how the InfoWorks CS software can be used to model the transport of ammonia nitrogen.