Marc Huygens

The erosion of cohesive mixed deposits: implications for sewer flow quality modelling.

Abstract The movement of sediments in sewers has been widely recognised as being strongly linked with poor sewer flow quality. Currently, empirically calibrated transport capacity relationships are used to estimate the movement of in-sewer sediments. The majority of these relationships were developed and calibrated with laboratory data sets that used uniformly sized granular sediment. In many combined sewers, there are both organic and inorganic sediments. The fine-grained organic sediments are thought to be able to develop considerable cohesive strength under certain conditions. This paper describes the results from laboratory experiments in which the erosion of non-homogeneous in-pipe sediment deposits was investigated. The types of sediment mixtures used ensured that a range of cohesive deposit strengths was developed. The measured bed load and suspended load were compared with transport capacity relationships currently used for sewer design. Significant divergence between the transport capacity predictions and experimental observations was discovered. It was seen that it is unwise to model in-sewer deposits as homogeneous and granular and that it is important to take into account the impact of deposit cohesion.

Physical Model Study Of A Vortex SeparatorOverflow

A detailed research project is set up to validate a vortex separator overflow construction. In this vortex separator, collected sewer water enters radially from the sewer pipe in a cylindrical inner reservoir. The passage flow to the treatment plant is situated in the bottom centre, while the overflow passes a radial weir into an outer shell reservoir. In a laboratory model the removal efficiency of this overflow structure is identified for several hydrodynamic flow operation modes by recording sediment redistribution over the structure. As a result of these series of experiments on a model of a vortex separator overflow, the efficiency of this kind of construction is identified as a function of both hydrodynamic parameters and lay-out features. Doing so, the vortex separator is introduced as an alternative overflow construction to control and manage combined sewer overflow (CSO)-events, leading to a less negative operation impact of combined sewer systems on the receiving waters.

Waterhammer protection with air vessels - A comparative study

As pressurized liquid transport systems need to be protected against waterhammer phenomena, different kinds of protection devices can be applied. Each of them has its own characteristics and advantages. In the whole scope of protec-tion installations, air vessels certainly offer the best guarantee for safe pipe line operation under variable conditions. To meet all operational conditions different types of air vessels are commercially available. The most important ones are the classical air vessel with gas bubble, eventually equipped with a rubber balloon and with a single connection to the main pipe; the classical air vessel with double connection which acts as a flow through system. In a more recent ver-sion of an air vessel, the normally isolated air bubble can be connected to the atmospheric pressure, again with a single or a double connection pipe (AARA-vessel). The principles and typical working schemes of all these types of air vessels are identified and briefly discussed. Based on some practical examples the application field of each type is defined and illustrated. Relevant design parameters are put in evidence

Design Of A Smart Sand Trap Construction As APart Of An Interregional Environmental Study

The Mark-Vliet river system transports bed material and heavily polluted suspended sediments to the Volkerak-Zoom lake. To protect the living, working and recreation areas in this catchment, a proper integrated water management is essential. A systematic control and sanitation of the polluted sediments in the river environment will help to stop the further degradation of the water system quality. Therefore, a transboundary collaboration between Belgian and Dutch authorities is set up to study and sanitate this interregional river catchment. To improve the water and river bed quality, an effect-oriented as well as source-oriented approach is followed. The inventory of pollution sources is translated into a sanitation plan for the competent authorities. The effect-oriented approach searches an optimum design and location of sand trap configurations in the catchment. As pollutants are mainly fixed to the fine suspended material, it is valuable to separate the relatively clean sand particles from the heavily polluted fine fraction. Hence, the amount of polluted (silt and mud) dredged material and consequently the treatment costs are reduced. Starting from an existing sand trap configuration, an adapted construction is designed through physical scale model tests taking into account the practical and economical issues of the project. The operation of the optimum sand trap configuration relies on three basic principles: an upstream bifurcation ensures a proper deflection of suspension transport in a parallel deviation; a downstream sill controls the flow distribution over the respective main and deviation branch for different regimes; an underwater sill at the entrance of the lateral deviation forces the transport of all sand material near the bottom into the sand trap. Transactions on Engineering Sciences vol 9,

Air Entrainment In Water Hammer Phenomena

In common waterhammer design, a detailed two-phase flow calculation is too demanding to preserve a handsome numerical tool. Nevertheless, implosion of gas or air bubbles in pressurized conduits introduces extra shock waves. As a result, possible fatigue corrosion or pipe instability strengthen the safety demands. Air inlet valves as a protection device enter air into a pipe system, by this reducing the transient wave celerity and the magnitude of the shock wave. Therefore, the impact of air entrainment on the waterhammer phenomena is studied to reveal its relative importance. Detailed calculations with an extended two-phase model reveal only small differences in absolute underpressure values in comparison with the traditional one-phase waterhammer design calculations.

Flume Experiments Of Sediment TransportIn Unsteady Flow

Adapted equipment of a test flume with semi-circular cross-section controls and measures flow and friction characteristics during the transient regime. A series of sediment transport measurements under unsteady flow conditions is performed for two types of non-cohesive material. Due to the inertia of the bed material, theres no agreement on form or time appearance between the unsteady friction velocity and the bedload transport. On the other hand an instantaneous relation between bedload transport and the friction velocity calculated with a steady state formula is revealed. The suspended material has obviously less inertia. Nevertheless suspension transport is also put proportional to the steady part of the friction velocity. A time shift, increasing with the unsteady character of the flow, appears between suspension transport and the steady part of the friction velocity. As a result, these experiments indicate the complex nature of unsteady sediment transport phenomena and initiate a fundamental understanding of these complex processes. Transactions on Engineering Sciences vol 18,

A computer controlled coastal scale model

To study the influence of underwater screens on near-shore sediment transport, a new single multitasking program is written to run on an AT 80286 based computer equiped with an electronic data-acquisition card. The program generates different coastal tidal cycli in a wave tank and concurrently registrates the relevant model parameters. These show that the imposed tidal sequences are closely followed in the model. Care has been taken to make the program as flexible as possible.