Mathematical Models for Pollution Control in the Usk Estuary

Abstract

The now Usk River Division of the Welsh National Water Development Authority was required to make several major policy decisions on water quality within the Usk Estuary. These were highly relevant to a series of large capital projects and , after a public enquiry » the Secretary of State for Wales required a scientific investigation to be initiated that would rationalise the method of arriving at the decisions. The process of biological degradation of pollutants would have to be understood. A number of models were reviewed » and also the attitude to the use of models by representatives of the public and management. Three types of models were developed for differing requirements of the overall management function : a Steady State Model for approximate trends that could be available quickly and can be adapted for use in economic/cost models, a time dependant multi-dimensional model for considering short term effects and dissipation of perturbations (pollution 'incidents') » and a semi-stochastic/deterministic model to utilise field data and generate realistic confidence limits on management projections. The models were so formulated as to be flexible and as interchangeable as possible. A number of projected capital plans were simulated by management for load variants and flow reductions. Problems were encountered because of the rapidity of the worlds second largest tidal rise, the antiquity of Newports drains system and the sometime overriding influence of the Severn Estuary. Telemetric monitoring proved inefficient because of field conditions. The awareness of management was developed in the appreciation of modelling and computing, to self sufficiency if required. Many routines were provided for the routine interpretation of data by the Pollution Control Department. The need for common modelling policy was recognised by WNWDA and these models were to be made available nationally through the Water Data Unit of the Department of the Environment for access at divisional level as an aid to management.