Developing a dynamical system model for an urban aquifer –Wadi system

Urban waste water production increases day by day and its safe treatment and disposal need efficient procedures. In many areas, such effluents are discharged to open water bodies such as lakes, rivers and sea coastal areas. Since there are no perennial streams in arid and semi-arid regions the disposal of treated outfalls is often to dry wadis. However developing an understanding of complex urban systems, where processes act at different space and time scales, is not easy. Dynamical systems approaches have been used for many years in complex feedback systems. So in this work the use of dynamical system modelling is investigated to see if this approach can help develop at least in semi-quantitative way an understanding good enough to aid managers of urban water systems where wadis are involved. The approach taken was to develop a flow and then a solute transport model for the urban system of Riyadh City - Wadi Hanifah. The softwares used was ‘Stella’, and a representation of two aquifers, two soil systems, the sewerage system, the water supply system, the non-urban catchments and the urban drainage system was set up and run using daily meteorological data for about 20 years. The model was compared with limited field data on water levels, flows, flooding, and water quality and modified until results were consistent with field data. Model was then investigated by looking at effects of changing a wide range of hydrogeological and other parameter values, including pipe leakage rates, rainfall, and water supply rate