Abstract:
The objective of this study was to develop a functional model of a given water distribution system (DMA 802) of Dhaka city which can be used to simulate different water supply management options effectively. In this context calibrated functional model analyses have been carried out for water distribution system of the selected DMA of Dhaka city.
In the process of developing and calibrating the functional water distribution model, the first step was to collect hydraulic and as-built data for the given water distribution system. The next steps involved skeletonisation of the hydraulic model for the DMA 802 using as-built information, adjustment of calibration parameters to a computationally acceptable level. The final step was preparation of the calibrated model which would be used as a functional model.
For calibration of a water distribution system, pipe roughness was considered as the primary calibration parameter in this study. In addition, pump curves were also adjusted for model calibration. Models were simulated considering the starting roughness coefficient (C) value of 110 and modified at each simulation at an interval of 5. The model output and observed data (from six observation points) matched within a reasonable extent for C value of 140 for HDPE pipes.
A sensitivity analysis on DMA 802 conducted by varying the roughness coefficient (C) resulted in a negative system pressure for C values up to 70 due to significant values considered for old pipes. However, as expected, the calibrated model predicted a significant rise in system nodal pressure for newly installed (as-built) pipes considering C values of 100 to 150 reflecting less pipe roughness. As anticipated, model output and the observed data at locations further away from the nodal points with installed flow meters did not show very good match. This may be improved by installing in-line flow meters within the grid.
The calibrated model may be used as a functional model to analyse different hydraulic scenarios and water quality analysis such as: analysis of water demand management, analysis of water sources management, analysis of valve management and water quality analysis etc. However, installation in-line flow meters at various nodal points of the DMA will ensure more accurate calibration resulting in better assessment of flow, eventually providing a reliable tool for establishing a better DMA system.
