New concept for optimized flushing of potable water networks< Back

BMBF 02WT0618
DVGW W 6/03/05

Abstract:

The discolouration of water in distribution systems is one of the most frequent reasons for quality based customer complaints. To avoid the problems and to raise the quality of the distributed water, flushing in an optimised interval is an efficient tool. Below the development of a model for the determination of optimised flushing intervals and the conversion in a programme is described. This programme, in combination with the algorithm to determine the necessary data base, enables to flush each pipe in a distribution area before a critical deposit level is reached.

The model is based on the results of investigation in different network investigation areas, which were flushed four times in half or one yearly interval, and on the results of trials with a test rig DN 80. The test rig includes 3 pairs of test pipes. The pairs cover in each case an old cast iron pipe (originating from one of the investigation areas) and a lined comparison pipe with similar roughness and diameter.

With the results of the trials on the test rig DN 80 it was possible to define a general method to differentiate between the deposit rations of input by load and by corrosion. This method is based on a network specific iron/manganese ration and allows a ratio specific calculation of the deposit growth.

In the next step the temperature influence of the deposit formation by corrosion was determined. Based on the differentiation method of the deposit ratios, the consideration of the temperature influence raises the accuracy of the deposit growth calculation.

Furthermore, the investigations showed a general link between the maximum daily flow conditions and the maximum possible deposit level, which is also the critical level. Considering this it was possible to define an algorithm for the calculation of the critical deposit level, depending on the thickness of the viscose sub layer at the maximum daily flow conditions.

The algorithm for the calculation of the critical deposit level, the method to differentiate the deposit ratios and the factor for the temperature influence for the deposit caused by corrosion was included in the model. Together with results of a hydraulic simulation and defined area specific measurements, the calculation of the optimised flushing intervals can by carried out in the calculation programme, which runs as a stand-alone version and could be linked to each hydraulic simulation software.