Experimental Study Of The Foreign Intrusion Events In Water Distribution Systems

Urban water supply system is an important urban infrastructure, providing basic guarantee for the development of social economy and people’s entertainment and life. When low or negative pressure events occur in the water supply network, pollutants surrounding the pipeline may intrude into the pipe through sealing leaks or other defects under the action of low or negative pressure, leading to the water quality decline, and endangering the public health. The volume of intrusion pollutants is an important indicator for the evaluation of the contamination degree of these pollution incidents. So it has a great significance for the risk assessment and prevention of these incidents to estimate the intrusion volume associated with low or negative pressure events accurately and quickly.Firstly, the physical model test based on volumetric method was improved and an experimental apparatus was built. The low or negative pressure events was induced by sudden valve closing. The experimental apparatus could simulate various leakage points with different sizes and external pressure head, and the test condition of the initial flow rate, internal pressure head and valve closing time control was under adjustment and control.Secondly, two groups of experiments associated with low or negative pressure events were carried out, one was with foreign intrusion and the other was not. The pressure change was recorded in real time by the data acquisition system. Two characteristic values (the maximum pressure drop value and the duration of negative pressure) were introduced to analyze the low or negative pressure events. With the characteristic values, the contrast analysis of the experimental results of the two groups and the analysis of factors influencing low or negative pressure events were both conducted.Thirdly, according to the experiment with foreign intrusion, the intrusion volume was determined by using the volumetric method, and the correlation of between the intrusion volume and the initial flow rate, valve closing time, upstream distance, size of leakage points and external pressure head was analyzed systematically.Finally, according to the data of the pressure and intrusion volume associated with low or negative pressure events, two empirical formulas were fitted for the calculation of the maximum pressure drop value and the duration of negative pressure, respectively. And on this basis, an empirical formula of the intrusion volume was also fitted. Then, by using the empirical formula, the complete curves of the intrusion volume versus the size of leakage points were drawn and a critical value of the size of leakage points was put forward.