مدل سازی و تحلیل هیدرولیکی شبکه توزیع آب شرب شهرک بزین شهر شیراز

Analyzing water distribution networks is very important under deficiency of fresh drinking water. Careful analysis of urban water supply systems has been much highlighted than before due to water scarcity and water crisis. Analysis of a water distribution network means that the hydraulic characteristic of a water suppling network should be evaluated to test the efficiency of the water supplying network in delivering water to the determined locations. Indeed, the main goal of construction of a water distribution system is to effectively deliver fresh drinking water to consumers with appropriate quality, quantity, and pressure over time. A high quality water distribution system should consist of some main features including: provide acceptable water quality that should not get deteriorated in the distribution pipes network; supply water at all the intended places with sufficient pressure head and sufficient amount of water during firefighting; be designed in a way that no consumer experiences water supply shut-off during maintenance of any part of the system; and also contain fairly watertight to reduce losses due to leakage.
In this paper, the Bezein water distribution network, located in west of Shiraz, Iran, with a total area of 77 hectares and the occupied area of 34 hectares, with 1907 connection and population of about 7,600 was selected as the case study. The network was simulated with WaterGEMS software. The WaterGEMS is multi-platform software which can model hydraulic and water quality of water distribution systems with the options of advanced interoperability, geospatial model-building, optimization, and management tools. The Bezein town is provided with a 150-millimeter diameter main pipe diverted from a 300-millimeter diameter pipeline that supplies drinking water for Shiraz city. The Bezein water distribution network includes pipelines with diameters of 150, 110, 100, 80 and 63 millimeters, which are made of asbestos, polyethylene, and PVC. An electromagnetic flow meter has recorded the discharge and pressure head of the entering flow to the Bezein town every 15 minutes. Based on the measurements, 471261 cubic meters of water with a pressure head of 60 meters entered the water supply network during 2012, indicating the per capita flow of 170 liters per day. Modeling water distribution system was performed by assigning required amount of water demand to each joint (water delivery location), based on appropriate monthly and hourly demand factors after introducing pipeline network plan of the Bezein water distribution network to the WaterGEMS software. The model has been calibrated according to 8 measured joints in the network with the root mean square error of 6.8 meters of water head. The results of model, including the hydraulic parameters of the water distribution network such as water discharge, velocity of flow in pipes, pressure of flow at joints, energy line, and hydraulic grade line, have been simulated during 2012 in every hour after calibration process.
Analysis indicates that the flow velocity was lower than 0.3 meter per second in more than 95 percent of pipes in the water distribution network, in August as the maximum consumption time of year. The flow velocity of 0.3 m/s is the minimum recommended velocity to prevent sedimentation in pipes of water distribution network based on standards. However, velocity of flow in all of the pipes of the network was lower than the recommended amount in the minimum consumption time of the year according to model analysis. Simulation have shown that pressure head in more than 50 percent of the joints was more than 50 meters which is the recommended pressure value in water distribution network. Low velocity in pipes increases the probability of sedimentation and, on the other hand, the high value of pressure head in pipes leads to leakage and will increase the risk of stress fracture in peak pressure hours of the water distribution network. According to analyses of hydraulic parameters, lack of optimized hydraulic condition in this network is possibly due to the use of high-diameter pipes as large as 150, 110, 100 and 80 mm. Results of this study express the necessity of determining hourly and monthly demand factors in terms of exact consumer needs for designing an optimal water distribution network and also emphasize analysis of water distribution systems with the Extended Period Simulation method, in order to evaluate and modify current problems.