To overcome the shortfalls in distribution of water, AMC proposed (2005-06) a Scheme of Augmentation of City Water Supply termed as “Parallel Water Supply Scheme” at an estimated cost of Rs.359.67 crore under Urban Infrastructure Development Scheme for Small and Medium Towns (UIDSSMT). Unfortunately AMC failed to provide water supply services and achieve the prescribe
In order to overcome various challenges, it was decided to develop a freshly designed water supply system for the entire city. The first task was to make GIS maps and then to create hydraulic model of existing and the new pipelines.
Following were the solutions proposed to improve water supply of city from Intermittent Water Supply to 24×7 Continuous Supply
- GIS Mapping
Often, it is observed that water utilities in the country do not have proper maps of water distribution pipe network due to apathy. Available drawings are manually sketched. Aurangabad water supply department had only one Auto CAD drawing of the existing distribution system but it was non-spatial. Water utility needs to prepare base maps. For creation of such maps, a satellite image with 0.5 m resolution is procured. This image is vectorized (digitized) for roads, buildings and water bodies etc. Pipe alignment survey is carried out and water infrastructure is then mapped on the geo-referenced base maps.
- Creation of Hydraulic Model
Hydraulic model is defined as “a process of creating a representation of an actual water supply system by using computer software.” Before the hydraulic model was invented, engineers had varied opinions of the distribution system just like the story of seven blind men who each had a different perception of an elephant. Old engineers were taking decisions based on rule of thumb and based on their own personal experience. However, after advent of the hydraulic model, engineers now know exact hydraulics of the pipe network.
- What Happens Inside GIS Based Hydraulic Model?
A. Pipe network consists of two types of equations – continuity equations and energy equations. Continuity equations are of linear nature whereas energy equations are non-linear. Because of heterogeneous nature (linear and non-linear), traditional statistical methods are unable to solve these equations. Therefore, many methods, such as Hardy-Cross, Newton Raphson, Global gradient methods have been in use to solve the network. Water GEMS software uses Global gradient method to analysis water network. Generally, a matrix of size equal to the number of pipes in the network is created inside the hydraulic model and then this matrix is solved by the computation engine of the hydraulic model software. For the sake of example, distribution system of the Aurangabad city with 1.2 million population, has 24,000 existing and proposed pipes in its distribution system. The hydraulic model created by the authors solved this huge size of matrix in each run of the model while making the design. The hydraulic model gives satisfactory answers about the hydraulic behavior (computation of flows in pipelines and pressures at each node) of the system using sound mathematical computations. For effective planning, execution and maintenance of the 24×7 water supply systems, hydraulic model simulating the system is a paramount activity. Unplanned and haphazardly laid pipelines are redesigned, refurbished and rehabilitated using hydraulic model.
B. Use of Existing Pipes
Out of existing pipes in the distribution system of a total length 790 kms, most of the pipes (650 kms) are of GI and non-metallic material. The rationale that is thought of is to discard old and leaking AC, PVC and GI pipes. Moreover, database of existing pipes with exact maps are required to prepare the GIS based hydraulic model which is used to design the system. Hence, the existing metallic pipes such as CI, DI and MS pipes are retained.
C. Giving Elevations and Demands to Nodes
GIS Contours are generated from the 3D stereo paired satellite image of Aurangabad city. This satellite image of 0.5 m resolution is obtained from National Remote Sensing Authority, Hyderabad. Elevations to each node are given using Terrain Extractor (TREX) utility of the WaterGEMS. In the absence of a consumer survey, demand to the nodes is given by the population density method. Land use land cover maps are obtained from the city development plan. The forecast of population is carried out and the population of next 15 and 30 years is distributed ward wise taking into consideration of the likely growth of the city. A GIS layer of the wards with population density is created in Arc GIS software which is used to give demands to the nodes by means of the Load Builder facility of the WaterGEMS. Thus, the basic hydraulic model is now ready.
4. Insufficient Number of Service Tanks
There are 66 existing tanks in the Aurangabad city, out of which 22 tanks are having less staging height and because of this flaw, these tanks cannot produce 12m residual nodal pressures, and therefore, they are abandoned. In addition to this, capacity of the existing tanks is insufficient, 11 tanks are either old sumps or ground service reservoirs. Hence, only 33 tanks are considered in the new design. The operational zones of these 33 existing tanks are optimally designed.
5. Design of Operational Zone
The existing distribution system of Aurangabad city is not functioning properly as it is found that proper operational zones are not designed at all. An operational zone is a service area in which water is supplied and distributed by a tank. Major problems with the existing distribution system network are (a) capacity of the tanks is not enough to cater the demand of its earmarked service area (operational zone) and (b) service tanks are found remaining empty or found overflowing. The transformation process into 24/7 system needs proper design of operational zones. Solution Suggested: It is desirable that the tank serving the particular zone neither gets empty nor overflows and should has sufficient capacity. The principle that is used for fixing the proper boundary of the operational zone is shown in Figure 1.
After carrying out the above exercise, it is found that a large area is unserved by the existing tanks. Therefore, 41 new tanks were needed to be designed.
5.1 A Scenarios of each Operational Zone
A scenario is a specific possibility. To plan an operational zone of existing and new tanks is a scenario. There is one built-in default scenario called the Base scenario. The base scenario is created for the entire city. Additional child scenarios from the base scenario are planned for each tank. These child scenarios reference the alternatives needed to perform and recall the results of each of your calculations. ‘Alternatives’ are the building blocks of scenarios. There are 15 different alternatives in WaterGEMS which are specific categorized data sets. In each scenario, the alternatives are placed together. Input data in the form of records is embedded in each alternative. In the model of Aurangabad three types of alternatives – active topology, demand and operational are used to form a scenario. Active topology is a powerful tool in WaterGEMS that is used to create the pipe network. A topology is called as the study of geometrical properties and spatial relations of the features like pipe, nodes, valves, tanks and reservoir etc. A topology of these features is created in the hydraulic model for entire city. Active topology is a tool that can make active or inactive a particular part of the pipe network. For example, in base scenario, entire pipe network is made active, however, in child scenario, it is required to make active only those pipe network that take part in computation.
6. Creating DMAs
District metering area (DMA) is a building block of any 24×7 water supply system. It is defined as a discrete area of a water distribution network. It is usually created by closing boundary valves or by permanently disconnecting pipes of adjoining areas. Bulk meter and Flow Controlling Valve (FCV) are installed at the entry point of each DMA. Difference of the volume of water that is coming into DMA and the volume of water consumed by the consumers gives value of NRW of the DMA. 185 such DMAs have been created for Aurangabad city. DMAs are so designed that there are on an average about 1,000 to 2,000 customers in each of them.
7. Design of Pipe Diameters
Steady State Method is used to design pipe sizes. Demand of 30 years is given to all the nodes and with a peak factor of 2 a model run is taken. Design is prepared in such a way that the velocity of flow is within 1.8 m/s and the residual nodal pressures are at least 12m. Darwin Designer is used to make optimum sizes of the pipes. Principle of optimization technique is shown in Figure 2.8. Large Number of Isolation Valves
The existing system of Aurangabad city has a large number (2,600) isolation valves which are operated by a large number of valve men. Thus, control of the operation of the distribution system becomes difficult. Solution Suggested: There is a facility in WaterGEMS software which makes use of “criticality analysis”. This feature has been used to determine optimum number of isolation valves.
9. Equitable Distribution of Flow and Pressure
A typical arrangement of water supply of the operational zone with two DMAs is shown in Figure 3.A tank supplies water to the two DMAs – DMA-1 and DMA-2. At the entry of each DMA, one isolation valve followed by a bulk meter and then flow control valve (FCV) along with pressure gauge are provided. This type of arrangement with FCV is necessary to regulate the flow into each DMA strictly as per the demand of that DMA. Pressure gauges help to monitor the pressures.
Submitted by Dr. Sanjay V. Dahasahasra
Dr. Sanjay V. Dahasahasra is a former Member Secretary of Maharashtra Jeevan Pradhikaran, Mumbai. He is former national President, Indian Water Works Association, Mumbai. He is post graduate (M. Tech.) in Environmental Engineering. In 1986, he was awarded Ph. D. degree in the field of water treatment. He has published 51 research papers and is a member of many organizations