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  • 1. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 46 VALIDATION OF DESIGN NORMS OF MULTI-VILLAGE WATER SUPPLY SCHEMES A.Raja Jeyachandra Bose1 , Dr.T.R.Neelakantan2 , Dr.P.Mariappan3 1 DGM/Water&Infra, Fichtner Consulting Engineers (India) Pvt. Ltd, Chennai and Research Scholar, SASTRA University, Thanjavur, TN. 2 Professor, School of Civil Engg., SASTRA University, Thanjavur, TN. 3 TWAD Board, 6A, Balasubramanian Nagar, Rajakkapatty, Dindigul-4, TN. ABSTRACT Trend in the method of providing community water supply scheme is changing with time due to various reasons. Depending upon the availability of safe source, schemes from hand pump to multi-village schemes are chosen. Most preferred option among the consumers is to have a multi-village water supply scheme from a perennial river source. Lot of such schemes are in operation and maintenance in the state of TamilNadu, which is generally a water-starved state. Reliability, cost, and sustainability of such schemes mainly depend on the design norms being adopted during project planning. Due to recent origin of the concept, no standard guidelines are available. A critical evaluation of the design guidelines has been done and suggestions made. Key Word: Multi-village water supply scheme, design guidelines, reliability, cost. INTRODUCTION In general, various schemes are being followed for providing drinking water supply to communities. Open well with manual drawal method was the oldest system. Hand pumps fitted in bore wells were introduced during seventies followed by individual power pump (IPP) scheme. Groundwater is the only source for all the above schemes. Due to increase in demand & drawal and reduction in ground water recharge activities, ground water table is fast depleting, coupled with deterioration in quality, making the ground water sources as non- reliable. To overcome the same, reliable surface water sources are being tapped and a new JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (JCIET) ISSN 2347 –4203 (Print) ISSN 2347 –4211 (Online) Volume 1, Issue 1, July-December (2013), pp. 46-56 © IAEME: www.iaeme.com/jciet.asp JCIET © IAEME
  • 2. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 47 concept of combined water supply scheme (CWSS) was formulated two decades back, to supply water to multi villages from a common source. Number of such schemes have been installed and brought into beneficial use in various parts of Tamilnadu, drawing water from river sources such as Cauvery, Vaigai, Tamirabarani etc., To name a few, CWSS to 674 habitations in Trichy district, 829 habitations in Thiruvarur and Nagapattinam districts, 3163 habitations in Ramanathapuram district are based on the above concept. Hogenakkal Water Supply and Fluorosis Mitigation Project, being implemented now, plans to cater to the drinking water requirement of 6755 rural habitations in Dharmapuri and Krishnagiri districts. Design norms adopted in the planning of such CWSS are mainly governed by the following factors: Configuration Per capita supply Velocity of flow Design Population Pipe material Capacity of Storage (Sump and Service Reservoir) System of Operation and Maintenance & Cost Performance reports on the functioning of CWSS always indicate a handful of un- served habitations, at any point of time, due to various reasons. Even though the planning and design is made to ensure simultaneous supply to all beneficiaries, it is observed that the planned objective could seldom be achieved during the operation and maintenance of the scheme and the system do not behave as expected. In most of the schemes, principle of operator based operation is being followed during O&M period to ensure supply to all beneficiaries, which solicit attention for all the factors listed above for validation. This paper critically reviews the above factors. Configuration Configuration of the scheme shall be decided with special reference to the O&M needs of the scheme. While finalizing the configuration, capacities and location of water treatment plant, booster stations, balancing reservoirs etc shall be fixed considering the O&M needs also. In practical, cost factors namely capital cost and maintenance cost (ie., per capita cost and cost per kilo litre) are given priority during project planning with least importance for the above factors. Sustainability and reliability are also to be considered in addition to the above aspects during the planning stage. Locating the water treatment plant (WTP) at the highest contour in the project area and gravitating water to all the villages from the Master Service Reservoir (MSR) is a common practice of configuration. A typical arrangement of a CWSS with Balancing Reservoir (MBR) near WTP is shown in Figure 1 below:
  • 3. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 48 Figure 1 - Model configuration of a CWSS Instead of gravitating water from single MSR to elevated service reservoirs (ESRs) located at the beneficiaries, it is preferable to locate zonal balancing reservoirs (ZBRs) at suitable locations i.e at the center of the group of villages. ZBRs may be fed by separate pumping mains from the clear water sump at WTP, if topography warrants or water may be conveyed from the MBR by gravity to the ZBRs (Figure 2). The WTP shall preferably be located close to a habitation so that the operation and maintenance staff will not hesitate to reside with their families in the quarters. Figure 2 - Configuration with ZBRs W T P MSR ESR 180 160 140 200 ZBR W T P MSR ESR 180 160 140 200
  • 4. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 49 Pipelines from MBR/WTP to ZBRs should be more reliable and accordingly the pipe material and joints should be chosen. Diameter of the pipe shall be fixed based on economical analysis. In the first configuration (Figure 1) many habitations will suffer without supply if breakdown occurs at any location whereas in the second configuration, only 2 to 3 ESRs would be left sans supply. The reliability of supply to all villages from MBR/WTP is quite equal as reliable pipe material is proposed upto ZBRs. In this case, the pipe sizes will be relatively less ensuring easy maintenance. It is preferable to have different outlets for the villages located in different directions (Domkondwar, 2000). Each ZBR should be located in such a way that the single outlet shall cover not more than four ESRs in the region where the gradient is higher. In plain areas, this shall be preferably less than 10. The topography of Tamil Nadu very rarely permits gravity system and most of the CWSS incorporate rising/pumping mains with or without boosters as shown in figure 3. Booster locations are decided based on the static head and length. Figure 3 - Configuration with booster station Each booster station may cover around 10 to 15 kms of length and about 100 meters of head. Number of villages (ESRs) included along the main and booster stations may vary according to the level difference. Residual head difference between the ESRs located in lowest and highest elevations should be less than 5 meters. Height of ESRs shall also be suitably fixed satisfying the residual pressure requirements. Booster stations in treated water pumping mains may be limited to two stages. Third stage pumping can be resorted to when a few tail end villages are to be covered. Mother tank concept has recently attracted the practitioners in this field due to its inherent merits. Mother tank is nothing but a storage tank which acts as buffer storage to absorb flow from the MBR during low consumption period and feeds the ZBRs during peak hours or any break down in the mains. Water coming from MBR will be collected in mother Source Sump cum Pump House Booster Booster Booster 100 180 220 300
  • 5. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 50 tank when the ZBRs are getting filled up one by one. It is an additional storage to ensure reliability. This concept is preferable for 24X 7 distribution plan. Schematic representation of the Mother tank is shown in figure 4. Figure 4 - Model configuration with mother tank LWL (Lowest water level) of MBR is to be fixed higher than the MWL (Maximum water level) of mother tank. MWL of all ZBRs is to be lower than the LWL of mother tank. Site selection / staging of mother tank is to be chosen / fixed accordingly. All the ZBRs should be provided with automatic flow control valve synchronized with the MWL. ESRs can also be suitably integrated with mother tank instead of ZBRs if situation demands. Per Capita Supply CPHEEO manual on water supply and treatment recommends per capita water supply levels for designing schemes. It varies from 40 lpcd to 150 lpcd depends on the classification of towns / habitation. CWSS are proposed to benefit both urban and rural communities, predominant one being the rural areas. During planning of such schemes, existing local sources are also taken into account and the final suggested demand from the proposed scheme is in the order of 15 lpcd or so. Pipe sizes are reckoned for the corresponding flow based on the optimization calculation and minimum pipe size consideration. In such a scenario, the carrying capacity of the proposed pipes is grossly under utilized. The impact of per capita supply on cost of installation is analyzed by considering a model scheme with ten habitations, which is listed in Table 1 below: MBR ZBR ZBR ZBR ZBR ZBR ZBR Mother tank
  • 6. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 51 Table 1 Requirement at various per capita supply levels Requirement (lpm) for various supply levels Habitation Per Capita Supply (lpcd) 15 25 40 Int Ult Int Ult Int Ult 1 7 9 12 15 19 24 2 4 5 7 8 11 13 3 12 13 20 22 32 35 4 17 19 28 32 45 51 5 8 9 13 15 21 24 6 8 9 13 15 21 24 7 10 13 17 22 27 35 8 13 17 22 28 35 45 9 7 9 12 15 19 24 10 11 14 18 23 29 37 Total 97 117 162 195 259 312 The requirement in lpm for each habitation is tabulated for various supply levels (lpcd). Total length of pipeline considered is 10 kms. Based on the pipe sizing arrived at, the installation cost works out to Rs.10.02, 12.82 and 14.48 lakhs for the supply levels of 15, 25, 40 lpcd respectively. Cost versus per capita is presented in figure 5 below and it is observed that the increase in cost is 25 % for the rise in supply level from 15 lpcd to 25 lpcd and 13% for 25 lpcd to 40 lpcd. Further it is also observed that only a marginal increase in pump capacity is required with no change in pipe size. Figure 5 - Per Capita Supply Vs Cost 9 10 11 12 13 14 15 10 15 20 25 30 35 40 45 Per Capita Supply Installation Cost, Rs. in lakh
  • 7. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 52 Velocity of flow Velocity of flow is an important factor which decides the pipe size and the carrying capacity. Regarding the maximum and minimum allowable velocities in conveying mains, it is generally suggested that the minimum shall be above the silting velocity and maximum shall be below the scouring velocity, and no specific value is suggested by any manual/guidelines. As the continuity equation mainly governs the flow, carrying capacity increases with the increase in velocity of flow for given diameter of pipe. In the optimization of rising mains, a compromise between velocity and frictional loss is generally considered. Velocity of the corresponding pipeline which yields the most economical cost considering all factors is considered and hence the optimum velocity varies with schemes. Figure 6 - Optimum Velocity A study of optimum velocity for 16 different water supply schemes, which is arrived at based on economical analysis is depicted in Figure 6 above. It is observed that the optimum velocity is in the range of 0.65 to 1.20 m/s. It is in agreement with the value of 1 m/s, as reported by Domkondwar. By selecting appropriate velocity of flow, the following advantages can be reaped: Reduction in pipe size and corresponding capital cost Ease in commissioning of the scheme and easy O & M Reduction in aging of water & maintaining residual chlorine & D.O For a particular CWSS, installation cost was studied by varying the velocity and the same is depicted in Figure 7 below: Figure 7 - Cost of scheme with velocity range A B C S1 0 10 20 ALTERNATE COST Rs IN CRORE A- Velocity - 0.20- 0.57 m/s B- Velocity - 0.40- 0.71 m/s C- Velocity - 0.65 - 1.20 m/s 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 SCHEME NUMBER V E L O C I T Y m /s
  • 8. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 53 Lesser velocity will consume more time for water to reach the tail end beneficiary. Quantum of water leaking will also be more during non-supply hours in the large diameter pipes. Velocity ranges obtained in the optimum size analysis (A, B, and C), indicate that the least cost combination results in the velocity range of 0.65 to 1.20 m/s. Estimation of optimum velocity and the computation of corresponding frictional losses in the conveying system are very important. Among the practicing engineers, Hazen Williams and Darcy Weisbach formulae are being used for the estimation of frictional loss in pipeline. The formulae and its merits and limitations are discussed below: Hazen William’s formula: V = 3.83 C d0.6575 * ( gs )0.5525 / ν 0.105 Where V- Velocity in mps, C- pipe roughness coefficient, d - Pipe diameter, g - acceleration due to gravity, s - slope, ν - viscosity of liquid Limitations of Hazen William’s formula: Widely followed Hazen William’s formula has its own inherent limitations. Numerical constant in the formula (0.849 in SI units) is arrived at based on the hydraulic radius of 1 foot and friction slope of 1/1000. Hence it is appropriate to use the same for the diameter and slope in that range. If the same is used for other ranges, it may result in an error of up to ±45% in estimation of frictional head loss. The formula is dimensionally inconsistent, since the Hazen-Williams C has the dimension of L-0.37 T-1 and therefore, is dependent on units employed. Further it is independent of pipe diameter, velocity of flow and viscosity. However to be dimensionally consistent and to be representative of friction conditions, relative roughness of pipe and Reynolds’s number or viscosity need to be accounted for. Darcy Weisbach’s formula: S = H/L = f V2 /2 g d where H- head loss due to friction over length L, f- Dimensionless friction factor Merits of Darcy Weisbach’s formula: The formula is dimensionally consistent. Applicable parameters i.e. velocity and diameter are included. The formula used in combination with Colebrook-White equation for ‘f’ value takes into account relative roughness and Reynolds’s number, which in turn includes viscosity. So, it is important to adopt appropriate equation to estimate velocity and corresponding friction loss. Design Population Population forecast is usually done to arrive at the design population for the project. Various methods are recommended by CPHEEO for this purpose. Average of forecasted population by arithmetical increase method, geometrical increase method and incremental increase method is generally adopted as design population. Sometimes, large variation in design population, ie., 5 to 6 times the base year population, is observed. But, these are to be restricted judiciously to 2 to 3 times of base value. Population density map may be used for the distribution of expected population in the project area. Anticipated growth of population shall be distributed to developed plots as well as vacant plots.
  • 9. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 54 Table 2 Population forecast statement Sl. No. Name Projected Population & Year As per census Year Base Year Year Int. Year Year Ult. year 2001 2009 2012 2021 2027 2036 2042 1 Gajanur 1474 1476 1477 1486 1495 1514 1530 2 Gajanur Agrahar 2172 3240 3783 6167 8738 15273 22665 3 Halle Honapura 794 877 936 1196 1441 1931 2358 4 Hosa Honapura 5 Hosahalli 2190 2435 2536 2871 3120 3537 3844 6 Lakshmi pura Total 6630 8028 8732 11720 14794 22255 30397 A case study for the population projection method and its observation is presented above in Table 2 wherein population forecast of six villages are listed. Actual survey was done during 2009. Various methods were used for the projection. The results obtained shows that the ultimate population for the village Gajanur Agrahar is about 10 times the 2001 census. In this case, a judicious decision, i.e 5 times the base year population may be considered for planning. Pipe Material Reliability of any piped water supply system mainly rests with the pipe material used. Major classifications of the pipe material are metallic and non-metallic. Choice of the pipe material is mainly influenced by the cost of the project. Materials such as asbestos cement, which are predominantly used earlier, are totally abandoned now. On the other hand, cost of certain pipe materials is becoming relatively cheaper due to improvement in manufacturing process and other influencing factors. Among the two options, metallic pipes are considered to be more reliable. Type of pipe joints is also playing an important role in the performance of the piping system. There are cases where the system failed due to improper selection of type of joint. For example, selection of socket and spigot joint with rubber rings for pipes laid underground in black cotton soil. Hence suitable pipe material and pipe joints are to be chosen considering reliability and cost. Capacity of Storage Component (Sump and Service Reservoir) Capacity of the storage structures such as sump is generally arrived at based on the CPHEEO norms and hours of pumping proposed. Capacity of the service reservoir is fixed based on mass curve analysis or design norms according to population. Cost of sump and SRs for five schemes and the total cost are tabulated in Table 3 below:
  • 10. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 55 Table 3 - Cost of Storage Component (Sump/SR) Vs Total cost Name of Scheme Cost of Sumps/SRs Rs Crore Total Cost Rs Crore Percentage 1 7.64 53.00 14 % 2 4.22 110.43 4 % 3 2.88 39.02 7 % 4 0.15 0.81 18 % 5 0.14 0.81 17 % It is observed that the share of above components in a project is in the range 4 to 17 percent, which is less than 1/5th of the project cost. Reliability of the system can be vastly improved if higher capacities of storage are considered. Another practical constraint observed is the lack of space for capacity addition of storage tanks in future for up-gradation of the distribution and conveying system, particularly in dense urban areas. Hence it is preferable to consider a higher capacity accordingly. Donkondwar suggested 12 hours capacity for service reservoirs and 4 hours capacity for ZBRs. In case of gravity system, higher capacity sump/SR results in containment of non-revenue water due to wastages during non-supply hours. System of Operation and Maintenance Simultaneous supply to all service reservoirs is the major design parameter invariably adopted in the design of all CWSS. But this is seldom achieved, particularly in major CWSS covering hundreds of habitations, due to various reasons. In such cases, water supply is ensured by the following ways: Operator based operation & Provision of head dissipating / boosting devices In operator based operation, the operator starts closing the control valves, one by one, controlling the flow to end reservoirs. Mostly, the valve is closed when SR starts overflowing. In such a scenario, the actual hydraulics of the system totally differs with that of the design stage, which is based on simultaneous flow to all SRs. But such typical cases are not analyzed while finalizing the design. Hence, it is always necessary to check the flow conditions for the operator based operation situation, which are designed otherwise. Cost Overall cost of the project includes cost of the source, conveying system, storage system and distribution system. Percentage cost of the conveying system versus the total cost for some projects are depicted in Figure 8 below:
  • 11. Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print), ISSN 2347 –4211 (Online), Volume 1, Issue 1, July-December (2013), © IAEME 56 Figure 8 - Percentage of Cost of pipeline It is observed that the conveying system absorbs 43 to 89 percent of total cost of the project. Hence more emphasis is to be paid while planning. A minimum of three alternatives shall be worked for choosing techno-economical option. CONCLUSION Proper planning and design is a pre-requisite to implement sustainable and reliable CWSS projects. Suitable configuration with judicious population forecast forms the base for proper planning. To ensure high reliability, proper material and joint is to be chosen. Velocity around 1.0 m/s will generally yield an economic combination of conveying mains. Higher capacity of storage structures will greatly influence the reliability of the system, which accounts for less than 20 % of cost of scheme. System of operation and maintenance of the project needs to be taken into consideration during project formulation stage itself. Monitoring and evaluation of performance of the schemes in operation shall be a continuous process and the feed shall necessarily be transferred to the planning table for proper review of the design guidelines adopted. REFERENCES 1. “Manual on Water Supply and Treatment”, Central Public Health and Environmental Engineering Organization, Ministry of Urban Development, Government of India, New Delhi, 1991. 2. Domkondwar, M.V., “Configuration of Regional Rural Water Supply Scheme for effective operation and maintenance”, Journal of IWWA, Vol. XXXIV, No: 4, PP: 261- 271, 2000. 3. Mariappan, P., “Rejuvenation of Rural Water Supply schemes – An experience”, Journal of IWWA, Vol. XXXIV, No: 1, PP: 1-3, 2002. 4. Pramod R. Bhave and Rajesh Gupta, “Design, Performance and Operation of Regional Rural Water Supply Systems”, Journal of IWWA, Vol. XXXIV, No: 4, PP: 273- 278, 2002. 1 2 3 4 5 6 7 8 0 10 20 30 40 50 60 70 80 90 SCHEME NUMBER PERCENTAGE COST OF PIPELINE TO TOTAL COST