water supply

Handbook on Works Audit -Water supply

Office of the Principal Accountant General (Civil Audit) Chennai

1

HANDBOOK ON

WATER SUPPLY



2 Water Supply and Treatment

1. PREAMBLE

Tamil Nadu Water Supply Drainage board (TWAD) is responsible for execution

of Water Supply Schemes / Drainage Schemes in Corporations, Municipalities, Panchayats, Villages in the entire State of Tamil Nadu except Chennai City where Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) is executing the work.

Government of India Ministry of Urban Development, Central Public Health and Environment Engineering Organisation published a Manual known as " Manual on Water Supply and Treatment ". This Manual has laid down the basic principles relating to planning, identification of sources of water, development and transmission, water treatment, distribution system testing and other related administrative aspects and also explain in details the proper approach to each problem.

The salient points relevant to audit together with various orders of Government and TWAD Board and audit approaches are given below. The CPHEEO Manual provisions indicated are with reference to the 1999 Publications.

2. PROJECT FORMULATION The objectives of any Water Supply System is to supply safe wholesome water in

adequate quantity at convenient points and at reasonable cost to the users. In order to encourage personal and household hygiene proper planning is necessary in the formulation and implementation of water supply projects.

Engineering decisions are required to fix the area and population to be served, the design period, the per capita water supply, the water required for the other needs in the area, the nature and location of facilities to be provided and points of water supply intake and waste water disposal.

Detailed investigation should be carried out in regard to nature of each source (surface or subsurface) its reliability for quality and quantity, the nature of development and type of treatment required and mode of the conveyance from the source to the consumers. Different alternatives should be considered in detail and the economically viable and technically feasible alternative should be selected by applying financial analysis techniques.

Four stages are involved in the formulation of a water supply project before the project is taken up for execution. They are

a. Preparation of preliminary report b. Conducting detailed Engineering survey



3 c. Preparation of Project Report. d. Preparation of detailed plans and estimates.

Preliminary report

The report should include a brief description about the topography, geological and hydro geological features of the community, existing water supply arrangement and need for the project. Further the report should discuss and include the following aspects also.

i. Identification of the area to be served with details of present population, existing water supply and sanitation facilities.

ii. Identification of the water requirement for various needs. iii. Estimation of water requirement for various needs. iv. Identification of the possible alternate projects and rough cost

estimation them (if possible) for installation. v. Details of engineering survey to be conducted and probable

time and personnel required for carrying out the survey. vi. Cost of the engineering survey.

An index map to a scale of 1 cm= 2km, a schematic diagram and a layout plan to a scale of 1 cm = 250m should be included in the report. Engineering Survey

The data required to be collected for the preparation of Project report initially and for the preparation of construction plans and detailed estimates later, comprises of the following.

i) Census population figures for the town for atleast five preceding decades.

ii) Present rate of water supply and factors that will affect future and industrial demand.

iii) Details of existing water supply and sewerage, electric and telephone facilities, the quality and quantity of existing water supply under average and adverse conditions and conditions of existing mains.

iv) Field survey and leveling work connected with source development, location for treatment plants, pumping stations and service reservoirs, alignment of transmission main and preparation of detailed maps for the distribution system with contours.

v) Master plan for that area. Further data to be collected for each of the component are as detailed below.

a. Surface sources i. Sanitary survey for 10 km upstream and 2 km

downstream of the proposed works to locate source of pollution, cremation ground etc.,

ii. Water sampling and quality analysis. iii. Minimum discharge in the river.



4 iv. Plan of river course 3 km upstream and 3 km downstream of the proposed off take.

v. Cross section of river upto and above MFL on either bank.

vi. Likely shifts of summer course of the rivers. vii. Sub soil details upto scour depth and hard strata.

b. Impounding reservoir i. Sanitary survey of entire catchment or atleast foreshore areas, existing

sources of pollution and possible pollution and remedial measures. ii. Survey of soil, vegetation and their effects on water quality. iii. Water analysis covering seasonal variations. iv. River flow or run off records, stream flow gauging, riparian rights. v. Continuous survey of water spread, dam alignment foundation details

and availability of materials. vi. MFL, LSWL and other particulars.

c. Infiltration works i. Quality of sub surface water. ii. Whether river is perennial? What is the lean surface flow in the

river? iii. A grid work of tell tale borings at 30-60m intervals for full width of

the river 120m upstream and 120m down steam, of the proposed site for infiltration works.

iv. Effective size and uniformity coefficient of sand at different depths. v. Maximum flood level and minimum summer water level. vi. Scour depth arrived at for the structures nearby constructed, by

PWD, Highways etc., d. Ground Water Source

i. Availability of ground water and its quality. ii. Geophysical survey to locate bores. iii. Examination of hydro geological and hydrological factors. iv. Topographical survey.

e. Pump houses and treatment works i. Topographical survey to decide the best location of treatment

plant. ii. Trial pit particulars and safe bearing capacity of soil.

f. Transmission main i. Alignment Plan ii. Longitudinal sections at 150m intervals, along the alignment. iii. Details of crossings of river, railway, road (National or State

Highways) iv. Trial pit particulars at 1 km intervals along the alignment (at closer

internal when there is vide variation) v. Safe bearing capacity of soil at level of pipe support.



5 vi. Soil analysis of soils met in the trench for indication of corrosiveness.

vii. Bedding or cushion to be provided at the bottom of the pipes depending on the type of soil met with.

g. Service Reservoir The following particulars are to be collected

i. Operational records to study storage requirements. ii. Highest elevation in the area of town are to be identified for

locating the Service Reservoirs. iii. Spot levels at site proposed for the Service Reservoir. iv. Contours of the town for dividing the area into numbers of zones. v. Foundation details. vi. Trial pit particulars to assess the safe bearing capacity of soil at the

site. vii. Maximum and minimum ground water levels.

h. Distribution System The following particulars are to be collected. i. Town map in the scale of 1:200 showing all streets with names. ii. Number of houses in each street, prospects of further development,

nature of houses, number of floors and height. iii. Kinds of roads. Such as concrete, BT, WBM roads iv. Town planning proposals. if any, with proposed approved layout. v. L.S. streets at 30m intervals. vi. Trail pit particulars at 500m intervals along the proposed

alignments vii. A plan showing the existing distribution lines, if available with year

of installation. viii The number of existing public fountains and existing house service

connection. i. Land plans

Survey Maps to be obtained from revenue authorities., SF Nos., Revenue classification of Land its ownership and cost of the land to be obtained for acquiring land for Service Reservoir, Pump house, treatment works. Project report

The administrative sanction for a project is to be accorded by the authority considering only the project report. The project report should therefore be prepared with great care incorporating adequate particulars like need for the project, details of engineering survey carried out, the alternate project evolved, their cost and merits etc.,

The following details are to be included in the project report. A narrative report describing the project with the following aspects. i. Historical retrospect leading to the demand of the project. ii. Short description of existing water supply facilities.



6 iii. Details of the different sources considered with their relative merits. iv. Raw water quality of the different sources and treatment envisaged. v. Engineering features of the head works and layout of the components

of head works. vi. Economic analysis for sizing of transmission main and Branch for

the conveyance of the water from the source to the community using ECP and Branch 3 Software.

vii. Capacity, and elevation and location of Service reservoirs. viii. Salient features of the distribution system like number of zones,

ground level variations in each zone. ix. Comparison of costs of alternatives and project as recommended.

The project report in a complete shape incorporating all the above details with estimates for installation of the project and for the annual operation and maintenance is to be submitted to the competent authority for according administrative sanction.

Preparation of detailed plans and estimates. On receipt of the administrative sanction to the project detailed hydraulic

design calculations for the distribution system using LOOP 4 Software and structural design calculations for the Service Reservoirs and other structures are worked out and the detailed working drawings are prepared in such a way that the construction of works are carried by the construction Engineers without any difficulty.

The following plans are to be prepared. 1. Index plan to a scale of 1 cm= 2 km 2. Schematic diagram and flow chart. 3. Detailed plans to a scale of 1 cm = 20m 4. Land plan schedules for Land Acquisitions. 5. Pert chart 6. Quarry map

The detailed bill of quantities, technical specification for each work, cost estimate for each component of works and abstract of total cost have to be prepared using COSTDAT and COMEST Software packages. For each estimate, a narrative report can be prepared and appended. The estimate is got technically sanctioned by the competent authority and only after the technical sanction, the project should be taken up for implementations. Conclusion

The formulation of a water supply project involves many phases of preparation and appropriate steps taken in all the phases will result in an economical and viable project. (TWAD Board Technical News letter July 1998 Manual on water supply & Treatment Chapter X of Manual for quality control on Water Supply works)



7

3. DESIGN & PLANNING 3.1. Objective (Para 2.1 Of CPHEEO)

The objective of a public protected water supply system is to supply safe and clean water in adequate quantity, conveniently and as economically as possible.

The water supply projects formulated by the various state authorities and local bodies at present do not contain all the essential elements for appraisal and when projects are assessed for their cost benefit ratio and for institutional or other funding, they are not amenable for comparative study and appraisal. Also, different guidelines and norms are adopted by the central and state agencies; for example, assumptions regarding per capita water supply, design period, population forecast, measurement of flow, water treatment, specifications of materials, etc. Therefore, the CPHEEO Manual on Water Supply & Treatment specify appropriate standards, planning, and design criteria to avoid empirical approach.

3.2 Basic Design Considerations (Para 2.2 Of CPHEEO)

Engineering decisions are required to specify the area and population to be served, the design period, the per capita rate of water supply, other water needs in the area, the nature and location of facilities to be provided, the utilization of centralized or multiple points of treatment facilities and points of water supply intake and waste water disposal. Projects have to be identified and prepared in adequate detail in order to enable timely and proper implementation. Optimization may call for planning for a number of phases relating to plant capacity and the degree of treatment to be provided by determining the capacities for several units, working out capital cost required, interest charges, period of repayment of loan, water tax and water rate. Uncertainties in such studies are many, such as the difficulties in anticipating new technology and changes in the investment pattern, the latter being characterized by increasing financing costs.

3.3 Design Period (Para 2.2.6 Of CPHEEO) Water Supply projects may be designed normally to meet the requirements

over a thirty year period after their completion. The time lag between design and completion of the project should also be taken into account which should not exceed two years to five years depending on the size of the project. The thirty year period may however be modified in regard to certain components of the project depending on their useful life or the facility for carrying out extensions when required and rate of interest so that expenditure far ahead of utility is



8 avoided. Necessary land for future expansion/ duplication of components should be acquired in the beginning itself. Where expensive tunnels and large aqueducts are involved entailing large capital outlay for duplication, they may be designed for ultimate project requirements.

Sl No. Items

Design period in

years 1 Storage by dams 50 2 Infiltration works 50 3 Pumping : i. Pump house (civil works ) 30 ii. Electric motors and pumps 15 4 Water treatment units 15

5 Pipe connection to several treatment units and other small appurtenances 30

6 Raw water and clear water conveying mains 30

7 Clear water reservoirs at the head works, balancing tanks and service reservoirs (overhead or ground level)

15

8 Distribution system 30 3.4 Population Forecast (Para 2.2.7 Of CPHEEO)

The design population will have to be estimated with due regard to all the factors governing the future growth and development of the project area in the industrial, commercial, educational, social and administrative spheres. Special factors causing sudden emigration or influx of population should also be foreseen to the extent possible.

A judgment based on these factors would help in selecting the most suitable method of deriving the probable trend of the population growth in the areas or areas of the project from out of the following mathematical methods, graphically interpreted where necessary. a) Demograph Method of population Projection:

This method takes into account the prevailing and anticipated birth rates and death rates of the region or city for the period under consideration. An estimate is also made of the emigration from and immigration to the city, growth of city area wise, and the net increase of population is calculated accordingly considering all these factors, by arithmetical balancing. b) Arithmetical Increase Method



9 This method is generally applicable to large and old cities. In this method the average increase of population per decade is calculated from the past records and added to the present population to find out population in the next decade. This method gives a low value and is suitable for well-settled and established communities. c) Incremental Increase Method

In this method the increment in arithmetical increase is determined from the past decades and the average of that increment is added to the average increase. This method increased the figures obtained by the arithmetical increase method. d) Geometrical Increase Method In this method percentage increase is assumed to be the rate of growth and the average of the percentage increases is used to find out future increment in population. This method gives much higher value and mostly applicable for growing towns and cities having vast scope for expansion. e) Decreasing Rate of Growth Method In this method it is assumed that rate of percentage increase decreases and the average decrease in the rate of growth is calculated. Then the percentage increase is modified by deducting the decrease in rate of growth. This method is applicable only in such cases where the rate of growth of population shows a downward trend. f) Graphical Method In this approach there are two methods. In one, only the city in question is considered and in the second, other similar cities are also taken into account. i) Graphical Method Based On Single City

In this method the population curve of the city (i.e. the Population vs. Past Decades ) is smoothly extended for getting future value. This extension has to be done carefully and it requires vast experience and good judgment. The line of best fit may be obtained by the method of least squares. ii) Graphical Method Based On Cities With Similar Growth Pattern

In this method the city in question is compared with other cities which have already undergone the same phases of development which the city in questions is likely to undergo and based on this comparison, a graph between population and decades is plotted. g) Logistic Method

The 'S' shaped logistic curve for any city gives complete trend of growth of the city right from beginning to saturation limit of population of the city. h) Method of Density



10 In this approach, trend in rate of density increase of population for each sector of a city is found out and population forecast is done for each sector based on above approach. Addition of sector-wise population gives the population of the city. Final Forecast

While the forecast of the prospective population of a projected area at any given time during the period of design can be derived by any one of the foregoing methods appropriate to each case, the density and distribution of such population within the several areas, zones or districts will again have to be made with a discerning judgement on the relative probabilities of expansion within each zone or district, according to its nature of development and based on existing and contemplated town planning regulations.

Wherever population growth forecast or master plans prepared by town planning or other appropriate authorities are available, the decision regarding the design population should take into account their figures.

Note: The calculation sheet for population forecast may be called for and the correctness of population forecast ensured. In TWAD Board, the population forecast was approved by CE concerned. A typical example is given in Annexure1.

In circular No.17/F.11168/JE6/P&D/2005 Dt.29.04.2005. TWAD Board had prescribed the following modus operandi for population projection for water supply and sewerage scheme for Rural and Urban Areas. For Urban :-

The population forecast cannot be generalized for all towns. * The ground reality and present developmental activities of the town and

future developments are to be considered during population forecast. * The population projection may be arrived through the following seven

methods on minimum four decade population and the best suitable among the derivations may be approved by the competent authority. Different method to be adopted for population projection for Urban Town:

i) Arithmetic Increase method ii) Incremental Increase method iii) Line of Fit Method iv) Geometrical Increase Method vi) Semi Log Method vii) Exponential Method viii) Decadal growth Rate Method for state / District average * For a normal town the projection arrived by exponential method is found is

to be reasonable and this method may be considered. * Justification note should be appended by the approving authority.



11 For rural :- Base year population (2006) = 1.03 time the 2001 census population Intermediate population (2021) = 1.10 time the 2006 population. Ultimate population (2036) = 1.20 times the 2006 population. Population Forecast before 2005:- (TWAD Board Circular No. 3 P&D/JE-6/2002 dt.08.04.2002.) For Urban:- Present population (2001) = population as per 2001 census Intermediate (2016) = to be arrived by different methods Ultimate (2031) with 2001 as the base year. For Rural:- Present Population (2001) = population as per 2001 census Ultimate population (2031) = 1.30 times of the present population. 3.5 Per Capita Supply (Para 2.2.8 of CPHEEO) Basic Needs

Piped water supplies for communities should provide adequately for the following as applicable:

(a) Domestic needs such as drinking, cooking, bathing, washing, flushing of toilets, gardening and individual air conditioning.

(b) Institutional needs. (c) Public purposes such as street washing or street

watering, flushing of sewers, watering of public parks.

(d) Industrial and commercial uses including central air conditioning

(e) Fire fighting (f) Requirement for livestock; and (g) Minimum permissible Unaccounted for water (UFW)

Recommended Per Capita Water Supply Levels for Designing Schemes.

Sl. No. Classification of Towns/Cities

Recommended Maximum Water Supply Levels (lpcd)

Table 2.1 CPHEEO Manual

1 Towns provided with piped water supply but without sewerage system

70

2 Cities provided with piped water supply where sewerage system is existing / contemplated

135



12 3

Metropolitan and Mega cities provided with piped water supply where sewerage system is existing / contemplated

150

Note:

(i) In urban areas, where water is provided through public standposts,40 lpcd should be considered:

(ii) Figures exclude Unaccounted for Water (UFW) which should be limited to 15%

(iii) Figures include requirements of water for commercial, institutional and minor industries. However, the bulk supply to such establishments should be assessed separately with proper justification.

Per Capita Water Supply Rate Prescribed by TWAD Board. 1 Rural habitations without house service connection (HSC) : 40 litres

2 Rural Habitation with HSC : 55

3 Town Panchayats (both Rural & Urban ) : 70

4 Municipalities : 90

5 Corporations : 120

3.6 Physical And Chemical Quality Of Drinking Water (Para 2.2.9 of CPHEEO)

The physical and chemical quality of drinking water should be in accordance with the recommended guidelines. The Parameters are given in Annexure II Audit Approach The objective of the Water Supply System is to supply safe and clean potable water in

adequate quantity conveniently and as economically as possible. Para 2.1 of CPHEEO Manual and also guidelines of the Board prescribes the per capita water supply to the designed period of the population forecast. But while evolving the CWSS/WSS towns and habitations already covered fully for ultimate stage through separate water supply scheme were included in the CWSS. The inclusion of those area already covered under separate Water Supply Scheme in the CWSS was superfluous, involving extra cost on creation of excess size and capacity of pumping main, sump, treatment plants, pumps and motor, etc.

By scrutinizing the details of the existing water supply to the towns, habitations included in the CWSS, we can notice the above type of audit observation.

By examining the water requirement estimate statement, it could be seen that bulk provision of water was made for many towns and habitations which were already



13 provided with Separate Water Supply Scheme and the ultimate stage of water supply had not been completed. In such cases, the necessity for such inclusion should be analysed. Many cases such bulk provisions were not warranted for and the provision of bulk provision remained unutilized which would increase the total requirement of water and ultimately increase the capacity of pumping main, treatment plant, sump, pump and motors, etc. involving extra cost.

A town may already been provided with water Supply Schemes for ultimate stage. To meet the shortfall if any, bulk provision was made in another CWSS which was under execution. In the meantime, another separate water supply improvement scheme was sanctioned and executed under another scheme. Thus cost involved in execution of the latter improvement scheme except cost on creation of distribution system was wasteful. This type could be brought out by close study of various water supply schemes & CWSS sanctioned and executed.

Duplication in creation of infrastructure due to formulating separate improvement scheme while existing scheme itself functioning well and had not completed its designed service life of 30 years (Ultimate stage).

Para 2.2 of CPHEEO Manual stipulates that the water supply projects shall be designed to meet the requirement for the population forecast at the prescribed per capita supply over a period of 30 years after their completion and prescribes the methods of forecasting the population during the period of design on the basis of latest census. Instead of designing the Schemes as per the provisions of the Manual, Water Supply Schemes sanctioned upto 2002 were designed taking base year as 1996/1991 and ultimate year as 2026/2021. This resulted in utilisation of infrastructure created for period much lesser than the prescribed 30 years.

Para 2.2.6 of CPHEEO Manual provides for designing Water Treatment units, clear water reservoirs at head works, balancing tanks (Sump) and Service Reservoirs of the Water Supply Projects for 15 years (intermediate Stage) to facilitate carrying out extensions when required and avoid expenditure far ahead of utility and interest on capital. But treatment plant, clear water sumps and service reservoirs were designed and constructed for 30 years (Ultimate stage). Thus creation of infrastructure far ahead of requirement was avoidable and wasteful.

Appendix 6.5 of CPHEEO Manual and PWD Code stipulates that the life of electric motor and pump is 15 years. As the electric motors and pump would lose their efficiency after 15 years of service life, erection of pump and motor for ultimate stage was wasteful and cost involved on execution of pump and motor for ultimate stage become wasteful.

Para 7.1 of CPHEEO Manual specifies the water treatment units which includes aerator, clariflocculator, filter, disinfector, softener, etc. The treatment plant constructed by Board comprised of those units. But they were constructed for ultimate requirements as against the intermediate requirements prescribed by CPHEEO Manual resulting in extra cost.

Clear water is collected in a sump before it is pumped to Service reservoir (vide Para 6.3.7 of the Notes on Water Supply Scheme issued by CE, PWD Chennai in 1971). Intermediate sumps are also constructed to reduce the pressure in the transmission main. The sump shall be designed for intermediate stage and its capacity depends on the discharge into the sump and detention time (discharge in lpm x detention time in



14 minutes). On a audit enquiry, the CE, TWAD Board, Southern Region, Madurai informed (November 2003) that the capacity of sump are designed generally for 30 to 60 minutes storage and storage period would vary depending on various factors such as hours of pumping, availability of power, and separate feeder main for power supply etc. Audit Scrutiny also disclosed that clear water sumps were designed for 15 to 180 minutes eventhough separate feeder main to provide 24 hours power supply was available and also constructed for the requirement of ultimate stage instead of intermediate stage involving extra cost.

Para 10.4.2 and Appendix 10.1 of CPHEEO Manual prescribes guidelines for estimation of storage capacity of the service reservoirs which depends on hours of pumping, demand and hours of supply, and shall be constructed for intermediate stage only. Para 19.3 of Notes on Water Supply Schemes issued by the Chief Engineer (PWD) Chennai in 1971 also indicates that the capacity of Service Reservoir is fixed on the basis of hours of pumping and the peak rate of supply. The peak rate of supply is usually taken to be twice the average rate and the capacity of service reservoir is fixed at 8 hours or one third of a days supply. The guidelines issued by Board in December 1982 also stipulated that the capacity of overhead service reservoirs in rural areas of a CWSS should be 50 per cent of the ultimate daily requirement of the individual habitation considering the limited hours of power supply. As such the capacity of service reservoir shall be one third of a days supply for intermediate stage in urban areas and half of the days supply for intermediate stage in rural areas of CWSS. But it is noticed that service reservoirs were designed and constructed for the requirement of ultimate stage instead of intermediate stage. In rural habitation covered under CWSS, the service reservoirs were designed and constructed for ultimate stage adopting the norms prescribed by Board in May 1998. For construction of overhead tank (OHT), service reservoirs in rural water supply power pump scheme which prescribed the capacity of OHT/SR on the basis of ultimate population of the range 150-500, 501-1250 and 1251-2500 at 10000, 30000 and 60000 litres capacity respectively. Construction of SR for ultimate requirement and also not observing the norms resulted in extra cost on construction of Service Reservoirs of higher capacity.

Para 2.2.8.3 of CPHEEO Manual recommends, per capita supply level for designing water supply schemes. The norms prescribed by Government of India under Rural Water Supply Schemes and also by Board in July 1998 stipulated for 40 lpcd. Whereas in case house service connection was provided for, it can be increased to 55 lpcd. But cases where all infrastructures were created adopting 55 lpcd, but house service connections were not effected subsequently. It should be verified whether specific undertaking was obtained from the local bodies before designing the CWSS adopting 55 lpcd. If not extra capacity involved could be objected to.

Cases where water supply scheme was designed adopting 1991 population as base year and actual requirement of the water in the initial reaches was not correctly worked. At the time of completion of the Scheme, the people in the initial reach would draw more water than the designed level. Cases of non-estimation of the actual requirement of water to the intended habitation were also available. Consequently water could not reach the tail end or intermediatary reaches. This necessitates laying far separate feeder main, intermediatary sump to regulate water



15 supply. The extra cost involved on this could be analysed and commented. This was due to poor investigation, defective design and execution and failure to assess the actual requirement before executing the work. DESIGN: Appendix 11.1 of CPHEEO Manual stipulated for designing the pumping main for 23 hours of pumping considering loss of one hour due to tripping and other minor interruption. Para 19.1 of the Note on Water Supply Schemes issued by the Chief Engineer (PWD), Chennai in 1971 also stipulates that pumping main can be designed to discharge 24 hours if service reservoirs are provided. In June 2002, Board had also instructed to design the CWSS for 20 hours of pumping if separate feeder main for power supply was provided. But with a view to provide cushion, pumping mains were designed for 16 to 20 hours pumping eventhough separate feeder main for power supply to pumping station connected with industrial line having 24 hours power supply. Due to reduction in hours of pumping the size of pumping main, pump sets and sumps had to be designed and constructed for higher capacity/size. Had 23 hours of pumping adopted, the discharge for the ultimate requirement would be much lesser and the infrastructures viz. Pumping main, Pump sets and Sump could have been designed and constructed at lesser capacity. NOTE: Upto 1998-99, TWAD Board had prescribed unit rate for various items of work which was dispensed with from 1999-2000 and comprehensive common Schedule of Rates for each items . Hence it is not possible to work out the extra cost on creation of assets for ahead of the requirement easily. Hence the unit rate prescribed by Board is adopted as basis from which the proportionate cost is worked out on the agreement value adopting ratio of proportion which would give the cost of construction of the required capacity of assets. The difference would give the extra cost. In letter No.101/P&D/98 dated 29.9.1998, TWAD Board communicated unit rates for various items of work for preparation of outline proposals for various components of urban and rural water supply schemes for the year 1998-99.



16

4. SOURCE OF WATER (Chapter 5 of CPHEEO Manual & chapter VII of Manual for Quality Control in Water supply works)

The sources for the water supply scheme are generally of the following two categories;

1. Surface water sources 2. Sub surface water sources

1.Surface water source Surface Water sources are from rivers lakes and reservoirs. The water from these sources are drawn and supplied the beneficiaries after proper treatment. If the river is not perennial, the storage of water is necessary for supplying during the dry period. Generally surface water is preferred for the following reasons.

1. When quality of ground water available in and around the beneficiary is not potable.

2. When large quantity of water is required for the scheme.

2. Sub surface water source In geological nature, Tamilnadu State can be categorized as hard rock areas, and sedimentary areas. The hard rock areas cover 73% area of the state and the sedimentary formations cover the remaining 27% area of the state. The sub-surface water is being tapped from the following sources.

1. Open wells 2. Bore wells 3. Infiltration wells and 4. Collector wells

2.1 Guidelines for location of infiltration well (TWAD Circular No

2/DO/P&D/2001 dt 5.2.2001)

The following procedures are to be followed in geophysical investigation for fixing up the location of an Infiltration well.



17 1.Resistively survey with geophysical equipment are carried out in grid pattern in the river bed/bank to assess the apparent resistively of the sub-surface strata and fixing location.

2.After conducting geo survey, probing is to be done to assess the sand depth where

the maximum is seen.

3. In the selected location of the probing where the maximum sand depth exist, the trial bore wells are to be drilled and soil samples analysed. The water sample should also be collected and analyzed for assessing the potability of water.

4. From the trial bore well, location of the proposed infiltration well have to be

located.

5. At the selected point, the confirmatory bore well to be drilled not only at the centre of the infiltration well but also in the periphery atleast six borewells.

6. Lithology of the trial bore wells should be prepared and the depth of the saturated

sand is analyzed.

7. The summer water level of the area of the investigation with reference to the saturated thickness is correlated.

8. The depth of the infiltration well depends on the saturated thickness of the area.

9. Yield from an infiltration well sunk for 3.5 m diameter in saturated aquifer of 4m

depth for a draw down of 2m is computed approximately as 1000 lpm.

10. The location of the infiltration well should be located in such a way to avoid interference between structures

2.2 Design criteria for Collector Wells

Collector wells with radial arms are generally proposed in river basins to tap maximum yield from deep saturated aquifer. This type of sources are proposed when the quantity of water requirement is very huge. Here also confirmatory bores have to be drilled to identify the depth of aquifer and to locate exact depth at which the radial arms to be driven.

Design Criteria

Diametre - 4 to 6 Thickness of well staining - 45 to 60cm Number of laterals - 8 to 16 (in radial directions) Length of laterals - 20 to 60m depending

(upon the saturated thickness of aquifer)

Size of laterals - 200 to 300mm dia slotted pipes.



18 Permissible velocity of flow in laterals - 0.06 mps Slot in laterals - 16% of the surface area of the laterals Note : The number, length and size of the laterals can be determined to obtain the required yield from the source.

3. Safe Yield

In all type of wells after completion of the construction, yield tests have to be conducted and safe yield has to be arrived after applying the correction factors. Depending upon the yield the required number of wells may be decided to supply the quantity required for the scheme. The CPHEEO Manual prescribes two types of safe ;yield tests for determining safe yield of the well viz. Pumping (Discharge) Test & recuperation test.

3. 1 Safe yield in Bore wells (Datamatrix of TWAD Board Engineers) For power pump schemes, the following multiplication factors have been evolved to arrive safe yield for the borewells drilled in hard rock area. When the yield test is conducted during summer months i.e. April August a factor of 0.9 may be adopted to the observed yield for determining the safe yield from borewell. For the yield tests conducted during other months a correction factor of 0.6 may be applied, for arriving at the safe yield. In case of Kanyakumari district the correction factor will be 0.9 for the months from March of June and it will be 0.6 for other months.

3.2.Pum ping Test (Discharge Test)

Pumping test is the most accurate, reliable and commonly used method to evaluate the hydraulic parameters of an aquifier, efficiency of a well, safer operational rates of pumping and selection of suitable pump. The methodology of a pumping test is highly varying in its application. The objective is limited to determine the aquifer parameters such as transitivity (T), Storage co-efficient (S), hydraulic conductivity (K) and well performance and safe yield for execution of water supply scheme. To study the parameters of transitivity, storage co-efficient and hydraulic conductivity, generally a constant discharge pumping test (aquifier performance test) is conducted. An aquifer performance test consists of pumping a well at certain constant rate and recording the drawdown both in pumping well and in the near by observation wells at specific times. To analyze the well performance, the step drawdown test (well performance test) is carried out. In step drawdown test, the drawdown in a pumping well is recorded at variable discharge in steps.



19 Efficiency of the well is the ratio of the critical drawdown (drawdown just outside of the casing) and actual drawdown measured in a well at a designed discharge of continuous pumping for a given period. Recuperation Test After the constant discharge test, when the pump is shut down, the water column in the well or borewell started rising. This rise in water column has to be noted in close intervals. The data collected on recouping water column will be useful to compute the aquifer parameters. Recuperation test are recommended for large diameter open wells. The bore wells/ open wells executed for major schemes are subjected to pumping tests. Pumping tests are also conducted before and after the hydro fracturing operations. Note:The result of discharge test of the well measured in V notch would be recorded in the prescribed table and the specific yield in lpm per cm of draw down derived from the table. This would be verified from the pumping test report and ensure safe yield of the well. In a similar manner specific yield obtained from Recuperation test in the well should be ascertained and the safe yield adopted by comparing both the report.

Minimum Distance of well from source of Contamination Contamination of Recommended Sources distances (in metres) Building sewer 15 Septic tank 15 Disposal field 30 Seepage pit 30 Cesspool 45

Audit Approach

According to the instruction of TWAD Board in B.P.No.75 dt.25.03.1990 various components of water supply scheme shall be executed after ensuring adequate quantity and quality of source. However, without ensuring the availability of adequate quantity of potable water, the pumping mains distribution system, overhead service reservoir etc work constructed resulting in unfruitful expenditure.

To ensure whether, sources (Borewell, collector well, infiltration well) created in conformity with the specification mentioned above. Analyze the failure to observe the guidelines and resultant financial and social objective implication.



20 Whether dependability and reliability of the source, quality of source ensured before creation of other infrastructures which ultimately resulted in wasteful expenditure on creation of infrastructures.

Whether proper investigation and test carried out to ensure reliable source to the designed quantity and factors affecting contamination of source which subsequently resulted in making the water not potable examined. The remedial measures proposed/taken has also to be analysed.

Whether permission was obtained from the District Collector/Water Utilisation Committee for drawal of water to the designed quantity.

5.Transmission of Water

(Chapter 6 of CPHEEO Manual) Water supply broadly involves transmission of water from the sources to the area of consumption through free flow channel or conduits or pressure main. Pipe line normally follow the profile of the ground surface quite closely. Gravity pipelines have to be laid below the hydraulic gradient. Pipes are of Cast Iron, Ductile Iron, mild steel, Prestressed concrete, reinforced cement concrete, GRP asbestos cement, plastic, etc. 5.1 Hydraulic of Conduits ( Pipe ) (PARA 6.2. OF CPHEEO Manual)

The design of supply of conduits is dependent on resistance to flow, available pressure or head allowable velocities of flow, scour, sediment transport, quality of water and relative cost..

Velocity:- There are a number of formulas available for use in calculating the velocity of flow. However Hazen William formula for pressure conduits and Mannings formula for free flow conduits have been popularly used.

a) The Hazen William formula is expressed as V= 0.849 C r0.63 S0.54 For circular conduits, the expression becomes V= 4.567 x 10-3 C d 0.63 S 0.54 And Q = 1.292 x 10-5 C d 2.63 S0.54

Where Q = discharge in cubic metre per hour d.=diameter of pipe in mm V = Velocity in MPS r.= hydraulic radius in m or hydraulic mean depth in meter = water area

wetted perimeter S = Slope of hydraulic gradeline C= Hazen-William co-efficient 5.2 Coefficient of Roughness (`C Value) (Para 6.2.2 of Cpheeo)



21 The co efficient of roughness (`C Value ) depends on Reynolds number and relative roughness. The Metallic pipes lined with cement mortar or epoxy and concrete pipe behave as smooth pipes. To reduce corrosion, increase smoothness and prolong the life of pipe materials, the metallic pipes are being provided with durable smooth internal lining. Unlined metallic pipes under several field conditions such as carrying water having tendency for incrustation and corrosion, low flow velocity and stagnant water under go substantial reduction in their carrying capacity with age. The value of the Hazen-William co-efficient `C value for new conduit materials and the value to be adopted for design purposes are given below. Hazen-Williams Co-efficient (Table 6.1 of CPHEEO Manual)

Pipe Material Recommended `C Value New Pipes Design purpose

Unlined Metallic pipes Cast Iron, Ductile Iron Mild Steel Galvanized Iron above 50mm dia Galvanized Iron 50mm dia and Below used for house service connections

Centrifugally Lined Metallic Pipes Cast Iron, Ductile Iron and Mild Steel pipes Lined with cement mortar or Epoxy

Upto 1200 mm dia Above 1200 mm dia Projection Method Cement Mortar Lined Metallic pipes Cast Iron, Ductile Iron and Mild Steel pipes Non Metallic pipes RCC spun concrete, prestressed Concrete Upto 1200 mm dia Above 1200 mm dia Asbestos Cement PVC, GRP and other Plastic pipes

130 140 120 120

140 145

130

140 145 150 150

100 100 100 55

140 145

110

140 145 140 145

5.3 Modified Hazen Williams Formula (Para 6.2.4 Of Cpheeo)

Hazen William formula has inherent limitation and under utilization. Hence the modified Hozen Williams formula has been derived from Darcy Weisbach and Colebrook white equations and obviates the limitations of Hazen Williams formula. The modified Hazen Williams formula derived for circular conduits as V= 143. 534 CR r 0.6575 S 0.5525 H = [ L ( Q / CR) 1.81 ] / 994.62 D 4.81



22 In which, V = velocity of flow in m/s ; CR = pipe roughness coefficient; ( 1 for smooth pipe; < 1 for rough pipes); r = hydraulic radius in m; S = friction slope; D = internal diameter of pipe in m; H = friction head loss in m; L = length of pipe in m; and Q = flow in pipe in m3/ s. A nomograph for estimation of head loss by Modified Hazen - Williams formula is presented in the Appendix 6.3 of CPHEEO manual 5.4 Effect of Temperature on Coefficient of Roughness ( 6.2.5 of CPHEEO)

Analysis carried out to evaluate effect of temperature (viscosity) on value of CR reveals that the maximum variation of CR for a temperature range of 10o C to 30o C is 4.5% for a diameter of 2000 mm at a velocity of 3.0 m / s In the light of this revelation, CR values are presented for average temperature of 20o C.

5.5 Experimental Estimation of CR Values ( 6.2.6 OF CPHEEO)

The coefficients of roughness in various pipe formulae are based on experiments conducted over a century ago. The values of Hazen Williams, C, Mannings n and roughness k values in Moodys Diagram have also been used on experimental data collected in early nineteenth century. There have since been major advances in pipeline technology. Both the manufacturing processes and jointing methods have improved substantially over the years and newer pipe materials have come into use. Continued usage of roughness coefficients estimated without recognition of these advances is bound to result in conservative design of water supply systems. Accordingly CR values of commonly used commercial pipe materials have been experimentally determined in a study conducted within the country. This study covered pipe diameters 100 to 1500 mm over a wide range of Reynolds numbers ( 3 x 104 to 1.60 x 106 ) encountered in practice. The results indicate that centrifugally spun CI, RCC, AC and HDPE pipes are hydraulically smooth when new and hence, CR = 1 for these pipes. The use of Hazen Williams C as per Table 6.1 results in under utilization of above pipe material when new. The extent of under utilization varies from 13 to 40 percent for CI pipes, 23 percent for RCC and AC pipes; and 8.4 percent for HDPE and PVC pipes.

The `C Value is the main contributory factor for deciding the size of the pipe. In case the `C value is understated the size of the pipe would automatically increase. The increase in discharge quantity of lined CI pipe is 40/45 per cent when compared to unlined CI pipes. Since the quantity to be discharged in the design of a particular section of pumping main remains constant, there would be



23 scope for reduction in diameter of the pipes used in that section. If the quantity of discharge and head lose were kept constant, the diameter of the pipes would be reduced using Hazen-Williams formula.

The following expression may be used to determine the reduced diameter of pipes when `C value is increased.

.d1= [c/c1 d2.63]1/2.63 (derived from Hazen William formula) where d= Diameter of pipe in mm as adopted in the design d1 = reduced diameter when `C value is increased c= `c value adopted in the design c1= Correct `C to be adopted as per CPHEEO manual

Illustration: Consider a pumping main with following parameters: Water to be discharged (k) = 4365 lpm Head loss (s) = 1/700 `C Value adopted ( C) = 100 Pipe used CI pipes (lined ) = 400 mm dia Velocity (v) = 0.579 m/sec Since `C value for lined pipes is 140 ,there would be scope for reduction in diameter of the pipe. It is to be noted that while reducing the diameter of the pipe we have to keep the Quantity of water to be discharged as constant. The hydraulic gradient may be kept constant or it may be increased. Note: Hazen William formula : Q = 1.292 x 10-5x, cd2.63 x S0.54 (1) If Q (Discharge) and S (hydraulic gradient are kept constant and C value is changed Then Q = 1.292 x 10-5 x C1d2.63 xS0.54 .(2) (1) divided by (2) 1= cd2.63/c1d12.63 d12.63=c/c1 d2.63 : d1= [c/c1 d2.63]1/2.63 The hydraulic gradient should not be reduced as it would cause increased pressure head which necessitate higher capacity pump sets and consequent additional expenditure. Hence while attempting reduction of size of pipe by increasing the `C value, care should be taken to keep both quantity of discharge and head loss as constants. Adopting the formula d1 =[c/c1 d2.63]0.38

Diameter of the pipe for C value of 140 would be d1=[1/1.4 (400)2.63]0.38 (4980693)0.38=350.73 mm or 350mm Thus the dia meter of the pipe is reduced from 400 mm to 350 due to increase of C value from 100 to 140. However we must ensure that due to reduction of size of pipe, the velocity should not be increased beyond limits. For



24 this, another expression of Hazen William formula (i.e.) V= 4.567 x 10-3c d0.63 x s0.54 Where d=350 mm and s= 1/700 Therefore V = 4.567 x 10-3 x 140 (350)0.63 x (1/700)0.54 4.567 x 10-3 x 140 x 3500.63 x (1/700)0.54 = 4.567 x 10-3 x 140 x 40.06 x 0.029

= 0.745 m/sec which is within normal limits adopted by TWAD Board. A typical discharge table for different size of pipe is given in Annexure IV

5.6 Reduction in Carrying Capacity of Pipes with Age. ( 6.2.7 of CPHEEO)

The values of Hazen Williams C are at present arbitrarily reduced by about 20 to 23 percent in carrying capacity of pipes with age. Studies have revealed that chemical bacteriological quality of water and velocity of flow affect the carrying capacity of pipes with age. The data on existing systems in some cities have been analyzed along with the experimental information gathered during the study, to bring out a rational approach to the reduction in carry capacity of pipes with age.

The CR values obtained in such studies have shown that, except in the case of CI and steel pipe while carrying corrosive water, the current practice of arbitrary reduction in C values as per Sec. 6.2.2. results in under utilization of pipe material to the extent of 38 to 71 percent for CI pipes for non corrosive water; 46 to 93 percent for RCC pipes and 2 to 64 percent for AC and HDPE pipes. 5.7. Design Recommendations for Use of Modified Hazen-Williams Formula ( 6.2.8 OF CPHEEO)

The following design recommendations are made to ensure effective utilization of pipe carrying capacity.

i) New CI, DI steel, RCC, AC and HDPE pipes behave as hydraulically smooth and hence CR of 1 is recommended.

ii) For design period of 30 years, no reduction in CR needs to be effected for RCC, AC, PVC and HDPE pipes irrespective of the quality of water. However, care must be taken to ensure self-cleansing velocity to prevent formation of slimes and consequent reduction in carrying capacity of these pipes with age.



25 iii) For design period of 30 years, 15 percent reduction is required for unlined CI & DI pipes if non corrosive water is to be transported. The design must also ensure self cleansing velocity.

iv) While carrying corrosive waters, unlined CI, DI and steel pipes will loose 47 and 27 percent of their capacity respectively over a design period of 30 years. Hence, a cost trade-off analysis must be carried out between chemical and bio-chemical correction of water quality, provision of a protective lining to the pipe interiors and design at reduced CR value for ascertaining the utility of CI, DI and steel pipe material in the transmission of corrosive waters.

Recommended CR values are presented in Table 6.4 The use of the recommended values in conjunction with Modified Hazen-Williams formula or the nomograph will permit fuller utilization of pipe materials.

RECOMMENDED CR VALUES IN MODIFIED HAZEN-WILLIAMS FORMULA( AT 20 oC)

Sl. No Pipe material

Diameter (mm) Velocity ( m/s) CR value when New

CR value for Design period of 30 years

From To From To

1 RCC 100 2000 0.3 1.8 1.00 1.00

2 AC 100 600 0.3 2.0 1.00 1.00

3 HDPE and PVC 20 100 0.3 1.8 1.00 1.00

4 CI/DI ( for water with positive Langeliers index) 100 1000 0.3 1.8 1.00 0.85*

5 CI/DI ( for water with negative Langeliers index) 100 1000 0.3 1.8 1.00 0.53 *

6

Metallic pipes lined with cement mortar or epoxy ( for water with negative

Langeliers index)

100 2000 0.3 2.1 1.00 1.00

7 SGSW 100 600 0.3 2.1 1.00 1.00

8 GI ( for water with negative Langeliers index)

15 100 0.3 1.5 0.87 (*) 0.74

(*) These are average CR values which result in a maximum error of + - 5 % in estimation of surface resistance. 5.8 Guidelines for Cost Effective Design of Pipelines.

The cost of transmission and distribution system constitutes a major portion of the project cost. It is desirable to adopt the following guidelines. i) The design velocity should not be less than 0.6m /s in order to avoid depositions and consequent loss of carrying capacity.



26 ii) In design of distribution systems, the design velocity should not be less than 0.6m/ s to avoid low velocity conditions which may encourage deposition and / or corrosion resulting in deterioration in quality. However, where inevitable due to minimum pipe diameter criteria or other hydraulic constraints, lower velocities may be adopted with adequate provision for scouring. iii) In all hydraulic calculations, the actual internal diameter of the pipe shall be adopted after accounting for the thickness of lining, if any instead of the nominal diameter or outside diameters ( OD). iv)In providing for head loss due to fittings, specials and other appurtenances, actual head loss calculations based on consideration included in subsection 6.2.9. should be done instead of making an arbitrary provision.

5.9 Pipe Materials ( Para 6.3 Of CPHEEO)

Pipelines are major investments in water supply projects. Therefore pipe materials shall have to be judiciously selected not only from the point of view of durability, life and over all cost which includes, the pipe cost, the installation and maintenance costs necessary to ensure the required function and performance of the pipeline throughout its designed life time.

Choice of Pipe Materials

Types of Pipes:

The various types of pipes used are:

a. Metallic pipes : C.I., D.I., M.S., G.I.

i)Unlined Metalic pipes. ii)Metallic pipes lined with cement mortar or epoxy lining

b. Non Metallic pipes

i) Reinforced Concrete, Prestressed Concrete, Bar wrapped Steel Cylinder Concrete, Asbestos Cement. ii) Plastic pipes : PVC, Polyethylene, Glass Reinforced Plastic, etc.

Selection of Pipes

* Several technical factors affect the final choice of pipe material such as internal pressures, coefficient of roughness, hydraulic and operating conditions, maximum permissible diameter, internal and external corrosion problems, laying and jointing, type of soil, special conditions, etc.



27 * Selection of pipe materials must be based on the following considerations: a)The initial carrying capacity of the pipe and its reduction with use, defined, for example, by the Hazen Williams coefficient. C. Values of C vary for different conduit materials and their relative deterioration in service. They vary with size and shape to some extent. b) The strength of the pipe as measured by its ability to resist internal pressures and external loads. c)The life and durability of pipe d)The case of difficulties in transportation, handling and laying and jointing under different conditions of topography, geology and other prevailing local conditions. e)The safety, economy and availability or manufactured sizes of pipes and specials f)The availability of skilled personnel in construction and commissioning of pipelines. g)The ease or difficulty of operations and maintenance.

The life and durability of the pipe depends on several factors including inherent strength of the pipe material, the manufacturing process along with quality control handling transportation laying and jointing of the pipeline surrounding soil conditions and quality of water. Normally the design period of pipelines is considered as 30 years.

Lined metallic pipelines are expected to last beyond the normal design life of 30 years. However, the relative age of such pipes depends on the thickness and quality of lining available for corrosion. The cost of the pipe material and its durability or design life are the two major governing factors in the selection of the pipe material. The pipeline may have very long life but may also be relatively expensive in terms of capital and recurring costs and, therefore, it is essential to carryout a detailed economic analysis before selecting a pipe material. The metallic pipes are being provided with internal lining either with cement mortar or epoxy so as to reduce corrosion, increase smoothness and prolong the life. Underground metallic pipelines may require protection against external corrosion depending on the soil environment and corrosive ground water. Protection against external corrosion is provided with cement mortar guiniting or hot applied coal-tar asphaltic enamel reinforced with fiberglass fabric yarn. The determination of the suitability in all respects of the pipeline for any work is a matter of decision by the Engineer concerned on the basis of the requirements for the scheme. It is necessary that a quantitative and qualitative assessment is made to arrive at the most economical and reliable pipe materials. The check list for selection of pipe materials prescribed in table 6.7 of CPHEEO is to be prepared to the facilitate the decision makers in selecting the



28 economical and reliable pipe materials for the given condition and it is strongly recommended for large and medium projects more than 15 mld. Risk factors should be identified clearly in the project report. Risk analysis should be carried out to arrive at the correct decision in selecting the pipe material. 1. Cast Iron (CI) Pipe (Para 6.4. CPHEEO)

CI pipes are vertically cast or centrifugally cast. Vertically cast Iron pipe shall confirm to IS 1537 1976 and the centrifugally cast spun iron pipe shall confirm to IS 1536: 2001. Vertically cast Iron pipes has been largely superceded by centrifugally spun cast iron pipes. Centrifugally cast iron (spun) pipe is available and manufactured to a diameter of 80mm to 1050mm. The CI pipe have been classified as LA, A and B classes according to their wall thickness. Class LA pipe have been taken as the basis for classification of pipe Class A pipe more 10% and Class B have 20% increase in thickness over Class LA.

Widely used because of its good casting qualities and continue to give satisfactory service even after a century of use.

The pipes are Spigot and socket type Several type of joints such as rubber gasket joint known as Tyton

joints, Mechanical joint and conventional joint know as Lead joints are used.

used for carrying potable water, sewer main etc. 2. Steel Pipe ( Para 6.5 of CPHEEO)

Manufacture of steel pipes shall be with mild steel plate grade Minimum tensile strength of 330 mpa, 410 mpa & 450 mpa confirming to IS 2062. ( Steel plate of Minimum tensile strength of 410 mpa is normally used) Larger size of pipe are made by welding together the edges of suitably

curved plates as per IS 3589: 2001. IS 3589 : 2001 stipulates the nominal size of steel pipe ranging 168.3mm

to 2540mm outer diameter with varying thickness of plate 2.6mm to 25mm.

To be provided protection against corrosion. As against internal corrosion rich cement mortar or epoxy lining should be done internally by centrifugal process. The outer coating for under ground pipe line may be in cement - sand guiniting or not applied coal-tar asphaltic enamel reinforced with fibre glass fabric yarn.

Small size of pipe having threaded ends could be joined with jointed materials like yarn.



29 3. Ductile Iron Pipes ( 6.6 Of CPHEEO)

Ductile iron confirming to IS 8329 : 2000 specification prescribes standards for centrifugally cast ductile iron pipe ( DI pipe). DI pipes are available in the range of 80mm to 1000mm diameter and in

length of 5.5 to 6m. DI pipes are normally provided with cement mortar lining at the factory by

centrifugal process. DI pipe have excellent properties of machinability, impact resistance,

high wear and tear resistance high tensile strength, ductility and corrosion resistance. Free from cracks.

These pipes are approximately 30% lighter than conventional CI pipes. DI fittings are manufactured conforming to IS 9523 : 1980 and the

laying and jointing done as in the case of CI pipe ( viz. rubber gasket etc.) 4. Asbestos Cement (AC) Pipes ( Para 6.7 of CPHEEO)

A.C. pipes conforming to IS : 1592 2003 was made of a mixture of Asbestos paste and cement compressed by steel roller to form laminated material of great strength and density. AC pipe are manufactured from class 10 to 25 and nominal diameters of

50mm to 1000mm with test pressure of 10 to 25 kg / cm 2. AC pipes are classified as class 10,15,20 & 25 kg / cm 2 respectively. Working pressure shall not be greater then 50% of the test pressure for pumping mains and 67% for gravity main.

AC pipes have two type of joints cast iron detachable ( CID) joints and AC coupling joints.

5. Concrete Pipe ( Para 6.8 of CPHEEO)

Reinforced cement concrete ( RCC ) pipes are classified as P1, P2 and P3 with test pressure of 2,4 and 6 kg / cm2 respectively. For use as gravity main, the working pressure should be 2/3 of the test pressure and for the pumping main, the working pressure should not exceed half of the test pressure. Jointed with RCC collars with jute yarn rope dipped in Cement mortar.

6. Pre stressed Concrete (PSC) Pipe ( Para 6.9 of CPHEEO)

The PSC pipes are ideally suited for water supply mains where pressure in the range of 6 kg / cm2 to 20 kg / cm2 are encountered. PSC pipes consists of a concrete lined steel cylinder with steel joint rings

welded to its ends wrapped with a helix of highly stressed wire and coated with dense cement mortar or concrete.



30 PSC pipes are jointed with flexible rubber rings. Confirming to IS 784 : 2001 specification. PSC pipe competes economically with steel for pipe diameter of 600mm

and above. The PSC pipes are classified as 4 KSC, 6 KSC, 8 KSC, 10 KSC, 12 KSC,

16 KSC, 18 KSC, and 20 KSC pipe and that denotes the working pressure excluding surge pressure and the site test pressure will be 1.5 times of the above working pressure vide IS 784 : 2001.

7. Bar Wrapped Steel Cylinder Pipes (BWSC Pipes) (Para 6.9.4 Of CPHEEO) (IS: 15155-2002)

Bar wrapped cylinder pipes (BWSC pipes) are being manufactured as per IS 15155-2002. BWSC pipe is a modified version of PSC pipes with steel cylinder embedded in it. The joints are welded and covered with cement mortar coating. The joints are more reliable than conventional rubber ring joints. The O&M expenditure would be less. It is advantagements to use BWSC pipe in water supply and sewerage projects on grounds of good hydraulic properties, long life better corrosion resistant properties etc., The BWSC pipe have been introduced as approved pipe material in TWAD schedule of rates for the year 2004-05, In Circular NO.43/AC/P&D/2005 Dt.04.10.2005, TWAD Board directed that the use of BWSC pipe has to be encouraged in water supply and sewerage projects in view of its techno economic advantage and lesser O&M cost. The technical committee instructed to consider BWSC pipe as are of the alternative in water supply and sewerage projects with Techno economic consideration.

8. Plastic Pipes ( Para 6.10 Of CPHEEO) Poly Vinyl Chloride ( PVC ) pipe conforming to IS 4898 1988. PVC

pipe have advantages of resistance to corrosion, light weight, toughness, rigidity, economical in laying, jointing and maintenance, case of fabrication.

Available in size of outer dia 20 to 315mm at working pressure of 2.5, 4, 6, 10 kg / cm2.

Superior compared to conventional pipe especially AC. Jointing of PVC can be made by solvent cement, rubber ring joint, flanged

joints, threaded joints. For bedding pipe trench is filled with sand and compacted by tapping with

wooden stick. Note: In Circular No.42/DO/P&D/2005 Dt.04.10.2005. TWAD Board instructed to considered PVC pipe upto 315 mm OD as one of the alternative in water supply and sewerage projects with techno economic consideration.

9. Polyethylene Pipes ( Para 6.11 of CPHEEO) High density polyethylene pipe ( HDPE) has excellent free flowing

properties.



31 Required for water distribution system ranging from 15-150mm dia and occasionally upto 350mm

Conforming to IS 4984 1987. They can withstand movement of heavy traffic HDPE pipes can be jointing by welding.

10. Medium Density ( MDPE) PIPE ( para 6.11) Manufactured conforming to ISO 4427 specification for carrying potable

water. The pipes are supplied in coil.

11. Glass fibre reinforced plastic (GRP)Pipes ( 6.12 of CPHEEO) GRP pipes are now manufactured in India conforming to IS 12709. The diameter range is from 350mm to 2400mm. The pressure class is

3,6,9,12 & 15 kgs / Sq.cm. The factory test pressures are 4.5,9,13.5, 18, 22.5 kg / sqcm. The factory test pressures are 6, 12, 18, 24 and 30 kgs / sq.cm.

Standard length are 6 and 12 meter. Widely used in foreign countries. GRP pipes are corrosion resistant and have smooth surface and high

strength, lighter in weight. Pipes are jointed by using double bell coupling.

12. G.I. Pipe.

The pipe shall be galvanized mild steel not finished seamless or welded or screwed and socketed conforming to the requirement of IS 1239 (Part.I) for medium grade

Shall with stand a test pressure of 50 kg / cm2 Normally used for hill areas.

5.10.Structural Requirements ( Para 6.13.1)

Structurally closed conduits must resist a number of different forces singly or in combination.

a) Internal pressure equal to the full head of water to which the conduit can be subjected ( ie. Hydrostatic Test pressure).

b) Unbalanced pressure at bends, constructions and closures which have been discussed in 6.16.18 of CPHEEO Manual.

c) Water hammer d) External load in the form of back fill, traffic and their own weight

between external supports (Piers or hangers). e) Temperature induced expansion and contraction. Internal pressure including water hammer creates transverse stress or hoop

tension. Bend and closures as dead ends of gates produce unbalanced pressures



32 and longitudinal stress. When conduits are not permitted to change length, variations in temperature like wise create longitudinal stress. External loads and foundation reactions ( Manner of support ) including the weight of the full conduit and atmospheric pressure produce flexural stress. 5.11 Depth of Cover: ( 6.13.4 Of CPHEEO)

One meter cover on pipeline is normal and generally sufficient to protect the pipe lines from external damage. When heavy traffic is anticipated, depth of cover has to be arrived at taking in to consideration of the structural and other aspects as detailed in 6.13.2 CPHEEO Manual. When freezing is anticipated 1.5m cover is recommended. 5.12. Testing of the Pipe Line ( Para 6.4.4. Of CPHEEO) After laying and jointing, the pipe line must be pressure tested to ensure that pipes and joints are found enough to withstand the maximum pressure likely to be developed under working conditions. The yield test pressure to be imposed should be not less than the maximum of the following. 1 times the maximum sustained operating pressure. 1 times the maximum pipeline static pressure. Sum of the maximum sustained operating pressure and the maximum

surge pressure. Sum of the maximum pipeline static pressure and the maximum surge

pressure subject to a maximum equal to the work test pressure for any pipe fitting incorporated.

The field test pressure should wherever possible be not less than 2/3 work test pressure appropriate to the class of pipe except in the case of spun iron pipes and should be applied and maintained for atleast four hours.

Where the field test pressure is less than 2/3 the work test pressure, the period of test should be increased to atleast 24 hours. The test pressure shall be gradually revised at the rate of 1 kg / cm2/minutes.

In case of gravity pipe, maximum working pressure shall be 2/3 work test pressure.

The hydrostatic test pressure at works and at field after installation and the working pressure for different classes of pipes are given in Annexure 5

5.13 Water Hammer (Surge Pressure ) (Para 6.17 CPHEEO) Occurrence If the velocity of water flowing in pipe is suddenly diminished, pressure would be develop in the pipe line due to frictional resistance and wave propagation. This pressure rise or water hammer is manifest as a series of shocks,



33 sounding like hammer blows, which may have sufficient magnitude to rupture the pipe or damage connected equipment. It may be caused by the nearly instantaneous or too rapid closing of a valve in the line or by an equivalent stoppage of flow which would take place with the sudden pressure. The pressure wave due to water hammer travels back upstream to the lintel end of the pipe, where it reverses and surges back and forth through the pipe , getting weaker on each successive reversal. The Velocity of the wave is that of an acoustic wave in an elastic medium, the elasticity of the medium in this case being a compromise between that of the liquid and the pipe. The excess pressure due to water hammer is additive to the normal hydrostatic pressure in the pipe and depends on the elastic properties of the liquid and pipe and on the magnitude.

Causes for Water hammer The Causes of water hammer are

i) rapid closure of valves ii) Sudden shut off or unexpected failure of power supply to centrifugal

pump. iii) Pulsation problems due to hydraulic rams and reciprocating pumps.

Computations for Water Hammer Maximum water pressure (which occurs at the critical time of closure Tc or any time less than Tc ) is given by the expression. H max = C Vo G Where, H max = maximum pressure rise in the closed conduct above the normal pressure in m, C = Velocity of pressure wave travel in m/sec., G = acceleration due to gravity, 9.81m/Sec2 Vo = normal velocity in the pipeline, before sudden closure. in m/sec. C = 1425 1+kd ECt Where, k = bulk modulus of water (2.07 x 108 kg/m2) d = diameter of pipe in m Ct = wall thickness of pipe in m and E = modulus of elasticity of pipe material in kg/m2 Table below gives of E that may be adopted for different materials. Values of E for Different Materials



34 Material E (kg/m2) Polyethylene soft 1.2 x 107 Polyethylene hard 9 x 107 P V C 3 x 108 Concrete 2.8 x 109 Asbestos Cement 3 x 109 Reinforced Cement Concrete 3.1 x 109 Prestressed Concrete 3.5 x 109 Cast Iron 7.5 x 109 Ductile Iron 1.7 x 1010 Wrought Iron 1.08 x 1010 Steel 2.1 x 1010

If the actual time of closure T is greater than the critical time Tc, the actual water hammer is reduced approximately in proportion to Tc/T. Water hammer wave velocity may be as high as 1370 m/s for a rigid pipe or as low as 850 m/s for a steel pipe and for plastic pipes may be as low as 200m/s. Control Measures The internal design pressure for any section of a pipeline should not be less than the maximum operating pressure or the pipeline static pressure obtaining at the lowest portion of the pipeline considering any allowance required for surge pressure. The maximum surge pressure should be calculated and the following allowances made:

(a) If the sum of the maximum operating pressure or the maximum pipeline static pressure which ever is higher and the calculated surge pressure does not exceed 1.1 times the internal design pressure, no allowance is required.

(b) If the sum exceeds 1.1 times the internal design pressure, then protective devices should be installed and

(c) In no case sum of the maximum operating pressure and the calculated surge pressure should exceed the field hydrastatic test pressure.

(d) Effect of water hammer could be controlled by

(i) installing special devices in the pipe lines (automatically controlled quick closing valves, bypasses and pressure relief valves.

(ii) employing surge tank- simplest of form of surge tank is a stand pipe placed at the end of the line next to the point of velocity control.

5.14 Economic Size of pumping :



35 The economical size of pumping main is based on analysis of the following factors. i) Design period or period of loan repayment ii) Quantities to be conveyed during different phases. iii) Different pipe sizes against corresponding hydraulic slopes. iv) Different pipe materials and relative costs as laid v) Recurring cost on power. vi) Cost replacement of pump sets at an intermediate stage of design period. Duty capacity and installed costs of pump sets required against

corresponding sizes of pipeline considered 5.15. Structural Loads on Rigid Pipes (Data matrix of TWAD Board Engineer) Structural loads on Rigid Pipes are due to (i) fill material (ii) concentrated load and (iii) superimposed uniformly distributed load. Elaborate procedure has been developed by Matson for calculation of structural loads under conditions of pipes in trench, which will be worked out by the designers. 5.16 Strength of Pipes for various Bedding

The manner in which the pipe is supported in trench and the nature of the backfill material affect the distribution of load and the internal stresses. Load factor of bedding and several type of bedding are indicated below It is customary to use two-thirds of the effective strength as design strength. Type of bedding Load Factor Ordinary bedding 1.5 First Class bedding 1.9 Concrete cradle bedding 2.25 to 3.4 Example: Let the load on a pipe (of certain diameter laid at required depth and trench width) due to fill material, concentrated moving load and superimposed uniformly distributed loads worked out in according with Matsons formula be 10000 kg/metre length. Let the three edge bearing strength of pipe be 7500 kg/metre. With a factor of safety of 1.50, safe permissible load = 7500/1.5 = 5000 kg/metre load factor required = 10000/5000 =2.0 Hence concrete bedding should be selected. For the same pipe with a structural load of 5000 kg/metre, the load factor is 1.0 and ordinary bedding will be sufficient. Thus the choice of the bedding to be selected depends on the structural load on the pipes calculated in terms of the procedure outlined above.



36 Audit Approach

PIPE

According to Para 6.3.1 of CPHEEO Manual, the cost of the pipe materials and its durability are the two major governing factors in the selection of pipe materials and the exercise prescribed in Ttable 6.7 of the ibid Manual the selection of pipe materials had to be carried out for selecting the economical and reliable pipe materials. The Manual also stipulates that selection of pipe for water supply works should be done economically as it involves major part of the project cost and designed on the basis of procedure stipulated in Appendix 6.5 Design for Economic Size of pumping main of ibid Manual. But while selecting the pipe materials for pumping main and conveying main of water supply schemes, techno-economic selection of pipe materials stipulated in the CPHEEO Manual was not adopted involving extra cost.

Cases will be available in designing pumping main adopting MS Pipe/CI Pipe/DI pipe instead of adopting PSC Pipes by erroneous adoption co-efficient of roughness (C value) for both metallic pipe lined with cement mortar or epoxy and prestressed concrete (PSC) pipe (ie. Value in both cases is 140). Para 6.9 of ibid Manual also stipulates that PSC pipe competes economically with metallic pipe for diameter 600 mm and above and ideally suited for water supply main where pressure is in the range of 6 kg/cm2 to 20 kg/cm2.

Cases for adoption of DI pipe instead of CI pipe or MS pipe where the designed pressure of pumping main is much below the working pressure of CI or MS Pipe.

According to TWAD Board Circular of February 1999, AC class 15 pipes upto to size of 300 mm dia could be used for pumping main. But cases of using PSC pipes/CI pipes/DI pipes could be identified and commented.

While designing the pumping main it would be verified whether intermediary sump was at higher ridge point so as to reduce the pressure head was provided so that comparatively lesser class of pipe could be used for the pumping main

Failure to provide intermediary sump and suitable device to control surge pressure resulting in frequent burst and leakage of pumping main leading for interruption in power supply. Such defective design and cost involved on rectification work had to be analysed and commented.

NOTE: While objecting use of metallic pipe the Board used to contend that the metallic pipe was used to avoid illegal tapping of water from main, to complete the work within the time schedule and prevalency of rocky reaches. Those contentions were not tenable due to the fact that illegal tapping was not possible in PSC pipes also and the Board had allowed the same time for manufacturing, supplying, laying, jointing PSC Pipes and MS pipes. Further Board used PSC Pipes in pumping main even for hard rock reaches in other similar water supply



37 schemes by providing sand cushion or refilling the trenches as stipulated in the Standard IS Specification.

Even where higher class of pipes are used than the actual requirement to withstand the designed pressure on the pumping and distribution main, cases of leakages were noticed. Consequently, water could not be pumped to the designed level and supply effected. This was due to distortion at flexible joint. Thus due to defective joints, water could not be supplied. This could be commented. On non achievement of the objective due to defective execution of work

Cases where PSC/CI/DI Pipe is used instead of AC Pipes on the ground that the pipeline has to be laid on heavy traffic area. This contention is not correct. According to Para 6.13.4 of CPHEEO Manual one metre cover on pipeline is normal and generally sufficient to protect the pipeline from external damage. When heavy traffic is anticipated, depth of the cover had to be arrived at taking into consideration of the structural and other aspects as detailed in Para 6.13.2 of CPHEEO Manual. In as much as the pipe line are laid along the road side, the question of increase in stress on the pipe causing damage would not arise. Besides the Board has not worked out extra cover if any required for.

6. SELECTION OF PUMPS (Chapter 11 of CPHEEO Manual)

1. In a water supply system pumping machinery serves the following purposes:

a) lifting water from the source (surface or ground ) to purification works or the service reservoir; b) boosting water from source to low service areas and to the upper floor of the storied buildings; and c) transporting water through treatment works, draining of settling tanks and of treatment units, withdrawing sludge, supplying water especially water pressure to operating equipment and pumping chemical solutions to treatment units.

While deciding the type of pump for the specific requirements, it is necessary to analyze different type of pumps and their suitability to meet the requirements. 2. The following pumps are generally used in water supply schemes.

a. Centrifugal pumps b. Jet pumps c. Turbine pumps (oil lubricated or water lubricated vertical pump) d. Submersible pumps.



38 3. The selection of pump sets for different types of sources and conditions are as follows:

4.1. Borewells (Chapter 7 of Quality Control Manual) Sl.No. Site condition Preferable

Pump Selection i. 100mm dia Bore well Jet pumps (Packer type )

Ii 150 mm dia Bore well(not straight) Jet Pumps (Packer type )

Iii 150mm dia Bore well with yield less than 50 lpm Jet Pumps (Packer type )

Iv 150 mm dia Bore well(with yield more than 50

lpm in urban area)

Submersible pumpsets

V 150 mm dia Bore well in rural area

a. yield between 50 & 100 lpm

b. yield more than 100 lpm

Jet (with jet setting 20 m )

Submersible pumpsets.

4.2.Wells and Other Sources Sl.No.

Site Condition Preferable pump selection

I Inside the river one or more number of Infiltration wells.

- Submersible pumpsets

Ii Inside the river one/more Infiltration wells with foot bridge arrangements.

- Turbine pumps

Iii Collector well connected the bank with foot bridge

- Turbine pumps

Iv Low lift raw water pumping, dry well built in the river / dam bank with suction head not to exceed 6m

- Centrifugal pumps

V For the above site condition when suction head exceeds 6m

- Turbine pumps

Vi Clear water ground level reservoir / sump - Centrifugal/Turbine pumps

Vii Clear water/raw water booster pumping station. - Centrifugal pumps Viii Lin

water supply

Documents

water supply handbook

water supply system

water treatment

water requirement

points of water supply

safe wholesome water

waste water disposal

audit approaches