Summer Storage Tanks : Design and Construction Aspects

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1 Summer Storage Tanks : Design and Construction Aspects C L N Sastry, B.E., F.I.E. (Former Engineer-in-Chief, Commissioner for Projects Formulation & Ex-Officio Secretary I&CAD Dept., Govt. of Andhra Pradesh) Adviser Water Resources Devt. Division, ESCI

2 Need for Summer Storage Tank When the source of drinking water supply scheme Is a river, tributary, major stream, and the flows in the river/ tributary/ major stream dwindle as the summer season approaches and there will be no water flowing in it during the summer periods ; Is an irrigation canal, and the canal will be closed after kharif or rabi season depending upon the contemplation of the irrigation project / scheme is for a single crop (kharif) or two crops for both kharif and rabi seasons. In both the cases, water cannot be tapped from the canal during the closure period every year. The above situations demand the need for planning of a summer storage tank to augment the drinking water supplies during the summer periods.

3 Summer Storage Tank near Canal Off-take

4 Source Where a surface water source is subject to an abstraction limit imposed by the Irrigation Department, this abstraction limit should be checked against the amount of water required. The abstraction limit will normally be given in terms of the amount of water that can be abstracted in one year. This can be compared with the amount of water required, estimated as follows: Water requirement = (P x q/ Sa) x 365 x (1 +u) cubic metres per year where P is the design population; q is the daily per-capita demand in litres; Sa is the daily supply from other sources in cubic metres; and U is the proportion of unaccounted for water, given in relation to the demand for water, including losses in the SST, losses in treatment and transmission and distribution losses. In the absence of accurate information, it may be taken as 0.5. The design population will be the number of people that it is intended to serve at the end of the design period - typically 15 to 30 years. Obviously, a slightly more complicated equation will be needed to account for different design demands in different areas and through different types of connection

5 Summer storage tank capacity When supply is from an irrigation canal, SST capacity must be sufficient to enable the desired level of service to be provided to all consumers over the period during which the canal is closed for maintenance. The Irrigation Department will normally provide information on the time over which no supply from a canal can be guaranteed, typically in the range 45 to 60 days but occasionally higher. This figure usually provides some factor of safety. For instance, if the canal is normally closed for one month each year, the period of closure will be specified as 45 days. The actual capacity of existing SSTs can be calculated from the formula: Capacity = (WDmax - WDmin) x A cubic metres Where WDmax and WDmin are the maximum and minimum water depths in m in the SST A is its area at mid-depth in sq m

6 This figure must be greater than the amount of storage required. This can be calculated as follows: Required storage = P x (Q + LSST + LBW) Where P is the period of closure in days; Q is the daily throughput of the water works in cubic metres; LSST is the estimated daily loss from SSTs, again in cubic metres. In genera!, this should not exceed 33% of daily production at the very most. LBW is the average amount of water used per day in desludging and backwashing filters. This is typically equal to about 5% of daily production.

7 Calculating SST losses The losses from SSTs are made up of evaporation losses and losses caused by percolation through the bund and bed of the SST. Evaporation losses are a function of the SST surface, water temperature, relative humidity and wind speed over the water surface. Typical evaporation rate of 7 mm/day when water temperature (Tw) is 30 C, relative humidity (RH) is 15%, and average wind speed is 3 km/hr.

8 Evaporation Rates for SST RH=15%, Tw=30C RH=30%, Tw=30C RH=15%, Tw=35C RH=30%, Tw=35C Wind Speed (km/hr.)

9 The calculation below shows how the evaporation losses from a 10 hectare SSA can be calculated for a 45 days closure period, at an evaporation rate of 7mm/day. -Evaporation losses = 45 days [ 7mm/day x 10 hectares x 10,000m 2/ hectare] = 31,500 m3 1,000 mm/m In the event that the storage available is less than that required to provide a full supply throughout the period of canal closure, the options for increasing SST capacity must be considered at an early stage in the planning process Percolation losses can only be calculated by direct measurement. This requires that the drop in level of the SST is measured when there is no inflow to or outflow from the SST. Measurements can be made with different depths of water in the SST while water is being delivered directly to the waterworks from the source. When calculating percolation rates, allowance must be made for evaporation losses, rainfall and any leakage through valves that cannot be fully closed. The daily percolation loss will be given by the equation: PL =A[(hd + rf) / D - e]/1000 Lv Where PL is the daily percolation loss in cubic metres A is the area of the SST in square metres ;

10 hd is the measured drop in water level over a period of D days in mm; rf is the rainfall recorded during the measurement period in mm; e is the average daily evaporation rate over the measurement period and Lv is the daily loss through valves in cubic metres. Note that the area of the SST will vary with water depth. This may be ignored for large SSTs but may have to be taken into account for smaller SSTs. Rainfall measurements should be obtained from the nearest meteorological station. Losses from valves should be estimated from direct measurements of leakage flow through inlet and outlet pipes if possible.

11 Selection of site for summer storage tanks Exploration of suitable existing tanks available in respect of location as well as storage capacity to minimize the high cost involved for the construction of summer storage tank If there are no existing tanks suitable, the location of the proposed summer storage tank should be such that the total cost involved should be as minimum as possible. Various alternative sites are to be studied to evolve an economical proposition. The site should not be of pervious strata like gravelly and sandy soils where the percolation losses are heavy. The strata should be suitable for founding earth bunds over it. if existing tank is selected for summer storage, rehabilitation of the system should be economical. the

12 If the source of the entire scheme is an existing reservoir, the intake well may be located where dead storage is maximum so that water can be drawn not only from live storage but also from dead storage. capacity of the summer storage tank The capacity of the summer storage tank includes The total quantity of water required for drinking and domestic purposes for the entire period of canal closure or the period of non-availability of water in the natural flowing source. Evaporation losses due to impounding of the water for the entire period of storage Percolation losses in the impounding area.

13 Percolation losses : The percolation losses depend on the nature of the soil of the area on which the summer storage tank is formed. Evaporation losses : Jan, Feb : 100 mm March : 175 mm April : 225 mm May : 250 mm June : 175 mm July, Aug., Sept. : Oct. : Nov., Dec., : 150 mm 125 mm 100 mm Total 1300 mm

14 Impounding Reservoir/ Summer Storage Tank Storage has to be provided for non-monsoon period plus allowance for silt, seepage, dead storage, and evaporation. It is recommended to explore possibility of using an existing tank to minimize the high cost of construction of impounding reservoir. If supply has to be drawn from existing tank or canal, it may be drawn from live storage and also have facility for intake works to draw water from dead storage for drinking water supply system. Intake well in SS tank is to be located where dead storage is maximum Layer-wise compaction of soils is to be ensured for the bund.

15 Design for capacity required: The summer storage tanks shall be provided for storing the requirement during the canal closure period. Canal closure periods vary from 3 to 9 months. Generally for closure periods up to 4 months, a minimum of 50% extra is provided in the storage towards percolation and evaporation losses. The pan evaporation Data as per CE/Minor Irrigation manual shall be used, for assessing the evaporation losses of a region for the canal closure period.

16 Case Study: Case 1: Canal Closure period upto 4 months. Storage Capacity Population as per 2001 census : 100 Considering 2009 as the commissioning year Present Population = 100(1+1/100)8 = 108 (Adopting 1% growth rate of population) The SS Tanks are designed for ultimate population after 2 decades Ultimate Population = 108(1+1/100)20 = 132 Raw Water Demand = 50 LPCD Canal Closure Period = 120 days Ultimate Daily Demand = 132x50 = 6600 Ltrs Storage Required for Canal Closure Period = 6600x120 = Ltrs or 792 cum Add 50% for Evaporation and Percolation Losses = 396 cum Storage Capacity Required = = 1188 cum.

17 Discharge through Pumping Main The discharge through pumping main from canal to SS tank shall be the summer storage discharge which is to be drawn during canal operation Period and the daily discharge required for the scheme. Storage for Canal Closure Period = L Canal Operation Period = 245 days Discharge per day for Summer Storage /245= 4849 L For 12 hours operation, discharge for summer storage= 4849/(12x60) = 6.73 LPM Ultimate daily demand = 6600 L Daily Discharge per day for 12 hours of operation = 6600/(12x60) = = 9.17 LPM Total Discharge through pipe = = LPM

18 Case 2: Canal Closure Period more than 4 months Population as per 2001 Census Considering 2009 as the commissioning year Present Population = 100(1+1/100)8 The SS Tanks are designed for Ultimate Population Ultimate Population = Raw Water Demand Canal Closure Period Ultimate Daily Demand = 132x50 Storage Required for Canal Closure Period 6600x240 or = 100 = 108 after 2 decades = 132 = 50 LPCD = 240 days = 6600 Ltrs = Ltrs 1584 cum

19 Let the depth of water in SS Tank be 4.0m. Consider TBP HLC in Ananthapur District as the source and the canal closure period from September to May. As per pan Evaporation Data, Cumulative Loss due to evaporation losses = mm or 1.59m Percentage for Evaporation Losses = [ (4-1.59) / 4] x 100 = 60.25% For Percolation Losses, the provision required is 15% to 20% Total Provision for percolation and Evaporation Losses = = 80.25% Add 80% for Evaporation and Percolation Losses = cum Storage Capacity Required = = cum

20 Discharge through Pumping Main The discharge through pumping main from canal to SS Tank shall be the summer storage discharge which is to be drawn during canal operation period and the daily discharge required for the scheme. Storage for Canal Closure Period = Ltrs. Canal Operation Period = = 125 days Discharge per day for Summer Storage = Ltrs. per day For 12 hours of operation, LPM discharge for summer storage= / (12x60) = Ultimate Daily Demand = 6600 Ltrs. per day Discharge per day for 12 hours operation = 6600/(12x60) = 9.17LPM Total Discharge through Pipe = = LPM Note: Diameter of pipe for pumping main can be obtained by using the formula 0.76(Lpm) )0.46. The class and type of pipe can be decided by considering frictional losses and other losses due to transmission, length of pipe, water hammer and static head available.

21 Bund formation i) Reconaissance The site selected for SS tank should be: Nearer to the Canal to minimize the raw water pumping length Should have adequate B.C soil depth to minimize the seepage losses (minimum of 60 cms) Rocky portions having faulty zones should be avoided. Borrow areas should be nearer to the site with required quantity of soil available for formation of bund

22 ii) Field investigations/survey Before grounding the work, trial pits have to be taken at the site at regular intervals to know the depth of BC soil available. Representative soil samples in required quantities shall be collected from the trial pits at site and borrow areas, duly identifying the trial pit numbers and the level at which the soil samples are collected. Undisturbed soil samples shall be collected in accordance with the procedures laid down in IS: and are tested in the laboratory for their suitability and classification.

23 The following tests are to be conducted to assess their suitability for embankment. Grain Size analysis Atterberg limits (Liquid Limit and Plastic Limit of Soil Consistency) Shrinkage limit Optimum moisture content Proctor s Density Shear strength at optimum moisture content and at 100% saturation Permeability at proctor s density. The soil classification should be done as per IS:

24 A survey has to be conducted and block levels at 30m interval have to be plotted to know the topographic features of the site. Based on the topographic features the available storage capacity at site can be calculated by plotting the contours at 0.10 to 0.50m interval. The storage capacity required is calculated by deducting the balance capacity available as per contour capacity calculations, after making a provision for dead storage (10 to 20 percent), from the design capacity. The capacity provided can also be checked by Block area method as per the Proforma given under. In this method the area between centerline of bund is identified. Average of 4 corners block levels (block levels formed by 30m interval levels) in a block is taken. The water column height in each block is calculated and added to get actual storage provided.

25 Capacity calculation by block area method Capacity calculations of S.S tank Data Off Take Level M.W.L T.B.L Top Width Side Slope Free Board

26 Block No. Avg. Length Breadth Block Depth GL in mt. in. mt Area Above OTL (sq.m ) in mt. Volume Depth Volume Length Volume Volume Above below below of bund of bund of bund Off take OTL OTL in mt. above OTL below OTL

27 Sumps Raw water sump It acts as an equalizing reservoir which enables the filters to work at a constant rate. Generally a circular sump is to be designed. The raw water sump is provided for collection of raw water from intake well. Water will be pumped from raw water sump to treatment units.

28 Operations to be carried out before formation of Earth Bund Site clearance Stripping Conveyance of soils from the approved borrow areas Spreading of the soils Extra width for trimming Breaking clods Extra watering Compaction with rollers Sectioning

29 Sample collection of soils for stripping Depth of stripping Type of vegetative cover on the soil Depth of stripping Soil containing light grass cover 5 to 7.5 cm Agriculture land to the bottom of the ploughed zone

30 The stripping should be done in advance If the existing surface soils are not suitable such as sands or sand mixed with B.C., all these un-suitable soils are to be removed till suitable strata for the banking is exposed. All the stripped material shall be deposited beyond the catch drain at the rear toe of embankment

31 Scarification The stripped surface under all canal embankments shall be loosened or scarified by means of plough or any other method Formation of Bund The thickness of embankment layer shall not exceed 25 cm (loose) before compaction and should be spread over the full width of the embankment Compaction shall be done by rollers or tampers to obtain specified density The thickness of the horizontal layer shall not be - more than 10 cm if compaction is performed by tampers; - 15 cm if compaction by 8 to 10 T Roller; - 30 cm, if compaction by pneumatic rollers. Extra width of 600 mm in thickness as measured perpendicular to the slope shall be provided on either side so that, when compacted, the sides of finished embankment slopes shall have not less than specified density

32 Borrow Areas The top soil with objectionable material should be removed to the required depth as ordered by the Engineer-in-Charge. No payment will be made for the stripped quantities Borrow area watering shall be done by the contractor in the manner specified by the Engineer-in-charge No payment shall be made for watering of the borrow area or drying the borrow area to reduce the moisture content

33 Optimum moisture content (OMC) The water content at which a soil can be compacted to the maximum dry unit weight by a given compactive effort is the OMC Too much or too little (water) is equally bad and is to be avoided. It is believed that only by experience is it possible to determine just the proper quantity of water to use with different classes of materials and their varying conditions. In rolling and consolidating of the bank, all portions that have a tendency of quake must be removed at once. It was not unit 1933 that a definite procedure for moisture and compaction control was established.

34 In a series of articles published in 1933, Proctor gave the principles of soil compaction and their application. Figure 90 shows the proctor compaction curve, which indicates that for a given compactive effort there is one water content, called the optimum water content, which produces the maximum density or smallest amount of total voids for a given cohesive soil. For greater compactive efforts on the same soil, different moisture -density curves are obtained, whose optimum points occur at the smaller water contents and at greater densitites than for lesser compactive efforts.

35 Foundations and Construction Materials

36 Water Content in Percent of Dry Weight

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50 Anantapur Drinking Water Supply Project * The parched earth holds no hope for this farmer * Bone deformations caused by excessive fluorine in the ground water

51 * The district of Anantapur is one of the most arid and backward districts in Andhra Pradesh. *The three major rivers Pennar, Hagari and Chitravathi that flow in the district are non-perennial and remain dry during the summer months. * Tanks and rivers run dry for most of the year and groundwater too is scarce. *Even the groundwater that is available is brackish and high in fluoride content.

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53 The excessive fluoride in the water was causing fluorosis leading to widespread skeletal and dental deformations. Thus, the people of Anantapur have for long been suffering due to lack of water even for drinking. The villagers had to trudge long distances in the harsh unforgiving heat to fetch water for their daily consumption.

54 In November 1995, Bhagawan Sri Satya Sai Baba announced His concern about the suffering of the people of Rayalseema due to lack of drinking water. He said, Rayalaseema should be ensured water supply all through the year. Today it is a Raallaseema (a rocky region). It must be transformed into a Ratnalaseema (land that glitters as a diamond).

55 In March 1995, the Sri Sathya Sai Central Trust had commenced work on a project to supply pure drinking water to villages in the drought-ravaged district of Anantapur. Bhagawan s mandate was simple and direct: Provide safe drinking water throughout the year to as many people as possible, in as many villages in the shortest possible time. Accordingly, a project plan was drawn up to bring water to the villages involving four kinds of schemes. The main strategy was to tap river water where available from dams, canals and river beds and then deliver the water through an elaborate network of storage reservoirs, booster pumps and pipes. The four schemes involved were:

56 PABR Direct Pumping Water is drawn from an already existing irrigation dam and is then distributed to the villages through a network of pipelines. For the project, water from the Penna Ahobilam Balancing Reservoir is sent for treatment to a rapid sand filtration system and then pumped to about 93 villages in the Kalyandurg, Atmakur and Udiripikonda sectors.

57 An infiltration well sunk on the bank of a river Infiltration Well Schemes In some areas, infiltration wells are sunk into riverbeds to tap water from underground streams. The subsoil water is then drawn throughout the year from these wells and fed to a collection well from where it is distributed to many places through a system of pumps. The water obtained is pure and requires very minimal treatment. Wells were sunk on the banks of the Chitravathi, Hagari and Pennar rivers for this purpose.

58 An offtake well drawing water from a massive summer storage tank Summer Storage Tank Schemes This method is used in places where the surface water dries up during acute summer conditions. Water is tapped from the Tunghabhadra Canal during the rainy season and is fed to a set of summer storage tanks, from which water is pumped during the dry season. The summer storage tanks are about 100 acres in extent. This scheme covers 97 villages.

59 Life just got easier; People collecting water from a cistern Constructed in the village Borewell Schemes This simple scheme covered 279 villages and involved drilling deep borewells and installing submersible pumps to draw out the water. This procedure was used wherever the groundwater was found to be sufficient and free from excessive fluoride content.

60 The first phase of the project was inaugurated on 18th November 1995 by the then Prime Minister of India, Shri P.V. Narasimha Rao in a function held at the Poornachandra Auditorium in Prasanthi Nilayam. Altogether, 731 villages were covered in the project at a cost of Rs.3000 million and was completed in a record time of eighteen months thanks not only to a dedicated team of workers from various establishments but also thousands of inspired villagers who contributed their mite to make this Divine project successful. A total of 1.25 million people were benefited by the project. The nightmare had at last ended for the people of Anantapur. The villagers will never again have to trek long miles for pure and safe drinking water, for it is now available almost at their doorstep. The frightening scepter of fluorosis too is behind them. For, Bhagawan, moved to compassion by their plight had resolved to wipe away their tears once and for all.

61 Project Statistics: About 2000 kilometres of pipeline of varying diameters were laid 43 sumps with capacities ranging from 1 lakh (0.1 million) litres to 25 lakh litres were constructed 18 balancing reservoirs with capacities ranging from 3 lakh litres to 10 lakh litres have been constructed on the top of hillocks Construction of 270 overhead reservoirs. Capacity: 40, litres 125 ground level reservoirs were set up. Capacity: 20,000 litres 80,000 litres. More than 1500 precast concrete cisterns of 2500 litres capacity have been installed in various villages. Each cistern has four taps for people to collect water.

62 The project was formally handed over to the Government of Andhra Pradesh in October This project has received much acclaim from the Government of India: The Ninth Five Year plan document of Government of India added a citation to the Trust in appreciation of the project, which read Sri Sathya Sai Trust has set an unparalleled example of private initiative in implementing a project on their own, without any state's budgetary support, a massive water supply project, with an expenditure of Rs. 3,000 million to benefit 731 scarcity and fluoride / salinityaffected villages and a few towns in Anantapur district of Andhra Pradesh in a time frame of about 18 months.

63 Postage stamp On 23rd November 1999, the Department of Posts, Government of India, released a postage stamp and a postal cover in recognition of the pioneering service rendered by Bhagawan Sri Sathya Sai Baba in addressing the problem of providing safe drinking water to the rural masses.

64 Following the Anantapur Drinking Water Supply Project, the Sri Sathya Sai Central Trust replicated the model to provide water to 320 villages in Medak and Mahabubnagar districts of Andhra Pradesh. Just as in Anantapur, the groundwater in these regions contains excessive concentration of fluorine. Pollution from industrial effluents had further aggravated the problem. The Trust stepped in to provide safe and pure drinking water to the people of these districts in the year 2001

65 District Map of Medak

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67 The project draws water mainly from the backwaters of the Jurala Project built on the Krishna River in Mahabubnagar district and from Manjeera River in Medak district. The project that cost Rs.530 million covered a total area of 640 sq.km benefiting an aggregate population of about 1 million in the two districts.

68 Sri Sathya Sai Water Supply Project For millions in Rayalaseema, Andhra Pradesh, getting pure drinking water was a daily drudgery. It meant trudging long distances and often in vain. And then, the Sri Sathya Sai Central Trust decided that the villagers need never again trek for something, which ought to be on their tap.

69 THE IMPOSSIBLE BEGAN TO TAKE SHAPE The result - Sri Sathya Sai Water Supply Project covering more than 700 villages in Ananthapur district and providing water to a million people who lived all their lives on the edge of drought and despair. This was made possible - in less than a year by Bhagawan Sri Sathya Sai Baba, who reached out, to the forgotten villages with a deep sense of urgency, and the project was completed with speed and efficiency. In November 1994, Sri Sathya Sai Central Trust, the Panchayat Raj department of Government of Andhra Pradesh and the construction unit of Larsen and Toubro moved quickly, submitting plans for providing drinking water to more than 700 villages and urban centers such as Ananthapur, Kadiri and Dharmavaram.

70 FOUR SCHEMES Sri Sathya Sai Water Supply Project consists of four schemes: Comprehensive Protected Water Supply Schemes involving infiltration wells, collection wells and associated pumping stations behind the Chitravati Balancing Reservoir at Paddakotla and Chinnakotla, covering 169 villages. Sources for other infiltration wells include Pennar and Hagari River, which cover 93 villages.

71 Direct pumping from Penna Ahobilam Balancing Reservoir and treatment through rapid sand filtration system. This consists of two major lines passing through Kalyandurg and Atmakur, covering 93 villages. Comprehensive Water Supply Schemes through seven summer storage tanks ranging up to 100 acres by tapping water from Tungabhadra High Level Canal, when water flows in the canal, covering 97 villages. The Protected Water Supply Scheme covers 279 villages. It involves drilling deep bore wells, construction of storage tanks and installation of pipeline networks. The spirit of involvement extended to thousands of villagers who pooled in their efforts to make the impossible come true.

72 Significant features that characterize the uniqueness of this project include: * Stringent time frame, * Vast magnitude, * Project cost funded by a charitable organization.

73 SALIENT FEATURES Laying of more than 2,000-km pipelines, ranging from 80 mm to 600-mm diameter. Construction of 43 pumps from 100,000 to 2,500,000 litre capacity. Construction of 18 balancing reservoirs at the top of hillocks with capacities ranging from 300,000 to 1,000,000 litres. Construction of 270 overhead reservoirs with capacities ranging from 40,000 to 300,000 litres. 125 ground level reservoirs with capacities ranging from 20,000 to 80,000 litres. Installation of more than 1,500 precast concrete cisterns of 2,500 litres capacity, with provision for four taps to be used by the villagers.

74 Behind it all is the power of commitment and service - a power that attracts many talents and creates a synergy of efforts directed towards changing the quality of life in the wilderness of Rayalaseema. And it all happened because of the underlying spirit of Bhagawan Sri Sathya Sai Baba just to create a New World for people long forgotten in the wilderness.

75 MEETING THE NEED OF MEDAK AND MAHBOOBNAGAR DISTRICTS Medak and Mahboobnagar districts of Telengana region in Andhra Pradesh are drought prone and fluoride affected. Bhagawan Sri Sathya Sai Baba willed that pure, safe drinking water must be literally poured into the parched life of people of the two districts. Hence the project took off during March 1999 and Sri Sathya Sai Central Trust, Puttaparthi provides drinking water to 320 habitations in these districts. 145 villages in Mahboobnagar and 175 villages in Medak districts profit from this project. 12 comprehensive protected water supply schemes were installed, covering 250 villages. Another 70 individual protected water supply schemes serve 70 villages with bore wells as sources.

76 The engineering work included the construction of civil structures such as water treatment plants, overhead reservoirs, ground level reservoirs, pump houses etc. as well as project management services for the execution of mechanical and electrical works. The total length of the pipelines is approximately 800 km including various types of pipes such as AC, PVC, HDPE, PSC, GI and MS of diameters ranging from 63 to 600 mm. Work commenced in May 1999 and a total of 290 villages were completed by 23rd November 2000, i.e. on the 75th birthday of Bhagawan Sri Sathya Sai Baba.

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