Barrages as a better alternative to Polavaram dam project

This discussion report suggests that barrages would be a better alternative to Polavaram Dam Project in Andhra Pradesh

BARRAGES AS A BETTER ALTERNATIVE  TO POLAVARAM DAM  POJECT

(Replies to Discussion Report of Advisory Committee on alternate proposals made for

Polavaram project by Sri.T.Hanumantha Rao, former Engineer-in-Chief, AP State)

 

Date: 06-03-2010                                                                   T.HANUMANTHA RAO

                                                                                                 Tel 040-23402048

 

(Note:  The technical views of Government experts presented in the Discussion Report(DR) of the State Government Advisory committee, are totally in variance with the concept and spirit of the alternative low barrages proposed by the author  on 26-10-2009 and also in the tabular statement (28-11-2009), the  Clarifications and the calculations (20-12-2009).  One of the reasons for the gap appears to be due to the fact that the Irrigation Engineering Officers who met the author initially had  promised to meet the author  later along with the relevant plans have not met him.  As a result a technically feasible, financially attractive and administratively superior design with far less submersions (& no human risk to 46 lakh lives due to dam break Tsunami type wave), is made out as a design that is exactly the opposite of what the author proposed as an alternative to Polavaram dam.  This is due to an inappropriate application of a technology which is in variance with the philosophy and concept of the Alternative Proposals (AP).  Technical details pertaining to these aspects and how the actual costs and submersion areas etc… would workout in the alternative proposals are briefly discussed below.)

 

  1. Number of Low barrages (3): The Concept of the alternative proposals(AP) is to obtain a usable (live) storage of 75 TMC at a number of low barrages, instead of at one place at Polavaram Dam, since the dam which among the other things involves in huge submersions as well as risks of dam break.  The storages created in these low barrages will entirely be ‘Live’ since water can be drawn upto bed level (Similar to flow in an unobstructed river) and hence there will be no dead storage or MDDL, as provided by Government experts in page 21 of the Discussion Report (DR).  There is no need to provide four prohibitively expensive barrages and obtain a storage of 222.225 TMC (Vide page 21 of DR) where as 75 TMC storage would be adequate (as contemplated in the original Polavaram Dam Proposal). These very big storages and high FRLs had contributed to the exorbitant cost of Rs.19,108.53 crores (Page 18 of DR).  If the Spirit and philosophy of alternative proposals are properly adopted by appropriate selection of Barrage sites, FRLs Storages and the cost of  proposals would workout to Rs.7143 crores (as described in detail in the later paras).  Again very high water levels (FRLs) than required were provided in page 21 Dr and this resulted in a huge submersion of a total of 345 villages, where as the high dam at Polavaram original proposal would submerge only 276 villages.  (Vide page 21 of DR). To put it mildly the designs worked out in the DR, lacks appreciation of the concepts and philosophy of the alternative proposals.  It has to be noted that only three low barrages (including Polavaram) were indicted in the tabular statement clarifications as against four calculated in the DR.  The proposal of Kunavaram barrage costing Rs.5,330 crores and submerging 202 villages (Vide page 21 of DR) has no place in the AP and has to be therefore deleted altogether.  The details of the barrages as provided in Dr and what these should be as per the concept of AP are discussed below.  As a result , it is now shown , how the cost as per the Alternative Proposals (Rs.7143 Crores) would be lesser than the cost of Original Polavaram (Rs.8713.09 crores) as well as Rs.19,108.53 Crores shown in DR Also the number of villages submerged as per the AP would be 72 no’s as against 276 no’s in the original Polavaram dam proposal as well as 345 shown in page 21 of Dr.  Generation of Hydropower as per AP is 1038 MW as against 201 MW shown in page 61 of Dr and 960MW of Original Polavaram proposal.  Any new concept will have problems in understanding in the initial stages and this alternative proposal is no exception to this.
  2. Polavaram Barrage:  Selection of site for a barrage is very important for technical reasons as well as economy.  This is possible only after a detailed investigation is done, keeping an eye on various possible alternative sites and their relative costs.  An improper site, though technically possible may result in the cost going up by two or three times more than an optimally selected site.  The cost of this lower barrage built upto maximum flood level is depicted in the DR as almost equal to the cost of a high dam provided in the original proposal.  Such a strange phenomenon should automatically lead to investigation of alternative economical sites for constructing the low barrage.  In the case of this low barrage, the site of the old dam proposal was selected in the DR.  At this site the barrage would be unduly long (3077 meters, vide page 21DR) This can be reduced to one third (say 1 Km long) by selecting a downstream site as indicated below.  For the original Polavaram Proposal, Constructing, concrete/masonry dam and providing spillway, Crest gates on the top of  dam are not possible in the river bed, since rocky foundations are not available at any reasonable depth in the river.  As such earthen dam was selected for the river portion and spillway located on the right bank where rocky strata is available.  In the case of a low barrage, since it will have to be designed as ‘Weirs on Sand’ principle (floating foundations) a suitable site on the downstream of the old proposal (at a distance of about 2.6km) and immediately down streams of the surplus course can be investigated for the low barrage site.  At this place, the river width from bank to bank is about 800 meters and about 1km long barrage can be constructed at this place.  The length and number of gates will have to be designed so as to get the required cross section area of the river under MFL conditions of 36 lakhs C/s discharge.  If the river width is not adequate for this purpose, the structure will have to be extended on either side and suitable approaches provided on the upstream and downstream sides.  16.48 meters depth of gates were provided in page 24 Dr.  This has to be increased to 20 meters depth so as to get the required cross section area, economise the design and keep sill of gates at bed level. 

Foundation raft concrete for the piers, will have to be designed so as obtain sufficient anchorage required for these gates. The bottom of gates will have to be kept at the average bed level, in order to facilitate drawal of water upto the bed level (for Godavari delta Rabi crop). In other words when gates are opened the river would be flowing down naturally as earlier, as if there is no obstruction.  This stored water from top of gates upto bed level can also be pumped for the requirements of the Polavaram canals, during the non flood periods.  There is no need to provide dead storage by keeping MDDL at 28.956, as provided in page 21 DR  The assumption that water stored above this MDDL only (4.204 TMC) is available for pumping is not correct.  For calculation of pumping during the flood period, the water levels are considered as varying from 28.956 and 30.48 in the DR. During this flood flow period of over 4 months the water levels will have to be maintained at near FRL of 30.48 by suitably regulating the barrage gates and allowing the excess flows down the barrage.  Thus it may be seen that there is no need to pump stored water, as long as there are flood flows in the river and the entire 169.61 TMC  demand of Polavaram (Page 37 of final report June 2007) during Khariff season can be pumped when the river is in floods and water is then available at near FRLs.

In the Polavaram Original proposals, the Rabi season demands of Godavari delta and Polavaram canals were contemplated to be met through the yields (flows in the river) and 75 TMC stored water.  In the Alternative proposals also, a similar method will have to be followed.  Stored water will have to be pumped from a level of 30.48 extending up to almost the bed level and to facilitate, this the suction foot valve will have to be kept at a level corresponding to the bed level in a depressed sump so as to avoid vortex problems.  The static head of pumping will than be increasing as the water levels fall from 30.48M to about 11.00 M  in the pond.  The quantity of water to be lifted from lower levels will be a fraction of the quantity of water to be lifted from higher levels and the actual power requirements to pump during January-May will have to be calculated on a weekly or fortnightly basis.  The installed pumping capacities (HP) to pump large quantities of water for Khariff Season requirements (from higher water levels) would be more than the required capacity to pump relatively a fraction quantity of water during the Rabi season (from the lower levels in the pond).

The cost of alternative Polavaram barrage is estimated in page21 Dr as Rs.3415 crores almost the same as the original Polavaram dam proposals which comprise of a high earth cum rock fill dam, separate spillway, bridge, lengthy surplus course over 3km long etc. (Rs.3630 crores) With proper selection of site for the alternative proposals, the earth dam in the river will get replaced by a gated structure and there will be no necessity for a separate spillway (similar to Kantalapalli and Dummagudem which are now under construction).  In such a case, the cost of barrage as per AP will get reduced to about ½ to 1/3rd of the original Polavaram dam proposals (e.g. cost of Kantalapalli barrage is Rs.880 crores).  The main cost will be due to gates of Size 18M x 20M, Rs.650 crores (based on figures given in page 26 of DR) 4 rows of 12m depth piles for 1km length of barrage (1000 x 4 x 12 x Rs.5900) Rs.28 crores, Spillway bridge 1km long Rs.8 crores (page 27 of DR) piers Rs77 crores (Page 27 Dr) and adding for all other items like aprons concrete, steel etc. (On the basis of Kantalapalli barrage) Rs.637 crores, the total cost of the alternate barrage would then workout to Rs.1400 crores, as against Rs.3415 crores provided in page21 DR. The topographical problem of aligning off take canals on either side will no more be an issue in the case of the down steam site for the low barrages of AP water can be drawn and pumped directly into the cisterns and the gravity canals can start immediately from the cisterns. There is no need to provide pumping mains on either side due to the advantage of plain terrain conditions being available on both the sides of the structure.  The canals can take off directly from the barrage structure without any need for separate pumping mains.

A gross storage capacity of 21.944 TMC is indicated in the design of DR (page 21) As pr the reservoir capacity tables (page 39, June 2007 report) the storage capacity at the proposed FRL 30.48(100ft) is 36.082 TMC.  Since the Kunavaram barrage proposal is not there in the AP design, the interception of storage due to Bhadrachalam & Sabari barrages as designed in the AP would be very low, sine the river bed levels at these places will be close to the FRL of 30.48.  If these interceptions in storage are considered as 1.082 TMC (to be actually calculated based on submersion area contour map) the storage available for usage would then be 35TMC and not 4.204 TMC as provided in page 21 Dr.  The reasons for this (as already discussed above) are that water stored and available up to bed level can either be drawn to the down stream side or pumped into canals and that there is no need to maintain an MDL of 28.956.  Gross and live storage capacities in the cases of Bhadrachalam and Sabari (Chatte Kunta) barrages were rightly shown as the same (vie page 21 of DR) and the same concept will have to be followed for this Polavaram barrage also.  Villages that would be submerged under this barrage at FRL 30.48 are noted as 66 nos in the DR (page21) out of this 32 villages are stated to be below FRL 30.48 M level and balance 34 villages above 30.48M level and extending upto 42.50 M (page 34 and 35 of DR) villages situated upto 12 M above FRL are shows under the list of submergible villages for the adduced reason that the ayacutdars lose approach to their fields due to water stored in the barrage.  The villagers can be provided with detoured cart tracks to approach their fields, and for this reason, they need not be asked to vacate their villages situated far above the FRL.  As such, the number of villages that will get submerged upto FRL 30.48 can be considered as 30 (vide page 129 of June 2007 report) and not 66 no’s as indicated in page 21 DR

  1. Kunavaram barrage:  As discussed in para 2 above this structure has no plae in the design of alternative proposals. As such the cost of Rs.5330 crores and submersion of 202 villages and other issues noted in the DR will automatically get eliminated.
  2. Bhadrachalam barrage:  In the DR, the FRL of this barrage is provided as 55.65M in order to obtain a gross and live storage capacities of 41.83 TMC & 41.63 TMC, respectively, submerging 58 villages.  There is no need to provide such high FRLFRL and submerge so many villages since it is enough to obtain a storage of about 25 TMC for the purpose f Alternative proposals.  As such if FRL of about 50.75 (with 20 M depth gates) is considered for this barrage t obtain a storage of about 25 TMC, the number of villages that would then get submerged, would get reduced to 26 that is less than half proposed in page21 DR.  The possibility of further reducing the number of villages under submersion by extending dykes on either side of barrage upto high ground (preventing outflanking) will have to be examined.  However this has to be actually worked out based upon submersion area contours.  Appropriate level and location of barrage site will have to be worked  out, so as to obtain a storage of about 25 TMC.  Length of barrage is indicated as 1858M in page 21 DR.  By an appropriate selection of site at a place either near the upstream kink or near the downstream kink, this length can be reduced to about 1100M.  Also for this purpose a site where bed level would be 30.50 can be investigated.  The cost of this barrage with reduced FRL from55.65 to 50.75 and reduced length would be about Rs.1200 crores, as against Rs.2970 crores provided in page 21 DR.
  3. Sabari Barrage:  As per DR page 21 a barrage at chatte Kunta on Sabari river was proposed where bed level is 30.155.  An FRL of 53.31 with gross and live storage of 17.75 TMC submersion of 19 villages and length of structure as 800 M were proposed at a cost of Rs.1180 crores (Page 27 of DR).  The FRL of 53.31 will have to be necessarily reduced to 44.72 (i.e.1M less than FRL of Old Polavaram dam proposals). Any increase in FRL (above 45.72) is unthinkable at this stage, as it would attract interstate problems with the upper states.  The alternative proposals should aim at solving interstate problems and not enhancing and hence an FRL of 44.72 is highly desirable to gain acceptance of the upper states.  The barrage site may be shifted to the downstream side, about half way between the state border and Kunavaram, where the bed level may be about 26.72M (18M depth gates) and width of rivers is less.  Since the FRL is drastically reduced from 53.31 to 44.72 the submersible villages will get reduced from 19 to 0 within Andhra Pradesh (page 50DR).  Also there will be no submersion of any village in the two upper states.  It may be noted in this context that more than 17 villages would get submerged in the upper states as per original dam proposals and the main objection of these states for Polavaram project is on account of this.  When site is shifted to the down stream side some villages here would get submerged.  The aim is to select an appropriate site, which gives storage of about 17 TMC with FRL at 44.72 and also limits the overall submersion of villages to less than 16 Dykes will have to be constructed on either side of barrage and taken upto high ground to prevent out taking (as indicated in above para). The cost of such a barrage with 18 M depth gates can be brought down from Rs.1180 crores to 900 crores by adopting the above measures (such as reduction in FRL from 53.31 M to 44.72M and reduction in length)
  4. Summary of costs submersion and power:  From the above paras, it can be seen that the cost of the three barrages at Polavaram, down stream of Bhadrachalam and Sabari as per the alternative proposals, would work out to Rs.3500 crores(1400+1200+900) as against Rs.12895 crores indicated in page 18 of DR.  The total number of villages that would be submerged under these three barrages as per the AP would be 72 Nos (30+26+16) as against 345 shown in DR and 276 no’s in original Polavaram dam proposal.  The total usable storage under these three barrages as per AP would be 79 TMC (35+25+17+2 due to storage between old dam site and proposal down stream site at Polavaram) as against 75 TMC required under the original Polavaram dam proposal.

In the comparison of costs (Page 18 of DR) the cost of original Polavaram project was indicated as Rs.8713.09 crores and that of the AP as Rs.19,108.53crores.  The details of alternative proposals will have to be corrected as indicated below, incorporating the changes indicated in the above paras.  Item I will get reduced from Rs.12,895 crores to Rs.3,500 crores.  Item2 can be the same as per original Polavaram proposals (Rs.940 crores and Rs.1800 crores), since the same amount of hydro power under alternative proposals would be generated.  Thus there would not be any decrease in costs(as explained in the power calculations). Item3 & 4 fro R&R, LA & Forests (Rs.2343.09 crores) provided under original Polavaram proposals will get reduced to about 1/4th  i.e Rs.600 crores in view of the submersion areas in AP getting reduced about 1/4th of the original dam proposal.  The item5 regarding pumping mains etc. Rs.1543 crores (page 58 DR) provided in AP will have to be reduced to Rs.303 crores as there will be no pumping mains as explained under para 3 above.

As against 182 MW power required for pumping provided in the DR, only 54 MW power is needed (as per calculations in AP due to reduction in ayacut).  For these reasons item 1 of the statement (page 58 DR) will get reduced to Rs.60 crores and items3 & 4 reduced to 243 crores and  thus a provision of Rs.303 crores will be adequate for this.  The total cost of Alternative proposals including Hydro power component would then work out to Rs.7143 crores (Rs.3500+940+1800+600+303=7143) as against Rs.19,108.53 crores provided in DR.  When compared to the original Polavaram project cost of Rs.8713.09 crores, the cost of AP would be cheaper by Rs.1570.09 crores.  Since the realistic submergence cost is expected to be about Rs.6000 crores, much higher than Rs.2343.09 crores provided in the original proposal, the actual cost of alternative proposal would be cheaper by more than Rs.4000 crores when compared to the original dam proposal.

  1. Power Generation:  It is mentioned in Page 60 of DR that 201 MW Hydro Power can be generated in the barrages proposal under alternative proposal as against 960 MW in Original Polavaram proposal. Details for this are not furnished.  As per calculations appended, the peak power generation would be 1038 MW (Bhadrachalam 423MW+Sabari 192MW+Polavaram423MW).  The peak heads at Bhadrachalam  would be 20.27M (50.75 -30.48), Sabari14.24M (44.72-30.48) and Polavaram 20M (30.48-10.48). These heads will be decreasing as the flood flow increases over a limit and virtually becomes zero under the Maximum flood flow conditions, since there will be no water level differences on the upstream and down stream sides at that time.  For example, if there is a flow of about 10 lakh cusecs in the river at Polavaram, water levels upstream of barrage would be maintained at about near FRL conditions of 30.48 and the flood would be allowed to flow through regulated opening of barrage gates.  Depending upon the river cross section, slope etc., water level on the down stream of barrage would then rise (say from 10.48 to 16.48) and the head would get reduced from 20M to 14M.  If the flood discharge gets reduced from 10 lakh cusecs to 1 lakh cusecs, the hydraulic head would increase from 14M to about 20M.  However there would be no hydro-power generation, during the few days of maximum flood flows occurring once in 1000 years.  This is due to no afflux during those rare events, when all the barrages gates are fully opened.  The actual power generation on a daily basis in a water year, will have to be calculated based on the discharges in the river.  This is similar to Hydro-power generation calculations in  a dam where water levels vary from MDDL (for power to FRL)

To assume that it is not possible to generate power in a barrage during the flood period because there would be no afflux is therefore not correct, for the reasons explained above.  Additional hydro-power units can be added on either side of the three barrages, and more power generated at a later date.

  1. Power consumed for lifting water into canals: The power charges to lift water into Polavaram canals will have to cover lifting of water required for diversion to Krishna basin, domestic and industrial needs of Visakhapatnam area and supply of water to an ayacut of 2.5lakhs acres under Polavaram project.  These would be as per calculations given in the alternative proposals and not as indicated in the DR.  The reasons for reduction of ayacut from 7.2 lakhs acres to 2.5 lakh acres are discussed below.  The reasons why cost of power charges would not be a liability on the project are also explained in these calculations (appended for ready reference).  Pumping additional quantities of water for Uttara Andhra Sujala Sravanthi or any other such project would be a charge on those projects and not on Polavaram project as explained below.
  2. Polavaram Ayacut:  In the clarifications given on AP dated 20-12-2009, the manner how the ayacut would get reduced from 7.20 lakh acres to 2.5 lakh acres were elaborated.  In the DR it was mentioned that 75 TMC storage is essential for the purpose of irrigating 7.20 lakhs acres under Polavaram project and 10.20 lakh acres under Godavari delta (Kharif and Rabi seasons) etc.  In the alternative proposals also, provision for this 75 TMC is made and there is no deduction in this.  However for cost of pumping equipment and pumping charges, realistic ayacut (2.5 lakh acres) under Polavaram project and all other demands (e.g. Krishna, Industrial, Godavari delta etc.) are retained without any reduction.

There is no need to delink Yeleru ayacut of 67,600 acres from Yeleru project and supply water to this area from Polavaram canals, so as to utilize this extent of water for the proposed new ayacut of Yeleru project lying above the Polavaram command.  The existing system of Yeleru aycut in Polavaram geographical command (67,600 acres) can continue under Yeleru project and water can be supplied to Yeleru ayacut above Polavaram command by pumping water from Polavaram canals and the scheme can be designed accordingly.  Polavaram left canal has adequate capacity for supplying the required additional discharge.

The total ayacut of 2,77,234 acres (page 51 DR) is shown as Visakhapatnam district (1,48,202 acres) Krishna district (61,901 acres) and West Godavari district (67,131 acres).  This will have to be analyzed with regard to what extent of area is already under irrigation through public lift irrigation schemes, tanks etc. where government funds were already spent.  A study has indicated that the area without any irrigation facility and where crops are raised under rain fed conditions, would be less than 1.8 lakh acres and that this much area only would need irrigation under Polavaram project.  Considered that private lift irrigation systems (e.g. tube wells, dug wells etc.) will have to be supplied water from Polavaram project and that M.I tanks ayacut in the command has to be deleted, this ayacut would get reduced from 2,77,234 acres to about 2.5 lakh acres.  It may be noted that ayacut under M.I tanks was deleted from the project commands in the cases of Nagarjuna sagar and SRSP.  The same procedure can be followed for Polavaram project also.

With regards to the existing lift irrigation projects covering an ayacut of 3,75,166 acres (Page 51DR) it is mentioned that the “life of some of the existing L.I scheme is already over and the life of other schemes will be over by the time Polavaram project is completed”.  It is also stated that “since they will have to be abandoned, there is a need to supply this ayacut of 3,75,166 acres under Polavaram project”.  Pushkara, Chagalnadu and Tadipudi L.I schemes comprising of 3,23,126  acres do not come under this category to be abandoned since they were also taken up for construction along with the Polavaram project at almost the same time or slightly earlier.  In fact these schemes are still under construction, partly completed and about to be completed.  With regard to the other four L.I. schemes comprising 52,040 acres there is no need to abandon them for the reason that their life is over and then supply water from Polavaram project.  Their life time can be extended by repairs and renewals where ever needed.  Many of the present major lift irrigation project under Jalayagnam are lift schemes and they cannot be abandoned after a life time of the pumping equipment of say 15 years.  By appropriate renewals, whenever needed their life times can be extended and brought on par with other major gravity flow projects.  The cost of renewals will have to be included in the maintenance cost and would not form part of capital cost.

From the above discussion, it can be inferred that the Polavaram project will have to supply water to an ayacut not exceeding 2.5 lakh acres. With  repard to Uttarandhra Sujala Sravanthi, Rudramkota irrigation and other lift irrigation projects from Polavaram canals (Page 59 DR) the cost of pumping equipment and pumping charges for lifting Godavari water will have to be borne under the respective schemes, as they cannot be a charge on the Polavaram project. They are not existing schemes and they would take shape only after Polavaram project is constructed.  They have to be designed on the basis of the available conditions in Polavaram project.  Also this lift from Godavari river would be relatively minor when compared to the big lifts required to pump Polavaram water to much higher areas.  Hence these costs will have to be deleted for purposes of comparison.  There is no need to abandon the existing L.I projects as discussed above. Such an action would result in wastage of public funds, since the civil works (such as pump houses, structures along pumping mains, immovable structures, cisterns etc..) executed at a high cost would all go to waste.

  1.  Interstate aspects and approvals for alternative proposals:  In page 11 of DR it is mentioned that in the case of the alternate proposals, fresh DPR will have to be prepared and clearances will have to be obtained, apart from fresh consultations and consent of the upper states and that all these would delay the project. The correct picture is indicated below. Since the alternative proposals are simple barrages, it may take 3 to 6 months time to prepare the Detailed Project Report and in the mean while all the required clearances can be obtained from the government of India.  Upper states would gladly welcome the low barrages proposals as no villages in their state would get submerged.  It may be noted that these states stalling the Polavaram project for the past several years on the main ground that more than 17 villages in their states would get submerged under the original Polavaram proposal. The alternative proposals would get completed much earlier than the dam since the structures are also simple and small.  There was no progress on the construction of the dam for the past 3 to 4 years for one reason or the other.  If the past experience of Orissa Government in stalling the Vamsadhara stge-II and Jhanjhavati projects for the past over two decades is any guide, there appears to be no hope for completing Polavaram dam as per original Polavaram in the near future.  Orissa government has already taken up this issue to the Supreme Court and it is also reported that certain clearances are not yet given to Polavaram dam.  In the case of these alternative proposals which give the same benefits of original Polavaram dam, all these stumbling blocks would automatically get eliminated and project completed very quickly at a lesser cost among the other several advantages elaborated above.  Even though it may take six months time to call for tenders for alternative proposals, this may have tobe viewed in the present context of yet to call for revised tenders fro dam, spillway, power blocks etc…
  2. Navigation: Though navigational facilities are provided in the original dam proposal (page 9 of DR) this navigational canal has to be taken through a tunnel (about 1.0km long) and as such small launches and boats only can ply.  There is no scope for sea going vessels to pass through such small canals and tunnels. In the alternative proposals, sea going vessels can be taken through the barrage locks and this would ultimately lead to the economic development of the whole Godavari area upto SRSP(upto 650 km distance) similar to what happened in St.Lawrence River (Sea Way), Mississippi etc in the USA .

Such economic development of Godavari basin through navigation of sea-going vessels will one for all get deprived, if Polavaram dam is executed as originally proposed, resulting in great loss to the nation.

 

                                                                                                  (T.HANUMANTHA RAO)

Encl: Design details  : 2 pages

          L.S. Sketch       :  1 page

          Extracts of DR          24 pages

          Extracts of June 2007, Report 3 pages

 

 POLAVARAM BARRAGE (ALTERNATIVES TO DAM)

DESIGN DETAILS

 

1. Discharges in canals (left & Right) in kharif season:

 (a)  Ayacut (total) = 2.5 lakh acres @a duty of 75 ac/cusec discharge= 2,50,000   = 3333 cusecs

                                                                                                                       75

 

 (b) Krishna Diversion in 120 days = 80 TMC

       Q in 1 day = 80/120 = 2/3

      @ 1 TMC/day discharge                = 11,574 c/s

      2/3 TMC/day discharge                  = 11,574 x 2/3 = 7,716 cusecs

 

(c) Domestic & Industrial water

      365 days = 24 TMC

      1 day = 24/365 TMC Q = 24/365 x 11574 =761 Cusecs

      Therefore Total Discharge in both the canals = a+b+c= 11,810 cusecs

                                                                     or 11810/35.316 = 334.5 Cumecs

     (Note: during the non Kharif season there will be pumping mainly for (c) requirement)

2. HP of pump sets required for both left & Right canals:-

     FSL Left Canal  =40.54 m

    Water level in barrage (Allowing 1m lower level during 4 month flood season) = 29.48m

    Therefore Static head = 11.06

     Adding Friction losses @ 10% = 1.10, total Head = 12.16m

    HP = 334.5 x 1000 x 12.16 /75 x 100/76 (eff. of motor  95%  x  eff ump 80% = 76%  )

   =  71,360HP or 71360 x 0.746 = 53235 kw or 54MW

 

3. POWER CONSUMPTION FOR PUMPING FROM RIVER TO CANALS:-

     Data

a)      Total max discharge in canals = 11810 cusecs or 334.5 cumecs

b)      Total head=12.16m; HP=71.360; KW= 53235 (54 MW)

c)      Maximum pumping would be in 4 months (120 days or 2840 hrs)

d)      In the other days of the year, pumping for Krishna delta and drinking water will be less and power consumed during this period can be considered as 30% of the peak power consumed in 120 days.

CALCULATION OF POWER CONSUMED:

KW hrs consumed in 120 days or 2880 hrs = 54,000 x 2880 = 15,552 x10(power 4)

KW hrs consumed during the other days in the year (say about 30% of above)

=4,448 x 10 (power 4) or  = 20,000 x 10 (power 4 ) or 2 x 10 (power 8)

Cost at Rs.1.50 per unit = 2 x 10 (power 8) x 1.5=3 x 10 (power 8) or Rs.30 crores

Thus the annual notional power consumption cost=Rs.30 crores.  This would be a notional profit to the irrigation Department, as hydro-power is produced with capital and maintenance cost borne by the irrigation Department.

4. POLAVARAM LOW BARRAGES –HYDRO-POWER GENERATION

1.Barrage D/s of Bhadrachalam:

 Q= 1,00,000c/s or 2832 cumecs on an average for peak power

H=20m (water level differences between U/s and D/s 50.75-30.48 = 20.27 or 20m) M.W.=cum x Head/75 x eff x 0.746 = 2832 x20/75 x 0.75x0.746=423 MW

Very large discharge axial flow turbines will have to be used.

2. Barrage across Sabari: Q = 65000 c/s or 1841 cum and H = 14m;

    44.72-30.48:14.24 or 14m MW = 1841 x 14/75 x 0.75 x 0.746 = 192 MW

3. Low barrage at Polavaram;  Q = 1 lakh c/s or 2832 cum & H = 30.48-10.48 = 20m 

    MW= 2832 x20/75 x 0.75 x 0.746 = 423 MW

4. Total Hydro power = 423 + 192+423 = 1038 MW

 

 

 

 

 

 

 

 

 

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