` Design Intent Memorandum of KAWATHA BARRAGE (STORAGE) PROJECT TAL. Balapur DISTT Akola MAHARASHTRA for Government of Maharashtra Water Resources Department CONSULTANTS WAPCOS LIMITED. (A Govt. of India Undertaking) 76- C, Sector -18, Gurgaon – 122015 September 2012
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Design Intent Memorandum of
KAWATHA BARRAGE (STORAGE) PROJECT
TAL. Balapur DISTT Akola MAHARASHTRA
for Government of Maharashtra Water Resources Department
CONSULTANTS WAPCOS LIMITED.
(A Govt. of India Undertaking) 76- C, Sector -18, Gurgaon – 122015
Kawatha Barrage (storage) Project is a proposed Minor Irrigation Project envisaging construction of R.C.C. Barrage across Mun River and earthen embankments on left and right flanks to irrigate 1722 ha of land. Mun River is a tributary of Purna River which is the main tributary of Tapi River. The Barrage site is located upstream of Village Kawatha in Balapur Taluka of Akola District. The location of the Barrage site at Latitude: 20' 50' 24 " and Longitude: 76' 46' 23" has been decided by the Project authorities. The catchment area up to Kawatha Barrage site is 2314.31 km2. 2.0 Hydrology
Hydrology of the project has been submitted by Project Authorities’ letter No.
WAP/Kawatha Barrage/Akola/2011 dated 7-02-2011 in the form of report titled: Volume – II Hydrology. The inputs provided in the report were further modified vide Executive Engineer, Akola Irrigation Division, Akola letter No 3550/TS-2/Kawatha Barrage/12 dated 15-05-2012 and No. 4317/TS-2/Kawatha Barrage/ 12 dated 8-06-2012 . The main design inputs for barrage on the above basis are as follows: i. 1 in 100 yr Flood = 9149.12 say 9150 cumecs ii. F. R. L. (Pond Level) = 242.5 m iii. 1 in 500 yr Flood / SPF = 12607 cumec iv. Observed HFL corresponding to 1 in 500 yr Flood / SPF = 246.63 m v. River Bed Slope = 0.0011 vi. Average River Bed Level = 232.5 m At Pond Level, the water shall spread inside the reservoir created by the embankment Dam. Before monsoon, the gates shall be opened fully so that the design discharge may pass safely through the barrage. It is intimated by Project authorities that the farmers shall lift water from the reservoir created through lift by themselves and as such no Outlet or Head Regulator is proposed. The design of embankment dam and hydro-mechanical works is not in the scope of work of WAPCOS. In the absence of G-D curve at the barrage site, cross sectional data provided in the drawing L – Section of Barrage Line has been used for the computation of G-D Curve. Manning's coeff has been assumed as 0.03 which is given in the Hydrology report. The un-retrogressed curve has been derived as per provisions of IS 2912. The River bed slope has been taken as 0.0011 which is provided in the report titled Volume – II Hydrology mentioned above. Vide letter No. 3329/TS-6/Kawatha Barrage/ 12 dated 6-07-2012 some observed water level values along with corresponding discharges were provided by Project Authorities. However these values were dependent on the passage of discharge through a saddle portion at 0.00 RD which shall not be there after construction of
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embankment dam, therefore, the G - D curve values computed as per above para were adopted for design of various components of barrage. Retrogression values of 0.3 m at high flood and 1.8 m for low discharges are adopted as per provisions of IS 6966. Following salient Water Levels (retrogressed as well as un-retrogressed) were computed on the basis of G-D curve : S. No.
3 Hydraulic Design 3.1 Waterway From the cross section of the river it was found that the average river bed level is about 232.5 m in the central portion of river. It was further intimated vide letter No. 3329/TS-6/Kawatha Barrage/ 12 dated 6-07-2012 that to protect right bank the waterway of barrage should not be provided beyond RD 640 m. Therefore the barrage waterway was required to be shifted towards 0 RD. As higher ground was found at LHS, the waterway was divided into two portions with different sill levels so as to minimise earthwork as well for better river training etc. The waterway has been provided as follows: 8 nos bays each of clear waterway of 15 m with crest level at 233.5 m and pier width 2.5 m have been provided on RHS. These bays are further divided into two portions of 4 bays each (separated by a double pier of thickness 5 m having 25 mm thick expansion joint with seal). On LHS, 5 no bays each of clear waterway 15 m with crest level at 236.5 m and pier width 2.0 m are proposed. A double pier of thickness 4.0 m having 25 mm thick expansion joint with seal has also been proposed to separate RHS and LHS portion of waterway. No. Width(m) Total (m) RHS Portion Bays 8 15 120 LHS Portion Bays 5 15 75 Piers RHS Portion 6 2.5 15 Double Pier RHS Portion 1 5.025 5.025 Piers in LHS Bays 4 2 8 Double Pier between RHS and LHS Portion 1 4.525 4.525 Total waterway between abutments = 227.55 m The above waterway has been provided to pass safely the design flood of 9150 cumec (1 in 100 yr Flood). The freeboard is checked for design flood of 12607 cumec (1 in 500 yr Flood). Due to uncertainty of computed G-D curve and safety of
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embankment dam provided on both sides of Barrage, the observed high flood level of 246.63 is considered for freeboard computation in place of computed value by G-D curve (which is lower than observed value at EL 246.53 m). Afflux for 1 in 100 year flood is about 0.27 m and for 1 in 500 year is about 0.75 m therefore affluxed HFL for 1 in 500 year flood is 247.38 m. It is seen from the calculations that the afflux is well within limits. Top of piers are provided with 1.52 m freeboard above this level at EL 248.9 m. The top deck level of bridge provided is further 2 m above at EL 250.9 m
See Annexure - II for detailed hydraulic calculations
3.2 Energy Dissipation Arrangement
Since rock level is very deep and barrage is founded on soil, a stilling basin has been provided to take care of excessive scouring and undermining of foundation.
The stilling basin requirement have been based on different conditions viz design discharge passing with 20% concentration and flood passing with various gate openings 1 m, 2m, 3m etc at pond level.
A condition has also been tested when 25% of design discharge (i.e. 2287.5 cum) is released from barrage through equal partial release from all gates of RHS portion and pond level is maintained on upstream.
Based on all such considerations and as per provisions of IS4997, stilling basin with cistern level at 230 m and length 30 m has been provided for RHS bays & stilling basin with cistern level at 232 m with 25 m length has been provided for LHS bays. Basin Blocks have also been provided in the basin.
See Annexure - II for detailed hydraulic calculations
3.3 Silt Factor
Silt factor has been taken as 1.09 as per value provided by Executive Engineer, Akola Irrigation Division, Akola vide letter No 3550/TS-2/Kawatha Barrage/12 dated 15/05/2012. 3.4 R.C.C. Cutoff Walls
Cut offs are barriers provided below the floor of the structure both at the upstream and downstream ends. They extend from bank to bank and also in the longitudinal direction along the flow. The main purpose of cut offs is to lengthen the seepage path below the structure and also to prevent piping action below the floor. RCC cutoffs are chosen due to relatively hard foundation strata where driving of sheet piles is difficult and sheet piles may get damaged leading to unsafe seepage flow beneath barrage.
Upstream cut off is required for safety against scour and also to reduce the seepage pressures beneath the floor. Downstream cut off is required for safety against scour and also safety against piping action. The cut offs in the longitudinal direction also known as cross cut offs provide boxing effect adding to the stability of the blocks / units of the structure. They should be continuous and leak proof. The depth to which these are taken below the floor levels depends on the safety factor adopted in the designs. As a general practice in the design of barrages and weirs on
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permeable foundation, seepage below barrage is natural but the magnitude of seepage will depend upon the permeability of foundation strata. However the scouring, exit gradient and piping are taken care.
For safety against scour the required depth for upstream / downstream cut-
offs are EL 226.93 m (u/s) / 221.56 m (d/s) for RHS bays and 232.28 m (u/s) / 228.24 m (d/s) for LHS bays respectively. However upstream / downstream cut-offs have been provided upto the level of EL 225 m (u/s) / 221.5 m (d/s) for RHS bays and 229.0 m (u/s) / 226.2 m (d/s) for LHS bays respectively for consideration like soil strata, uplift force distribution etc. Since relatively impermeable strata may be encountered at the downstream cutoff location above EL 221.5 m and this may cause the uplift pressure to build up below the raft floor, it is proposed to provide 1200 mm thick layer of pervious material (sand) overlain by 600 thick inverted filter. Pressure release pipes shall be provided with outlet in basin blocks and end sill to safely release the water pressure. Non-return valves shall also be provided to avoid ingress of water below the raft. Cross cutoffs shall also be provided below double piers and abutments. The grade of concrete proposed for RCC cut off is M20 MSA 20.
3.5 Flexible protection works
Flexible protection works in the form of CC blocks and loose stone launching apron have been designed as per provisions of IS: 6966 on the upstream and downstream of the Barrage. The C.C. blocks of 1.5X1.5X0.9m size over 0.6m thick spawls on the upstream end of barrage floor and over 0.60m thick inverted filter and partly over 0.60m spawls have been provided on the downstream side of RCC floor.. The C.C. blocks on upstream and downstream end are provided to cater scour 1.5R and 2.0R for a length of 1D and 1.5D, where ‘D’ is the depth of scour below apron level and ‘R’ is the normal Lacey’s scour depth. Beyond C.C. blocks protection with loose stone apron both on the upstream and downstream ends have been provided. While computing the requirements of this loose stone apron, launching slope of 2:1 has been considered. The protections works are designed for a design flood corresponding to 9150 cumecs. This protection works form first line of defence for the barrage against scouring and shall need monitoring, maintenance and renewal as per requirement after every flood season. 3.6 Looseness Factor:
The looseness factor has been worked out to be 0.5. 3.7 Exit Gradient:
The foundation strata consists mainly of alluvial deposits and conglomerates. The fresh (hard) rock is encountered at considerable depth. The cut-offs have been taken up to El 225.00 m (u/s) / EL 221.5 m (d/s) for RHS bays and 229.0 m (u/s) / 226.2 m (d/s) against scour, seepage and exit gradient condition. With this arrangements, the exit gradient worked out as per Khosla’s formula is more than 1 in 6 against the safe exit gradient of 1 in 6 to 7 as per IS:6966.
For Hydraulic Design refer Annexure-II.
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4.0 Raft Floor
R.C.C raft foundation has been provided due to following considerations. i. The soil below foundation is having low safe bearing capacity. By combining
the footings of piers with raft, the unit pressure on the soil below piers get redistributed due to redistribution of pressure over raft.
ii. If random distribution of compressive zones exists in the soil foundation, raft structure acts as a bridge over the compressible zones and the differential settlements are minimized.
iii. A raft floor takes advantage of the weight of piers to resist the uplift pressure. iv. In seismic areas as in the present case raft foundation is structurally superior
in comparison of gravity floor with large thickness which is more vulnerable to cracking. The piers and abutments/ end piers are constructed monolithically in RCC M20 MSA40. For the purpose of structural design of raft: it would be divided into various zones depending on the intensity of loading transferred to the raft from external loading through piers. The raft would be designed as beam on elastic foundation.
Earthquake Forces:
According to IS:1893-2002 classifications, the location of the barrage falls under Earth Quake Zone-III. The design horizontal acceleration coefficient according to the above codes is 0.12 and vertical acceleration is 0.08. The earthquake forces are analyzed with the seismic coefficient method.
The following forces have been considered for the analysis and design of raft. (i) Dead Loads of Gantry cum Road bridge, piers and raft. (ii) Live Load due to Gantry cum Road Bridge IRC class A (iii) Impact and breaking effects of live loads (iv) Temperature forces transmitted through bridge bearings (v) Dead and live load of gates, stoplogs counter weights and hoist bridge (vi) Braking effect of gantry crane (vii) Buoyancy (viii) Differential hydrostatic pressure with one gate open and other adjacent gate
closed (ix) Seismic forces and moments and (x) Hydrodynamic forces due to earthquake. To resist the worst combination of the above forces and moments raft
thickness of 2.5m for RHS and 2.0 m for LHS portion is proposed. 5.0 Stability Analysis 5.1 Piers & Abutments
The top of the piers has been kept at EL248.9 to hold the gates clear off the maximum flood while making ample allowance for passing the floating debris under the gate. The height of the piers in the zone away from Gate Bridge and Gantry cum road bridge zones have been reduced as per dispersion requirement of loads. On downstream side the pier height is reduced from 248.9 to 238.5 m in incremental way allowing partial submergence of the piers on d/s and no submergence on u/s under pond level condition. The height of the piers away from gate bridge and gantry bridge is kept as minimum as possible and extended upto the ends of raft for
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countering the uplift, to avoid excessive cantilever action of raft and dead weight requirement while computing the overall stability of the structure. The barrage is divided into three units with 4+4+5 bays. Each unit is separated from other with a double pier. The units localize the settlements if any and allow expansion and make easy of construction. 5.2 Stability
The stability of gated barrage is checked against sliding, floating during flood condition and overturning for both non earth quake and earth quake conditions as per IS:6512. The factor of safety against sliding are more than the desired safe values of 1.5 and 1.2 respectively. For all possible combination of forces the resultant falls within the middle third and it is safe against overturning and tension. The maximum base pressures worked out for NEQ and EQ conditions are below the safe bearing pressure. The factor of safety against floating under flood condition is adequate.
6.0 Flared out Walls/ Flank Walls/ Guide Bunds
In continuation of the abutments, flank walls are provided on the upstream and downstream side. The flank walls ensure smooth entry and exit of water from diversion structure. Guide bunds are provided beyond flank walls to further train the inflow and outflow of discharge through barrage. These details are being worked out and are tentatively shown in the drawings. 7.0 Geotechnical Investigation:
The Geotechnical investigation were carried out by Project authorities. The
following reports prepared by Project Authorities were forwarded to WAPCOS: 1. Geotechnical Report, Geological Division, CDO, Nasik 2. Revised Geotechnical Report prepared by M/S Shreya Services, Nagpur
8.0 Bridge:
A single Lane Gantry cum Road Bridge for class 'A' loading without foot-path is provided on the barrage portion. The width of bridge is taken as 6.5 m to accommodate the gantry. The bridge deck top level is provided at 250.9 m whereas the embankment top may be kept at EL 248.9 m Therefore, in continuation of this bridge, approaches for app. Length of 40 m on embankments dam top with 1 in 20 slope may be provided to connect the bridge deck level with embankment top level as per actual site conditions. The embankment Dam top width may also be reduced from 6.5 m to required top width in this transition zone as per actual site conditions.
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References 1. IS: 2912:1999 Liquid Flow Measurements in Open Channels - Slope-Area
Method. 2. IS:4997:1968 Criteria for design of hydraulic jump type stilling basins with horizontal and sloping apron 3. IS: 6512: 1984 Criteria for design of solid gravity dams. 4. IS: 6966-Part 1: 1989 Guidelines for hydraulic design of barrages and weirs:
Part 1 Alluvial Reaches. 5. IS:14344-Design and construction of Diaphragm for under seepage Control-
Code of Practice. 6. CBIP Publication No.179_Manual on Barrages and Weirs on Permeable
Foundation Vol-I&II. 7. M. Hetenyi-Beams on Elastic Foundation. 8. IRC-5-Standard Specifications and code of practice for Road Bridges-
Section I-General Features. 9. IRC-6- Standard Specifications and code of practice for Road Bridges-
A P R V QSummation 4422.01 843.04 5.2453168 3.3375125 14758.522
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
Hydraulic Calculations for Design flood As per IS 6966
A. Design FloodDesign Flood Discharge (1 in 100 yr) =Q= 9150 cumecshas been taken as provided by Project Authorities for design of all components of Barrage except Freeboard for which Design Discharge has been taken as 1 in 500 yr flood = Q' =
12607 cumec as provided by Project authorities.
B. Lacey's Regime Width
Lacey’s Regime width = 4.83√Q = 462.017 m
C. Looseness FactorNo. Width(m)Total (m)Sill Elevation (m)
----------Total waterway between abutments= 227.5 mHenceLooseness factor 0.4924 say 0.5
D. Intensity of DischargeIntensity of discharge = Q / Total width provided between abutments
= Discharge per unit widthDischarge per unit width = q = 40.2198 cumec/mSilt Factor = f = 1.09 (By Project Authorities)
E. Scour DepthScour Depth= 15.3983 for looseness factor<1
Hence Scour Depth = R = 15.4 m
F. Velocity of ApproachVelocity of Approach = Va = q/R = 2.61195 m/sHead due to velocity = Ha = Va
2/(2g) = 0.34772 m
Mallikpur Curve
31
2
35.1
fqR
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
G. Water way calculation with 8 bays at EL 233.5 (RHS portion) and 5 bays at 236.5 (LHS portion)for Design Discharge(1 in 100 yr flood) 9150 cumecsWith all gates fully opened
Water Level corresponding to design flood(Un-Retro.) = 245.63 mAfflux assumed = = 0.2691 mAffluxed Water Level = 245.90 mSill Level of the RHS Portion = = 233.5 m
Dischage Q1 from RHS PortionDrownded Weir Formula = C L ( (H +Ha)
3/2 - Ha3/2)
Drowning ratio = d/s HFL - crest level of spillwayu/s HFL - crest level of spillway
ThereforeDrowning Ratio = 0.9783 i.e. 0.9783Cd = 1.17373 (from Mallikpur Curves)L = 120H = 12.40
Discharge Q1 = = 6381.02 cumecs
Discaharge Q2 from LHS BaysSill Level of the LHS Bays = = 236.5 m
Drownded Weir Formula = C L ( (H +Ha)3/2 - Ha
3/2)Drowning ratio = d/s HFL - crest level of spillway
u/s HFL - crest level of spillway
ThereforeDrowning Ratio = 0.97137 i.e. 0.9714Cd = 1.22152 (from Mallikpur Curves)L = 75H = 9.40
Discharge=Q2 = 2768.98 cumecs
Hence Total Discharge = =Q1+Q2= 9150 cumecs
Hence Affluxed HFL for 1 in 100 yr discharge is calculated as 245.9 m
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
H. Afflux Calculation for Discharge(1 in 500 yr flood) 12607 cumecsWith all gates fully opened
Water Level corresponding to design flood(Un-Retro.) = 246.63 mAfflux assumed = = 0.7472 mAffluxed Water Level = 247.38 mSill Level of the RHS Portion = = 233.5 m
Dischage Q1 from RHS PortionDrownded Weir Formula = C L ( (H +Ha)
3/2 - Ha3/2)
Drowning ratio = d/s HFL - crest level of spillwayu/s HFL - crest level of spillway
ThereforeDrowning Ratio = 0.94616 i.e. 0.9462Cd = 1.34737 (from Mallikpur Curves)L = 120H = 13.8772
Discharge=Q1 = 8641.27 cumecsDiscaharge Q2 from LHS BaysSill Level of the LHS Bays = = 236.5 m
Drownded Weir Formula = C L ( (H +Ha)3/2 - Ha
3/2)Drowning ratio = d/s HFL - crest level of spillway
u/s HFL - crest level of spillway
ThereforeDrowning Ratio = 0.93131 i.e. 0.9313Cd = 1.41372 (from Mallikpur Curves)L = 75H = 10.88
Discharge=Q2 = 3965.73 cumecs
Hence Total Discharge = =Q1+Q2= 12607 cumecs
Hence Affluxed HFL for 1 in 500 yr discharge is calculated as 247.38 m
J. Conclusions
Computed affluxed waterlevel for design discharge of 1 in 500 yr flood is 247.38 m.
Piers shall be taken 1.52 m above this affluxed water levelHence Pier Top = 247.38 + 1.52 = 248.90 m Bridge Top = 248.9 + 2 = 250.9 m
A slope of 1 in 20 shall be provided at the embankment top for length= 40 m on either side
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
K. Cistern Parameters
The cistern levels are calculated for design flood of 1 in 100 yr flood. For determination of levels and length 20 % concentration is considered. G-D curves computed for river is used for various levels
cistern Level shall also be checked for condition when all gates are opened by 1; 2; 3 m etc.at pond Level conditionAs per cl 4.3.1.1 of IS 6531 "Canal Head Regulator - Criteria and Design"Discharge through partly open gates = 2/3 C√(2g) (H1
3/2-H23/2)
g= Acc due to gravity = 9.81 m/s2
H1 = Head upto bottom level of gate openingH2 = Head upto top level of gate opening C = Constant whose value varies from 0.85 to 1.2 depending upon many factorTaking C = 1Pond Level = 242.5 mSill level of Centrl Bays = 233.5For opening = 1 mH1 = 9 mH2 = 8 mDischarge for one gate opening =12.9121 cumecsTotal Discharge = 103.297 cumecs all 8 RHS bays openD/s HFL for such case = 232 m top level of End Sill
Cistern Level 230.229Cistern Length 8.52141For opening = 2 mH1 = 9 mH2 = 7 mDischarge for one gate opening =25.0404 cumecsTotal Discharge = 200.323 cumecs all 8 RHS bays openD/s HFL for such case = 233 m RetrogressedCistern parameter for such case
For opening = 3 mH1 = 9 mH2 = 6 mDischarge for one gate opening =36.3305 cumecsTotal Discharge = 290.644 cumecs all 8 RHS bays openD/s HFL for such case = 233.5 m Retrogressed
For opening = 4 mH1 = 9 mH2 = 5 mDischarge for one gate opening =46.7149 cumecsTotal Discharge = 373.719 cumecs all 8 RHS bays openD/s HFL for such case = 234 m Retrogressed
Cistern Level 230.81Cistern Length 14.6588Hence Provide Centrl Bays Stilling basin at cistern top elevation 230 m and length
30 m along with Basin blocks
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
Similarily for LHS BaysDischarge through partly open gates = 2/3 C√(2g) (H1
3/2-H23/2)
g= Acc due to gravity = 9.81 m/s2
H1 = Head upto bottom level of gate openingH2 = Head upto top level of gate opening C = Constant whose value varies from 0.85 to 1.2 depending upon many factorTaking C = 1Pond Level = 242.5 mSill level of LHS Bays = 236.5For opening = 1 mH1 = 6 mH2 = 5 mDischarge for one gate opening =10.3844 cumecsTotal Discharge = 51.922 cumecs all 5 LHS bays openD/s HFL for such case = 234.5 m top level of End SillCistern parameter for such case
For opening = 2 mH1 = 6 mH2 = 4 mDischarge for one gate opening =19.7758 cumecsTotal Discharge = 98.8791 cumecs all 5 LHS bays openD/s HFL for such case = 234.5 m top level of End SillCistern parameter for such case
For opening = 3 mH1 = 6 mH2 = 3 mDischarge for one gate opening =28.0555 cumecsTotal Discharge = 140.277 cumecs all 5 LHS bays openD/s HFL for such case = 234.5 m top level of End Sill
These levels shall be further checked for safe exit gradients
9150
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
M. CC Blocks (Protection works)No concentration is taken in this caseSilt Factor = f = 1.09For RHS BaysDesign Discharge= Q = 9150 cumecsDischarge through RHS bays = Q1 = 6382.00 cumecs
1.5 R 24.7817 m U/S Scour Depth 2.0 R 33.0422 m D/S Scour Depth
River Bed Level u/s 232.5 mRiver Bed Level d/s 232 m
For U/S CC block CalculationDepth of Scour below Apron = D = U/S Apron Level -(Affluxed HFL- U/S Scour Depth(1.5R))
Therefore D = 11.65 m
For D/S CC block CalculationDepth of Scour below Apron = D = D/S Apron Level - (D/S HFL - D/S Scour Depth(2R))
Therefore D = 20.11 mD/S CC block Protection is 1.5 times the depth of Scour
1.5 D = 30.1683 m
Hence Provide CC Blocks 8 rows u/s and 20 rows d/s Ten rows of CC blocks shall be provided over inverted filter and ten rows over stone spawls seperated by a curtain wall as shown in drawing
For LHS BaysDesign Discharge= Q = 9150 cumecsDischarge through LHS bays = Q2 = 2769.00 cumecs
1.5 R 19.9851 m U/S Scour Depth2.0 R 26.6468 m D/S Scour Depth
Apron Level u/s 236 mApron Level d/s 234 m
For U/S CC block Calculation
Depth of Scour below Apron = D = U/S Apron Level -(Affluxed HFL- U/S Scour Depth(1.5R))Therefore D = 10.36 m
For D/S CC block Calculation
Depth of Scour below Apron = D = D/S Apron Level - (D/S HFL - D/S Scour Depth(2R))Therefore D = 15.72 m
D/S CC block Protection is 1.5 times the depth of Scour 1.5 D = 23.5752 m
Hence Provide CC Blocks 7 rows u/s and 16 rows d/s Eight rows of CC blocks shall be provided over inverted filter and Eight rows over stone spawls seperated by a curtain wall as shown in drawing
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
N. Launching apron
RHS Bays Upstream -
Depth of scour below the floor level on U/S side = L = 11.65 M (1.5R with u/s WL)Consider slope to be 2H : 1V Then launched length = √(5)* L = 26.054 MIf 1 m thickness of launching apron is adoped Qty of stones=26.054 M3For 1.5 m thick Launching apron, length of unlaunched apron=17.369 m
RHS Bays Downstream -
Depth of scour below the floor level on D/S side = L = 20.112 M (2R with d/s WL)Consider slope to be 2H : 1V Then launched length = √(5)* L = 44.972 MIf 1 m thickness of launching apron is adoped Qty of stones=44.972 M3For 1.5 m thick Launching apron, length of unlaunched apron=29.982 m
Hence Provide 1500 thick launching apron for length 18 m u/s and 30 m d/s
LHS Bays Upstream -
Depth of scour below the floor level on U/S side = L = 10.36 M (1.5R with u/s WL)Consider slope to be 2H : 1V Then launched length = √(5)* L = 23.155 MIf 1 m thickness of launching apron is adoped Qty of stones=23.155 M3For 1.5 m thick Launching apron, length of unlaunched apron=15.436 m say 16 m
LHS Bays Downstream -
Depth of scour below the floor level on D/S side = L = 15.72 M (2R with d/s WL)Consider slope to be 2H : 1V Then launched length = √(5)* L = 35.144 MIf 1 m thickness of launching apron is adoped Qty of stones=35.144 M3For 1.5 m thick Launching apron, length of unlaunched apron=23.429 m say 24 m
Hence Provide 1500 thick launching apron for length 16 m u/s and 24 m d/s
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
O. Flared Out Walls
Flared out walls are to be provided on upstream and downstream of Barrage between LHSbays and RHS bays and also between embankment and adjoining LHS / RHS Abutment
Flared out Walls between RHS bays and LHS bays
Design DataU/S D/S
1 Apron Level LHS bay = 232.5 m 232 m2 Apron Level RHS bay = 236 m 234 m3 Level Difference = 3.5 m 2 m4 Silt factor = 1.09 (See Hydraulic Design memo)
Design Parameters1 Top thickness of Flareed out wall
Minimum Top thickness of flared out /flank wall is 600 mm C. 5.7.1.1 of IS 11130 "Criteria for Structural design of Barrages and weirs"However 1500 mm is adopted as top thickness.
2 Length of Flank WallThe length of the flankwall as per cl 5.7 of IS 11130 UpstreamAt guide bund (upstream end of upstream flaredout wall) slope provided to the sides:
2 H : 1 VFor 3.5 m level difference Horizonal Length= 7 m
Vertical Length = 3.5 mSloping length L1= 7.82624 m
Length of upstream wall 2 to 2.5 times L1Length of upstream wall 15.6525 to 19.5656 m
However Provide 16 m length of flared out wall as shown in drawing
DownstreamAt guide bund (downstream end of downstream flank wall) slope provided to the sides:
2 H : 1 VFor 2 m level difference Horizonal Length= 4 m
Vertical Length = 2 mSloping length L2= 4.47214 m
Length of upstream wall 2.5 to 3 times L2Length of upstream wall 11.1803 to 13.42 m
However Provide 12 m length of flared out wall as shown in drawing
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
Flared out Walls between LHS Abutment and Embankment Dam
Design DataU/S D/S
1 Apron Level LHS bay = 236 m 234 m2 NSL Embankment dam side = 248.9 m 248.13 m3 Level Difference = 12.9 m 14.13 m4 Silt factor = 1.09 (See Hydraulic Design memo)
Design Parameters1 Top thickness of Flareed out wall
Minimum Top thickness of flared out /flank wall is 600 mm C. 5.7.1.1 of IS 11130 "Criteria for Structural design of Barrages and weirs"However 1500 mm is adopted as top thickness.
2 Length of Flank WallThe length of the flankwall as per cl 5.7 of IS 11130 UpstreamAt guide bund (upstream end of upstream flaredout wall) slope provided to the sides:
2 H : 1For 12.9 m level difference Horizonal Length= 25.8 m
Vertical Length = 12.9 mSloping length L1= 28.8453 m
Length of upstream wall 2 to 2.5 times L1Length of upstream wall 57.6906 to 72.1132 m
However Provide 70 m length of flared out wall as shown in drawing
DownstreamAt guide bund (downstream end of downstream flank wall) slope provided to the sides:
2 H 1For 14.13 m level difference Horizonal Length= 28.26 m
Vertical Length = 14.13 mSloping length L2= 31.5956 m
Length of upstream wall 2.5 to 3 times L2Length of upstream wall 78.9891 to 94.79 m
However Provide 80 m length of flared out wall as shown in drawing
Kawatha Barrage Project
Hydraulic Calculations Annexure- II
Flared out Walls between RHS Abutment and Embankment Dam
Design DataU/S D/S
1 Apron Level RHS bay = 232.5 m 232 m2 NSL Embankment dam side = 248.9 m 248.13 m3 Level Difference = 16.4 m 16.13 m4 Silt factor = 1.09 (See Hydraulic Design memo)
Design Parameters1 Top thickness of Flareed out wall
Minimum Top thickness of flared out /flank wall is 600 mm C. 5.7.1.1 of IS 11130 "Criteria for Structural design of Barrages and weirs"However 1500 mm is adopted as top thickness.
2 Length of Flank WallThe length of the flankwall as per cl 5.7 of IS 11130 UpstreamAt guide bund (upstream end of upstream flaredout wall) slope provided to the sides:
2 H : 1For 16.4 m level difference Horizonal Length= 32.8 m
Vertical Length = 16.4 mSloping length L1= 36.6715 m
Length of upstream wall 2 to 2.5 times L1Length of upstream wall 73.343 to 91.6788 m
However Provide 75 m length of flared out wall as shown in drawing
DownstreamAt guide bund (downstream end of downstream flank wall) slope provided to the sides:
2 H 1For 16.13 m level difference Horizonal Length= 32.26 m
Vertical Length = 16.13 mSloping length L2= 36.0678 m
Length of upstream wall 2.5 to 3 times L2Length of upstream wall 90.1694 to 108.20 m
However details in this regard shall be finalized after receipt of contour map of downstream area of Barrage
Kawatha Barrage Project
Exit gradient Calculation Annexure-II
Pond Level 242.5
CrestH = 10.5
U/S RiverBed 232.5
232 D/S River Bed
Stilling Basin 230.0
U/S CutOff
d = 10.5225 RHS Bay
D/S Cutoff
221.5
b= 64
Exit Gradient Calculations
Maximum water head acting for exit gradient = H = 10.5Depth of downstream cutoff = d = = 10.5Total Floor Length = b = 64
α = b/d = 6.095238
λ = 3.588362 Where
Exit Gradient = GE = 0.168036 Where GE =
or I in 6.0 Hence Safe
1dH
211 2
Kawatha Barrage Project
Exit gradient Calculation Annexure-II
Pond Level 242.5
CrestH = 8.5
U/S RiverBed 236
234 D/S River Bed
Stilling Basin 232.0
U/S CutOff
d = 7.8229 LHS Bay
D/S Cutoff
226.2
b= 62
Exit Gradient Calculations
Maximum water head acting for exit gradient = H = 8.5Depth of downstream cutoff = d = = 7.8Total Floor Length = b = 62