HYDRAULIC MODEL STUDIES
Hydraulic structures like dams, barrages, canal structures, bridge structures are very expensive from construction and maintenance point of view. It becomes very difficult many times for a design or a field engineer to understand the proper functioning of the structure during operation and therefore it becomes essential to test the model of such structures hydraulically in the laboratory before its construction.
GERI has got such well-equipped hydraulic laboratory where the Nation's prestigious Sardar Sarovar (Narmada) Dam models, as well as other national level hydraulic structures are tested. The Institute has facility to test hydraulic models of irrigation, canal as well as bridge structures in flumed models or comprehensive models. The Institute has its own tubewells, pumping system as well as canal network for carrying out the experimental works. The experimental works are carried out on priority & workload basis. Here is a team of experienced engineers for the hydraulic model construction and to carry out the analytical part.
Following important model studies of the state are conducted;
1. Sardar Sarovar Project Spillway:
- Spillway capacity: 24.50 lacs cusecs or 69400 cumecs
- The testing work was with reference to upstream reservoir water levels, flow characteristics, spillway capacity, energy dissipating arrangement design, pressure profile over the spillway section, downstream tail race channel design as well as downstream scour pattern.
2. Kun Aqueduct on Narmada Main Canal:
- Discharging capacity: 4632 cumecs
- Testing works for upstream flow/ scour characteristics as well as river training works.
3. Tapi Bridge Structure:
- Discharging capacity: 34000 m3/s
- Testing for upstream, downstream flow as well as scour characteristics observations. Necessity of number of bridge spans as well as river training works, bank protective measures and scour around the piers.
4. Bhadbhut barrage on physical Model
The physical models have been proved to be the best tools for solving the complex flow problems especially in case of dams, weirs and the barrage etc worldwide. With a view to assess the various hydraulic parameters in the complex flow conditions of this composite barrage structure, physical model study of Bhadbhut barrage is being carried out by GERI under the guidance of National Consultants.
View of location of Barrage and sea
View of model shows river reach from Shuklatirth
to the sea and the gauge post and sea
U/S and D/S side of Golden Bridge and
Railway Bridge of Bharuch
MAIN OBJECTIVES OF BHADBHUT BARRAGE
n To create storage of fresh water released from Sardar Sarovar Project
n Domestic water supply to Bharuch, Ankleshwar and other towns/ villages
n Industrial water supply to Dahej, GIDC, PCPIR, GNFC and other industries
n To check salinity ingress and improve river water quality
n To create new road connectivity from Hazira, Olpad, Hansot, Bhadbhut to Dahej
n Flood protection to areas along left bank of Narmada river and conservation / reclamation of land
n To divert fresh water from Narmada river to proposed Kalpasar lake
5. Auxiliary Spillway for Medha Creek Tidal Regulator:
- Discharging capacity: 11081 cumecs
- Experimental work was carried out to ascertain flow characteristics, scour pattern, total effect of river/ tidal waves, energy dissipating arrangements.
5. Garudeshwar Weir.
6. Sukhi Dam Spillway.
7. Panam Dam Spillway.
8. Ukai Dam Spillway.
9. Dolatpura Weir.
10. Meshwo Bridge on Sabarmati weir.
11. Sankheshwar Bechraji Bridge on River Rupen of Mehsana District.
- Discharging capacity: 5993 cumecs
- The structure was tested for flow/ scour characteristics as well as river training works.
Sankheshwar Becharaji - Rupen river - Mehsana: Bridge hydraulic model study for right bank guide bund
12. Sabarmati escape structure
Sabarmati escape structure on Narmada Main canal - A typical and unique study of an escape structure was carried out. The discharging capacity of the structure is 450 cumecs of water with 11 m fall was experimented. A typical energy dissipating arrangement with three tiered stepped - horizontal appron was suggested based on hydraulic model research studies.
Sabarmati escape structure on Narmada main canal - Hydraulic research studies in progress
The Institute takes high interest in carrying out hydraulic model studies of structures outside the Department as well as the parent state. Important hydraulic model studies carried out for state of Rajasthan is as under;
1. Mahi Hydel Phase II
2. Bisalpur Spillway
3. Bilas Irrigation Project Spillway
4. Som Kamla Amba Project
5. Mansi Wankal Project Spillway:
- Discharging capacity: 2850 cumecs
- Experiments for spillway capacity, pressure profile, energy dissipating arrangement & downstream scour pattern were conducted.
Mansi Wankal spillway project - Rajasthan - Hydraulic model for energy dissipating arrangement studies
6. Gosunda Project spillway
Hydraulic Research Studies of Tidal Regulator Cum Recharge Scheme:
Various Tidal Regulator are being planned or constructed across many rivers in the vicinity that are very near to the sea in coastal areas of South Gujarat as well as Saurashtra in Gujarat State. This type of structures are mainly constructed to prevent saline water intrusion towards the river upstream and to store sweet water on upstream river side & the structure. The rivers have high flood discharge and to safely negotiate this flood, masonry or concrete types of structures are constructed.
In the field Hydraulic laboratory of GUJARAT ENGINEERING RESEARCH INSTITUTE (GERI) VADODARA attempts were made by flumed model studies for the following objectives.
(i) To assess the upstream reservoir levels for the proposed structure.
(ii) To check the adequacy of efficacy of the D/s energy dissipating arrangement and to determine water profile / pressure over slopping apron for 25%, 50%, 75% & 100% of the proposed design flood.
(iii) To determine the scour characteristics on D/s of the weir for various percentage of flood.
The experimental observations visualized following facts.
(i) It was seen that adopted weir section functions well.
(ii) No negative pressures was developed over the entire weir section.
(iii) The weir works as a submerged structure and therefore proper formation of hydraulic jump was not seen. However a drowned jump scenario was developed in the model.
OPTIMISATION OF THE LENGTH OF HORIZONTAL APRON OF THE SPILLWAY UNDER SUBMERGED FLOW (CREST) CONDITION
In large hydraulic structures like spillways, weirs provision of effective energy dissipating arrangement is prerequisite requirement to protect the D/s topography and structures against the high velocity flood to reduce erosion in the D/s of the structure in natural river. When tail water rating curve approximately follows the hydraulic jump curve is slightly above or below it, then hydraulic jump type stilling basin with horizontal apron provides the best solution for energy dissipation having suitable rock condition. However when there is no free flow condition & there is excess tail water depth, under that situation submerged crest flows condition is observed. Under that condition no specific design criteria / guide lines are available so far in any of the standards. Bureau of Indian Standards (BIS) and other authorities have laid down specific guide lines only for the free flow condition. The same are being adopted by the designers for the submerged flow conditions in designing the horizontal length of apron which seems to be much higher and required to be reduced as it was seen experimentally that under the submerge flow the full length of apron in not required.
In the field Hydraulic Laboratory of GUJARAT ENGINEERING RESEARCH INSTITUTE (GERI) VADODARA attempts were made to frame the guide lines for the optimisation of the length of horizontal apron type of energy dissipator in case of submerged flow condition through hydraulic model studies.
A case study of Bhadar – II dam where 52 m long horizontal apron is provided at the toe of spillway the design flood 26380 cumecs having FRL @ 53.10 m crest @ 41.83 m with 27 Nos. of Radial gates , spillway length 405.32 m & TWL 48.70 m causing submergence of 60%. Experimental study was carried out in a flumed Hydraulic model of 1:50 Geometrically similar scale by reproducing two spans of the spillway. (37.18m width of proto). The flume was provided with discharge measuring devices and on D/s having wall an one side & on other side perspex (Transparent sheet) was provided so that flow characteristics and erosion can be visulized and studied.
Experiments were carried out for different apron length of 25m, 30m, 35m, 42.5m & 52 m by releasing 100% (26380 Cumecs) & 75% (19785 Cumecs) flood water keeping tail water levels as per site gauge discharge curve.
The model study was also carried out keeping apron length fixed say 30 m & charging D/s tail water level to 48.70 m, 49.70m,50.70 m, 51.70 m & 52.70 m (Raising
1 m Tail Water height for each set by keeping FRL constant @ RL 53.1 m by releasing 100%, 75%, 50% & 25% design discharge.
Experimental study revealed that apron length under submerged flow condition can be reduced up to 30% or 70% length is only required as the whole length of horizontal apron under submerged crest flow condition does not contribute towards energy dissipator. Thus it was confirmed by “HYDRAULIC MODEL TESTS” that for submerged crest flow the horizontal apron length can be optimised.
IMPORTANCE OF RIVER TRAINING WORKS AND HYDRAULIC MODELS
River Training works are the structures adopted on the river to guide the river flow, confine the flow in the channel, to control the bed configuration and to ensure safe disposal of flood.
Structures like bridges, cross drainage works, weirs and barrages etc. constructed across the river need badly the supporting training works as they are very important to prevent the river to discharge its course and make stable waterway, to reduce the erosion and to guide the flood water passing safely without flooding surrounding areas. It is also important to protect the approach embankments, river banks by deviating the river flow away from attacking banks.
To conform the design of structure by hydraulic model is one of the best economical method which will ensure safety of the structure as well as to minimise post construction activities like repairs and maintenance. It will also help in predicating disposal of bed and suspended load.
Various methods are adopted for river training as stated below.
(1) Guide banks.
(2) Spurs or Groynes
(3) Bank protection with launching aprons
(4) Marginal embankments or levees.
(5) Artificial cut offs
(6) Pitched islands.
Gujarat Engineering Research Institute situated at Gotri in Vadodara stated its hydraulic Research studies since 1971. The institute at its hydraulic laboratory carries out basic research as well as studies proposed by the clients for spillway / dams, weirs, canal and bridges, River training works, river bank protection works of bridges etc. the dam structures are tested and studied for their flood passing capacities, effective functioning of energy dissipating arrangements, upstream submergence, gate calibration and bank erosion. The canal structures are tested for their capacity, alignment, river training works as well as bank protection works. The bridge structures are studied to see the effect of the meandering nature of river, adequacy of the structure to pass the flood, alignment of structures, bank protective measurers and also necessity & therefore the lay outs of river training works. The aim behind carrying out hydraulic model studies is to ascertain proper functioning of the structures after construction or to suggest remedial measures for their effective working. Post construction studies are also carried out. Some of the hydraulic model studies carried out for river training works are highlighted below.
(1) MEN SYPHON AQUEDUCT ON NMC @ CH 17.10 KM.
(2) ORSANG AQUEDUCT STRUCTURE ON NARMADA MAIN CANAL (NMC) @ CH 48.590 KM.
(3) KARAD AQUEDUCT ON NMC @ CH 106.60 KM
(4) DRAINAGE SYPHON ON NMC @ CH 188.25 KM
(5) MALIYA BRANCH CANAL STRUCTURE ON SAURASHTRA BRANCH CANAL @ CH 96.157 KM
(6) BODELI NASWADI BRIDGE STRUCTURE
(7) TAPI RIVER BRIDGE STRUCTURE
(8) RUPEN BRIDGE @ CH 224 KM OF SANKHESHWAR- BECHRAJI ON STATE HIGH WAY
(9) AHMEDABAD MEHSANA PALANPUR BRIDGE @ CH 41.81/8/KM ON STATE HIGHWAY.
(10) BRIDGE ON RIVER KHARI ON PRANTIJ HASOL ROAD @ CH 8 TO 9 KM OF STATE HIGHWAY
(11) DODIWADA BRIDGE ACROSS RIVER RUPEN IN MEHASANA DISTRICT.
From the studies it can be said that hydraulic structures of aqueduct, canal syphon, bridges, when they are required to be designed under unpredictable site conditions, gives fruitful results for better and safe performance of the structure. Time has taught us that HYDRAULIC MODEL observation are fairly matching with the field (proto) structure performance.
HYDRAULIC ASSESSMENT OF CHECKDAM THROUGH HYDRAULIC MODEL TECHNIQUE
Now a days check dams are constructed in large number in our state and therefore require proper attention for their design aspects, so that they function efficiently and give good results to the users for a longer duration.
In order to evaluate various Hydraulic design parameters considered, it was proposed by Ground Water Resources Development Corporation (GWRDC) who are associated with the construction of Check dams in the state, to test the performance of the Check dam in the Hydraulic laboratory of GERI, Vadodara.
GWRDC proposed a typical check dam to test the same with Hydraulic model study technique with the following main features.
v Location: Near village Samadhiyala across river Kalubhar, Ta. Umarda Dist. Bhavnagar.
v Length :- 155 m
v Height 2.20 m
v Apron length: 8.45 m
v Apron El: 97.20 m
v Crest EL : 99.40 m
v Max. Design Flood : 1276 m3/s
A physical working flumed model which obeys Fraudes law has been constructed in the field hydraulic laboratory of GERI Vadodara keeping Geometrically similar scale (GSS) 1:10 to observe its functioning through one Perspex sided wall. The flume width is 0.95 m which represent 9.5 m of proto (field) length.
The model was tested for various ranges of discharges i.e 1276 m3/s (100%), 638 m3/s (50%) with 60% submergence in the downstream for different length of apron viz 8.45m, 6.45m, 5.45m & 4.45m to observe the structures hydraulic performance.
From the Hydraulic model experiments it can be concluded that check dam if being under submerged flow then there is no much scour difference even if the apron length is reduced up to 40% of its total length (The scour observed was maximum 1.5m below GL in all cases)
Economy is therefore feasible in reducing length of apron under submerged crest flow condition without harming the factor of safety of structure.
CBIP Research Paper “Optimisation of Various Parameters of Large Escape Structure through Hydraulic model studies”
The mega project of the state, Sardar Sarovar Dam delivers its water to its command area through 460 Km long Narmada Main Canal (NMC). NMC crosses drains, rivers. NMC at its ch 229.34 km has to dispose off its surplus water to Sabarmati river. NMC carries discharge of 450m3/s and it was planned to lower down that water from the height of 11.0m was brought down by stepped-apron type energy dissipating arrangement. The escape structure is provided with 3 gates of 7.0 x 4.0m size, followed by ogee shape & three aprons with their auxiliary appurtenant structures like basin blocks & endsill.
Through comprehensive hydraulic model studies it was established that at such a height of 11.00m & discharge intensity 20.0 m3/s/m three stepped escape structure with gradual widening can dissipate the energy of the flowing water, if necessary the widening of tail channel (following the structure) can also be thought of to keep water velocities under control & to lower down the scour in tail channel.
v The first ogee shaped fall provided is of 7.5m height supported by 35.0 m long apron & with appurtenant structure.
v The second fall provided is of 2.63 m height, supported with 30m long apron & appurtenant structure.
v The third fall is of 2.0m height & supported by 25.0m apron with necessary appurtenant structure.
The construction of this structure is completed & operative.
HYDRAULIC MODEL STUDIES OF “ORB” TYPE FLEXIBLE STRUCTURE WITH GABIONS
The Hydraulic model tests for the overflow type rock fill barrier (ORB) structure is carried out in the field Hydraulic Laboratory of GUJARAT ENGINEERING RESEARCH INSTITUTE VADODARA.
Features of the ORB structure are as stated below.
|HFL||7.53m / 7.72 m|
|CREST RL||4.20 m|
|HEIGHT OF THE STRUCTURE||4.00 m|
|DESIGN DISCHARGE||5646 m3/s|
|U/S SLOPE OF THE SECTION||2:1|
|D/S SLOPE OF THE SECTION||3:1|
|GABION PITCHING DETAILS||3m x1m x 0.6m on slopes and @ top surface & 1m x 1m x 1m in apron.|
|APRON LENGTH||10 m on either side|
|DIAPHRAGM WALL||From RL 0.2 m to 2.7m in the Central part of core having 0.6m width covered with I.P & sand material.|
At 5646 m3/s, the design discharge the u/s & d/s slopes are stable & no movement of gabions on apron stones is observed keeping HFL @ R.L.7.70m & TWL RL 6.90m. However keeping free TWL @ RL 3.00 m with other parameters same model showed the movement of gabions provided at the top of the structure, the displacement of about 0.50m (proto length) was visualized with torn connecting plastic threads, therefore in sufficient tail water level condition which is the worst condition.
The Hydraulic model tests is further conducted with following weir changes
(1) A lower tier of 3 x 1 x 0.6 m size gabions below the top crest layer along with are row of additional under lying gabion in top most part area of u/s with the adjoining & underlying gabions.
(2) A double larger of 1m x 1m x 1m gabions in the entire 10 m apron length.
Along with above changes the model visualized that @ 5646 m3/s (100%) design discharge the u/s water level is observed at RL 8.30 m and velocities vary from 1.07 to 1.64 m/s. The formation of Hydraulic Jump takes place at D/s ch. 22.00m. The d/s velocities vary from 5.80 to 10.66 m/s. The maximum scour observed is at R.L (-)3.80 m at ch 49.50 m on sandy bed (FM 2.40 )with Average D/s G.L @ R.L 0.20m. Under this condition crest gabions are found undisturbed, U/S and D/S slope gabions are also seen stable, the apron is also not disturbed
The present experimental work for “ORB” test is the first of its kind tried here in the field hydraulic laboratory of the institute. The experimental results therefore be carefully co-related with the field observations before implementing on the field.
Vagrech (ORB Structure) 2D Model GS Scale 1:15
Under the subject of research related to hydraulic structures, the Institute has published forty-six research papers at National as well as State level workshops/ seminars. A few of them are given merit certificates also.
Tapi River Mega Model from Ukai Dam to its Confluence with the Sea
Government of Gujarat has entrusted the work of physical model study of Tapi River to assess inundation effect and work out flood protection measures for Surat city, nearby area, the d/s industrial area etc. for release of various discharges including flood hydrographs upto peak of 16 Lacs cusecs. The effect of neap and spring tide situation with flood in the Tapi River will also be assessed. CWPRS provides technical guidance and consultancy services for the model.
The comprehensive (3-D) Hydraulic Model of Tapi River from Ukai dam to its confluence with the sea admeasuring length 145 km (prototype) is being constructed at Gotri campus of GERI, Vadodara. Government has appointed Dr. Z.S. Tarapore as the Prime Consultant for Tapi River Model. Flooding zones will be assessed and necessary protection works will be suggested, with the help of model studies.
The Institute therefore invites any query related to research of hydraulic structures required to be done within or outside the state. A prompt response as well as deep and timely action is also promised.