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Aquatic Procedia 4 ( 2015 ) 341 – 348

INTERNATIONAL CONFERENCE ON WATER RESOURCES, COASTAL AND OCEAN ENGINEERING (ICWRCOE 2015) Effect of Mega Bridge on Hydro-morphodynamics of Waterfront Facilities in Wide Estuarine Harbours- A Sustainable Development

A.A. Purohit a*, M.M. Vaidya a, K.A. Chavan a, M.D. Kudale a

aCentral Water & Power Research Station, Khadakwasla P.O, Pune 411024,

Abstract

Mumbai being traditionally the epicentre of India’s commerce, the narrow stretch of land ( Island) has seen a steady increase in population despite obvious spatial constraints. Hence for easing the pressure on the island city, development of on east has been identified. However lack of easy connectivity to Navi Mumbai has stunted its growth and pressure on Mumbai’s infrastructure viz. roads/bridges continues to mount. As such to cater the need of road traffic/avoid traffic jams, it is inevitable to have Mega Bridge (MTHL) connecting Mumbai to Navi Mumbai spanning across entire width (17 km) of wide estuarine region, wherein major ports viz. Mumbai and Jawaharlal Nehru exist. These ports are facing problem of increased siltation. Hence to assess effect of MTHL consisting of hundreds of piers, which may have detrimental effect on existing waterfront facilities from hydro-morphodynamic aspect, studies are essential to ensure that development is sustainable. The effect of MTHL under complex hydrodynamic condition is compared by developing mathematical model for Mumbai/JN port area. The model shows 95% and 90% agreement for water level & current respectively with the prototype. The effect of Mega Bridge, studied from hydro-morphodynamic considerations on existing waterfront facilities in Mumbai/JN port area is insignificant and may not hamper smooth functioning and as such is a sustainable development.

Crown© 201 5Copyright The Authors. © 2015 Published Published by by Elsevier Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015. Peer-review under responsibility of organizing committee of ICWRCOE 2015 Keywords:Estuary; Hydrodynamics; Harbour; Macro tides; Mega bridge; Unstructured Mesh

1. Introduction

The various developing countries in Asia like China, Malaysia, South Korea, Singapore etc. are developing their infrastructural facilities at an exponential rate. The biggest democratic country in the world, India; is not an

* Corresponding author. Tel.: +0-91-020-24103508; fax: +0-91-020-24381004. E-mail address: [email protected]

2214-241X Crown Copyright © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015 doi: 10.1016/j.aqpro.2015.02.046 342 A.A. Purohit et al. / Aquatic Procedia 4 ( 2015 ) 341 – 348

exception to this and is also expanding its facilities almost at the same pace. These infrastructure developments are in the form of new road/rail networks, industries, townships, bridges, airports as well as major/minor ports to serve the need of waterborne transport in the country. Rapid modernisation and globalisation of the world in last few decades has necessitated India to carry out these infrastructural developments at speedy rate to fulfill the present requirements and cope up with the demands of future. In order to boost the economy, government has adopted policy of liberalisation and globalisation. Many private companies as well as joint venture organisations are coming up in the country to support Govt. policy of building power plants, minor port facilities, bridges, road networks etc. Waterborne transport facilities being the cheapest mode of transport, many coastal structures are being built in the country to explore the benefits of its resources. Presently, thirteen major ports and hundreds of minor ports are serving the country to cater the needs of waterborne transport. However, existing port facilities are not sufficient to cater future demands. In view of above, majority of new waterfront developments in the form of berths/jetties, docks etc. are being built either along the coastline or in estuarine/riverine areas. These developments require reclamations to stack material, bridges/approaches etc. Many townships are also being built in nearby area by reclaiming water area. Hence it is likely that it will alter the flow field at existing waterfront facilities, which may have adverse impact from hydro-morphodynamic consideration.

Amongst the existing major ports in India, ports such as Mumbai, Jawaharlal Nehru (JN), Haldia, Kolkata and are natural/estuarine ports and are situated well inside the estuary/creek or are in the gulf region, while remaining ports are on open coast with breakwaters to achieve tranquility at berths for safe loading/unloading of ships. Mumbai and JN Ports are on West Coast of India and their locations in are shown in Fig.1.

Fig. 1. Location Plan of Mumbai & JN Port area

Mumbai is a mega city of India and is not only the capital of state but also financial capital of the country. The city is well equipped with various infrastructures and connected to the rest of the country with transport facilities like rail/road networks and also to other countries with air and waterborne transport connectivity. Due to rapid industrialisation and Mumbai being traditionally the epicentre of India’s commerce, this narrow stretch of land (Mumbai Island) has seen a steady increase in population in the last three decades despite obvious spatial constraints. Hence, development of Navi Mumbai has been identified as an urgent requirement for easing pressure on the island city. Also many suburbs are being developed on the eastern side of Mumbai City in , Panvel and Dharamtar creek areas either by various Governmental or Non-Governmental organisations. However lack of easy A.A. Purohit et al. / Aquatic Procedia 4 ( 2015 ) 341 – 348 343 connectivity to the mainland (Navi Mumbai), has stunted the growth and pressure on the island’s infrastructure continues to mount (2012). In order to cater the need of road traffic and avoid traffic Jams, Maharashtra Govt. has constructed number of flyovers in Mumbai city and still more are being built. However they are not sufficient and hence the problem of traffic jams right from Fort area in Mumbai up to city and beyond exists. All vehicles have to pass Sion/ area to reach , which takes considerable time of about 2-3 hours during peak hours of traffic. Hence in order to connect the Island of Mumbai (west side) to main land (east side) there is a great need to have Mega Bridge (MTHL) crossing the entire . The Government intends to provide a road and metro-link between on the island city of Mumbai with Chirle in Navi Mumbai on the mainland side, which passes through the harbour area of Mumbai & JN port as shown in Fig.2.

Fig. 2. Location plan of proposed Mumbai Trans Harbour Link (MTHL)

The peculiarity of Mumbai/JN harbour is that, it has ultra-wide estuarine entrance of about 10 km and it extends in Thane creek having water spread up to 30-40 km north. Also type of tide prevailing being macro semi-diurnal in nature with spring tidal range of about 5.0 m, large volume of tidal flux gets exchanged in and out of Thane creek during tidal cycle. This results in strong tide induced currents during flood/ebb tide and also significant sediment transport. The harbour areas of these ports are well protected from waves due to Salsette/Mumbai Island on the west and mainland on the east.

The infrastructure developments in Navi Mumbai area are in the form of real estates, road/rail networks and waterfront structures in the form of Jetties, Wharfs etc. These developments are carried out mainly by reclaiming low lying areas. Major port like JN is also developing rapidly by planning a couple of kilometre long mega container terminal and reclamation in few hundred Hectares for stacking the containers. These developments will have some effect on siltation in the Harbour area. At present, the rate of siltation is not alarming, but it cannot be ignored also. Development of any facility/infrastructure may have detrimental effect on existing waterfront facilities and as such in order to have new development as a sustainable development, it is essential to study its impact on hydro- morphodynamics of entire harbour region. In tidal action is dominant than waves and it creates movement of large water mass to fill and empty the creeks, resulting in movement of sediment. Bed material in the harbour is very fine in nature and is brought in suspension by disturbance and is transported to and fro depending on direction and speed of tidal current. Tidal current plays an important role in transportation and redistribution of bed material within the harbour. In view of Mega Bridge (MTHL) being planned entirely crossing the Thane creek, wherein many piers are to be constructed; it may affect flow field and hence assessing effect of proposed development on existing waterfront structures in Thane creek from tidal hydrodynamic considerations is essential.

344 A.A. Purohit et al. / Aquatic Procedia 4 ( 2015 ) 341 – 348

2. Existing berthing Facilities in Mumbai harbour and Oceanographic phenomena

The berthing facilities available in Thane/Panvel Creeks near Mumbai are mainly for berthing of either large container/crude/ bulk carriers, which are operated by Mumbai & JN Port Authorities. However, many small berthing facilities/waterfront structures in the form of wharfs, piled jetties, ferry terminals also exist in this region, which are owned either by private companies or government undertakings to cater the need of passenger transport or material handling. The spring tidal range being about 5.0 m, small jetties/berths situated in shallow water depths/near tidal flats can be operated mainly during high water levels, owing to limitations on draft requirement and high maintenance dredging expenditure. Thus information on tides, tidal currents and sediment concentration in such complex region govern the layout/design of marine facilities to finalise the alignment of berths/navigational channel, jetties, minimization of siltation for efficient operability of berths. Planning of any new mega development certainly has to be studied to assess its effect on existing waterfront facilities by studying the physical oceanographic processes using modeling technique with the help of collected oceanographic field data. Thus various oceanographic parameters such as tides, currents and grain sizes of bed material at various locations all along alignment of MTHL shown in Fig.3 were collected for lunar tidal cycle (2014) to simulate prevailing hydrodynamics in Thane creek and typical plot of time series collected is shown in Fig.4.

Fig. 3. Location plan of oceanographic data collected along Mega bridge(MTHL)

Fig. 4.Tide and current strength-direction data measured near MTHL bridge site A.A. Purohit et al. / Aquatic Procedia 4 ( 2015 ) 341 – 348 345

The data collected reveal that for spring tides with range of 5 m, amplification of tide between Apollo bunder and Vashi bridge/Ulwe is about 40 cm. The low water lag during spring tide is about 10-20 minutes, while high water lag varies up to 30/20 minutes. During neap tides, there is no tidal amplification between Apollo bunder and Vashi/Ulwe, while the time lags of low and high waters are about 10 minutes. The current measurements indicate that during spring tide, current strength is relatively more in western area of harbour than in eastern area. The peak spring flood currents in Thane creek area vary from 0.5 m/sec to 0.93 m/sec, while the peak ebb current strength varies from 0.56 m/sec to 1.07 m/sec. The ebb current is stronger than flood current and direction is fairly uniform. The peak neap current strength during flood varies from 0.32 m/sec to 0.49 m/sec, while peak neap ebb current strength varies from 0.21 m/sec to 0.63 m/sec. The current directions during flood tide varies between 60-85 degree north near western side (island city), while at central portion behind the Elephanta wake zone, there is drastic change seen in current direction during flood tide which is between 20-50 degree north. The current direction near main land side happens to vary between 65-90 degree north, in view of flow moving towards tidal flats approaching mouth of Panvel creek. The material at bed and in suspension happens to be clayey with D50 less than 4 microns. The suspended sediment concentration (SSC) varies between 0.1 and 1.2 gm/lit during various seasons. In order to study flow conditions prevailing across the entire Thane creek under existing condition and to assess effect of Mega Bridge on the existing waterfront facilities, mathematical model developed is described below.

4. Mathematical model for Mumbai Harbour area

The studies were carried out by using TELEMAC-2D finite element software (2007), which considers solution of hydrodynamic equations of Saint Venant. The model considers depth-averaged velocities. The water levels & velocities are computed by solving matrices for each element at number of nodes of triangular element.

4.1. Descritisation of the domain area The domain area of the model extends up to Karanja on south wherein about 11 m depth in navigational channel [with respect to Chart Datum (CD) of Apollo Bundar] represents deep portion of creek, part portion of Panvel creek (Ulwe Bunder) and Thane creek up to Vashi Bridge in the north. The total area of domain is about 193 sqkm. Triangular finite elements with fine resolution near shoreline, around islands/ navigational channel area etc. were adopted for true simulation of steep slopes and effect of islands on flow pattern. Coarser mesh as shown in Fig.5 was adopted in relatively deeper areas to optimize number of elements and minimise simulation time. Thus mesh generated can effectively reproduce hydrodynamic condition without compromising on the quality of results.

Fig. 5.Domain area and finite element mesh descritisation 346 A.A. Purohit et al. / Aquatic Procedia 4 ( 2015 ) 341 – 348

4.2. Simulation and calibration of model The measured water levels during year 2013 were used as boundary conditions at open boundaries of model area viz. Vashi Bridge, Ulwe Bunder and southern boundary between Karanja & Mumbai port for model with existing bathymetry condition for simulating the hydrodynamics prevailing in the domain area. Field data collected in respect of currents at different points was used for calibrating the model. Information of bed samples indicates that majority of sediment is clay; however in some areas like , , Butcher reef; rocky outcrops exist. In area like BARC-Vashi bridge shore/coastline, mangroves do exist. As such appropriate variable friction factors were adopted for simulating hydrodynamic conditions. A comparison is made with the velocities predicted by mathematical model and the observed velocities at locations, wherein field data was collected. Simulation and calibration of model for “Hydrodynamics” at a typical current location is shown in Fig.6.

a b

Fig. 6. (a) Comparison of proto & model current strength (b) Comparison of proto & model current direction at location -2

The comparison of water level observed in model and in prototype near JNPT area is shown in Fig.7. The information about water levels/current strength at important existing waterfront facilities is obtained from model.

Fig. 7. Comparison of model and prototype water level near JN port area

4.3. Study for impact of Mega Bridge on various waterfront facilities The model is modified by incorporating each pier (3 m Dia.) of Mega Bridge at spacing of 50 m & 150 m centre to centre. The zoomed portion of element descritisation for piers is shown in Fig.8. The interpolated depths were assigned at nodal points of element to represent the depths and hydrodynamic equations are solved for depth and velocity. The modified model was run again for hydrodynamic condition to determine the water levels/velocities at important existing locations shown in Fig. 9a, wherein it was measured for without Mega bridge condition also. A.A. Purohit et al. / Aquatic Procedia 4 ( 2015 ) 341 – 348 347

Fig. 8.Domain area and zoomed portion of finite element mesh descritisation near MTHL bridge

The results are compared to assess impact of Mega Bridge from hydrodynamic considerations and typical comparison of velocity at JN port location is shown in Fig.9b. a b

Fig. 9.(a) Locations of waterfront facilities (b) Comparison of current strength before and after Mega Bridge

Based on the hydrodynamic simulation and study for assessing effect of Mega bridge, comparison of flow condition at existing waterfront facilities in terms of velocity is shown in Fig.10a.The estimation of morphological changes in terms of siltation at same waterfront facilities is obtained by coupling hydrodynamic model with sediment module to assess the effect of Mega bridge on siltation pattern. The material at bed and in suspension being clay, based on Krone (1962) and Parthenaides (1965, 2010), siltation model is calibrated for known rates of siltation. The comparison of unit rate of deposition/erosion at various waterfront facilities is shown in Fig. 10b.

a b

Fig. 10.(a) % Reduction/Increase in Current Strength (b)Comparison of unit rate of deposition/erosion at various waterfronts 348 A.A. Purohit et al. / Aquatic Procedia 4 ( 2015 ) 341 – 348

5. Results and Discussions The hydrodynamic studies carried out to simulate prevailing flow conditions (i.e. simulation of tide and current strength/direction at various locations across the width of Mumbai harbour) reveal that use of unstructured mesh (FEM) is a promising tool in simulating complex hydrodynamic conditions in estuary under consideration. The tide level in model is about 95% in agreement with prototype tide, while current is about 90% in agreement with prototype current. Thus well calibrated hydrodynamic model enables to provide good comparison of hydrodynamics before and after the development of proposed MTHL on various waterfront facilities in Mumbai/JN harbour area as each and every pier dimension of entire Mega bridge is modelled with fine resolution. The impact of Mega Bridge (MTHL) spanning across the entire width of Thane creek on hydrodynamics at various waterfront facilities on Mumbai and side reveal that percentage increase/reduction in current strength is insignificant and as such the waterfront facilities may not face problem of smooth operability even with existence of Mega Bridge. Only the location of Pirpav being in close proximity of bridge pier and on tidal flats, the reduction in prevailing feeble current strength will not pose problem of normal functioning of facility. In view of insignificant changes in flow field at various waterfront facilities, the morphological changes in terms of unit rate of deposition/erosion will not also hamper its functioning. Thus such type of study proves its importance in assessing effect of mega developments like bridges (hundreds of piers) on various existing waterfront facilities from hydro-morphodynamic consideration to prove that whether proposed development is sustainable or not.

6. Conclusions

The following broad conclusions highlight the effect of Mega Bridge on the existing waterfront facilities. x The present waterfront facilities in the harbour area of Mumbai and Jawaharlal Nehru ports are facing problem of increase in siltation rates due to various developmental activities in nearby water areas. Modeling is essential to assess impact of proposed Mega developments on functioning/operability of the existing waterfront facilities in complex wide estuarine region and whether the same are sustainable or not. x Simulation of hydrodynamic conditions for a complete lunar tidal cycle across the wide estuarine region provides a clear picture about modification in hydrodynamic flow field (increase/ reduction in current strength) at the existing waterfront facilities due to proposed development of Mega Bridge spanning over the width of estuary, wherein hundreds of piers are under consideration. x At many important port facilities such as PV docks (Mumbai port), Mazgaon dock, NSICT/BPCL (JN Port) etc., effect of bridge is insignificant on flow field/ (current strength-direction) i.e. less than 5%. The Pir-Pau area being in the close vicinity of bridge (less than 250 m) and on tidal flats wherein current strength is less, there is overall reduction in current strength by about 10%. x In view of negligible variation in current strength over the harbour areas due to Mega Bridge, the morphological changes in terms of unit rate of deposition/erosion will not affect the functioning of existing waterfront facilities and as such project is techno-economically viable and sustainable. x The studies reveal that there is amplification of tide at Mega bridge location, hence bottom level of pile caps should be above highest high tide level prevailing at Bridge and is kept at 6.2m CD to minimise obstruction.

Acknowledgement

The authors are grateful to Shri. S. Govindan, Director, Central Water and Power Research Station, Pune (India) for his continuous encouragement and motivation for carrying out the research work.

References

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