Evaluating the Impacts of an Improperly Designed          Bridge across the Batticaloa Lagoon                             ...
Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoonrich variety of aquatic flora (mainly ...
S. Santharooban And M. ManobavanOutline of the ProblemEven though this New Bridge and contiguous road is extended for less...
Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoonbloom3 (Chladophora sp dominates the a...
S. Santharooban And M. Manobavan                   250                                                                    ...
Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa LagoonDevelopment of a Conceptual ModelAs al...
S. Santharooban And M. Manobavan                          water in lagoon water out flow              water inflow        ...
Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoon    (a)    1: Depth of water 2: Amount...
S. Santharooban And M. Manobavanvariation of depth of lagoon, amount of suspended solid particles andsedimentation.The sim...
Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoon   •   The reduced velocity, resulted ...
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Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoon

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My first paper published in water professionals day symposium held in Post Graduate Institute of Agriculture (PGIA), University of Peradeniya, Sri Lanka on 1st Oct. 2005

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Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoon

  1. 1. Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoon S. Santharooban Department of Zoology, Eastern University, Sri Lanka, Batticaloa, Sri Lanka And M. Manobavan North East Costal Community Development Project, Batticaloa, Sri LankaAbstractThis research paper mainly focuses on the negative repercussions, resulting fromthe construction of a New Bridge (Puthupalam), on the Batticaloa lagoon.Construction of a New Bridge across Batticaloa lagoon is an adverse modification,which will change the spatial structure of the Batticaloa lagoon whilesimultaneously destruct the biodiversity of the lagoon. In this research, simulationmodeling approach is used to support the hypothesis, which assumes that this NewBridge negatively impacts on the lagoon ecosystem by reducing the depth whichwill change the spatial system of the Batticaloa lagoon. In this respect,commercially available modeling software STELLA® (Version 7.0.3) was used toconceptually develop a simulation model, called N-BIOL (New Bridge Impact onLagoon) based on the idea of literature and the measurements of lagoon depth andwater velocity, which showed the differences on either side of the New Bridge.According to the simulated outputs, it is obvious that this New Bridge graduallyreduces the depth over time, which leads to the change of spatial structure of theBatticaloa lagoon.Keywords: Ecosystem, Simulation model, Spatial structure, SedimentsIntroductionLagoons are an important part of the cultural landscape of the Batticaloa district.The Batticaloa lagoon (7o 24’- 7o 46’ N and 81o 35’- 81o 49’ E) is the largest ofthree lagoons (i.e. Batticaloa lagoon, Vakarai lagoon and Valaichchenai lagoon) inthe Batticaloa district and it occupies an area of 168 square kilometers and is 56 kmlong (Shanmugaratnam, 1995). The maximum depth of the lagoon is about fourmeters (Scot, 1989). More than 90% of the lagoon is located in Batticaloa district,but the southern end near Kalmunai is located in the Ampara district. The deepbroad lagoon leads into the sea by three Bar mouths, namely Paalameenmadu Barmouth in Batticaloa, Periyakallar Bar mouth and Koddaikallar Bar mouth. Theflow of the water is towards the bar mouth when the Bar mouth is remains open(mostly during the rainy season) and vice versa. This lagoon supportseconomically and esthetically to those, who are living closer to it, as it comprises a Water Professionals’ Day Symposium – October, 2005
  2. 2. Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoonrich variety of aquatic flora (mainly mangroves) and fauna. In addition to this,Batticaloa lagoon and its peripheral systems act as a form of natural rainwaterharvesting mechanism and can be considered as an important groundwaterrecharging zone (Manobavan and Jeyakumar, 2004). The Batticaloa lagoon alsoacts as a shock absorber of the Tsunami impact (within its limit) via its peripheralwetlands and interconnected channels (Manobavan, 2005). The Batticaloa lagooncomprises several islands within it, namely Puliyantheevu, Mantheevu,Erumaitheevu (Buffalo Island), Sirayatheevu, Elubutheevu (Bone Island). In theseislands, the Puliyantheevu is important island as it holds central city of theBatticaloa. Population is mainly concentrated in this island and this created a needto have bridges across the Batticaloa lagoon to connect the island with the mainland of the Batticaloa district. As a result, three bridges, namely KoddamunaiBridge, Puthur Bridge and New Bridge (Puthupalam1) were constructed across theBatticaloa lagoon (Figure 01). The objective of this research paper is to evaluatethe negative environmental impacts, generated by the construction of a New Bridgein the Batticaloa lagoon.Figure 01: Location of Bridges across the Batticaloa lagoon (L and R represent theLeft and Right sides, respectively of the New Bridge, and the Bridge is 9.0 mwide).1 ‘Tamil’ word for New Bridge and this was constructed in the year of 1985. Water Resources Research in Sri Lanka
  3. 3. S. Santharooban And M. ManobavanOutline of the ProblemEven though this New Bridge and contiguous road is extended for less than quarterkilometer over the Batticaloa lagoon, it allows only a small opening for theprovision of the natural water flow. Hence, this bridge and associated road acts aspartial impoundments or as a quasi-dam across the lagoon. This partialimpoundment of this road is suspected to be creating lots of problems on lagoonsystem dynamics and its spatial structure. And, it is also suspected to be changingthe biodiversity of the lagoon. This bridge may alter the flow regime by reducingthe water velocity of the lagoon due to its insufficient openings. According to theresults obtained from sampling2, the velocity variation curve was plotted (Figure02c). According to Figure 02c, when water flows from left to right across thebridge, the current velocity is decreased in right side or vice versa. This reductionin velocity is resulted from partial impoundments and it is also obvious from thegraph (Figure 02c) that the velocity under the bridge is high. This can be explainedby using Equation 1.AV = k [01]Where; k – Flow rateA – The cross sectional area of the stream V- Fluid velocityThis equation can be applied to incompressible and non-viscous fluid undergoingsteady flow on a streamline (Roger, 1981). In applying this equation (Eq. 1) to thislagoon system, when the water velocity is increased as the cross sectional areadecreases i.e. when width of the lagoon decreases, the water velocity is increased tomaintain an equal flow rate in all points. It is important to note here that when thevelocity under the bridge increases, the soil erosion is accelerated. This issupported from the results of sampling as shown in Figure 02a, where the P is theproximal point to the bridge (at the edge) and has high depth and S is the distalpoint to bridge (120 m from either side) and has low depth and Q and R are pointsin between (The distance between each two point is 40 km). This indicates theerosion of lagoon bed under the bridge. This eroded bed load will accumulate inone side leading to the further depth reduction.Allan (1995) stated that extensive phytoplankton blooms often develop as aconsequence of slowed passage of water. In supporting this comment, it wasobvious that there was heavy accumulation of waste, aquatic macrophytes, algal2 Sampling was done periodically across the New Bridge from 6th December 2004to 11th April 2005 to measure the water current velocity and lagoon depth in eitherside of the New Bridge (Figure 01) Water Professionals’ Day Symposium – October, 2005
  4. 4. Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoonbloom3 (Chladophora sp dominates the algal bloom in the left side of the bridge)the in left side of the lagoon due to the New Bridge and contiguous road. When allthese accumulates decompose, the suspended solid particles increase, which inturns increasing the turbidity of the water (Figure 02b). According to Figure 02b, itis obvious that the turbidity is high in many points in the left side than in the rightside. The results further show that turbidity is significant difference between twosides of the bridge (t= 2.871, p= 0.014 for two tail two sample student t-test).Hence, these increased loads of suspended solid particles undergo sedimentation bythe influence of reduced current velocity. This increased sedimentation will resultthe reduction of depth in this area. This can be supported by the results, whichshowed a statistically significant difference in two sides (t= -8.077, p= 0.00 for thetwo tail two sample student t-test) and this can be shown by the graph (Figure 02d),which clearly indicates that the average depth of the center of lagoon is high inright side (R) than in left.As the depth is reduced then again velocity of the water is reduced according to thefollowing Manning equation for velocity of flow in a channel (in metric units) 1 2 / 3 1/ 2U = R S [2] nWhere; R is the hydraulic radius about equal to mean depth for most channels, S isthe energy gradient; approximately the slope of the water surface and n is theManning resistance coefficient (Barns, 1967).Apart from this New Bridge (Puthupalam), there is another bridge, called PuthurBridge, which also lacks the proper natural water flow. As a result, a pond likeportion, enclosed by two bridges was created in left side (L) of the New Bridge(Figure 01). Hence, as a combined effect of these two bridges, there will be aheavy depth reduction in the area of the lagoon, enclosed by the New Bridge andPuthur Bridge. This in future makes the change in the lagoon spatial system. Inthis research, the modeling approach is used to predict the temporal changes of thelagoon depth.Hypothesis:Batticaloa lagoon has been divided in to two half by the construction of the NewBridge (Puthupalam), which negatively impacts on lagoon system by creating thedepth reduction in lagoon and this depth reduction will change the spatial processof the Batticaloa lagoon overtime. Water Resources Research in Sri Lanka
  5. 5. S. Santharooban And M. Manobavan 250 50 L R Turbidity (FAU) 200 L R 40 Depth (cm) 150 30 100 20 50 10 0 0 P Q R S 1 2 3 4 5 6 7 8 9 10111213 Location from Bridge Week s P is proximal point to New Bridge and S is the distal point to New Bridge (a) (b) (a) L Under Bridge 0.6 R 200 L R 0 180 0.4 160 0 140 Depth (cm) 0.2 120 0 100 Velocity (M/S) 0 80 1 2 3 4 5 6 7 8 9 10 11 12 13 0 60 -0.2 - 40 20 -0.4 - 0 1 2 3 4 5 6 7 8 9 10111213 -0.6 - Weeks We eks -0.8 - Water flow direction from L to R is assumed as positive and from R to L is assumed as negative (c) (d)Figure 02: Graphical results of sampling carried out across the New Bridge inlagoon; (a) Depth of lagoon in different localities from New Bridge; (b) Turbidityvariation on either side of New Bridge; (c) Variation in water velocity in either sideof Bridge; (d) Variation in lagoon depth in either side of the Bridge. Water Professionals’ Day Symposium – October, 2005
  6. 6. Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa LagoonDevelopment of a Conceptual ModelAs already mentioned, a modeling approach is used to predict the changes infuture. A model is a formulation that mimics real world phenomena and by meansof which predictions can be made (Odum, 1971). We can continually study thebehavior of systems by creating mental or conceptual models of them. Theconceptual model uses the conceptual idea of the modeler. In this research, aconceptual model was developed using commeciallly available modeling softwareSTELLA® Version 7.0.3. The STELLA software provides a simple, icon-basedlanguage that enables ones to construct their understanding of any dynamicphenomenon, occurring in the world. A conceptual model was developed as shownin Figure 03, based on the idea of literature evidences and sampling data, presentedin section 2.0. Based on the conceptual model (Figure 03), another conceptualmodel, called N-BIOL (New Bridge Impacts on Lagoon) was developed usingSTELLA modeling platform. This is shown in Figure 04. This STELLAconceptual model was simulated for ten years to obtain the simulation output. Length of New Bridge Road across the lagoon is increased Velocity of water in Water flowing width either side of road is Waste, phytoplankton and of lagoon is reduced aquatic macrophytes are decreased accumulated Sedimentation is increased Velocity under the bridge increases Changes in spatial Depth of lagoon is structure of decreased lagoon Erosion of lagoon bed is accelerated Temperature of water increasesFigure 03: Conceptual model developed based on literature evidence and results ofsampling by authors. Water Resources Research in Sri Lanka
  7. 7. S. Santharooban And M. Manobavan water in lagoon water out flow water inflow stagnation of accumulates concentration of accumulates ~ ~ Turbidity inflow of accumulates accumulates Water velocity out flow of accumulates Depth of water inflow of solid particles sedimentation amount of suspended solid particles out flow of solid paticles water temperatureFigure 04: The model developed using the STELLA modeling software.Simulation Results and DiscussionThe simulation output shown in following Figure 5a, indicates that the amount ofsuspended solid particles increases while accumulate fluctuate with time. Becauseof the reduced out flow of accumulates by the crossing structure, they retains in thelagoon and at the same time they undergo decomposition, thereby accumulatesfluctuate with time. However, suspended solid particles are recruited with time asaccumulates undergo decomposition, so that, the amount of suspended solidparticles increases with time. However, it is expected that there will be seasonalvariations as accumulates have high rate of settlement in the non-rainy seasons, andcould undergo a state of disturbance in the wet season. Hence, the simulationshows seasonal lows and highs, though the general trend as a whole is that of anincreasing one for the amount of suspended particles in the lagoon bed. Water Professionals’ Day Symposium – October, 2005
  8. 8. Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoon (a) 1: Depth of water 2: Amount of suspended solid particles 3: Sedimentation (b)Figure 05: Simulation outputs of Model N-BIOL (a) Temporal variation ofamount of accumulates and amount of suspended solid particles; (b) Temporal Water Resources Research in Sri Lanka
  9. 9. S. Santharooban And M. Manobavanvariation of depth of lagoon, amount of suspended solid particles andsedimentation.The simulation output, shown in Figure 05b, indicates that the sedimentationprocess increases overtime as the suspended solid particles increases.Sedimentation can also be increased due to the reduction of current velocity.However, it is not shown in the computer simulated model. And this output alsoindicates the depth variation overtime, which is our key concern. According to thisoutput, depth of the lagoon will gradually decrease overtime. This reduction willbe possible in the portion of lagoon, where the accumulations are high. Hence, thisdepth reduction now was observed in left side of the New Bridge after twenty yearsof time period. Moreover, it should be noted that as shown in Figure 05b, theseasonal fluctuation in accumulates influences the seasonal fluctuation of the depthas well. Therefore, in the Batticaloa lagoon especially in left side of the NewBridge (Figure 01), which is enclosed by the presence of two bridges, namely NewBridge (Puthupalam) and Puthur Bridge, the lagoon depth will be reducedgradually with time. As a result, the lagoon bed will be raised (since its depth isreduced) and in the long run it will evolve into a semi-dry land, which will be driedout in dry seasons and be flooded in wet seasons. This will lead to disturb thebiodiversity even further. This is supported by the modeling outputs (Figure 05),and the lagoon depth will be reduced further in future affecting the aquaticbiodiversity.It should be noted that since the simulations outputs are the result of a conceptualmodeling exercise, hence the validation of the model output results against the fielddata gathered becomes impossible. Whilst this could be taken as a weaker elementin this exercise, considering the timeframe and the resources needed, such avalidation becomes an activity that is beyond the scope of this project.ConclusionsThe New Bridge functions as a partial impoundment across the Batticaloa Lagoonand increases the sedimentation over space and time in the area of the lagoon,enclosed by the New Bridge and Puthur Bridge. Increased levels of sedimentationcould be due to the following reasons: • During the rainy season, lagoon receives floodwater which carries huge amount of debris and sand. • When the floodwater drain from the lagoon through the New Bridge, only the surface water drains, while debris and sand accumulate on the bottom. • Algal blooms, waste accumulation, and aquatic macrophyets also increase the sedimentation when they undergo decomposition. Water Professionals’ Day Symposium – October, 2005
  10. 10. Evaluating the Impacts of an Improperly Designed Bridge across the Batticaloa Lagoon • The reduced velocity, resulted from partial stagnation of water also increases the sedimentation. • Therefore, depth of lagoon, especially the area, enclosed by the New Bridge and Puthur Bridge will gradually decrease overtime. • Furthermore, increased algal bloom will facilitate the plant succession, which leads to the formation of dry vegetation in that particular locality.Therefore, as hypothesized in section 2.0, this New Bridge and contiguous roadstructure negatively impacts on the Batticaloa lagoon by creating the depthreduction and hence, it will create the change in the spatial structure of theBatticaloa lagoon and a reduction of the biodiversity consequently.ReferencesAllan, J.D. (1995). Stream ecology, structure and function of running waters.Chapman and Hall publication, pp: 310-323.Barns, H.H. (1967). Roughness characteristics of natural channel. U.S. GeologicalSurvey, Water supply paper, 1849. pp 213Manobavan, M., and Jeyakumar, P. (2004). Utilization of natural peripheral waterbodies adjoining the Batticaloa lagoon for fresh water harvesting and/orrecharging: Reflection on the Keeriodai experience. Lanka Rainwater HarvestingForum, The Eight Symposium.Manobavan, M. (2005). Some hypothesis on the behavior of the Batticaloa lagoonand peripheral wetland systems to the tsunami wave: An earth systems perspective.available athttp://www.eusl.info/inPerspective/DrManobavan/Some%20hypotheses%20(Revised).pdfOdum, P.E. (1971). Fundamentals of ecology. Saunders College Publishing (3rded).Roger, M. (1981). A-Level physics (4th edn), Stanley Thorne publisher Ltd, pp:197.Scot, A.D. (1989). A directory of Asian wetlands. IUCN, The world conservationunion, Cambridge, pp: 605-606.Shanmugaratnam, N. (1995). The need for and steps towards a master plan forsuitable utilization of the Batticaloa lagoon. Report to NORAD, pp: 1. Water Resources Research in Sri Lanka

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