Impacts of Jetty Construction on the Wave Heights Off the Kiashahr Lagoon S

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Impacts of jetty construction on the wave heights off the Kiashahr lagoon S. A. Azarmsa,1∗ M. Esmaeili,2 and A. Karami Khaniki3 1Faculty of Marine Sciences, Tarbiat Modares University, Gisha, Tehran, Iran 2Faculty of Marine Sciences, Chabahar Maritime University, Chabahar, Iran 3Soil Conservation and Watershed Management Research Center, Tehran, Iran ∗Corresponding author: [email protected]

Coastal managers and ecologists are confronted with tasks to estimate wave heights in the Kiashahr sea area, since hydrodynamic factors can profoundly impact this environment. In this study, wind data and an empirical wind wave predicting model were used to estimate deepwater wave characteristics in the Kiashahr sea area; while a numerical model was used to determine wave characteristics in shallow waters. Wave heights were also determined and compared at different stations before and after construction of 2 jetties at the lagoon mouth to evaluate their efficiency in wave height reduction. Results revealed that wave height is in the range of 0.8 to 1.2 m at Sefid Rud river mouth. Significant wave height reduction in the range of 0.15 to 1.2 m occurred at the entrance of the lagoon due to construction of the jetties. This attenuation of wave energy may result in some impacts on the ecosystem health of Kiashahr lagoon such as increased sedimentation, reduction in flushing rates, dumping of garbage and consequently, more pollution.

Keywords: wind, Caspian Sea, Iran

Introduction into a bay with broad entrance to the sea and exposed it to more energetic waves, similar to the situation Sustainable management of aquatic ecosystems in the 1950s. The marshy grassland and sand-dune demands a deep understanding and ability to predict areas at the mouth of the Sefid Rud have, however, the behavior of the marine environment. Kiashahr remained more or less unchanged mainly because of Lagoon lies immediately east of the mouth of the a huge amount of sedimentation in the river mouth Sefid Rud (river) in the southwest of the Caspian which has reduced the water depth and has kept that ◦ Sea at geographical coordinates on the 39 57 E area from higher and more energetic waves. ◦ and 37 26 N (Figure 1). The lagoon has evolved Waves can profoundly impact the environment in as a result of wide variations in water levels. In the coastal areas (Keddy, 1982; Fonseca and Bell, 1998; early 1970s it was a shallow, brackish coastal lagoon Fonseca et al., 1998a; Ashworth, 2001). Cheong and with fringing marshes in an area of coastal sand- Okada (2001) studied the effects of wave and tidal dunes and grassland; it was fed by local run-off, and actions on the penetration of spilled oil stranded drained north-east through a narrow channel into the on tidal flats, and thus on the tidal flat ecosystem. Caspian Sea, having formed in 1960 as a result of the Waves are responsible for thermal mixing, coastal falling level of the Caspian Sea and development of erosion and accretion. The re-suspending of bed ma- coastal sand spits. The 1.8 m rise in the level of the terials by waves in shallow waters has large effects Caspian Sea since 1978 has converted the wetland upon material balance and water quality, as well.

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Aquatic Ecosystem Health & Management, 12(4):358–363, 2009. Copyright C 2009 AEHMS. ISSN: 1463-4988 print / 1539-4077 online DOI: 10.1080/14634980903354726

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Figure 1. Location of the Kiashahr sea area. Two jetties were constructed at the Kiashahr lagoon shore wave, NSW, module (Danish Hydraulic Insti- mouth to ﬁx the lagoon entrance and prevent it from tute, 2003) has been used to simulate the wave prop- migration over time. Construction of jetties, more- agation, growth and decay of short period waves in over, has resulted in reduction of wave penetration near-shore areas and to estimate wave heights be- into the lagoon. The objective of this paper is to fore and after construction of jetties on the mouth of determine the wave characteristics in the Kiashahr Kiashahr lagoon. The model is a stationary, direc- sea area and to study the efﬁciency of these jetties tionally decoupled, parametric model (Holthuijsen in reducing wave heights. et al., 1989) and includes the effects of refraction and shoaling due to varying depth, wave generation Material and methods due to wind (Johnson, 1998), and energy dissipation due to bottom friction and wave breaking (Battjes Wind data were collected from Anzali station and and Janssen, 1978) as well. The effects of current on analyzed to determine wind roses in the study area. these phenomena are also included. The model cov- Deepwater wave characteristics have been deter- ers the whole Kiashahr lagoon and its vicinity with mined by using wind statistics and Sverdrup-Munk- an approximate area of 72 km2 (Figures 2, 3). The Bretschneider, SMB, method (U.S. Army Corps of grid includes 170 × 170 nodal points distributed Engineers, 2002; Azarmsa, 2003). MIKE 21 near- every 50 m in x and y directions. The bathymetry of the study area is modeled with 1:5000 scale.

Figure 2. Bathymetry of the study area before jetties construction. Figure 3. Bathymetry of the study area after jetties construction.

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Table 1. Model setup information for selected directions.

NNW Wind Duration (hour) Wind Speed (m s−1)P%Hs(m)Ts(s)P%Hs(m)Ts(s) 3 2 5.00 0.2 2.2 4.86 0.2 2.2 5 2.77 0.6 3.3 3.06 0.6 3.3 8 1.09 0.9 4.0 1.18 0.9 4.0 11 0.41 1.3 4.7 0.42 1.3 4.7 14 0.10 1.8 5.2 0.11 1.8 5.2 17 0.04 2.0 5.5 0.03 2.0 5.5 20 0.01 2.6 6.0 0.01 2.6 6.0 6 2 0.45 0.3 3.1 0.45 0.3 3.1 5 0.23 0.9 4.6 0.32 0.9 4.6 8 0.09 1.6 5.7 0.12 1.6 5.7 11 0.03 2.3 6.6 0.05 2.3 6.6 14 0.01 3.0 7.4 0.02 3.0 7.4 9 2 0.05 0.3 3.0 0.05 0.3 3.0 5 0.03 1.3 5.7 0.02 1.3 5.7 8 0.01 2.1 7.0 0.02 2.1 6.9 NE E Duration (hour) Wind Speed (m s−1)P%Hs(m)Ts(s)P%Hs(m)Ts(s) 3 2 5.45 0.2 2.2 4.18 0.2 2.2 5 1.96 0.6 3.3 2.15 0.6 3.3 8 0.39 0.9 4.0 0.22 0.9 4.0 11 0.14 1.3 4.7 0.01 1.3 4.7 14 0.02 1.8 5.2 6 2 0.54 0.3 3.1 0.43 0.3 3.1 5 0.14 0.9 4.6 0.25 0.9 4.6 8 0.03 1.6 5.7 0.02 1.6 5.7 9 2 0.04 0.3 3.0 0.03 0.3 3.0 5 0.01 1.3 5.7 0.02 1.3 5.7 8 0.01 2.1 7.0

Considering yearly deepwater wave characteris- to 20 m s−1 in these directions. Local wind duration tics in the region, 50 regional models (Table 1) were ranges from 3 to 9 hours. Northeasterly (8.73%) set up to model wave conditions in the Kiashahr and easterly (7.31%) winds with maximum speed sea area before and after construction of the jetties of 14 m s−1 and 11 m s−1, respectively, are in the (100 models in total). The probability of occurrence second and third order of importance. Increase in of each specific wind duration and speed class and wind duration and speed results in increase of wave thus, resulted deepwater wave field, is given as P% in height and period, but decrease of the probability of Table 1 for each direction. The model results in- occurrence. The waves with 0.2 m height and 2.2 clude: significant wave height, average wave period, s period are more frequent (19.49%), although the and average wave direction at all nodal points of northerly and northwesterly waves with 3.0 m height model mesh in shallow waters for each model set up. and 7.4 s period and yearly probability of occurrence of 0.02% and 0.01%, respectively, are rare, but the Results and discussions most crucial waves in the study area (Table 1). Model results for four representative cases before Winds are calm about 63% of the time. The north- and after construction of the jetties are considered westerly (10.72%) and northerly (10.32%) winds are and discussed here (eight cases in total). Specifi- more dominant (Table 1). Wind speed ranges from 2 cations of their deepwater waves inputted into the

Figure 4. Station locations considered for wave height comparisons.

model and propagated toward coastal waters are pre- sented in Table 2. In each case, wave characteristics calculated at each nodal point (in total 170 × 170 = 28900 points covering the whole model area). For the purpose Table 2. Specifications of deepwater wave for each representa- of comparison, here, wave heights are shown and tive case. discussed only at 11 stations (nodal points) in the model area (Figure 4). Probability of Height Period Results reveal that wave height is in the range of No. Direction occurrence [%] [m] [s] 0.8 to 1.2 m at Sefid Rud river mouth (Station P4) 1 NW 0.02 3.0 7.4 and is usually less than wave height in nearby loca- 2 N 0.41 1.3 4.7 tions (Station P3 and P5), mainly because of river 3 NE 0.01 2.1 7.0 flow and wave interactions (Figures 5–8). Even af- 4 E 0.02 1.6 5.7 ter construction of the jetties, wave height has not

Figure 5. Wave height comparisons for northwesterly deepwater waves with 3.0 m height, 7.4 s period and 0.02 probability of occurrence.

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Figure 6. Wave height comparisons for northerly deepwater waves with 1.3 m height, 4.7 s period and 0.41 probability of occurrence.

Figure 7. Wave height comparisons for northeasterly deepwater waves with 2.1 m height, 7.0 s period and 0.01 probability of occurrence.

Figure 8. Wave height comparisons for easterly deepwater waves with 1.6 m height, 5.7 s period and 0.02 probability of occurrence.

considerably changed in deepwater stations P1, P10 References and P11 and near the Sefid Rud river mouth (stations P2-P5). However, significant wave height reduction Ashworth, M., Proctor, R., Holt, J.T., Allen, J.I., Blackford, in the range of 0.15 to 1.2 m has occurred at stations J.C., 2001. Coupled Marine Ecosystem Modelling on High- Performance Computers. In: W. Zwieflhofer and N. Kreitz P6-P8. At lagoon mouth (station P8), only the east- (Eds.), Developments in Teracomputing, pp. 150–163. World erly waves (Figure 8) are more significant following Scientific, London. the jetties construction and still may have consid- Azarmsa, S. A., 2003. Sensibility of predicted wave height to erable influence on other hydrodynamic factors and wind duration. Int. J. Science and Engineering Vol. 14 (5), thus, aquatic ecosystems in the Kiashahr lagoon. 221–233. Battjes, J.A., Janssen J.P.F.M., 1978. Energy loss and set-up due Conclusions to breaking of random waves, p. 569–587. Proc. 16th Int. Conf. on Coastal Eng., Hamburg, Construction of two jetties at Kiashahr lagoon Cheong, C. J., Okada M., 2001. Effects of spilled oil on the has resulted in improving wave conditions in that tidal flat ecosystem-evaluation of wave and tidal actions using a tidal flat simulator, water Sci. Technol., Vol. 43(2), area. The influences of northerly, northwesterly, and 171–177. northeasterly waves have been considerably reduced Danish Hydraulic Institute, 2003. Near-shore spectral wind-wave after the construction of the western jetty. As a re- module, Danish Hydraulic Institute, Manual of MIKE 21, 74. sult, wave energy and related impacts on the lagoon Fonseca, M.S., Bell, S.S., 1998. Influence of physical setting environment have decreased; harbor entrance has on seagrass landscapes near Beaufort, North Carolina, USA, become a calm place and the wave penetration into Mar. Ecol. Prog. Ser. 171, 109–121. the harbor has reduced. Moreover, small vessels can Fonseca M.S., Kenworthy W.J. and Paling, E., 1998a. Restoring seagrass ecosystems in high disturbance environments. In: now have an easier and safer access to the lagoon and Ocean Community Conference, 1998 Nov 16–19. NOAA, thus, monitoring and management of the ecosystem The Marine Technology Society, Baltimore, MD. has become more feasible. However, increased sed- Holthuijsen, L.H., Booij, N., Herbers, T.H.C., 1989. A prediction imentation, reduction in flushing rates, dumping of model for stationary, short-crested waves in shallow water garbage and more pollution are possible potential with ambient current, Coastal Eng. Vol. 13, 23–54. impacts on the ecosystem health of Kiashahr lagoon Johnson, H.K., 1998. On modeling wind-waves in shallow and that would arise as a consequence of this attenuation fetch limited areas using the method of Holthuijsen, Booij and Herbers. J. Coastal Research 14(3), 917–932. of wave energy. Keddy, P.A., 1982. Quantifying within-lake gradients of wave energy: interrelationships of wave energy, substrate parti- Acknowledgements cle size and shoreline plants in Axe Lake, Ontario Aquatic Botany Vol. 14, 41–58. The authorities of Iran meteorological organiza- U.S. Army Corps of Engineers, 2002. Coastal Engineering Man- tion are thanked for providing necessary informa- ual; Estimation of Near-shore Waves, Part II, Chapter 3, tion. ASCE, Vicksburg.

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