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. 358 Aquatic Ecosystem Health & Management, 12(4):358–363, 2009. Copyright C 2009 AEHMS. ISSN: 1463-4988 print / 1539-4077 online DOI: 10.1080/14634980903354726 Downloaded from http://read.dukeupress.edu/aehm/article-pdf/12/4/358/886459/358azarmsa.pdf by guest on 29 September 2021 Azarmsa et al. / Aquatic Ecosystem Health and Management 12 (2009) 358–363 359 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 construc- tion. Figure 3. Bathymetry of the study area after jetties construction. Downloaded from http://read.dukeupress.edu/aehm/article-pdf/12/4/358/886459/358azarmsa.pdf by guest on 29 September 2021 360 Azarmsa et al. / Aquatic Ecosystem Health and Management 12 (2009) 358–363 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 Downloaded from http://read.dukeupress.edu/aehm/article-pdf/12/4/358/886459/358azarmsa.pdf by guest on 29 September 2021 Azarmsa et al.