Açık kanalda batmış bitkinin akıma etkisi

Öz

Son 30 yılda ekosistem ve dünya için vazgeçilmez bir rolü olan bitki tarlalarının kıyı ve akarsu hidroliği üzerindeki etkilerini incelemek çok önem kazanmıştır. Akım ve bitki örtüsü arasındaki girişim, katı madde taşınımını, akarsu jeomorfolojisini ve akarsu bölgesindeki yaşam alanını önemli derecede etkilemektedir. Doğal bitki tarlalarının şüphesiz en önemli özelliği rastgele bir karaktere sahip olmalarıdır. Doğal bir bitki alanında, bitkinin yüksekliği, çapı, şekli, bükülme sertliği ve mekânsal dağılım gibi birçok parametre rastgele olarak olaya etkili olmaktadır [2]. Bu nedenlerden dolayı, akım alanı ve bitki örtüsü arasında meydana gelen etkileşimin anlaşılması akarsu düzenlemeleri ve akım kontrol durumları için oldukça önemlidir. Bu çalışmada, kısmi bitki örtüsüne sahip akarsularda bulunan batık bitki örtüsü ve akım arasındaki etkileşim deneysel olarak incelenmiştir. Deneylerde, düşük ve yüksek yoğunlukta (N1=172 IP/m² ve N2=1142 IP/m²) olmak üzere iki farklı bitki yoğunluğu kullanılmıştır. Kanalda x ekseni yönünde (13 farklı noktada), yanal mesafelerde (11 farklı noktada) ADV (Acoustic Doppler Velocimeter) ile üç farklı derinlikte düşey hız ölçümleri yapılmıştır. Bu çalışmada bitki tabakasının varlığının, akımın hızında bir azalmaya neden olduğu ve bitki yoğunluğunun artışıyla beraber hızdaki azalmanın daha etkin bir hale geldiği görülmüştür. Bu çalışmanın, literatürde art-iz bölgesi ile ilgili sınırlı sayıda olan çalışmalara katkı sağlayacağı düşünülmektedir.

Anahtar Kelimeler

• : Bitki parçası,art-iz bölgesi,batık bitki

The effect of submerged vegetation on the open channel flow

Öz

In the last 30 years, it has become very important to examine the effects of vegetation fields on the coastal and fluvial areas, which have an indispensable role for the ecosystem and the world. The interference between current and vegetation greatly affects the sediment transport, river geomorphology and habitat in the river area. Doubtlessly, one of the most important features of natural vegetation fields is the randomness. In a natural vegetation field, many parameters such as the diameter and height of the plants, their shape, bending stiffness and spatial distribution can be observed as random parameters [2]. For these reasons the interaction between flow and vegetation should be understand very well in terms of river management and flow control. In this study, interaction between submerged vegetation layer and flow at partially vegetated river flows was investigated experimentally. Rare and dense vegetation intensity (N1=172 IP/m² and N2=1142 IP/m²) was considered in the experiments. Velocity measurements were made at three different depths in the channel x-axis direction (at 13 points) and y-axis direction (at 11 points) using ADV (Acoustic Doppler Velocimeter). In this study, it was observed that the presence of the plant caused a decrease in the current speed and with the increase of the plant density, the reduction in speed became more pronounced. It is assumed that this study will contribute to the understanding of wake region.

Anahtar Kelimeler

• Vegetation patch,wake region,submerged vegetation

Kaynakça

1. Afzalimehr, H., Najfabadi, E.F., and Singh, P.V., Effect of Vegetation on Banks on Distribution of Velocity and Reynolds Stress under Acceleration Flow, Journal of Hydraulic Engineering, 15, 9, 708-713, (2010).
2. Akgül, M.A., Yilmazer, D., Oguz, E, Kabdasli, M.S., and Yagci, O., The effect of an emergent vegetation (i.e. Phragmistes Australis) on wave attenuation and wave kinematics, Journal of Coastal Research: Special Issue, 65, 1, 147–152, (2013).
3. Fischer-Antze, T., Stoesser, T., Bates, P., and Olsen, N.R.B. 3D numerical modelling of open-channel flow with submerged vegetation. Journal of Hydraulic Research, 39, 3, 303–310, (2001).
4. Fonseca, M.S., and W.J. Kenworthy, Effects of current on photosynthesis and distribution of seagrasses, Aquatic Botany, 27, 59-78, (1987).
5. Haung, B., Lai, G and Qiu, J., Experimental research on influence of vegetated floodplains upon flood carrying capacity of river, Journal of Hydrodynamics, Ser. A, 14, 4, 468-474, (1999).
6. Huai, W.X., Zeng, Y.H., Xu, Z.G. and Yang, Z.H. Three-layer model for vertical velocity distribution in open channel flow with submerged rigid vegetation. Advances in Water Resources, 32, 487-492, (2009).
7. Järvelä, J., Influence of vegetation on flow structure in floodplains and wetlands, In Sánchez-Arcilla A, Bateman A, editors, 3rd IAHR Symposium on River, Coastal and Estuarine Morphodynamics, Barcelona, 1-5 September 2003. Madrid: IAHR, 845-856, (2003).
8. Järvelä, J., Effect of submerged flexible vegetation on flow structure and resistance. Journal of Hydrology, 307, 233-241, (2005).

9. Li, Y., Wang, Y., Anim, D.O., Tang, C., Du, W., Ni, L., Yu, Z., and Acharya, K. Flow characteristics in different densities of submerged flexible vegetation from an open-channel flume study of artificial plants. Geomorphology, 204, 314–324, (2014).
10. Nepf, H.M., Drag, turbulence, and diffusion in flow through emergent vegetation, Water Resources, 35, 2, 479-489, (1999).
11. Nepf, H.M. and Vivoni, E.R., Flow Structure in depth limited, vegetated flow, Journal of Geophysical Research, 105, C12, 28547-28557, (2000).
12. Nepf, H. M., Flow and treansport in regions with aquatic vegetation, Annual Review Fluid Mechanics, 44, 123-42, (2012).
13. Nezu, I. and Okamoto, T., Large eddy simulation of 3-D flow structure and mass transport in open channel flows with submerged vegetations, Journal of hydro-Environment Research, 4, 185-197, (2010).
14. Ni, H. and Gu, F., Roughness coefficient of non-submerged reed, Journal of Hydrodynamics, Ser. A, 20, 2, 167-173, (2005).
15. Okamoto T., and Nezu, I., Spatial evolution of coherent motions in finite-length vegetation patch flow, Environmental Fluid Mechanics, 13, 417-434, (2013).
16. Raupach M.R., Canopy Transport Processes, In: Steffen W.L., Denmead O.T. (eds) Flow and Transport in the Natural Environment: Advances and Applications, Springer, Berlin, Heidelberg, 95-127(1988),
17. Sarker, A., Flow measurement around scoured bridge piers using Acoustic-Doppler Velocimeter-ADV, Flow measurement and instrumentations, 9, 217-227, (1998).
18. Stephen, U. and Gutknecht, D., Hydraulic resistance of submerged flexible vegetation, Journal of Hydrology, 269, 27-43, (2002).
19. WinADV32(v.2.027) Manual 2009
20. Wilson, C.A.M.E. Flow resistance models for flexible submerged vegetation. Journal of Hydrology, 342, 3-4, 213–222, (2007).
21. Yüksel Ozan, A., Bitki parçasının açık kanal en kesiti boyunca neden olduğu akım yapısı, Pamukkale Üniversitesi Mühendislik Bilimleri Dergisi, PAJES-71300, DOI: 10.5505/pajes.2016.71300, (2016).
22. Zhu, L. and Chen, Q., Numerical modelling of surface waves over submerged flexible vegetation, American Society of Civil Engineers, Journal of Engineering Mechanics, 142, 8, A40115001-1/A4015001-12, (2015).