Flow structure along the cross-section of an open-channel caused by patch of submerged vegetation

Vegetation is crucial part of ecosystem in natural rivers. The flow structure changed mostly in streamwise, lateral, and vertical directions because of the Kelvin-Helmholtz instability caused by vegetated canopy. In this study, the flow characteristics under the effect of limited-length submerged vegetation patch were investigated experimentally. The rigid submerged vegetation layer with 1.2 m length, 0.6 m width were used to simulate limited-length submerged vegetation patch in the experiments. The vegetation layer was composed using rigid circular plastic dowels with 0.01 m diameter and 0.05 m height. Two different vegetation densities which are N1=161 IP/m2 and N2=1149 IP/m2 were used to obtain the effect of vegetation density. The velocity measurements were performed using ADV. According to the results obtained, the presence of vegetation causes strong gradient in the flow structure over the cross-section of the channel. Higher vegetation intensity causes higher velocity gradient in the velocity distribution. Additionally, “S-curve” shaped depth averaged stream-wise velocity profile was obtained along the cross-section with steeper curve for higher vegetation intensity. Turbulent kinetic energy was obtained higher in the vegetated part comparing to non-vegetated part. Furthermore, turbulent kinetic energy peak occurs at the vegetation interface between inner and outer layer in the vegetated part for higher vegetation intensity. Beside this, strong momentum exchange appears at the interface between the inner layer and outer layer at the vegetated part for higher vegetation intensity. The discharge capacity of the channel was also examined and found that discharge capacity decreases with increasing vegetation density.

Bitki parçasýnýn açýk kanal enkesiti boyunca neden olduðu akým yapýsý

Akarsulardaki bitki yapýsý ekosistemin önemli bir parçasýdýr. Akým yapýsý, bitki tabakasý nedeniyle meydana gelen Kelvin-Helmholtz istikrarsýzlýðýndan dolayý akým doðrultusunda, yanal ve düþey doðrultularda ciddi miktarda deðiþmektedir. Bu çalýþmada, sýnýrlý uzunlukta batýk bitki parçasýnýn etkisindeki akým yapýsý deneysel olarak araþtýrýlmýþtýr. Deneylerde sýnýrlý uzunlukta batýk bitki parçasý, 1.2 m uzunluðunda ve 0.6 m geniþliðinde rijit batýk bitki tabakasý kullanýlarak benzeþtirilmiþtir. Bitki tabakasý, 0.01 m çapýnda ve 0.05 m yüksekliðinde dairesel kesitli rijit plastik boru parçalarý kullanýlarak benzeþtirilmiþtir. Bitki yoðunluðunun etkisini belirlemek için, N1=161 IP/m2 and N2=1149 IP/m2 olmak üzere iki farklý yoðunlukta bitki tabakasý kullanýlmýþtýr. Hýz ölçümleri ADV kullanýlarak yapýlmýþtýr. Elde edilen sonuçlara göre, bitki tabakasý kanal enkesiti boyunca akým yapýsýnda ciddi bir deðiþime neden olmaktadýr. Büyük yoðunluða sahip bitki tabakasý, hýz daðýlýmýnda daha yüksek oranda hýz deðiþimine sebep olmuþtur. Buna ilaveten, kanal enkesiti boyunca derinlik ortalama hýz daðýlýmýnda, büyük yoðunlukta daha dik olmak kaydýyla, bir S-eðrisi belirlenmiþtir. Türbülans kinetik enerji, bitki tabakasýnýn olduðu bölgede bitki tabakasý olmayan bölgeye nazaran daha fazla meydana gelmiþtir. Ayrýca en yüksek türbülans kinetik enerji deðeri, yüksek yoðunlukta bitki tabakasýnýn bulunduðu kýsýmda, bitki ile akým arasýndaki sýnýr bölgede meydana gelmiþtir. Bunun yaný sýra büyük yoðunlukta, bitki tabakasýnýn bulunduðu kýsýmda, bitki ile akým arasýndaki sýnýr bölgede kuvvetli momentum deðiþimi belirlenmiþtir. Ayrýca, kanalýn debi kapasitesi incelenmiþ ve bitki yoðunluðundaki artýþýn debi kapasitesini azalttýðý görülmüþtür.