کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
5765092 1626608 2017 15 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Critical bed shear stress and threshold of motion of maerl biogenic gravel
ترجمه فارسی عنوان
استرس برش بستر بحرانی و آستانه حرکت ماسه بیوژنیک مئرل
کلمات کلیدی
پویایی رسوب، حرکت ذرات، ذخایر بیولوژیکی، استرس برشی، رودولیت، ایرلند - گالوی بیل،
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات زمین شناسی
چکیده انگلیسی


- Critical bed shear stress of maerl beds has been determined experimentally.
- Maerl is from three contrasting environments: beach, open marine and intertidal.
- Law of the Wall method is compared with Turbulent Kinetic Energy method.
- Maerl falls below Shields curve for quartz sediment with same sieve diameter.
- Relative grain protrusion is key factor lowering critical Shields parameter.

A determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility, rate of erosion and deposition in conservation management. The critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free-living maerl beds in three contrasting environments (open marine, intertidal and beach) in Galway Bay, west of Ireland. The bed shear stress was determined using two methods, Law of the Wall and Turbulent Kinetic Energy, in a rotating annular flume and in a linear flume. The velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed. The critical Shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand. The critical Shields parameters for the maerl particles from all three environments fall below the Shields curve. Along with a previously reported correlation between maerl grain shape and settling velocity, these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter. The intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment. In samples with a high percentage of maerl and low percentage of siliciclastic sand, the lower density, lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment. At velocities ∼10 cm s−1 higher than the threshold velocity of grain motion, rarely-documented subaqueous maerl dunes formed in the annular flume.

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ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Estuarine, Coastal and Shelf Science - Volume 194, 15 July 2017, Pages 128-142
نویسندگان
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