انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة
الكلية كلية الهندسة
القسم الهندسة البيئية
المرحلة 4
أستاذ المادة نسرين جاسم حسين المنصوري
13/07/2018 17:21:05
Instructional Objectives On completion of this lesson, the student shall be able to learn the following: 1. The mechanics of sediment mo vement in alluvial rivers 2. Different types of bed fo rms in alluvial rivers 3. Quantitative assessment of sediment transport 4. Resistance equations for flow 5. Bed level changes in alluvial channe ls due to natural and artificial causes 6. Mathematical modelling of sediment transport 2.10.0 Introduction In Lesson 2.9, we looked into the aspects of sediment generation due to erosion in the upper catchments of a river and their transport by the river towards the sea. On the way, some of this sediment mi ght get deposited, if the stream power is not sufficient enough. It was noted that it is the shear stress at the riverbed that causes the particles near the bed to move provided the shear is greater than the critical shear stress of the particle which is proportional to the particle size. Henc e, the same shear generated by a particular flow may be able to move of say, sand particles, but unable to cause movement of gravels. The particles which move due to the average bed shear stress exceeding the critical shear stress of the particle display different ways of movement depending on the flow condition, sediment size, fluid and sediment densities, and the channel conditions. At relatively slow shear stress, the particles roll or slide along the bed. The particles remain in continuous cont act wit the bed and the movement is generally intermittent. Sediment material transported in this manner is termed as the contact load . On increasing the shear st ress, some particles loose contact with the bed for some time, and hop or bounce from one point to another in the direction of flow. The sediment particles moving in this manner fall into the category of saltation load . Contact load and saltation load together is generally termed as bed load , that is, the sediment load that is transported on or near the bed. The further increase in shear stress, the particles may go in suspension and remain thus due to the turbulent fluc tuations and get carried downstream by stream flow. These sediment particles are termed as suspension load . In most natural rivers, sediments are mainly transported as suspended load. Bed load and suspended load together constitute, what is termed as, total load . A knowledge of the rate of total s ediment transport for given flow, fluid and sediment characteristics is necessary for the study of many alluvial river processes. Engineers always need to bear in mind t he fact that alluvial streams carry not only water but also se diment and the stability of a stream is closely linked with the sediment and transpor t rate. Alluvial channels must be
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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