Sediments transport

Lecture 5Jyoti Anischit

Roll 10

Stream morpho hydrologic parameters, flow velocity discharge measurement

• stream planform parameters1. Sinuosity2. Radius of curvature3. Meander length and width

STream planform parameters• Sinuosity, meander belt width, meander wavelength and radius of

curvature The planform geometry is well attributed by various parameters: sinuosity, meander wavelength, meander belt width, and radius of curvature.

• Sinuosity (K) is the ratio of stream channel length to down-valley distance.

• Meander wavelength (Lm) of the river is the distance between two successive crests or two successive trough of the curved channel.

• Meander belt width (Wblt) is a straight line between the crest of the bend to the crest of the next bend lying downstream, or is the distance between lines defining the confinement of the lateral boundaries of the channel.

• Radius of curvature (Rc ) is the radius of a circle drown through the apex of the bend and the two Legend Major road Watershed boundary

• Channel length • Belt length (m• Sinuosity A river's sinuosity is its tendency to move back and forth

across its floodplain, in an S-shaped pattern, over time. As the stream meanders across the flood plain, it may leave behind scars of where the river channel once was. A stream that doesn't meander at all has a sinuosity of 1.

• Meander belt width (m) • Meander wave length • Radius of curvature (m• Slope (m/m) • Average slope

MOrpho hydrologic parameters

1. Width2. Cross section3. Depth4. Maximum depth5. Flood prone width

Vertical velocity distribution

• Vegetation plays an important role in altering flow characteristics (such as velocity distribution, Reynolds number, and Manning coefficient) compared with nonvegetated conditions in rivers [1]. Generally, the vertical velocity distribution is related directly to the bed shear stress for nonvegetation flow, while, for vegetated flow, it is mainly decided by the vegetation drag since the vegetation roughness is much larger than river bed roughness [2]. The influence mechanism of aquatic plant on flow is very complicated, which is dependent not only on the cross-sectional shape of river, water depth, discharge but also on the species, bending rigidity, distribution, shape of vegetation, and whether it is submerged

Velocity profile measurement

• Aeolian or eolian (depending on the parsing of æ) is the term for sediment transport by wind. This process results in the formation ofripples and sand dunes. Typically, the size of the transported sediment is fine sand (<1 mm) and smaller, because air is a fluid with lowdensity and viscosity, and can therefore not exert very much shear on its bed.

• Bedforms are generated by aeolian sediment transport in the terrestrial near-surface environment. Ripples[1] and dunes[2] form as a natural self-organizing response to sediment transport.

• Aeolian sediment transport is common on beaches and in the arid regions of the world, because it is in these environments that vegetation does not prevent the presence and motion of fields of sand.

• Deposits of fine-grained wind-blown glacial sediment are called loess.

Glacial

• As glaciers move over their beds, they entrain and move material of all sizes. Glaciers can carry the largest sediment, and areas of glacial deposition often contain a large number of glacial erratics, many of which are several metres in diameter. Glaciers also pulverize rock into "glacial flour", which is so fine that it is often carried away by winds to create loess deposits thousands of kilometres afield. Sediment entrained in glaciers often moves approximately along the glacialflowlines, causing it to appear at the surface in the ablation zone.

Discharge measurement:Area velocity method

• The most practical method of measuring stream discharge is through the velocity-area method. Discharge is determined as the product of the cross-sectional area of the water times velocity. Measuring the average velocity of an entire cross section is impractical, so the USGS uses what's called the mid-section velocity-area method. Using this method, the width of the stream is divided into a number of increments, each usually containing no more than 5% of the total discharge. For each incremental width, stream depth and average velocity are measured. The current meter is placed at a depth where average velocity is expected to occur. For shallow sections, this is at 0.6 of the distance from the water surface to the streambed. When depths are large, the average velocity is best estimated by measuring velocity at 0.2 and 0.8 the distance from the water surface to the streambed. The product of velocity, depth and width of the section is the discharge through that increment of the cross section. The total of the incremental discharges equals the discharge of the stream.