(63) Answer:

At the younger stage of a stream different size and shapes of hard rock particles are added to the flow due to rapid mechanical weathering action. These particles have sharp edges at the very beginning of its formation. However, intensive mechanical weathering action at the younger stage of a river causes to remove sharp and irregular edges of such partials mentioned above with the long distance of their travel in the flow path. This is mainly due to the action of mechanical erosion at the early stages of the river flow. Finally, mechanical weathering of the long distance transported particles cause to produce well rounded particles with smooth surfaces.

(62) Answer:

If we take the cross section of the meander, out side of the curve of meandering channel has a high flow velocity than its inner side curve and tend to produce turbulent flow at the outer side of the meander. Therefore at the outer side of the curve experience more erosion. Because the turbulent flow causes to erode the bank including the bottom of the stream, under the conditions of the mechanical weathering. By the way at the inner side of the meandering curve, sediments of the stream flow tend to settle at its bank. Due to such sediment deposits, further decrease of flow velocity will be taken place.

Answer for Q (61):

Type 1 - This diagram shows younger stage of the river flow. Because it tends to form “V” shaped valley with steep sides of its flow path. It is due to erosion of its bed more rapidly than it erodes its bank. Further it has almost straight flow path. It does not consist of deposition of sediments. These all are due to high velocity of river flow under the highest gradient condition than older and younger stages of a river flow.

Type 2 - It indicates older stage of a river flow. According to the diagram the river flows, forming very broad valley with flat plain. The broad flat plain formed mainly due to sedimentation process and erosion of valley walls of the river at its older stage.Additionally at this stage the river carryout large amount of sediments with its flow and it causes to decrease the stream flow velocity at this stage of flow. Further, river has significant meanders and tends to form oxbow lakes on its flow path. This is due to decrease of flow velocity under the lowest gradient conditions of the main river comparatively with other two stages (younger & mature) of the river flow.

According to the above explanation given under the Type 1 and Type 2, it can that the find difference of stream velocities with relate to different ages of stream formation. Therefore type 1 that the stream at younger stage, it has higher average flow velocity than the older age is represented by the type 3.

(17) Correct answer: (3) gentle slope and permeable soil

When rain water flows on the surface with the gentle slope, it tends to flows with low velocities than it on the steep slops. Water flows with low velocities take more time to move from one place to another place. It causes water to expose for a longer time durations to infiltrate (or sock downwards of the soil formations). Therefore infiltration capacity is higher at the gentle slops than at the steep slope with same conditions.

Permeable soils have higher infiltration capacities than impermeable soils. For example, in loose sand soils have higher infiltration capacity than clayey soils.

Therefore permeable soil with gentle slope surfaces allows the most infiltration of rain water.