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Journey of a River - Birth of a River: Tributaries and Watershed

Grade 5CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Source is the starting point of a river, usually located in high-altitude areas like mountains or hills where glaciers melt or springs emerge.

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A Tributary is a smaller stream or river that flows into and joins a larger main river. This process increases the total volume of water (H2OH_2O) in the main channel.

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A Confluence is the specific point where two or more flowing bodies of water, such as a tributary and a main river, meet.

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A Watershed (also called a Drainage Basin) is the entire area of land where all the water that falls under it or drains off it goes into the same river system.

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A Water Divide is a high land area or ridge, like a mountain range, that separates one watershed from another, directing the flow of water in different directions.

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Rivers flow from a higher elevation to a lower elevation due to the force of gravity. The steepness of this flow is known as the River Gradient.

📐Formulae

Gradient=Change in ElevationHorizontal Distance\text{Gradient} = \frac{\text{Change in Elevation}}{\text{Horizontal Distance}}

Total Flow=Main River Flow+Tributary Flow\text{Total Flow} = \text{Main River Flow} + \text{Tributary Flow}

River Discharge (Q)=Cross-sectional Area (A)×Velocity (v)\text{River Discharge (Q)} = \text{Cross-sectional Area (A)} \times \text{Velocity (v)}

💡Examples

Problem 1:

In a mountain range, the 'River Ganga' receives water from three main tributaries in its upper course. If the main stream carries 45004500 units of water and the three tributaries bring 12001200, 850850, and 900900 units respectively, calculate the total units of water flowing after the last confluence.

Solution:

To find the total flow, we add the volume of the main stream to the volumes of all tributaries: 45001200850+9007450\begin{array}{r} 4500 \\ 1200 \\ 850 \\ + 900 \\ \hline 7450 \end{array} The total water flow is 74507450 units.

Explanation:

A river grows in size as it moves downstream because tributaries add their water volume to the main channel at various confluence points.

Problem 2:

A river starts at an elevation of 5000 m5000\text{ m} and reaches a valley at 2000 m2000\text{ m} over a horizontal distance of 100 km100\text{ km}. Calculate the change in elevation.

Solution:

Change in elevation = Starting Height−Ending Height\text{Starting Height} - \text{Ending Height} 5000−20003000\begin{array}{r} 5000 \\ - 2000 \\ \hline 3000 \end{array} The change in elevation is 3000 m3000\text{ m}.

Explanation:

The change in elevation determines how fast a river flows in its upper course; a larger drop usually means a faster, more energetic river.