Streamflow, or channel runoff, is the flow of water in streams, rivers, and other channels, and is a major element of the water cycle. The record of flow over time is called a hydrograph.

Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. Surface runoff is a major component of the water cycle.

A stream is a body of water with surface water flowing within the bed and banks of a channel. The flow of a stream is controlled by three inputs – surface water, subsurface water and groundwater. The surface and subsurface water are highly variable between periods of rainfall.

hydrologic cycle–the cyclic transfer of water vapor from the Earth’s surface via evapotranspiration into the atmosphere, from the atmosphere via precipitation back to earth, and through runoff into streams, rivers, and lakes, and ultimately into the oceans.

The water cycle shows the continuous movement of water within the Earth and atmosphere. It is a complex system that includes many different processes. Liquid water evaporates into water vapor, condenses to form clouds, and precipitates back to earth in the form of rain and snow.

Mechanisms that cause changes in streamflow

• Runoff from rainfall and snowmelt.
• Evaporation from soil and surface-water bodies.
• Transpiration by vegetation.
• Ground-water discharge from aquifers.
• Ground-water recharge from surface-water bodies.
• Sedimentation of lakes and wetlands.

8 Different Types of Streams

• Alluvial Fans. When a stream leaves an area that is relatively steep and enters one that is almost entirely flat, this is called an alluvial fan.
• Braided Streams.
• Deltas.
• Ephemeral Streams.
• Intermittent Streams.
• Meandering Streams.
• Perennial Streams.
• Straight Channel Streams.

Nile River

Factors Affecting a River’s Velocity

• Channel Shape. The shape of the channel affects the velocity of a river.
• Volume of Water. The volume of water that flows through a river within a given amount of time — known as the discharge — also affects its velocity.
• Smooth and Rough Channels.
• Riverbed’s Gradient.

As one moves along a stream in the downstream direction: Discharge increases, as noted above, because water is added to the stream from tributary streams and groundwater. As discharge increases, the width, depth, and average velocity of the stream increase. The gradient of the stream, however, will decrease.

What three factors affect how fast a river flows and how much sediment it can erode? A river’s slope, volume of flow, and the shape of its streambed.

1. Toward the middle of a river, water tends to flow fastest; toward the margins of the river it tends to flow slowest. 2. In a meandering river, water will tend to flow fastest along the outside bend of a meander, and slowest on the inside bend.

Flood Erosion and Deposition: As flood waters rise, the slope of the stream as it flows to its base level (e.g., the ocean or a lake) increases. Also, as stream depth increases, the hydraulic radius increases thereby making the stream more free flowing. Both of these factors lead to an increase in stream velocity.

Velocity increases as more water is added to rivers via tributary rivers. This means that less of the water is in contact with the bed of the river and the mouth so there is less energy used to overcome friction. Hence rivers flow progressively faster on their journey downstream.

In the middle course the river has more energy and a high volume of water. The gradient here is gentle and lateral (sideways) erosion has widened the river channel. The river channel has also deepened. A larger river channel means there is less friction, so the water flows faster.

It’s well known that rivers increase in size as they transport water from their source in their headwaters to the mouth. The river channel becomes wider and deeper and as a result its cross-sectional area increases. In the upper course of the river bedload is larger and more angular.

Most river erosion happens nearer to the mouth of a river. On a river bend, the longest least sharp side has slower moving water. Here deposits build up. On the narrowest sharpest side of the bend, there is faster moving water so this side tends to erode away mostly.

Waves washing over rocks on the beach is the correct example of natural erosion because waves from any water body are naturally generated by the effect of wind and gravity these can wipe the surface materials present over the rocks on the beach.

The agents of soil erosion are the same as of other types of erosion: water, ice, wind, and gravity. Soil erosion is more likely where the ground has been disturbed by agriculture, grazing animals, logging, mining, construction, and recreational activities.

Erosion is the movement of particles away from their source. Example of erosion: Wind carries small pieces of rock away from the side of a mountain. Chemical Weathering: – Decomposition of rock and soil due to chemical reactions.

Five agents of erosion are gravity, running water, glaciers, waves, and wind.

Rain, rivers, floods, lakes, and the ocean carry away bits of soil and sand and slowly wash away the sediment. Rainfall produces four types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion.

Examples of Water Erosion

• Canyons. A good example is the Grand Canyon, which was formed by the Colorado River.
• Caves. Flowing water curves out caves over thousands of years.
• Coastal Erosion. When waves hit the shoreline, the impact is sufficient to cause erosion of the coasts.
• River Banks.

These are inter-rill erosion, rill erosion, gully erosion, and streambank erosion.

Water erosion is the detachment and removal of soil material by water. The process may be natural or accelerated by human activity. Water erosion wears away the earth’s surface. Sheet erosion is the more-or-less uniform removal of soil from the surface.

These particles move away from the field, and end up in streams and waterways. Three types of water erosion can occur, sheet, rill, and gully.

The four main types of river erosion are abrasion, attrition, hydraulic action and solution.

Water erosion. This includes the splashing of soil particles by raindrop impact; sheet erosion whereby a layer of topsoil is removed by flowing water; and gully erosion where a channel is formed. Gullies are often perceived as the most serious form of water erosion because they are obvious features in the landscape.