Question

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. How does discharge vary according to the stream's length, the climate, and position along the stream course? (C)

Short answer

Discharge in a stream varies according to its length, climate, and position along the stream course. Longer streams with more tributaries and precipitation tend to have higher discharge, while shorter and drier streams have lower discharge. Discharge generally increases as the stream flows downstream, due to the accumulation of water from various sources and the influence of the stream's slope. Climate also significantly affects discharge, with higher precipitation leading to increased discharge and lower precipitation resulting in reduced discharge.

Step-by-step solution

Stream Length

As the stream's length increases, its discharge generally increases as well. This is because, as the stream flows longer distances, it gains more water from tributaries (smaller streams and rivers joining the main stream), precipitation, and other sources, resulting in a higher flow volume. Additionally, longer streams generally drain larger areas and are more likely to capture water from various sources, contributing to increased discharge.

Climate

Climate plays a significant role in the variation of discharge in a stream. In regions with high precipitation, streams tend to have a higher discharge due to the increased input of water. Conversely, in arid regions or areas with low precipitation, there might be less water available to contribute to the stream flow, leading to lower discharge values. Moreover, the seasonality of precipitation can also affect discharge, as streams in areas with distinct wet and dry seasons might experience significant fluctuations in discharge throughout the year.

Position along the Stream Course

The position along the stream course also affects the discharge. Near the headwaters (the start of a stream), discharge will be low because the stream has only just begun to accumulate water. As the stream flows downstream, it will receive more water from tributaries, ground seepage, and precipitation, gradually increasing in discharge. Also, the stream's slope can influence the discharge; steeper inclines speed up the flow of water, while gentler slopes may slow it down. In conclusion, the discharge of a stream varies according to its length, the climate, and position along the stream course. Longer streams with abundant water sources and a higher amount of precipitation tend to have a higher discharge, while short streams and those in drier regions have lower discharge values. The position along the stream course also plays a critical role, with discharge typically increasing as it moves downstream from its source.

Key concepts

Stream Length

A stream's discharge is deeply influenced by its length. As streams extend over greater distances, they tend to gather more water, which results in increased discharge. The longer a stream flows, the more chances it has to pick up additional water from tributaries. This includes smaller streams and rivers that merge into the main stream.
This process is akin to combining multiple streams of water, naturally boosting the volume of water being carried.
Moreover, longer streams usually cover larger drainage areas. This means they can also capture more precipitation and groundwater, which adds to the overall discharge.
Some key factors contributing to increased discharge in longer streams include:

• Increased surface area collecting rainwater
• Contributions from other water sources like tributaries
• Various environmental conditions along the length of the stream

Climate Impact on Streams

The climate where a stream exists significantly affects its discharge. Higher precipitation regions naturally supply more water to streams, leading to a higher discharge.
Conversely, in regions with little rainfall, streams could have much lower discharges simply because there is less water available.
The variability of weather patterns, such as wet and dry seasons, can also change how much water flows in a stream over time. Streams in areas with distinct seasonal changes could see a marked increase in water flow during wet seasons and a corresponding decrease during dry periods.
To sum up some of the climate influences on stream discharge:

• High precipitation = higher stream discharge
• Low precipitation = potential for lower discharge
• Seasonal changes can lead to fluctuations in discharge rates

Stream Course

The position along a stream's route or course is crucial for understanding its discharge at different points.
Close to the headwaters, which is where the stream starts, the discharge tends to be low. This is because the stream is just beginning and hasn't had much opportunity to collect water.
As it journeys downstream, the stream picks up more water from nearby tributaries, rainfall, and ground seepage. This results in a gradual increase in discharge.
The terrain also plays its part; streams with steep gradients can move water faster, which might increase discharge rates. But on gentler slopes, the flow can slow down, affecting discharge differently.
Here's a quick guide on how the stream course influences discharge:

• Upstream (headwaters) = generally lower discharge
• Downstream = increasing discharge as more water is collected
• Slope affects flow speed and consequently the discharge