River Discharge

What is River Discharge?

The discharge of a river (or stream) is the volume of water that streams past a point in the river’s course every second. The volume is estimated in cubic meters (m3), and it is every second, so the units of discharge are cubic meters a second or m3s-1. Unintentionally, 1m3s-1 is equivalent to 1 cumec, so the discharge of a river is regularly estimated in cumecs because it is somewhat simpler to state. Discharge is ordinarily estimated at checking stations that are arranged at various points along the river. 

The discharge of a river changes after some time, contingent upon a couple of variables. The most influential factor is climate. After overwhelming precipitation, the discharge of the river will be higher because there is more water entering the river. The climate influences discharge such a considerable amount that there is a unique chart that we can construct called a hydrograph, which shows precipitation and discharges in a similar diagram and makes it simple to understand how rapidly precipitation influences the discharge of a river. A storm hydrograph is a particular kind of hydrograph that shows precipitation and discharge during and after a storm. The primary distinction between a typical hydrograph and a storm hydrograph is that a storm hydrograph is over a lot shorter timeframe. The following is an anecdotal storm hydrograph of the river Shui: 

Illustration graphing river discharge

There is a bend demonstrating the discharge of the river, and there is a progression of bars indicating a little (genuinely substantial) precipitation. There is a couple of things to note on this chart. First is the slack time. The slack time is the time distinction between the pinnacle precipitation and the pinnacle discharge. A long slack time shows that it requires some investment for precipitation to enter the river. Then again, a short slack time shows that the precipitation is entering the river reasonably fast. The rising projection is the unpredictable piece of the discharge line that has a positive inclination, demonstrating that the discharge is expanding. The falling part is the contrary demonstrating that the discharge is decreasing. 

Elements Affecting a Storm Hydrograph 

The Drainage Basin 

Various things affect the state of a hydrograph. One factor is the state of the waste basin. Waste basins appear in a wide variety of shapes. Generally, circular shapes are basic and are progressively lengthened and narrowed. In a circular waste basin, the river’s hydrograph can regularly be portrayed as “showy” because it will have a genuinely steep rising projection and a high pinnacle discharge. This is because all focus points in the seepage basin are (once more, generally) equidistant from the river, so all the precipitation arrives in the river simultaneously. 

The size of the waste basin affects the hydrograph. Huge basins will have high pinnacle discharges since they experience more precipitation, and yet they will have more extended slack occasions than smaller basins because the water takes more time to arrive in the rivers. 

Basins with soak inclines will have a high pinnacle discharge and a short slack time because the water can travel quicker downhill. Finally, the seepage thickness of a basin will influence the slack time and the steepness of the falling projection. Basins with bunches of streams and rivers (a high seepage thickness) will have a short slack time and a genuinely steep falling projection since water will deplete rapidly. 

Soil and Rock Type 

In a case when a river is surrounded by non-permeable and impermeable rocks (e.g., mudstone), it will have a high pinnacle discharge and a short slack time. Impermeable rocks will not let water permeate, constraining the water to travel in overland streams. This is a lot quicker than ground flow, interflow and throughflow, so the slack time is diminished. Moreover, non-permeable rocks cannot store water, so the pinnacle discharge of a river is expanded as more water enters the river instead of being stored in the waste basin. 

The soil’s capacity to allow water to penetrate has a comparative impact on the predominant stone type in a seepage basin. Unconsolidated soils permit water to permeate and collect in a seepage basin; what is more, water seeps gradually through the soil using throughflow. This decreases the pinnacle discharge while expanding the slack time of a river. Then again, mud soils do not permit water to penetrate. Therefore, water ventures rapidly as an overland stream, lessening the slack time of a river. 

Climate and Weather

The power of a storm will affect the pinnacle discharge of the river. More rainwater equals more water in the river, so a higher discharge. The kind of storm (or precipitation) that happens is not immediately clear. A winter storm (for example, snow) will bring about an expansion in the river’s discharge when the snow dissolves, yet this frequently will not be for quite a while so the slack time will be tremendous. 

If the downpour has been vigorous, the ground might be waterlogged, diminishing the slack time, because water will be unable to penetrate and instead will travel overland in streams. Likewise, if the atmosphere has been hot and dry or cold, the ground will be hard, and water will not permeate and instead stream overland, lessening the slack time and expanding the pinnacle discharge. 

Vegetation Cover 

In a case when the territory encompassing the river has thick vegetation spread, at that point, bunches of precipitation will be blocked, extraordinarily expanding the slack time. The pinnacle discharge will also diminish because the vegetation will assimilate the water and lose it through transpiration and evaporation. 

Human Activity 

People will typically cover the soil in impermeable materials like landing areas or stabilisers, which build up surface runoff and diminish the measure of water stored, expanding the pinnacle discharge and lessening the slack time. As water does not penetrate effectively in urban regions, people frequently manufacture storm drainage that runs directly into a river, decreasing the slack time and expanding the river’s pinnacle discharge. 

Hydrographs 

A hydrograph shows how a river reacts to a time of precipitation. 

The bar graph shows precipitation. The line diagram shows the river discharge. The time between top precipitation and pinnacle discharge is the slack time. The rising limb and falling limb are on either side. 

Peak discharge – the most significant measure of water held in the channel. 

Pinnacle precipitation – the most extreme measure of precipitation (millimeters). 

Slack time – the time taken between top precipitation and pinnacle discharge. 

Rising appendage – shows the expansion in discharge on a hydrograph. 

Falling appendage – shows the arrival of discharge to ordinary/base stream on a hydrograph. 

Base stream – the typical discharge of the river. 

The slack time can be short or long, contingent upon various components. For instance, if there is no vegetation in a region, the water runs off into the river faster; in this way, it would have a short slack time. Conversely, if there is much vegetation in the zone, the slack time would be longer as the plants would block the precipitation. A short slack time implies water is arriving in the river rapidly, so there is a greater possibility of a flood. 

Variables impacting slack time include: 

  • Size of seepage basin 
  • Vegetation 
  • Valley side steepness 
  • Soil type 
  • Breaking down Storm Hydrographs 

It is common for inquiries concerning hydrographs to come up in the test. However, that is OK; these are ordinarily 2 or 4 imprint addresses that request that you read something off a diagram or depict the chart – simple imprints. The somewhat more difficult inquiries are the ones that require you to clarify a hydrograph because these expect you to think. We should take a look at the storm hydrograph for the anecdotal river Shui once more: 

Whenever requested to depict the hydrograph, you could cite the slack time, top discharge and remark on the slope of the rising and falling limbs (recall, state estimations off of the chart). Instead, your approach could be to clarify the hydrograph’s shape. These reasons are all the components we talked about before. You have to express a factor and then clarify how and why it influences the state of the hydrograph. 

For the River Shui’s hydrograph, we could state that the high pinnacle discharge and the precarious rising limb indicates that the waste basin is round. In this case, the precipitation will land at focus points equidistant from each other and arrive in the river generally at a similar time, creating the high pinnacle discharge. 

Summary

Physical Factors Affecting Storm Hydrographs 

There is a scope of physical components that influence the state of a storm hydrograph. These include: 

1. Enormous waste basins get more precipitation, so have a higher pinnacle discharge contrasted with smaller basins. Smaller basins, by and large, have shorter slack occasions since the precipitation does not have as far to travel. The state of the waste basin likewise influences overflow and discharge. Waste basins that increasingly become more round lead to shorter slack occasions and a higher pinnacle discharge than those that are long and thin because the water has a shorter distance to travel to a river. 

2. Seepage basins with soak sides will, in general, have shorter slack occasions than shallower basins. This is because water streams more rapidly on the precarious slants down to the river. 

3. Basins that have numerous streams (high seepage thickness) channel more rapidly and have a shorter slack time. 

4. In a case when the seepage basin is now soaked, at that point, surface spillover increments because of the decrease in influx. Rainwater enters the river faster, decreasing slack occasions, as surface overflow is quicker than baseflow or through the stream. 

5. In a case when the kind of stone inside the river basin is impermeable, surface overflow will be higher, throughflow and penetration will likewise be diminished with a significant decrease in slack time and an expansion in top discharge. 

6. If a waste basin has much vegetation, this will have a critical effect on a storm hydrograph. Vegetation captures precipitation and eases the progress of water into river channels. This expands the slack time. Water is additionally lost because of evaporation and transpiration from the vegetation. This diminishes the pinnacle discharge of a river. 

7. The amount of precipitation can affect a storm hydrograph. Substantial storms bring about more water entering the waste basin, which results in a higher discharge. The kind of precipitation can likewise be affected. The slack time is probably going to be more pronounced if the precipitation is snow instead of a downpour. This is because snow takes some to liquefy before the water enters the river channel. When there is a fast liquefying of snow, the pinnacle discharge could be high. 

Human Factors Affecting Storm Hydrographs 

There are a number of human factors that influence the state of a storm hydrograph. These include: 

1. Waste frameworks that have been made by people lead to a short slack time, and high pinnacle discharge as water cannot vanish or penetrate the soil. 

2. In a territory that has been urbanized, the utilization of impermeable structure material such as roads and buildings have less capacity to store rainfall. This implies influx levels abatement and surface run-off increments. This prompts a short slack time and an expansion in top discharge. 

Key Terms 

Hydrograph – a diagram that shows river discharge and precipitation over some time. 

Flood – when the limit of a river to ship water is surpassed, and water streams over its banks. 

Base stream – the base flow of the river relates to the ordinary everyday discharge of the river and is the result of groundwater saturating the river channel. 

Storm stream – storm overflow occurring because of storm precipitation, including both surface and throughflow. 

Bankfull discharge – the highest discharge that a specific river channel is fit for conveying without flooding. 

Pinnacle discharge – the point on a flood hydrograph when river discharge is at its most prominent. 

Pinnacle precipitation – the point on a flood hydrograph when precipitation is at its most prominent. 

Slack time – the timeframe between pinnacle precipitation and pinnacle discharge.

Read more about River Drainage Patterns

References

  • Discharge & Hydrographs. (n.d.). Retrieved from Geography AS Notes: https://geographyas.info/rivers/discharge-and-hydrographs/
  • River discharge. (n.d.). Retrieved from JKGeography: https://www.jkgeography.com/river-discharge.html
  • River Management. (n.d.). Retrieved from BBC>CO: https://www.bbc.co.uk/bitesize/guides/zg4tfrd/revision/2
  • Rivers – Discharge. (n.d.). Retrieved from Internet Geography: http://www.geography.learnontheinternet.co.uk/topics/discharge.html

Cite/Link to This Article

  • "River Discharge". Geography Revision. Accessed on May 26, 2022. https://geography-revision.co.uk/a-level/physical/river-discharge/.

  • "River Discharge". Geography Revision, https://geography-revision.co.uk/a-level/physical/river-discharge/. Accessed 26 May, 2022.

  • River Discharge. Geography Revision. Retrieved from https://geography-revision.co.uk/a-level/physical/river-discharge/.