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Streamflow/Discharge and Hydrograph

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Stream flow is the quantity of water flowing in the stream or channel.

Streamflow is the amount or quantity of water which drains as surface flow from the catchments or watershed.

Streamflow from an area represents the integrated result of all hydrological and meteorological factors which year, season to season and day to day depending on rainfall and snow melting.


Ephemeral or seasonal flow:

It is produced in direct response to rainfall, as the stream channel lies above the water table and do not intersect groundwater (water table below stream channel). The channel stream is called influent stream. There is no water in the channel before rainfall and flow cease shortly rainfall stops.
Ephemeral or seasonal flow - Streamflow - Forestrypedia

Perennial flow:

It occurs where the groundwater basin is large enough to supply water continuously without water table dropping below the channel bottom (water table intercepts the aquifer). The channel is called effluent stream. The flow is sustained continuously and there can be the rapid rise of water during high-intensity rainfall.
Perennial flow - Streamflow - Forestrypedia

Intermittent flow:

It is sustained extended periods of time during the rainy or snow season. Here water table goes comes above. For certain periods of the year, it ceases to flow when base flow supply stops and there is no snow.
Intermittent Flow - Streamflow - Forestrypeida


            The water reaches the stream flow in the following four ways.

Direct rainfall over the stream:-

It is a very small portion of the precipitation because open water channels do not occupy much of catchment area.

Surface runoff or overland flow:

When the intensity of rainfall is higher than the infiltration rate, then after infiltration the excess water will flow over the land surface to the channel and is called surface runoff. The quantity of water moving towards the stream is called overland flow. The surface runoff becomes streamflow for the nearest channels. It almost always accompanied by erosion of the soil.

Subsurface flow or interflow:

Some of the water which infiltrates the soil surface may move laterally through the upper soil layers until it enters a stream and is called subsurface or interflow. It reaches the stream later and its basin (watershed).

Base flow groundwater flow or Dry weather flow:-

Some of the rainwater percolates downward under gravity through the soil merge into the water table and if the water table intersects the stream channels and water appears in streams, it is called base flow, groundwater flow or dry water flow. It does not contribute to streamflow surge but rather sustains the base flow of streams at times of no precipitation.


Measurement of water yield for land mass

  • Old unit (cft/ sec)
  • New unit (cubic meter/ sec)
  • Discharge of watershed

Q = Area × velocity
(Unit) Q = m3 / sec


  • It is the interrelationship b/w time and stream flow when graphically represented.” OR; “When discharge is plotted over time, the resulting curve is called hydrograph.
  • The contribution to total stream system flow from the different sources (ie surface flow, subsurface flow, and groundwater flow) have been estimated from hydrograph
  • The total flow at any moment is the sum of three components.
  • It is the chronological/graphical representation of stream system
    • Surface runoff contribution to stream discharge, soon after the commencement of the storm and relatively large amount of water is contributed.
    • The second component of total flow is Subsurface runoff its peak comes down after some time the stream peak.
    • Groundwater component shows almost no correlation with the rainfall pattern, there is no peak in the curve

Parts of Hydrograph:

  • It consists of:
    • Rising limb:

    • RL is caused by surface runoff and somehow reflects storm pattern and basin characteristics. The storm hydrograph of a catchment of shallow soil shows a steep rise immediately while in a deep soil catchment, the peak will be moderate.
    • Peak Flow:

    • When sub-surface flow-joining the stream flow, and the stream flow is at the maximum at that time.
    • Point of Inflection:

    • Ther is a slight kink (deflection) where recession line begins, it is the point of inflection. At that time, both surface end subsurface flow stops.
    • Falling limb:

    • Falling limb shows the groundwater or base flow and in largely independent of storm characteristics.

Hydrograph - Streamflow - Forestrypedia

Types of Hydrograph:

  • There are two types of Hydrograph:
  1. Perennial Hydrograph
  2. Seasonal Hydrograph

Perennial Hydrograph:

The hydrograph b/w time and perennial stream flow are called Perennial Hydrograph.
It will never touch the zero.
Perennial Flow - Hydrograph - Forestrypedia

Seasonal Hydrograph:

The hydrograph b/w time and seasonal streamflow is called S. hydrograph
In this case, the graph starts at zero points and can come again to zero points.
Seasonal Hydrograph - Streamflow - Forestrypedia

For correction and improvements please use the comments section below.

Naeem Javid Muhammad Hassani is working as Conservator of Forests in Balochistan Forest & Wildlife Department (BFWD). He is the CEO of Tech Urdu ( Forestrypedia (, All Pak Notifications (, Essayspedia, etc & their YouTube Channels). He is an Environmentalist, Blogger, YouTuber, Developer & Vlogger.

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