The rising and falling limbs of hydrographs illustrate the changes in river discharge following periods of rainfall.

A hydrograph is a graphical representation that depicts the rate of flow (discharge) over time at a specific point in a river or any water channel. It serves as an essential tool in hydrology, the field that studies water’s properties, distribution, and its effects on the Earth’s surface. The rising and falling limbs are critical components of a hydrograph.

The rising limb, often referred to as the concentration curve, represents the segment of the graph where river discharge increases in response to rainfall. This limb starts at the minimum discharge level, just before the onset of rainfall, and extends to the peak discharge point, which is the highest point on the graph. The steepness of the rising limb is influenced by several factors, including the intensity and duration of the rainfall, the saturation level of the soil, and the characteristics of the river’s catchment area.

Conversely, the falling limb, known as the recession curve, illustrates the decline in river discharge following the peak. This section shows how the river returns to its normal or base flow levels. The rate at which discharge decreases is affected by factors such as the rate of infiltration (the process by which water on the surface enters the soil), evaporation rates, and transpiration (the mechanism by which moisture moves through plants from roots to small pores on the underside of leaves, where it evaporates into the atmosphere).

In summary, the rising and falling limbs of a hydrograph provide crucial insights into a river’s response to rainfall. They help us understand the relationship between rainfall and river discharge and are instrumental in predicting and managing flood events.