The shape of the recession limbs of a hydrograph refers to the decline in streamflow after a storm event. It is an important aspect of hydrological analysis as it helps in understanding the response of a watershed to precipitation events. The recession limb represents the base flow of a river or stream, which is the portion of streamflow that is sustained between storm events.



Basin characteristics are the physical and hydrological properties of the drainage basin that influence the shape of the recession limbs. These characteristics include:

1. Size and Shape: The size and shape of the watershed affect the time it takes for runoff to reach the river channels. A larger watershed with a complex shape will have a longer response time, resulting in a longer recession limb.

2. Soil and Geology: The type of soil and underlying geology determine the infiltration capacity of the basin. Soils with high permeability will allow water to seep into the ground more easily, resulting in a faster recession limb. On the other hand, impermeable soils or rocks will lead to slower infiltration and a slower recession limb.

3. Vegetation Cover: The presence of vegetation in the basin affects the amount of interception, evaporation, and transpiration, which ultimately influence the amount of water entering the river channels. Vegetation cover can also impact the storage and release of water, thus affecting the recession limb shape.



Storm characteristics, on the other hand, refer to the properties of the precipitation event itself that can influence the shape of the recession limb. These characteristics include:

1. Intensity and Duration: The intensity and duration of a storm determine the amount of water that enters the river channels. A high-intensity, short-duration storm will result in a rapid increase in streamflow, followed by a steep recession limb. Conversely, a low-intensity, long-duration storm will lead to a slower rise in streamflow and a gentler recession limb.

2. Antecedent Moisture Conditions: The moisture conditions before a storm event also play a role in shaping the recession limb. If the basin is already saturated from previous rainfall, the soil will have a reduced capacity to absorb water, resulting in a faster runoff and a steeper recession limb.



While both basin characteristics and storm characteristics influence the shape of the recession limbs of a hydrograph, the correct answer is option 'C' - basin characteristics only. This is because basin characteristics have a more dominant and lasting impact on the shape of the recession limb compared to storm characteristics, which are more temporary and event-specific. Understanding the basin characteristics is crucial for predicting and managing water resources effectively.