Question

What is a falling limb of a synthetic unit hydrograph?

• A. A part of hydrograph where discharge decreases
• B. Peak discharge of hydrograph
• C. A part of hydrograph where discharge increases
• D. The total volume of water in the hydrograph

Hint:

• A hydrograph plots discharge (flow rate) against time.
• Key parts of a hydrograph:
  • Rising limb: Discharge increases.
  • Peak (crest): Maximum discharge.
  • Falling limb (recession limb): Discharge decreases.
• This terminology applies to all types of hydrographs, including storm hydrographs and unit hydrographs (derived or synthetic).

Answer 1

The Correct Option is A

A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, or other channel carrying flow. A typical storm hydrograph (resulting from a rainfall event) has several key components:

• Rising Limb (option c): The portion of the hydrograph where the discharge is increasing. This reflects the arrival of runoff from the catchment as a result of rainfall.
• Crest Segment (Peak Discharge) (option b): The highest point on the hydrograph, representing the maximum discharge during the event.
• Falling Limb (Recession Limb) (option a): The portion of the hydrograph where the discharge is decreasing after the peak. This represents the withdrawal of water from storage in the catchment (e.g., channel storage, surface detention, interflow, and eventually baseflow).
• Baseflow Separation Line: A line drawn on the hydrograph to separate direct runoff (from the storm event) from baseflow (groundwater contribution).

A unit hydrograph is a hydrograph of direct runoff resulting from 1 unit (e.g., 1 cm or 1 inch) of effective rainfall occurring uniformly over a catchment area at a uniform rate during a specified duration. A synthetic unit hydrograph is a unit hydrograph derived for an ungauged catchment (where rainfall and streamflow data are insufficient to derive it directly) using empirical formulas based on catchment characteristics. Regardless of whether it's a storm hydrograph, unit hydrograph, or synthetic unit hydrograph, the term "falling limb" consistently refers to the part of the hydrograph where discharge decreases after reaching its peak. Option (d) The total volume of water in the hydrograph is represented by the area under the hydrograph curve, not a specific limb. \[ \boxed{\text{A part of hydrograph where discharge decreases}} \]