Reference

The main assumptions underlying the unit hydrograph theory include:

1. Linearity: The response of the watershed is linear. This means that if the rainfall input is doubled, the direct runoff is also doubled.

2. Time Invariance: The relationship between rainfall and runoff does not change over time. The shape of the unit hydrograph remains constant regardless of the timing of the rainfall event.

3. Uniform Rainfall Distribution: Rainfall is assumed to be uniformly distributed over the entire drainage area.

4. Fixed Duration: The rainfall has a specific duration, and the unit hydrograph represents the runoff resulting from one unit of rainfall over this specified duration.

These assumptions simplify the complex nature of hydrological systems, making it easier to analyze and predict runoff patterns. More details can be found in the full article here.