Runoff Coefficient

Definition

The runoff coefficient is a dimensionless factor used to estimate the amount of precipitation that will convert to runoff for a specific area, considering the land use, soil type, and slope. This coefficient plays a vital role in hydrological modeling as it helps predict surface runoff during events like storms, directly influencing design storm development and hydrograph analysis.

5 Must Know Facts For Your Next Test

1. The runoff coefficient varies between 0 (no runoff) and 1 (all precipitation becomes runoff), depending on factors such as land cover and soil characteristics.
2. Higher runoff coefficients are typically associated with impervious surfaces like concrete, while lower coefficients are found in forested or grassland areas.
3. Runoff coefficients are critical for calculating peak flow rates and total runoff volumes during design storms.
4. The empirical methods for determining runoff coefficients often involve using tables or charts that relate land use types to specific coefficients.
5. In hydrological modeling, adjusting the runoff coefficient can significantly influence flood predictions and water resource management strategies.

Review Questions

• How does the runoff coefficient influence the prediction of surface runoff during design storm events?
  • The runoff coefficient directly impacts the estimation of surface runoff by quantifying how much of the precipitation will contribute to runoff based on various factors like land use and soil type. In design storm development, selecting an appropriate runoff coefficient is crucial for accurately predicting peak flows and managing potential flooding. By analyzing these coefficients alongside storm data, engineers can better design drainage systems and infrastructure to handle expected water flow.
• Discuss the relationship between the runoff coefficient and hydrographs in terms of understanding watershed behavior during rainfall events.
  • The runoff coefficient influences hydrographs by determining the timing and magnitude of runoff response within a watershed. A higher runoff coefficient means more immediate and intense surface runoff, leading to steeper hydrograph peaks. This relationship helps in understanding how different land uses and soil conditions affect watershed behavior during rainfall events, allowing for better flood risk assessment and management strategies.
• Evaluate how variations in land use can alter the runoff coefficient and consequently impact hydrological modeling outcomes.
  • Variations in land use, such as urbanization or deforestation, can significantly alter the runoff coefficient by changing the permeability of surfaces. For instance, replacing natural vegetation with impervious surfaces increases the runoff coefficient, leading to more rapid and greater runoff volumes during storms. This change impacts hydrological modeling outcomes by potentially underestimating infiltration rates and overestimating peak flows, necessitating adjustments in flood prediction models and water resource management approaches.

Related terms

Infiltration: The process by which water on the ground surface enters the soil, affecting the amount of runoff.

Watershed: An area of land where all the water that falls on it drains into a common outlet, impacting how runoff is calculated.

Hydrograph: A graphical representation of stream flow over time, showing how runoff changes in response to precipitation events.