The correct answer is D. All of the above.
A. The maximum rate of storm runoff is called peak drainage discharge. This is the maximum amount of water that flows over a given area during a storm.
B. Rational method of estimating peak run off, may be used precisely for areas less than 50 hectares. This method is based on the assumption that the runoff from a given area is proportional to the area and the intensity of the rainfall.
C. The period after which the entire area starts contributing to the runoff, is called the time of concentration. This is the time it takes for water from the most distant part of the area to reach the outlet.
The rational method is a simple and widely used method for estimating peak runoff. It is based on the following equation:
$$Q = C I A$$
where:
- $Q$ is the peak runoff (in cubic meters per second)
- $C$ is the runoff coefficient (a dimensionless number that depends on the type of land use)
- $I$ is the intensity of rainfall (in millimeters per hour)
- $A$ is the drainage area (in hectares)
The rational method is most accurate for areas less than 50 hectares. For larger areas, the method becomes less accurate because it does not take into account the effects of topography and other factors.
The time of concentration is the time it takes for water from the most distant part of the area to reach the outlet. It is calculated using the following equation:
$$t_c = \sqrt{\frac{L^2}{D}}$$
where:
- $t_c$ is the time of concentration (in seconds)
- $L$ is the length of the longest overland flow path (in meters)
- $D$ is the average depth of flow (in meters)