The runoff from a catchment is estimated by the following methods: 1. Standard Tables 2. Empirical Formulae 3. Rainfall Runoff Correlation. Method # 1. Standard Tables: Observations of precipitation and the resulting runoff were taken for a number of catchments having different characteristics. Tables are prepared showing the relation between precipitation and the resulting runoff, taking into consideration the catchments. [...]
For any time duration, the average depth of rainfall falling over a catchment can be found by the following three methods: 1. The Arithmetic Mean Method 2. The Thiessen Polygon Method 3. The Isohyetal Method. 1. The Arithmetic Mean Method: The simplest of all is the Arithmetic Mean Method, which taken an average of all the rainfall depths as shown [...]
The factors affecting the runoff are as follows: 1. Precipitation 2. Size and Shape of the Catchment Area 3. Geographical Characteristics 4. Meteorological Characteristics 5. Drainage Net 6. Other Factors. Factor # 1. Precipitation: The runoff is clearly a function of precipitation, its intensity, its duration and its coverage. More the intensity, more will be the runoff. The infiltration rate [...]