Question

a. Explain how the catchment area is determined when calculating surface runoff.

b. How can the adverse effects of urban development on downstream runoff be minimized? Name the principles and discuss.

Answer 1

a. The catchment area is calculated by adding all the area through which the rain water will come into the stream or river via drains etc. The areas are multiplied by the runoff coefficient for eg all the concreted area is calculated and added up and multiplied by runoff coefficient, similarly are grassed area is calculated and added up and then multiplied by its runoff coefficient etc.

b. The adverse effect of urban development can be minimised by following methods:

1. By separate drains for sewer and rain water: separate drains for sewer and rain water shall be provided so that the river or ground water doesn't get polluted and remains usable. It also help in keeping rain water contamination free if it is stored for reuse.

2. By water reservoirs: Building reservoirs helps in maintaining healthy flow of water throughout the year so that our need for the year can be fulfilled and the area fetch by the runoff stream is also livable throughout the year