Question

“runoff coefficient” and a “hydrologic abstraction”?
a.   What is the method or concept in question and how is it used?
b.   Why does it matter to engineers or to engineering hydrologists? Why should we care?
c.   What are the primary strengths or weaknesses of the method or concept?
d.   What would have made it easier for you to understand the method or concept? Here, for example, you might imagine that you are giving advice to a friend taking this course next year: what do you think they would really benefit from knowing about this concept?

Answer 1

A. Runoff coefficient represents the proportion of rainfall that results into runoff. It is ratio of runoff to rainfall. In actual when rainfall occurs then there are some abstractions from this falling water like evaporation, evapotransporation and infiltration due to which whole rainfall do not result into runoff. Some portion of rainfall is eleminated due to these abstractions.

B. It matters to Engineering hydrologistic because they are responsible persons to maintain data of rainfall and runoff and losses dus to these hydrologistic abstraction. These hydrologistic data is important to be maintained properly and accurately as this data is basis of design of storm sewers, rain water harvesting system and drainage system.

C. Primary strength of concept:- This method provides data important for reference foe design of water utilitues and sewers and also this data is kept on record for many years for references.

Weakness of concept:- Runoff coefficient is calculated from data of ground water level, evaporation basis of Pan coefficient, and runoff data which may not be fully accurate.

D. Basics of this concept :-

There are three type of major losses from rainfall that are Infiltration, evaporation and evapotranspiration.

Infiltration is loss due to rainfall water goes inside the ground and increase ground water level.

Evaporation:- This loss is due to evaporation of rainwater from ponds lakes river and sea.

Evapotransoiration:- This loss is due to interception of water by trees and buildings and then evaporation from surface of them.

Runoff coefficient can be calculated by evaluating rain data, ground water level, evaporation data and runoff data in various entities.

This runoff coefficient for a watershed is helpful in calculating runoff volume which will be helpful in design of storm sewers and drainage system.