Step 1: Understanding the Concept:
The question asks for a term that represents a ratio of water output (discharged by a drain) to water input (precipitation) over a certain period. This is a measure of the performance or effectiveness of a drainage system.
Step 2: Detailed Explanation:
Let's define the terms related to drainage:
(A) Drainage efficiency: This is a broad term that can have several specific definitions depending on the context. In a general sense, it refers to the effectiveness of a drainage system. One way to express this is by comparing the amount of water removed by the system to the total amount of water that needed to be removed (e.g., precipitation or irrigation excess). The ratio described in the question, (Volume discharged) / (Volume from precipitation), is a form of drainage efficiency, representing how efficiently the system removes the rainfall input.
(B) Drainage coefficient: This is a {design parameter}, not a performance ratio. It is defined as the depth of water (in cm or inches) that a drainage system is designed to remove from the drainage area in a 24-hour period. It's an expression of the required drainage {rate}, not an efficiency ratio of output vs. input.
(C) Hydraulic conductivity: This is a property of the soil itself. It measures the ease with which water can move through the soil pores. It is a key factor in drainage design but is not a ratio of volumes.
(D) Drainage porosity (or Drainable pore space): This is the volume of water that a saturated soil can drain under the influence of gravity, expressed as a fraction of the total soil volume. It's a property of the soil, not a performance measure of a drainage system.
The question describes a ratio of output volume to input volume, which is a classic definition of an efficiency.
Step 3: Final Answer:
The ratio of water discharged by a drain to the precipitation received is a measure of the system's performance, known as drainage efficiency. Therefore, option (A) is the correct answer.