IMD non-recording (Symon’s) rain gauge – common standard specification Which of the following pairs correctly states the most commonly used IMD standard non-recording rain gauge specification (collector aperture and receiving bottle capacity)?

Introduction / Context:
Standardization of rain gauges ensures inter-comparable measurements across a national network. In India, the Symon’s non-recording gauge is widely deployed with specific dimensions for the collector and receiving bottle.

Given Data / Assumptions:

• Non-recording gauge (manual daily reading).
• IMD standard configuration commonly issued to stations.
• Standard measuring cylinder used for reading the collected volume as rainfall depth.

Concept / Approach:
The collector area determines the conversion from collected volume to rainfall depth (Depth = Volume / Area). A 200 sq. cm orifice paired with a 4 L bottle is the classic IMD non-recording specification, providing adequate storage for heavy rain events before observation time.

Step-by-Step Solution:
Identify IMD’s widely used non-recording gauge setup.Match the pair to options → 200 sq. cm collector with 4 L bottle.

Verification / Alternative check:
Hydrology manuals summarizing IMD practice specify a 200 cm² orifice with 4 L capacity as the standard reference for non-recording gauges.

Why Other Options Are Wrong:

• (b) and (d) assign the smaller 100 cm² orifice to large bottle capacities not typical of the standard.
• (c) 10 L is larger than standard practice for the commonly issued Symon’s gauge.

Common Pitfalls:
Confusing non-recording Symon’s gauges with tipping-bucket or weighing gauges, which have different specifications and are used for intensity recording.

Final Answer:
200 sq. cm collector and 4 litres bottle