If we superimpose the map of tank irrigation on the map of well irrigation in India, we find a negative relationship between them. Which statements best explain this pattern?

Introduction / Context:
This question tests conceptual understanding of irrigation geography in India, particularly the relationship between different irrigation methods. Tank irrigation and well irrigation are both traditional techniques, but they tend to dominate in different physical environments. The question says that where tank irrigation is common, well irrigation tends to be less developed, and vice versa, indicating a negative relationship. We must analyse four given statements to see which ones logically explain this spatial pattern.

Given Data / Assumptions:

• Statement 1: Tank irrigation predates well irrigation.
• Statement 2: Tank irrigation is found in areas with impervious surface layers.
• Statement 3: Well irrigation requires sufficient ground water reserves.
• Statement 4: Other forms of irrigation are not available.
• The maps show that when tank irrigation is dominant in a region, well irrigation is relatively less common, and the reverse also holds.

Concept / Approach:
Tank irrigation depends on surface storage of rainwater in small reservoirs, which is especially useful in areas where the underlying rock is hard and does not allow easy percolation of water. In such areas, ground water reserves are limited, so well irrigation is difficult. On the other hand, well irrigation needs good aquifers and adequate ground water availability, which typically occurs in regions with permeable soils and sub strata. Therefore, regions with good ground water potential favour wells and do not rely heavily on tanks, while regions with poor ground water conditions depend more on tanks. This directly relates to statements about impervious layers and ground water reserves.

Step-by-Step Solution:
Step 1: Evaluate Statement 1. Tank irrigation being older than well irrigation may be historically true in some areas, but age alone does not create a negative spatial relationship on present day maps. Step 2: Evaluate Statement 2. Areas with impervious surface layers do not allow much infiltration, so rainwater does not easily recharge ground water. This favours surface tanks, which collect and store rainfall for later use. Step 3: Evaluate Statement 3. Well irrigation requires sufficient ground water reserves, which usually develop in permeable formations. Where this is available, wells become popular and tanks are relatively less important. Step 4: Evaluate Statement 4. The absence of other forms of irrigation may explain why any irrigation method is used at all, but it does not explain the specific negative relationship between tanks and wells. Step 5: From this analysis, Statements 2 and 3 directly address physical conditions that cause one method to flourish where the other is weak, so they explain the observed pattern.

Verification / Alternative check:
A brief look at Indian irrigation maps shows tank irrigation concentrated in hard rock regions of peninsular India, such as parts of Tamil Nadu, Karnataka, and Andhra Pradesh, while well irrigation is more common in alluvial plains with better ground water, such as Punjab, Haryana, and western Uttar Pradesh. This geographic distribution matches the logic that impervious rocks favour tanks and good aquifers favour wells. Therefore, statements about surface imperviousness and ground water reserves provide the most accurate explanation of the negative relationship.

Why Other Options Are Wrong:

• Statement 1: The fact that tank irrigation predates well irrigation historically does not by itself explain why the two maps are negatively correlated today.
• Statement 4: The non availability of other irrigation methods is too general and does not specifically link the rise of tanks to the decline of wells or vice versa.
• Any option that includes 1 or 4 as the main explanation gives more weight to historical or general factors rather than to the physical conditions that directly create the observed spatial pattern.

Common Pitfalls:
A major pitfall is to treat all statements that look true as automatically relevant. Statement 1 may sound plausible but does not answer the specific why of the map pattern. Another error is not paying attention to the phrase negatively related and instead focusing on which method seems more modern. The exam expects you to connect the type of rock, infiltration, and ground water availability to the choice of irrigation method, which is captured accurately by statements 2 and 3.

Final Answer:
The negative relationship between tank irrigation and well irrigation is best explained by Statements 2 and 3 only.