Step 1: Understanding the Concept:
On sloping or uneven terrain, the water pressure inside a drip irrigation lateral will vary along its length due to changes in elevation. Drippers at lower elevations will experience higher pressure than those at higher elevations. This pressure difference will cause non-pressure compensating drippers to have a non-uniform discharge rate, with lower drippers emitting more water. The question asks for the type of dripper designed to solve this problem.
Step 2: Detailed Explanation of Dripper Types:
Let's analyze the options:
(A) Online non-pressure compensating drippers: These are simple drippers (emitters) that are punched into the lateral pipe. Their discharge rate is directly dependent on the operating pressure. If pressure varies due to elevation changes on a slope, their discharge will also vary, leading to non-uniform irrigation. They are not suitable for slopes.
(B) In-line drippers: This describes the method of installation (the dripper is part of the pipe itself) rather than its hydraulic function. In-line drippers can be either pressure compensating or non-pressure compensating. So, this term is not specific enough.
(C) Online pressure compensating drippers: These drippers are designed with a flexible internal diaphragm or a similar mechanism that automatically adjusts the size of the water outlet in response to changes in pressure. This allows the dripper to deliver a nearly constant discharge rate over a wide range of operating pressures. Because they can maintain a uniform flow rate even when the pressure changes due to elevation differences on slopes and difficult terrain, they are the most suitable choice for such conditions.
(D) Adjustable discharge type drippers: These drippers allow the user to manually adjust the flow rate. While this provides flexibility, it does not automatically compensate for pressure variations along the line. They are not ideal for ensuring uniformity on slopes.
Step 3: Final Answer:
Pressure compensating drippers are specifically designed to provide uniform water application on slopes and in long laterals where pressure variations occur. Therefore, option (C) is the correct answer.